path: root/doc/doc-src/spec.src

. $Cambridge: exim/doc/doc-src/spec.src,v 1.1 2004/10/07 15:04:35 ph10 Exp $
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.index @$1, @$2, etc. $it{see numerical variables}
.index address||rewriting $it{see rewriting}
.index CR character $it{see carriage return}
.index CRL $it{see certificate revocation list}
.index delivery||failure report $it{see bounce message}
.index dialup $it{see intermittently connected hosts}
.index failover $it{see fallback}
.index fallover $it{see fallback}
.index filter||Sieve $it{see Sieve filter}
.index ident $it{see RFC 1413}
.index LF character $it{see linefeed}
.index maximum $it{see limit}
.index NUL $it{see binary zero}
.index process id $it{see pid}
.index RBL $it{see DNS list}
.index redirection $it{see address redirection}
.index return path||$it{see also envelope sender}
.index SSL $it{see TLS}
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. ======================================================

.push
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.nofoot
.space 8ld
$chead{University of Cambridge Computing Service}
.space 2ld
$chead{Specification of the Exim Mail Transfer Agent}
.space 3ld
by
.space 1ld
Philip Hazel
.space ~~sys.leftonpage - 15*~~sys.linedepth
.justify left
University Computing Service
New Museums Site
Pembroke Street
Cambridge CB2 3QH
United Kingdom
.blank
.tabs 6
$it{phone:} $t +44 1223 334600
$it{fax:}   $t +44 1223 334679
$it{email:} $t ph10 $it{at} cus.cam.ac.uk
.blank
Edition for Exim ~~version, ~~versionmonth ~~versionyear
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$c$rm{Copyright (c) University of Cambridge ~~versionyear}


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.
.
.
.
. ============================================================================
.chapter Introduction
.set runningfoot "introduction"

.if ~~sys.fancy
$c$bi{If I have seen further it is by standing on the shoulders of giants.}##(Isaac Newton)
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$c"If I have seen further it is by standing on the shoulders of giants."
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$e (Isaac Newton)
.else
\*If I have seen further it is by standing on the shoulders of giants.*\
(Isaac Newton).
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.blank 4

Exim is a mail transfer agent (MTA) for hosts that are running Unix or
Unix-like operating systems. It was designed on the assumption that it would be
run on hosts that are permanently connected to the Internet. However, it can be
used on intermittently connected hosts with suitable configuration adjustments.

Configuration files currently exist for the following operating systems: AIX,
BSD/OS (aka BSDI), Darwin (Mac OS X), DGUX, FreeBSD, GNU/Hurd, GNU/Linux,
HI-OSF (Hitachi), HP-UX, IRIX, MIPS RISCOS, NetBSD, OpenBSD, QNX, SCO, SCO
SVR4.2 (aka UNIX-SV), Solaris (aka SunOS5), SunOS4, Tru64-Unix (formerly
Digital UNIX, formerly DEC-OSF1), Ultrix, and Unixware. Some of these operating 
systems are no longer current and cannot easily be tested, so the configuration 
files may no longer work in practice. 

There are also configuration files for compiling Exim in the Cygwin environment
that can be installed on systems running Windows. However, this document does
not contain any information about running Exim in the Cygwin environment.

The terms and conditions for the use and distribution of Exim are contained in
the file \(NOTICE)\. Exim is distributed under the terms of the GNU General
Public Licence, a copy of which may be found in the file \(LICENCE)\.

The use, supply or promotion of Exim for the purpose of sending bulk,
unsolicited electronic mail is incompatible with the basic aims of the program,
which revolve around the free provision of a service that enhances the quality
of personal communications. The author of Exim regards indiscriminate
mass-mailing as an antisocial, irresponsible abuse of the Internet.

Exim owes a great deal to Smail 3 and its author, Ron Karr. Without the
experience of running and working on the Smail 3 code, I could never have
contemplated starting to write a new MTA. Many of the ideas and user interfaces
were originally taken from Smail 3, though the actual code of Exim is entirely
new, and has developed far beyond the initial concept.

Many people, both in Cambridge and around the world, have contributed to the
development and the testing of Exim, and to porting it to various operating
systems. I am grateful to them all. The distribution now contains a file called
\(ACKNOWLEDGMENTS)\, in which I have started recording the names of
contributors.

.section Exim documentation
.index documentation
.em
This edition of the Exim specification applies to version ~~version of Exim.
Substantive changes from the ~~previousversion edition are marked by bars in
the right-hand margin in the PostScript, PDF, and plain text versions of the
document, and by green text in the HTML version, as shown by this paragraph.
Changes are not marked in the Texinfo version, because Texinfo doesn't support
change bars. Minor corrections and rewordings are not marked.
.nem

This document is very much a reference manual; it is not a tutorial. The reader
is expected to have some familiarity with the SMTP mail transfer protocol and
with general Unix system administration. Although there are some discussions
and examples in places, the information is mostly organized in a way that makes
it easy to look up, rather than in a natural order for sequential reading.
Furthermore, the manual aims to cover every aspect of Exim in detail, including
a number of rarely-used, special-purpose features that are unlikely to be of
very wide interest.

.index books about Exim
An `easier' discussion of Exim which provides more in-depth explanatory,
introductory, and tutorial material can be found in a book entitled
.if ~~html
[(A HREF="http://www.uit.co.uk/exim-book/")]
$it{The Exim SMTP Mail Server},
[(/A)]
published by UIT Cambridge. 
.else
$it{The Exim SMTP Mail Server}, published by UIT Cambridge
(\?http://www.uit.co.uk/exim-book/?\).
.fi

This book also contains a chapter that gives a general introduction to SMTP and
Internet mail. Inevitably, however, the book is unlikely to be fully up-to-date
with the latest release of Exim. (Note that the earlier book about Exim,
published by O'Reilly, covers Exim 3, and many things have changed in Exim 4.)

.index \(doc/NewStuff)\
.index \(doc/ChangeLog)\
.index change log
As the program develops, there may be features in newer versions that have not
yet made it into this document, which is updated only when the most significant
digit of the fractional part of the version number changes. However,
specifications of new features that are not yet in this manual are placed in
the file \(doc/NewStuff)\ in the Exim distribution. All changes to the program
(whether new features, bug fixes, or other kinds of change) are noted briefly
in the file called \(doc/ChangeLog)\.

.index \(doc/spec.txt)\
This specification itself is available as an ASCII file in \(doc/spec.txt)\ so
that it can easily be searched with a text editor. Other files in the \(doc)\
directory are:
.display rm
.tabs 18
\(OptionLists.txt)\   $t $rm{list of all options in alphabetical order}
\(dbm.discuss.txt)\   $t $rm{discussion about DBM libraries}
\(exim.8)\            $t $rm{a man page of Exim's command line options}
\(filter.txt)\        $t $rm{specification of the filter language}
\(pcrepattern.txt)\   $t $rm{specification of PCRE regular expressions}
\(pcretest.txt)\      $t $rm{specification of the PCRE testing program}
\(Exim3.upgrade)\     $t $rm{upgrade notes from release 2 to release 3}
\(Exim4.upgrade)\     $t $rm{upgrade notes from release 3 to release 4}
.endd
The main specification and the specification of the filtering language are also
available in other formats (HTML, PostScript, PDF, and Texinfo). Section
~~SECTavail below tells you how to get hold of these.


.section FTP and web sites, and mailing list
.index web site
.index FTP site
The primary distribution site for Exim is an FTP site, whose contents are 
described in \*Where to find the Exim distribution*\ below. In addition,
there is a web site at \?http://www.exim.org?\ by courtesy of Energis Squared,
formerly Planet Online Ltd, who are situated in the UK. The site is mirrored in
a number of other countries; links to the mirrors are listed on the home page.
The web site contains the Exim distribution, and you can also find the
documentation and the
.index FAQ
.if ~~html
[(A HREF="FAQ.html")]
.fi
FAQ
.if ~~html
[(/A)]
.fi
online there, as well as other relevant material.

.index mailing lists||for Exim users
Energis Squared also provide resources for the following mailing lists:
.display rm
.tabs 28
$it{exim-users@@exim.org}          $t general discussion list
$it{exim-announce@@exim.org}       $t moderated, low volume announcements list
.endd
You can subscribe to these lists, change your existing subscriptions, and view
or search the archives via the
.if ~~html
[(A HREF="http://www.exim.org/maillist.html")]
.fi
mailing lists
.if ~~html
[(/A)]
.fi
link on the Exim home page. The $it{exim-users} mailing list is also forwarded
to \?http://www.egroups.com/list/exim-users?\, an archiving system with
searching capabilities.

.section Exim training
.index training courses
From time to time (approximately annually at the time of writing),
lecture-based training courses are run by the author of Exim in Cambridge, UK.
Details can be found on the web site
.if ~~html
[(A HREF="http://www-tus.csx.cam.ac.uk/courses/exim/")]
.fi
\?http://www-tus@.csx@.cam@.ac.uk/courses/exim/?\.
.if ~~html
[(/A)]
.fi

.section Bug reports
.index bug reports
.index reporting bugs
Reports of obvious bugs should be emailed to \*bugs@@exim.org*\. However, if
you are unsure whether some behaviour is a bug or not, the best thing to do is
to post a message to the $it{exim-users} mailing list and have it discussed.


.section Where to find the Exim distribution
.rset SECTavail "~~chapter.~~section"
.index FTP site
.index distribution||ftp site
The master ftp site for the Exim distribution is
.display rm
.if ! ~~sys.fancy
.indent 0
.fi
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim?\
.endd
Within that directory there are subdirectories called \(exim3)\ (for previous
Exim 3 distributions), \(exim4)\ (for the latest Exim 4 distributions), and
\(Testing)\ for occasional testing versions. Those mirror sites that I know
about are listed in the file
.display rm
.if ! ~~sys.fancy
.indent 0
.fi
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/Mirrors?\
.endd
In the \(exim4)\ subdirectory, the current release can always be found in
files called
.display rm
\(exim-$it{n.nn}.tar.gz)\
\(exim-$it{n.nn}.tar.bz2)\
.endd
where $it{n.nn} is the highest such version number in the directory. The two
files contain identical data; the only difference is the type of compression.
The \(.bz2)\ file is usually a lot smaller than the \(.gz)\ file.
.index distribution||signing details
.index distribution||public key
.index public key for signed distribution
The distributions are signed with Philip Hazel's GPG key.
The corresponding public key is available from a number of keyservers, and
there is also a copy in the file:
.display rm
.if ! ~~sys.fancy
.indent 0
.fi
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/Public-Key?\
.endd
The signatures for the tar bundles are in:
.display rm
\(exim-$it{n.nn}.tar.gz.sig)\
\(exim-$it{n.nn}.tar.bz2.sig)\
.endd

When there is only a small amount of change from one release to the next, a
patch file may be provided, with a final component name of the form
.display rm
\(exim-patch-$it{n.nn}-$it{m.mm}.gz)\
.endd
For each released version, the log of changes is made separately available in
the directory
.display rm
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/ChangeLogs?\
.endd
so that it is possible to find out what has changed without having to download
the entire distribution.

.index documentation||available formats
The main distribution contains ASCII versions of this specification and other
documentation; other formats of the documents are available in separate files
inside the \(exim4)\ directory of the FTP site:
.display rm
\(exim-html-$it{n.nn}.tar.gz)\
\(exim-pdf-$it{n.nn}.tar.gz)\
\(exim-postscript-$it{n.nn}.tar.gz)\
\(exim-texinfo-$it{n.nn}.tar.gz)\
.endd
These tar files contain only the \(doc)\ directory, not the complete
distribution, and are also available in \(.bz2)\ as well as \(.gz)\ forms.

.index FAQ
The FAQ is available for downloading in two different formats from
.display rm
.if ! ~~sys.fancy
.indent 0
.fi
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/FAQ.txt.gz?\
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/FAQ.html.tar.gz?\
.endd
The first of these is a single ASCII file that can be searched with a text
editor. The second is a directory of HTML files, normally accessed by starting
at \(index.html)\. The HTML version of the FAQ (which is also included in the
HTML documentation tarbundle) includes a keyword-in-context index, which is
often the most convenient way of finding your way around.

.section Wish list
.index wish list
A wish list is maintained, containing ideas for new features that have been
submitted. From time to time the file is exported to the ftp site:
.display rm
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/WishList?\
.endd
Items are removed from the list if they get implemented.


.section Contributed material
.index contributed material
At the ftp site, there is a directory called
.display rm
.if ! ~~sys.fancy
.indent 0
.fi
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/Contrib/?\
.endd
which contains miscellaneous files contributed to the Exim community by Exim
users. There is also a collection of contributed configuration examples in
.display rm
.if ! ~~sys.fancy
.indent 0
.fi
\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/config.samples.tar.gz?\
.endd
These samples are referenced from the FAQ.


.section Limitations
.index limitations of Exim
.numberpars $.
Exim is designed for use as an Internet MTA, and therefore handles addresses
in RFC 2822 domain format only.
.index bang paths||not handled by Exim
It cannot handle UUCP `bang paths', though simple two-component bang paths can
be converted by a straightforward rewriting configuration. This restriction
does not prevent Exim from being interfaced to UUCP as a transport mechanism,
provided that domain addresses are used.
.nextp
.index domainless addresses
.index address||without domain
Exim insists that every address it handles has a domain attached. For incoming
local messages, domainless addresses are automatically qualified with a
configured domain value. Configuration options specify from which remote
systems unqualified addresses are acceptable. These are then qualified on
arrival.
.nextp
.index transport||external
.index external transports
The only external transport currently implemented is an SMTP transport over a
TCP/IP network (using sockets, including support for IPv6). However, a pipe
transport is available, and there are facilities for writing messages to files
and pipes, optionally in \*batched SMTP*\ format; these facilities can be used
to send messages to some other transport mechanism such as UUCP, provided it
can handle domain-style addresses. Batched SMTP input is also catered for.
.nextp
Exim is not designed for storing mail for dial-in hosts. When the volumes of
such mail are large, it is better to get the messages `delivered' into files
(that is, off Exim's queue) and subsequently passed on to the dial-in hosts by
other means.
.nextp
Although Exim does have some facilities for scanning incoming messages, these 
are not comprehensive enough to do full virus or spam scanning. Such operations 
are best carried out using additional specialized software packages.
.endp



.section Run time configuration
Exim's run time configuration is held in a single text file that is divided
into a number of sections. The entries in this file consist of keywords and
values, in the style of Smail 3 configuration files. A default configuration
file which is suitable for simple online installations is provided in the
distribution, and is described in chapter ~~CHAPdefconfil below.


.section Calling interface
.index Sendmail compatibility||command line interface
Like many MTAs, Exim has adopted the Sendmail command line interface so that it
can be a straight replacement for \(/usr/lib/sendmail)\ or
\(/usr/sbin/sendmail)\ when sending mail, but you do not need to know anything
about Sendmail in order to run Exim. For actions other than sending messages,
Sendmail-compatible options also exist, but those that produce output (for
example, \-bp-\, which lists the messages on the queue) do so in Exim's own
format. There are also some additional options that are compatible with Smail
3, and some further options that are new to Exim. Chapter ~~CHAPcommandline
documents all Exim's command line options. This information is automatically
made into the man page that forms part of the Exim distribution.

Control of messages on the queue can be done via certain privileged command
line options. There is also an optional monitor program called \*eximon*\, which
displays current information in an X window, and which contains a menu
interface to Exim's command line administration options.


.section Terminology
.index terminology definitions
.index body of message||definition of
The \*body*\ of a message is the actual data that the sender wants to transmit.
It is the last part of a message, and is separated from the \*header*\ (see
below) by a blank line.

.index bounce message||definition of
When a message cannot be delivered, it is normally returned to the sender in a
delivery failure message. The term \*bounce*\ is commonly used for this action,
and the error reports are often called \*bounce messages*\. This is a
convenient shorthand for `delivery failure error report'. Such messages have an
empty sender address in the message's \*envelope*\ (see below) to ensure that
they cannot themselves give rise to further bounce messages.

The term \*default*\ appears frequently in this manual. It is used to qualify a
value which is used in the absence of any setting in the configuration. It may
also qualify an action which is taken unless a configuration setting specifies
otherwise.

The term \*defer*\ is used when the delivery of a message to a specific
destination cannot immediately take place for some reason (a remote host may be
down, or a user's local mailbox may be full). Such deliveries are \*deferred*\
until a later time.

The word \*domain*\ is sometimes used to mean all but the first component of a
host's name. It is $it{not} used in that sense here, where it normally
refers to the part of an email address following the @@ sign.

.index envelope, definition of
.index sender||definition of
A message in transit has an associated \*envelope*\, as well as a header and a
body. The envelope contains a sender address (to which bounce messages should
be delivered), and any number of recipient addresses. References to the
sender or the recipients of a message usually mean the addresses in the
envelope. An MTA uses these addresses for delivery, and for returning bounce
messages, not the addresses that appear in the header lines.

.index message||header, definition of
.index header section||definition of
The \*header*\ of a message is the first part of a message's text, consisting
of a number of lines, each of which has a name such as ::From::, ::To::,
::Subject::, etc. Long header lines can be split over several text lines by
indenting the continuations. The header is separated from the body by a blank
line.

.index local part||definition of
.index domain||definition of
The term \*local part*\, which is taken from RFC 2822, is used to refer to that
part of an email address that precedes the @@ sign. The part that follows the
@@ sign is called the \*domain*\ or \*mail domain*\.

.index local delivery||definition of
.index remote delivery, definition of
The terms \*local delivery*\ and \*remote delivery*\ are used to distinguish
delivery to a file or a pipe on the local host from delivery by SMTP over
TCP/IP to a remote host.

.index return path||definition of
\*Return path*\ is another name that is used for the sender address in a
message's envelope.

.index queue||definition of
The term \*queue*\ is used to refer to the set of messages awaiting delivery,
because this term is in widespread use in the context of MTAs. However, in
Exim's case the reality is more like a pool than a queue, because there is
normally no ordering of waiting messages.

.index queue runner||definition of
The term \*queue runner*\ is used to describe a process that scans the queue
and attempts to deliver those messages whose retry times have come. This term
is used by other MTAs, and also relates to the command \runq\, but in Exim
the waiting messages are normally processed in an unpredictable order.

.index spool directory||definition of
The term \*spool directory*\ is used for a directory in which Exim keeps the
messages on its queue -- that is, those that it is in the process of
delivering. This should not be confused with the directory in which local
mailboxes are stored, which is called a `spool directory' by some people. In
the Exim documentation, `spool' is always used in the first sense.



.
.
.
.
. ============================================================================
.chapter Incorporated code
.set runningfoot "incorporated code"
.index incorporated code
.index regular expressions||library
.index PCRE
A number of pieces of external code are included in the Exim distribution.
.numberpars $.
Regular expressions are supported in the main Exim program and in the Exim
monitor using the freely-distributable PCRE library, copyright (c) 2003
University of Cambridge. The source is distributed in the directory
\(src/pcre)\. However, this is a cut-down version of PCRE. If you want to use
the PCRE library in other programs, you should obtain and install the full
version from \?ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre?\.

.space 1ld
.nextp
.index cdb||acknowledgement
Support for the cdb (Constant DataBase) lookup method is provided by code
contributed by Nigel Metheringham of Planet Online Ltd. which contains the
following statements:
.rule
.push
.if ~~sgcal
.fontgroup 9
.font 0
.fi
Copyright (c) 1998 Nigel Metheringham, Planet Online Ltd

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.

This code implements Dan Bernstein's Constant DataBase (cdb) spec. Information,
the spec and sample code for cdb can be obtained from
\?http://www.pobox.com/@~djb/cdb.html?\. This implementation borrows some code
from Dan Bernstein's implementation (which has no license restrictions applied
to it).
.newline
.pop
.rule
The implementation is completely contained within the code of Exim.
It does not link against an external cdb library.
.space 1ld
.nextp
.index SPA authentication
.index Samba project
.index Microsoft Secure Password Authentication
Client support for Microsoft's \*Secure Password Authentication*\ is provided
by code contributed by Marc Prud'hommeaux. Server support was contributed by 
Tom Kistner. This includes code taken from the Samba project, which is released
under the Gnu GPL.

.space 1ld
.nextp
.index Cyrus
.index \*pwcheck*\ daemon
.index \*pwauthd*\ daemon
Support for calling the Cyrus \*pwcheck*\ and \*saslauthd*\ daemons is provided
by code taken from the Cyrus-SASL library and adapted by Alexander S.
Sabourenkov. The permission notice appears below, in accordance with the
conditions expressed therein.

.rule
.push
.if ~~sgcal
.fontgroup 9
.font 0
.fi
Copyright (c) 2001 Carnegie Mellon University.  All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

.if ~~sgcal
.cancelflag $npbracket
.flag $npbracket "" "."
.fi
.numberpars
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.nextp
Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
.nextp
The name `Carnegie Mellon University' must not be used to
endorse or promote products derived from this software without
prior written permission. For permission or any other legal
details, please contact
.display rm
Office of Technology Transfer
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA  15213-3890
(412) 268-4387, fax: (412) 268-7395
tech-transfer@@andrew.cmu.edu
.endd
.nextp
Redistributions of any form whatsoever must retain the following
acknowledgment:
.newline
.push
.indent ~~sys.indent + 3em
.justify left
$it{This product includes software developed by Computing Services
at Carnegie Mellon University (\?http://www.cmu.edu/computing/?\).}
.newline
.pop
.endp    
.if ~~sgcal
.cancelflag $npbracket
.flag $npbracket "(" ")"
.fi

CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.newline
.pop
.rule

.space 1ld
.nextp
.index monitor
.index X-windows
.index Athena
The Exim Monitor program, which is an X-Window application, includes
modified versions of the Athena StripChart and TextPop widgets.
This code is copyright by DEC and MIT, and their permission notice appears
below, in accordance with the conditions expressed therein.

.rule
.push
.if ~~sgcal
.fontgroup 9
.font 0
.fi
Copyright 1987, 1988 by Digital Equipment Corporation, Maynard, Massachusetts,
and the Massachusetts Institute of Technology, Cambridge, Massachusetts.
.blank
$c All Rights Reserved
.blank
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation, and that the names of Digital or MIT not be
used in advertising or publicity pertaining to distribution of the
software without specific, written prior permission.

DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR
ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
SOFTWARE.
.newline
.pop
.rule
.endp



.
.
.
.
. ============================================================================
.chapter How Exim receives and delivers mail
.set runningfoot "receiving & delivering mail"

.section Overall philosophy
.index design philosophy
Exim is designed to work efficiently on systems that are permanently connected
to the Internet and are handling a general mix of mail. In such circumstances,
most messages can be delivered immediately. Consequently, Exim does not
maintain independent queues of messages for specific domains or hosts, though
it does try to send several messages in a single SMTP connection after a host
has been down, and it also maintains per-host retry information.


.section Policy control
.index policy control||overview
Policy controls are now an important feature of MTAs that are connected to the
Internet. Perhaps their most important job is to stop MTAs being abused as
`open relays' by misguided individuals who send out vast amounts of unsolicited
junk, and want to disguise its source. Exim provides flexible facilities for
specifying policy controls on incoming mail:
.numberpars $.
.index ~~ACL||introduction
Exim 4 (unlike previous versions of Exim) implements policy controls on
incoming SMTP mail by means of \*Access Control Lists*\ (ACLs). Each list is a
series of statements that may either grant or deny access. ACLs can be used at
several places in the SMTP dialogue while receiving a message. However, the
most common places are after each \\RCPT\\ command, and at the very end of the
message. The sysadmin can specify conditions for accepting or rejecting
individual recipients or the entire message, respectively, at these two points
(see chapter ~~CHAPACL). Denial of access results in an SMTP error code.
.nextp
An ACL is also available for locally generated, non-SMTP messages. In this 
case, the only available actions are to accept or deny the entire message.
.nextp
When a message has been received, either from a remote host or from the local
host, but before the final acknowledgement has been sent, a locally supplied C
function called \*local@_scan()*\ can be run to inspect the message and decide
whether to accept it or not (see chapter ~~CHAPlocalscan). If the message is
accepted, the list of recipients can be modified by the function.
.nextp
After a message has been accepted, a further checking mechanism is available in
the form of the $it{system filter} (see chapter ~~CHAPsystemfilter). This runs
at the start of every delivery process.
.endp

.section User filters
.index filter||introduction
.index Sieve filter
In a conventional Exim configuration, users are able to run private filters by 
setting up appropriate \(.forward)\ files in their home directories. See 
chapter ~~CHAPredirect (about the \%redirect%\ router) for the configuration 
needed to support this, and the separate document entitled 
.if ~~html
[(A HREF="filter_toc.html")]
.fi
\*Exim's interfaces to mail filtering*\
.if ~~html
[(/A)]
.fi
for user details. Two different kinds of filtering are available:
.numberpars $.
Sieve filters are written in the standard filtering language that is defined by 
RFC 3028.
.nextp
Exim filters are written in a syntax that is unique to Exim, but which is more 
powerful than Sieve, which it pre-dates.
.endp
User filters are run as part of the routing process, described below.


.section Message identification
.rset SECTmessiden "~~chapter.~~section"
.index message||ids, details of format
.index format||of message id
.index id of message
.index base62
.index base36
.index Darwin
.index Cygwin
Every message handled by Exim is given a \*message id*\ which is sixteen
characters long. It is divided into three parts, separated by hyphens, for
example \"16VDhn-0001bo-D3"\. Each part is a sequence of letters and digits,
normally encoding numbers in base 62. However, in the Darwin operating
system (Mac OS X) and when Exim is compiled to run under Cygwin, base 36 
(avoiding the use of lower case letters) is used instead, because the message 
id is used to construct file names, and the names of files in those systems are
not case-sensitive.

.index pid (process id)||re-use of
The detail of the contents of the message id have changed as Exim has evolved.
Earlier versions relied on the operating system not re-using a process id (pid)
within one second. On modern operating systems, this assumption can no longer
be made, so the algorithm had to be changed. To retain backward compatibility, 
the format of the message id was retained, which is why the following rules are 
somewhat eccentric:
.numberpars $.
The first six characters of the message id are the time at which the message
started to be received, to a granularity of one second. That is, this field
contains the number of seconds since the start of the epoch (the normal Unix
way of representing the date and time of day).
.nextp
After the first hyphen, the next six characters are the id of the process that
received the message.
.nextp
There are two different possibilities for the final two characters:
.numberpars alpha
.index \localhost@_number\
If \localhost@_number\ is not set, this value is the fractional part of the
time of reception, normally in units of 1/2000 of a second, but for systems
that must use base 36 instead of base 62 (because of case-insensitive file
systems), the units are 1/1000 of a second.
.nextp
If \localhost@_number\ is set, it is multiplied by 200 (100) and added to
the fractional part of the time, which in this case is in units of 1/200
(1/100) of a second.
.endp
.endp
After a message has been received, Exim waits for the clock to tick at the
appropriate resolution before proceeding, so that if another message is
received by the same process, or by another process with the same (re-used)
pid, it is guaranteed that the time will be different. In most cases, the clock
will already have ticked while the message was being received.

.section Receiving mail
.index receiving mail
.index message||reception
The only way Exim can receive mail from a remote host is using SMTP over
TCP/IP, in which case the sender and recipient addresses are tranferred using
SMTP commands. However, from a locally running process (such as a user's MUA),
there are several possibilities:
.numberpars $.
If the process runs Exim with the \-bm-\ option, the message is read
non-interactively (usually via a pipe), with the recipients taken from the
command line, or from the body of the message if \-t-\ is also used.
.nextp
If the process runs Exim with the \-bS-\ option, the message is also read
non-interactively, but in this case the recipients are listed at the start of
the message in a series of SMTP \\RCPT\\ commands, terminated by a \\DATA\\
command. This is so-called `batch SMTP' format,
but it isn't really SMTP. The SMTP commands are just another way of passing
envelope addresses in a non-interactive submission.
.nextp
If the process runs Exim with the \-bs-\ option, the message is read
interactively, using the SMTP protocol. A two-way pipe is normally used for
passing data between the local process and the Exim process.
This is `real' SMTP and is handled in the same way as SMTP over TCP/IP. For
example, the ACLs for SMTP commands are used for this form of submission.
.nextp
A local process may also make a TCP/IP call to the host's loopback address
(127.0.0.1) or any other of its IP addresses. When receiving messages, Exim
does not treat the loopback address specially. It treats all such connections
in the same way as connections from other hosts.
.endp

.index message||sender, constructed by Exim
.index sender||constructed by Exim
In the three cases that do not involve TCP/IP, the sender address is
constructed from the login name of the user that called Exim and a default
qualification domain (which can be set by the \qualify@_domain\ configuration
option). For local or batch SMTP, a sender address that is passed using the
SMTP \\MAIL\\ command is ignored. However, the system administrator may allow
certain users (`trusted users') to specify a different sender address
unconditionally, or all users to specify certain forms of different sender
address. The \-f-\ option or the SMTP \\MAIL\\ command is used to specify these
different addresses. See section ~~SECTtrustedadmin for details of trusted
users, and the \untrusted@_set@_sender\ option for a way of allowing untrusted
users to change sender addresses.

Messages received by either of the non-interactive mechanisms are subject to 
checking by the non-SMTP ACL, if one is defined. Messages received using SMTP 
(either over TCP/IP, or interacting with a local process) can be checked by a 
number of ACLs that operate at different times during the SMTP session. Either 
individual recipients, or the entire message, can be rejected if local policy 
requirements are not met. The \*local@_scan()*\ function (see chapter
~~CHAPlocalscan) is run for all incoming messages.

Exim can be configured not to start a delivery process when a message is
received; this can be unconditional, or depend on the number of incoming SMTP
connections or the system load. In these situations, new messages wait on the
queue until a queue runner process picks them up. However, in standard
configurations under normal conditions, delivery is started as soon as a
message is received.




.section Handling an incoming message
.index spool directory||files that hold a message
.index file||how a message is held
When Exim accepts a message, it writes two files in its spool directory. The
first contains the envelope information, the current status of the message,
and the header lines, and the second contains the body of the message. The
names of the two spool files consist of the message id, followed by $tt{-H} for
the file containing the envelope and header, and $tt{-D} for the data file.

.index spool directory||\(input)\ sub-directory
By default all these message files are held in a single directory called
\(input)\ inside the general Exim spool directory. Some operating systems do
not perform very well if the number of files in a directory gets very large; to
improve performance in such cases, the \split@_spool@_directory\ option can be
used. This causes Exim to split up the input files into 62 sub-directories
whose names are single letters or digits.

The envelope information consists of the address of the message's sender and
the addresses of the recipients. This information is entirely separate from
any addresses contained in the header lines. The status of the message includes
a list of recipients who have already received the message. The format of the
first spool file is described in chapter ~~CHAPspool.

.index rewriting||addresses
Address rewriting that is specified in the rewrite section of the configuration
(see chapter ~~CHAPrewrite) is done once and for all on incoming addresses,
both in the header lines and the envelope, at the time the message is accepted.
If during the course of delivery additional addresses are generated (for
example, via aliasing), these new addresses are rewritten as soon as they are
generated. At the time a message is actually delivered (transported) further
rewriting can take place; because this is a transport option, it can be
different for different forms of delivery. It is also possible to specify the
addition or removal of certain header lines at the time the message is
delivered (see chapters ~~CHAProutergeneric and ~~CHAPtransportgeneric).


.section Life of a message
.index message||life of
.index message||frozen
A message remains in the spool directory until it is completely delivered to
its recipients or to an error address, or until it is deleted by an
administrator or by the user who originally created it. In cases when delivery
cannot proceed -- for example, when a message can neither be delivered to its
recipients nor returned to its sender, the message is marked `frozen' on the
spool, and no more deliveries are attempted.

.index frozen messages||thawing
.index message||thawing frozen
An administrator can `thaw' such messages when the problem has been corrected,
and can also freeze individual messages by hand if necessary. In addition, an
administrator can force a delivery error, causing a bounce message to be sent.

.index \auto@_thaw\
There is an option called \auto@_thaw\, which can be used to cause Exim to
retry frozen messages after a certain time. When this is set, no message will
remain on the queue for ever, because the delivery timeout will eventually be
reached. Delivery failure reports (bounce messages) that reach this timeout are
discarded.
.index \timeout@_frozen@_after\
There is also an option called \timeout@_frozen@_after\, which discards frozen
messages after a certain time.

.index message||log file for
.index log||file for each message
While Exim is working on a message, it writes information about each delivery
attempt to the main log file. This includes successful, unsuccessful, and
delayed deliveries for each recipient (see chapter ~~CHAPlog). The log lines
are also written to a separate $it{message log} file for each message. These
logs are solely for the benefit of the administrator, and are normally deleted
along with the spool files when processing of a message is complete.
The use of individual message logs can be disabled by setting 
\no@_message@_logs\; this might give an improvement in performance on very
busy systems.

.index journal file
.index file||journal
All the information Exim itself needs to set up a delivery is kept in the first
spool file, along with the header lines. When a successful delivery occurs, the
address is immediately written at the end of a journal file, whose name is the
message id followed by $tt{-J}. At the end of a delivery run, if there are some
addresses left to be tried again later, the first spool file (the $tt{-H} file)
is updated to indicate which these are, and the journal file is then deleted.
Updating the spool file is done by writing a new file and renaming it, to
minimize the possibility of data loss.

Should the system or the program crash after a successful delivery but before
the spool file has been updated, the journal is left lying around. The next
time Exim attempts to deliver the message, it reads the journal file and
updates the spool file before proceeding. This minimizes the chances of double
deliveries caused by crashes.


.section Processing an address for delivery
.rset SECTprocaddress "~~chapter.~~section"
.index drivers||definition of
.index router||definition of
.index transport||definition of
The main delivery processing elements of Exim are called $it{routers} and
$it{transports}, and collectively these are known as $it{drivers}. Code for a
number of them is provided in the source distribution, and compile-time options
specify which ones are included in the binary. Run time options specify which
ones are actually used for delivering messages.

.index drivers||instance definition
Each driver that is specified in the run time configuration is an \*instance*\ 
of that particular driver type. Multiple instances are allowed; for example, 
you can set up several different \%smtp%\ transports, each with different 
option values that might specify different ports or different timeouts. Each
instance has its own identifying name. In what follows we will normally use the
instance name when discussing one particular instance (that is, one specific 
configuration of the driver), and the generic driver name when discussing
the driver's features in general.

A $it{router} is a driver that operates on an address, either determining how
its delivery should happen, by routing it to a specific transport, or
converting the address into one or more new addresses (for example, via an
alias file). A router may also explicitly choose to fail an address, causing it
to be bounced.

A $it{transport} is a driver that transmits a copy of the message from Exim's
spool to some destination. There are two kinds of transport: for a $it{local}
transport, the destination is a file or a pipe on the local host, whereas for a
$it{remote} transport the destination is some other host. A message is passed
to a specific transport as a result of successful routing. If a message has
several recipients, it may be passed to a number of different transports.

.index preconditions||definition of
An address is processed by passing it to each configured router instance in
turn, subject to certain preconditions, until a router accepts the address or
specifies that it should be bounced. We will describe this process in more
detail shortly. As a simple example, the diagram below illustrates how each
recipient address in a message is processed in a small configuration of three
routers that are configured in various ways.

.if ~~sys.fancy
.figure "Routing an address" rm
.indent 0
.call aspic
centre ~~sys.linelength;
magnify 0.8;
boundingbox 30;
    ibox depth 14 "address";
B:  arrow down 44;
    textdepth 14;
A:  box width 100 "first router" "conditions ok?";
    arrow right "yes";
C:  box width 100 "run" "first router";
    arrow down "fail";
D:  ibox depth 20 "address bounces";

    arc clockwise from right of C "accept";
    arrow down 10;
    ibox "queue for" "transport";

    arrow down from A align bottom of D plus (0,-20) "no"(-6,20)/r;
E:  box width 100 "second router" "conditions ok?";
    arrow right "yes";
F:  box width 100 "run" "second router";
    line right 100 "redirect";
    line up align middle of B;
    arrow left to middle of B "new addresses";

    line down 20 from bottom left of F plus (30,0);
    arrow left align centre of E "decline";

    line down 20 from bottom right of F plus (-30,0);
    arrow right "fail";
    ibox width 64 "address" "bounces";

    arrow down 64 from E "no"(-6,20)/r;
G:  box width 100 "third router" "conditions ok?";
    arrow right "yes";
H:  box width 100 "run" "third router";
    arc clockwise from right of H "accept";
    arrow down 10;
    ibox "queue for" "transport";

    line down 20 from bottom of H;
    arrow left align centre of G "decline";
    arrow down 64 from G "no"(-6,20)/r;

    ibox "no more routers" "address bounces";
.endcall
.endfigure
.elif !~~html
.display asis

       address
          |
          |<------------- new addresses -----------------------------
          V                                                         |
  -----------------                -----------------                |
  | first router  |----- yes ----->|     run       |--- accept      |
  | conditions ok?|                | first router  |      |         |
  -----------------                -----------------      |         |
          |                                |              V         |
       no |                           fail |          queue for     |
          |                                V          transport     |
          |                         address bounces                 |
          |                                                         |
          V                                                         |
  -----------------                -----------------                |
  | second router |----- yes ----->|     run       |----redirect ----
  | conditions ok?|                | second router |
  -----------------                -----------------
          |                            |       |
       no |                            |       |
          |<-------- decline -----------       --- fail ---> address
          |                                                  bounces
          V
  -----------------                -----------------
  | third router  |----- yes ----->|     run       |--- accept
  | conditions ok?|                | third router  |      |
  -----------------                -----------------      |
          |                                |              V
       no |                                |          queue for
          |<-------- decline ---------------          transport
          |
          V
   no more routers
   address bounces
.endd
.else
[(img src="routing.gif" alt="Routing an address")][(br)]
.fi
To make this a more concrete example, we'll describe it in terms of some actual
routers, but remember, this is only an example. You can configure Exim's
routers in many different ways, and there may be any number of routers in a
configuration.

The first router that is specified in a configuration is often one that handles
addresses in domains that are not recognized specially by the local host. These
are typically addresses for arbitrary domains on the Internet. A precondition
is set up which looks for the special domains known to the host (for example,
its own domain name), and the router is run for addresses that do $it{not}
match. Typically, this is a router that looks up domains in the DNS in order to
find the hosts to which this address routes. If it succeeds, the address is
queued for a suitable SMTP transport; if it does not succeed, the router is
configured to fail the address.

The example pictured could be a configuration of this type. The second and
third routers can only be run for addresses for which the preconditions for
the first router are not met. If one of these preconditions checks the
domain, the second and third routers are run only for domains that are somehow
special to the local host.

The second router does redirection -- also known as aliasing and forwarding.
When it generates one or more new addresses from the original, each of them is
routed independently from the start. Otherwise, the router may cause an address
to fail, or it may simply decline to handle the address, in which case the 
address is passed to the next router.

The final router in many configurations is one that checks to see if the
address belongs to a local mailbox. The precondition may involve a check to
see if the local part is the name of a login account, or it may look up the
local part in a file or a database. If its preconditions are not met, or if
the router declines, we have reached the end of the routers. When this happens,
the address is bounced.


.section Processing an address for verification
.index router||for verification
.index verifying||address, overview
As well as being used to decide how to deliver to an address, Exim's routers 
are also used for \*address verification*\. Verification can be requested as 
one of the checks to be performed in an ACL for incoming messages, on both 
sender and recipient addresses, and it can be tested using the \-bv-\ and 
\-bvs-\ command line options.

When an address is being verified, the routers are run in `verify mode'. This 
does not affect the way the routers work, but it is a state that can be 
detected. By this means, a router can be skipped or made to behave differently
when verifying. A common example is a configuration in which the first router
sends all messages to a message-scanning program, unless they have been
previously scanned. Thus, the first router accepts all addresses without any
checking, making it useless for verifying. Normally, the \no@_verify\ option 
would be set for such a router, causing it to be skipped in verify mode.



.section Running an individual router
.rset SECTrunindrou "~~chapter.~~section"
.index router||running details
.index preconditions||checking
.index router||result of running
As explained in the example above, a number of preconditions are checked before
running a router. If any are not met, the router is skipped, and the address is
passed to the next router. When all the preconditions on a router $it{are} met,
the router is run. What happens next depends on the outcome, which is one of
the following:
.numberpars $.
\*accept*\: The router accepts the address, and either queues it for a
transport, or generates one or more `child' addresses. Processing the original
address ceases, 
.index \unseen\ option
unless the \unseen\ option is set on the router. This option
can be used to set up multiple deliveries with different routing (for example,
for keeping archive copies of messages). When \unseen\ is set, the address is
passed to the next router. Normally, however, an \*accept*\ return marks the
end of routing.

.index case of local parts
.index address||duplicate, discarding
If child addresses are generated, Exim checks to see whether they are
duplicates of any existing recipient addresses. During this check, local parts
are treated as case-sensitive. Duplicate addresses are discarded. Each of the
remaining child addresses is then processed independently, starting with the
first router by default. It is possible to change this by setting the
\redirect@_router\ option to specify which router to start at for child
addresses. Unlike \pass@_router\ (see below) the router specified by
\redirect@_router\ may be anywhere in the router configuration.
.nextp
\*pass*\: The router recognizes the address, but cannot handle it itself. It
requests that the address be passed to another router. By default the address
is passed to the next router, but this can be changed by setting the
\pass@_router\ option. However, (unlike \redirect@_router\) the named router
must be below the current router (to avoid loops).
.nextp
\*decline*\: The router declines to accept the address because it does not
recognize it at all. By default, the address is passed to the next router, but
this can be prevented by setting the \no@_more\ option. When \no@_more\ is set,
all the remaining routers are skipped.
.nextp
\*fail*\: The router determines that the address should fail, and queues it for
the generation of a bounce message. There is no further processing of the
original address unless \unseen\ is set on the router.
.nextp
\*defer*\: The router cannot handle the address at the present time. (A database
may be offline, or a DNS lookup may have timed out.) No further processing of
the address happens in this delivery attempt. It is tried again next time the
message is considered for delivery.
.nextp
\*error*\: There is some error in the router (for example, a syntax error in
its configuration). The action is as for defer.
.endp
If an address reaches the end of the routers without having been accepted by
any of them, it is bounced as unrouteable.
The default error message in this situation is `unrouteable address', but you 
can set your own message by making use of the \cannot@_route@_message\ option. 
This can be set for any router; the value from the last router that `saw' 
the address is used.

Sometimes while routing you want to fail a delivery when some conditions are
met but others are not, instead of passing the address on for further routing.
You can do this by having a second router that explicitly fails the delivery
when the relevant conditions are met. The \%redirect%\ router has a `fail' 
facility for this purpose.



.section Router preconditions
.rset SECTrouprecon "~~chapter.~~section"
.index router||preconditions, order of processing
.index preconditions||order of processing
The preconditions that are tested for each router are listed below, in the
order in which they are tested. The individual configuration options are
described in more detail in chapter ~~CHAProutergeneric.
.numberpars $.
The \local@_part@_prefix\ and \local@_part@_suffix\ options can specify that
the local parts handled by the router may or must have certain prefixes and/or
suffixes. If a mandatory affix (prefix or suffix) is not present, the router is
skipped. These conditions are tested first. When an affix is present, it is
removed from the local part before further processing, including the evaluation
of any other conditions.
.nextp
Routers can be designated for use only when not verifying an address, that is, 
only when routing it for delivery (or testing its delivery routing). If the 
\verify\ option is set false, the router is skipped when Exim is verifying an 
address.
Setting the \verify\ option actually sets two options, \verify@_sender\ and 
\verify@_recipient\, which independently control the use of the router for 
sender and recipient verification. You can set these options directly if 
you want a router to be used for only one type of verification.
.nextp
If the \address@_test\ option is set false, the router is skipped when Exim is 
run with the \-bt-\ option to test an address routing. This can be helpful when 
the first router sends all new messages to a scanner of some sort; it makes it 
possible to use \-bt-\ to test subsequent delivery routing without having to
simulate the effect of the scanner.
.nextp
Routers can be designated for use only when verifying an address, as
opposed to routing it for delivery. The \verify@_only\ option controls this.
.nextp
Certain routers can be explicitly skipped when running the routers to check an
address given in the SMTP \\EXPN\\ command (see the \expn\ option).
.nextp
If the \domains\ option is set, the domain of the address must be in the set of
domains that it defines.
.nextp
If the \local@_parts\ option is set, the local part of the address must be in
the set of local parts that it defines. If \local@_part@_prefix\ or
\local@_part@_suffix\ is in use, the prefix or suffix is removed from the local
part before this check. If you want to do precondition tests on local parts
that include affixes, you can do so by using a \condition\ option (see below)
that uses the variables \$local@_part$\, \$local@_part@_prefix$\, and
\$local@_part@_suffix$\ as necessary.
.nextp
If the \check@_local@_user\ option is set, the local part must be the name of
an account on the local host.
If this check succeeds, the uid and gid of the local user are placed in 
\$local@_user@_uid$\ and \$local@_user@_gid$\; these values can be used in the
remaining preconditions.
.nextp
If the \router@_home@_directory\ option is set, it is expanded at this point,
because it overrides the value of \$home$\. If this expansion were left till 
later, the value of \$home$\ as set by \check@_local@_user\ would be used in 
subsequent tests. Having two different values of \$home$\ in the same router 
could lead to confusion.
.nextp
If the \senders\ option is set, the envelope sender address must be in the set
of addresses that it defines.
.nextp
If the \require@_files\ option is set, the existence or non-existence of
specified files is tested.
.nextp
.index customizing||precondition
If the \condition\ option is set, it is evaluated and tested. This option uses
an expanded string to allow you to set up your own custom preconditions.
Expanded strings are described in chapter ~~CHAPexpand.
.endp

Note that \require@_files\ comes near the end of the list, so you cannot use it
to check for the existence of a file in which to lookup up a domain, local
part, or sender. However, as these options are all expanded, you can use the
\exists\ expansion condition to make such tests within each condition. The
\require@_files\ option is intended for checking files that the router may be
going to use internally, or which are needed by a specific transport (for
example, \(.procmailrc)\).


.section Delivery in detail
.index delivery||in detail
When a message is to be delivered, the sequence of events is as follows:
.numberpars $.
If a system-wide filter file is specified, the message is passed to it. The
filter may add recipients to the message, replace the recipients, discard the
message, cause a new message to be generated, or cause the message delivery to
fail. The format of the system filter file is the same as for Exim user filter
files, described in the separate document entitled
.if ~~html
[(A HREF="filter.html")]
.fi
\*Exim's interfaces to mail filtering*\.
.if ~~html
[(/A)]
.fi
.index Sieve filter||not available for system filter
(\**Note**\: Sieve cannot be used for system filter files.)
Some additional features are available in system filters -- see chapter
~~CHAPsystemfilter for details. Note that a message is passed to the system
filter only once per delivery attempt, however many recipients it has. However,
if there are several delivery attempts because one or more addresses could not
be immediately delivered, the system filter is run each time. The filter
condition \first@_delivery\ can be used to detect the first run of the system
filter.
.nextp
Each recipient address is offered to each configured router in turn, subject to
its preconditions, until one is able to handle it. If no router can handle
the address, that is, if they all decline, the address is failed. Because
routers can be targeted at particular domains, several locally handled domains
can be processed entirely independently of each other.
.nextp
.index routing||loops in
.index loop||while routing
A router that accepts an address may set up a local or a remote transport for
it. However, the transport is not run at this time. Instead, the address is
placed on a list for the particular transport, to be run later. Alternatively,
the router may generate one or more new addresses (typically from alias,
forward, or filter files). New addresses are fed back into this process from
the top, but in order to avoid loops, a router ignores any address which has an
identically-named ancestor that was processed by itself.
.nextp
When all the routing has been done, addresses that have been successfully
handled are passed to their assigned transports. When local transports are
doing real local deliveries, they handle only one address at a time, but if a
local transport is being used as a pseudo-remote transport (for example, to
collect batched SMTP messages for transmission by some other means) multiple
addresses can be handled. Remote transports can always handle more than one
address at a time, but can be configured not to do so, or to restrict multiple
addresses to the same domain.
.nextp
Each local delivery to a file or a pipe runs in a separate process under a
non-privileged uid, and these deliveries are run one at a time. Remote
deliveries also run in separate processes, normally under a uid that is private
to Exim (`the Exim user'), but in this case, several remote deliveries can be
run in parallel. The maximum number of simultaneous remote deliveries for any
one message is set by the \remote@_max@_parallel\ option.
.em
The order in which deliveries are done is not defined, except that all local 
deliveries happen before any remote deliveries.
.nem
.nextp
.index queue runner
When it encounters a local delivery during a queue run, Exim checks its retry
database to see if there has been a previous temporary delivery failure for the
address before running the local transport. If there was a previous failure,
Exim does not attempt a new delivery until the retry time for the address is
reached. However, this happens only for delivery attempts that are part of a
queue run. Local deliveries are always attempted when delivery immediately
follows message reception, even if retry times are set for them. This makes for
better behaviour if one particular message is causing problems (for example,
causing quota overflow, or provoking an error in a filter file).
.nextp
.index delivery||retry in remote transports
Remote transports do their own retry handling, since an address may be
deliverable to one of a number of hosts, each of which may have a different
retry time. If there have been previous temporary failures and no host has
reached its retry time, no delivery is attempted, whether in a queue run or
not. See chapter ~~CHAPretry for details of retry strategies.
.nextp
If there were any permanent errors, a bounce message is returned to an
appropriate address (the sender in the common case), with details of the error
for each failing address. Exim can be configured to send copies of bounce
messages to other addresses.
.nextp
.index delivery||deferral
If one or more addresses suffered a temporary failure, the message is left on
the queue, to be tried again later. Delivery of these addresses is said to be
\*deferred*\.
.nextp
When all the recipient addresses have either been delivered or bounced,
handling of the message is complete. The spool files and message log are
deleted, though the message log can optionally be preserved if required.
.endp


.section Retry mechanism
.index delivery||retry mechanism
.index retry||description of mechanism
.index queue runner
Exim's mechanism for retrying messages that fail to get delivered at the first
attempt is the queue runner process. You must either run an Exim daemon that
uses the \-q-\ option with a time interval to start queue runners at regular
intervals, or use some other means (such as \*cron*\) to start them. If you do
not arrange for queue runners to be run, messages that fail temporarily at the
first attempt will remain on your queue for ever. A queue runner process works
it way through the queue, one message at a time, trying each delivery that has
passed its retry time.
You can run several queue runners at once.

Exim uses a set of configured rules to determine when next to retry the failing
address (see chapter ~~CHAPretry). These rules also specify when Exim should
give up trying to deliver to the address, at which point it generates a bounce
message. If no retry rules are set for a particular host, address, and error
combination, no retries are attempted, and temporary errors are treated as
permanent.


.section Temporary delivery failure
.index delivery||temporary failure
There are many reasons why a message may not be immediately deliverable to a
particular address. Failure to connect to a remote machine (because it, or the
connection to it, is down) is one of the most common. Temporary failures may be
detected during routing as well as during the transport stage of delivery.
Local deliveries may be delayed if NFS files are unavailable, or if a mailbox
is on a file system where the user is over quota. Exim can be configured to
impose its own quotas on local mailboxes; where system quotas are set they will
also apply.

If a host is unreachable for a period of time, a number of messages may be
waiting for it by the time it recovers, and sending them in a single SMTP
connection is clearly beneficial. Whenever a delivery to a remote host is
deferred, 
.index hints database
Exim makes a note in its hints database, and whenever a successful
SMTP delivery has happened, it looks to see if any other messages are waiting
for the same host. If any are found, they are sent over the same SMTP
connection, subject to a configuration limit as to the maximum number in any
one connection.



.section Permanent delivery failure
.index delivery||permanent failure
.index bounce message||when generated
When a message cannot be delivered to some or all of its intended recipients, a
bounce message is generated. Temporary delivery failures turn into permanent
errors when their timeout expires. All the addresses that fail in a given
delivery attempt are listed in a single message. If the original message has
many recipients, it is possible for some addresses to fail in one delivery
attempt and others to fail subsequently, giving rise to more than one bounce
message. The wording of bounce messages can be customized by the administrator.
See chapter ~~CHAPemsgcust for details.

.index ::X-Failed-Recipients:: header line
Bounce messages contain an ::X-Failed-Recipients:: header line that lists the
failed addresses, for the benefit of programs that try to analyse such messages
automatically.

.index bounce message||recipient of
A bounce message is normally sent to the sender of the original message, as
obtained from the message's envelope. For incoming SMTP messages, this is the
address given in the \\MAIL\\ command. However, when an address is
expanded via a forward or alias file, an alternative address can be specified
for delivery failures of the generated addresses. For a mailing list expansion
(see section ~~SECTmailinglists) it is common to direct bounce messages to the
manager of the list.



.section Failures to deliver bounce messages
.index bounce message||failure to deliver
If a bounce message (either locally generated or received from a remote host)
itself suffers a permanent delivery failure, the message is left on the queue,
but it is frozen, awaiting the attention of an administrator. There are options
which can be used to make Exim discard such failed messages, or to keep them
for only a short time (see \timeout@_frozen@_after\ and
\ignore@_bounce@_errors@_after\).



.
.
.
.
. ============================================================================
.chapter Building and installing Exim
.set runningfoot "building/installing"

.index building Exim
.section Unpacking
Exim is distributed as a gzipped or bzipped tar file which, when upacked,
creates a directory with the name of the current release (for example,
\(exim-~~version)\) into which the following files are placed:
.display rm
.if !~~sys.fancy && ~~sgcal
.tabs 16
.else
.tabs 22 
.fi
\(ACKNOWLEDGMENTS)\ $t contains some acknowledgments
.newline
\(CHANGES)\      $t contains a reference to where changes are documented
\(LICENCE)\      $t the GNU General Public Licence
\(Makefile)\     $t top-level make file
\(NOTICE)\       $t conditions for the use of Exim
\(README)\       $t list of files, directories and simple build instructions
.endd
Other files whose names begin with \(README)\ may also be present. The
following subdirectories are created:
.display rm
.if !~~sys.fancy && ~~sgcal
.tabs 16
.else
.tabs 22
.fi
\(Local)\        $t an empty directory for local configuration files
\(OS)\           $t OS-specific files
\(doc)\          $t documentation files
\(exim@_monitor)\$t source files for the Exim monitor
\(scripts)\      $t scripts used in the build process
\(src)\          $t remaining source files
\(util)\         $t independent utilities
.endd
The main utility programs are contained in the \(src)\ directory, and are built
with the Exim binary. The \(util)\ directory contains a few optional scripts
that may be useful to some sites.

.section Multiple machine architectures and operating systems
.index building Exim||multiple OS/architectures
The building process for Exim is arranged to make it easy to build binaries for
a number of different architectures and operating systems from the same set of
source files. Compilation does not take place in the \(src)\ directory. Instead,
a \*build directory*\ is created for each architecture and operating system.
.index symbolic link||to build directory
Symbolic links to the sources are installed in this directory, which is where
the actual building takes place.

In most cases, Exim can discover the machine architecture and operating system
for itself, but the defaults can be overridden if necessary.

.section DBM libraries
.rset SECTdb "~~chapter.~~section"
.index DBM||libraries, discussion of
.index hints database||DBM files used for
Even if you do not use any DBM files in your configuration, Exim still needs a
DBM library in order to operate, because it uses indexed files for its hints
databases. Unfortunately, there are a number of DBM libraries in existence, and
different operating systems often have different ones installed.

.index Solaris||DBM library for
.index IRIX, DBM library for
.index BSD, DBM library for
.index Linux, DBM library for
If you are using Solaris, IRIX, one of the modern BSD systems, or a modern
Linux distribution, the DBM configuration should happen automatically, and you
may be able to ignore this section. Otherwise, you may have to learn more than
you would like about DBM libraries from what follows.

.index \*ndbm*\ DBM library
Licensed versions of Unix normally contain a library of DBM functions operating
via the \*ndbm*\ interface, and this is what Exim expects by default. Free
versions of Unix seem to vary in what they contain as standard. In particular,
some early versions of Linux have no default DBM library, and different
distributors have chosen to bundle different libraries with their packaged
versions. However, the more recent releases seem to have standardised on the
Berkeley DB library.

Different DBM libraries have different conventions for naming the files they
use. When a program opens a file called \(dbmfile)\, there are four
possibilities:
.numberpars
A traditional \*ndbm*\ implementation, such as that supplied as part of
Solaris, operates on two files called \(dbmfile.dir)\ and \(dbmfile.pag)\.
.nextp
.index \*gdbm*\ DBM library
The GNU library, \*gdbm*\, operates on a single file. If used via its \*ndbm*\
compatibility interface it makes two different hard links to it with names
\(dbmfile.dir)\ and \(dbmfile.pag)\, but if used via its native interface, the
file name is used unmodified.
.nextp
.index Berkeley DB library
The Berkeley DB package, if called via its \*ndbm*\ compatibility interface,
operates on a single file called \(dbmfile.db)\, but otherwise looks to the
programmer exactly the same as the traditional \*ndbm*\ implementation.
.nextp
If the Berkeley package is used in its native mode, it operates on a single
file called \(dbmfile)\; the programmer's interface is somewhat different to
the traditional \*ndbm*\ interface.
.nextp
To complicate things further, there are several very different versions of the
Berkeley DB package. Version 1.85 was stable for a very long time, releases
2.$it{x} and 3.$it{x} were current for a while, but the latest versions are now
numbered 4.$it{x}. Maintenance of some of the earlier releases has ceased. All
versions of Berkeley DB can be obtained from
.display rm
\?http://www.sleepycat.com/?\
.endd
.nextp
.index \*tdb*\ DBM library
Yet another DBM library, called \*tdb*\, has become available from
.display rm
\?http://download.sourceforge.net/tdb?\
.endd
It has its own interface, and also operates on a single file.
.endp
.index \\USE@_DB\\
.index DBM||libraries, configuration for building
Exim and its utilities can be compiled to use any of these interfaces. In order
to use any version of the Berkeley DB package in native mode, you must set
\\USE@_DB\\ in an appropriate configuration file (typically
\(Local/Makefile)\). For example:
.display asis
USE_DB=yes
.endd
Similarly, for gdbm you set \\USE@_GDBM\\, and for tdb you set \\USE@_TDB\\. An
error is diagnosed if you set more than one of these.

At the lowest level, the build-time configuration sets none of these options,
thereby assuming an interface of type (1). However, some operating system
configuration files (for example, those for the BSD operating systems and
Linux) assume type (4) by setting \\USE@_DB\\ as their default, and the
configuration files for Cygwin set \\USE@_GDBM\\. Anything you set in
\(Local/Makefile)\, however, overrides these system defaults.

As well as setting \\USE@_DB\\, \\USE@_GDBM\\, or \\USE@_TDB\\, it may also be
necessary to set \\DBMLIB\\, to cause inclusion of the appropriate library, as
in one of these lines:
.display asis
DBMLIB = -ldb
DBMLIB = -ltdb
.endd
Settings like that will work if the DBM library is installed in the standard 
place. Sometimes it is not, and the library's header file may also not be in
the default path. You may need to set \\INCLUDE\\ to specify where the header
file is, and to specify the path to the library more fully in \\DBMLIB\\, as in 
this example:
.display asis
INCLUDE=-I/usr/local/include/db-4.1
DBMLIB=/usr/local/lib/db-4.1/libdb.a
.endd

There is further detailed discussion about the various DBM libraries in the
file \(doc/dbm.discuss.txt)\ in the Exim distribution.


.section Pre-building configuration
.index building Exim||pre-building configuration
.index configuration for building Exim
.index \(Local/Makefile)\
.index \(src/EDITME)\
Before building Exim, a local configuration file that specifies options
independent of any operating system has to be created with the name
\(Local/Makefile)\. A template for this file is supplied as the file
\(src/EDITME)\, and it contains full descriptions of all the option settings
therein. These descriptions are therefore not repeated here. If you are
building Exim for the first time, the simplest thing to do is to copy
\(src/EDITME)\ to \(Local/Makefile)\, then read it and edit it appropriately.

There are three settings that you must supply, because Exim will not build
without them. They are the location of the run time configuration file
(\\CONFIGURE@_FILE\\), the directory in which Exim binaries will be installed
(\\BIN@_DIRECTORY\\), and the identity of the Exim user (\\EXIM@_USER\\ and
maybe \\EXIM@_GROUP\\ as well). The value of \\CONFIGURE@_FILE\\ can in fact be
a colon-separated list of file names; Exim uses the first of them that exists.

There are a few other parameters that can be specified either at build time or
at run time, to enable the same binary to be used on a number of different
machines. However, if the locations of Exim's spool directory and log file
directory (if not within the spool directory) are fixed, it is recommended that
you specify them in \(Local/Makefile)\ instead of at run time, so that errors
detected early in Exim's execution (such as a malformed configuration file) can
be logged.

.index \(Local/eximon.conf)\
.index \(exim@_monitor/EDITME)\
If you are going to build the Exim monitor, a similar configuration process is
required. The file \(exim@_monitor/EDITME)\ must be edited appropriately for
your installation and saved under the name \(Local/eximon.conf)\. If you are
happy with the default settings described in \(exim@_monitor/EDITME)\,
\(Local/eximon.conf)\ can be empty, but it must exist.

This is all the configuration that is needed in straightforward cases for known
operating systems. However, the building process is set up so that it is easy
to override options that are set by default or by operating-system-specific
configuration files, for example to change the name of the C compiler, which
defaults to \gcc\. See section ~~SECToverride below for details of how to do
this.


.section Support for iconv()
.index \*iconv()*\ support
The contents of header lines in messages may be encoded according to the rules 
described RFC 2047. This makes it possible to transmit characters that are not 
in the ASCII character set, and to label them as being in a particular 
character set. When Exim is inspecting header lines by means of the \@$h@_\ 
mechanism, it decodes them, and translates them into a specified character set 
(default ISO-8859-1). The translation is possible only if the operating system
supports the \*iconv()*\ function.

However, some of the operating systems that supply \*iconv()*\ do not support
very many conversions. The GNU \libiconv\ library (available from
\?http:/@/www.gnu.org/software/libiconv/?\) can be installed on such systems to
remedy this deficiency, as well as on systems that do not supply \*iconv()*\ at
all. After installing \libiconv\, you should add 
.display asis
HAVE_ICONV=yes 
.endd 
to your \(Local/Makefile)\ and rebuild Exim.


.section Including TLS/SSL encryption support
.rset SECTinctlsssl "~~chapter.~~section"
.index TLS||including support for TLS
.index encryption||including support for
.index \\SUPPORT@_TLS\\
.index OpenSSL||building Exim with
.index GnuTLS||building Exim with
Exim can be built to support encrypted SMTP connections, using the \\STARTTLS\\
command as per RFC 2487. It can also support legacy clients that expect to 
start a TLS session immediately on connection to a non-standard port (see the 
\-tls-on-connect-\ command line option).

If you want to build Exim with TLS support, you must first install either the 
OpenSSL or GnuTLS library. There is no cryptographic code in Exim itself for
implementing SSL.

If OpenSSL is installed, you should set
.display asis
SUPPORT_TLS=yes
TLS_LIBS=-lssl -lcrypto
.endd
in \(Local/Makefile)\. You may also need to specify the locations of the
OpenSSL library and include files. For example:
.display asis
SUPPORT_TLS=yes
TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
TLS_INCLUDE=-I/usr/local/openssl/include/
.endd

If GnuTLS is installed, you should set
.index \\USE@_GNUTLS\\
.display asis
SUPPORT_TLS=yes
USE_GNUTLS=yes
TLS_LIBS=-lgnutls -ltasn1 -lgcrypt
.endd
in \(Local/Makefile)\, and again you may need to specify the locations of the
library and include files. For example:
.display asis
SUPPORT_TLS=yes
USE_GNUTLS=yes        
TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt
TLS_INCLUDE=-I/usr/gnu/include
.endd
You do not need to set \\TLS@_INCLUDE\\ if the relevant directory is already
specified in \\INCLUDE\\. Details of how to configure Exim to make use of TLS 
are given in chapter ~~CHAPTLS.



.section Use of tcpwrappers
.index tcpwrappers, building Exim to support
.index \\USE@_TCP@_WRAPPERS\\
Exim can be linked with the \*tcpwrappers*\ library in order to check incoming
SMTP calls using the \*tcpwrappers*\ control files. This may be a convenient
alternative to Exim's own checking facilities for installations that are
already making use of \*tcpwrappers*\ for other purposes. To do this, you should
set \\USE@_TCP@_WRAPPERS\\ in \(Local/Makefile)\, arrange for the file
\(tcpd.h)\ to be available at compile time, and also ensure that the library
\(libwrap.a)\ is available at link time, typically by including \-lwrap-\ in
\\EXTRALIBS@_EXIM\\. For example, if \*tcpwrappers*\ is installed in
\(/usr/local)\, you might have
.display
USE@_TCP@_WRAPPERS=yes
CFLAGS=-O -I/usr/local/include
.newline
EXTRALIBS@_EXIM=-L/usr/local/lib -lwrap
.endd
in \(Local/Makefile)\. The name to use in the \*tcpwrappers*\ control files is
`exim'. For example, the line
.display
exim : LOCAL  192.168.1.  .friendly.domain.example
.endd
in your \(/etc/hosts.allow)\ file allows connections from the local host, from
the subnet 192.168.1.0/24, and from all hosts in \*friendly.domain.example*\.
All other connections are denied. Consult the \*tcpwrappers*\ documentation for
further details.


.section Including support for IPv6
.index IPv6||including support for
Exim contains code for use on systems that have IPv6 support. Setting
\\HAVE@_IPV6=YES\\ in \(Local/Makefile)\ causes the IPv6 code to be included;
it may also be necessary to set \\IPV6@_INCLUDE\\ and \\IPV6@_LIBS\\ on systems
where the IPv6 support is not fully integrated into the normal include and
library files.

IPv6 is still changing rapidly. Two different types of DNS record for handling
IPv6 addresses have been defined. AAAA records are already in use, and are
currently seen as the `mainstream', but another record type called A6 is being
argued about. Its status is currently `experimental'. Exim has support for A6
records, but this is included only if you set \\SUPPORT@_A6=YES\\ in
\(Local/Makefile)\.


.section The building process
.index build directory
Once \(Local/Makefile)\ (and \(Local/eximon.conf)\, if required) have been
created, run \*make*\ at the top level. It determines the architecture and
operating system types, and creates a build directory if one does not exist.
For example, on a Sun system running Solaris 8, the directory
\(build-SunOS5-5.8-sparc)\ is created.
.index symbolic link||to source files
Symbolic links to relevant source files are installed in the build directory.

.em
\**Warning**\: The \-j-\ (parallel) flag must not be used with \*make*\; the 
building process fails if it is set.
.nem

If this is the first time \*make*\ has been run, it calls a script that builds
a make file inside the build directory, using the configuration files from the
\(Local)\ directory. The new make file is then passed to another instance of
\*make*\. This does the real work, building a number of utility scripts, and
then compiling and linking the binaries for the Exim monitor (if configured), a
number of utility programs, and finally Exim itself. The command \*make
makefile*\ can be used to force a rebuild of the make file in the build
directory, should this ever be necessary.

If you have problems building Exim, check for any comments there may be in the
\(README)\ file concerning your operating system, and also take a look at the
.if ~~html
[(A HREF="FAQ.html")]
.fi
FAQ,
.if ~~html
[(/A)]
.fi
where some common problems are covered.



.section Overriding build-time options for Exim
.index build-time options, overriding
.rset SECToverride "~~chapter.~~section"
The main make file that is created at the beginning of the building process
consists of the concatenation of a number of files which set configuration
values, followed by a fixed set of \*make*\ instructions. If a value is set
more than once, the last setting overrides any previous ones. This provides a
convenient way of overriding defaults. The files that are concatenated are, in
order:
.display rm
\(OS/Makefile-Default)\
\(OS/Makefile-)\<<ostype>>
\(Local/Makefile)\
\(Local/Makefile-)\<<ostype>>
\(Local/Makefile-)\<<archtype>>
\(Local/Makefile-)\<<ostype>>-<<archtype>>
\(OS/Makefile-Base)\
.endd
.index \(Local/Makefile)\
where <<ostype>> is the operating system type and <<archtype>> is the
.index building Exim||operating system type
.index building Exim||architecture type
architecture type. \(Local/Makefile)\ is required to exist, and the building
process fails if it is absent. The other three \(Local)\ files are optional,
and are often not needed.

The values used for <<ostype>> and <<archtype>> are obtained from scripts
called \(scripts/os-type)\ and \(scripts/arch-type)\ respectively. If either of
the environment variables \\EXIM@_OSTYPE\\ or \\EXIM@_ARCHTYPE\\ is set, their
values are used, thereby providing a means of forcing particular settings.
Otherwise, the scripts try to get values from the \uname\ command. If this
fails, the shell variables \\OSTYPE\\ and \\ARCHTYPE\\ are inspected. A number
of $it{ad hoc} transformations are then applied, to produce the standard names
that Exim expects. You can run these scripts directly from the shell in order
to find out what values are being used on your system.


\(OS/Makefile-Default)\ contains comments about the variables that are set
therein. Some (but not all) are mentioned below. If there is something that
needs changing, review the contents of this file and the contents of the make
file for your operating system (\(OS/Makefile-<<ostype>>)\) to see what the
default values are.


.index building Exim||overriding default settings
If you need to change any of the values that are set in \(OS/Makefile-Default)\
or in \(OS/Makefile-<<ostype>>)\, or to add any new definitions, you do not 
need to change the original files. Instead, you should make the changes by
putting the new values in an appropriate \(Local)\ file. For example,
.index Tru64-Unix build-time settings
when building Exim in many releases of the Tru64-Unix (formerly Digital UNIX,
formerly DEC-OSF1) operating system, it is necessary to specify that the C
compiler is called \*cc*\ rather than \*gcc*\. Also, the compiler must be 
called with the option \-std1-\, to make it recognize some of the features of
Standard C that Exim uses. (Most other compilers recognize Standard C by 
default.) To do this, you should create a file called \(Local/Makefile-OSF1)\
containing the lines
.display
CC=cc
CFLAGS=-std1
.endd
If you are compiling for just one operating system, it may be easier to put 
these lines directly into \(Local/Makefile)\.

Keeping all your local configuration settings separate from the distributed
files makes it easy to transfer them to new versions of Exim simply by copying
the contents of the \(Local)\ directory.


.index NIS lookup type||including support for
.index NIS@+ lookup type||including support for
.index LDAP||including support for
.index lookup||inclusion in binary
Exim contains support for doing LDAP, NIS, NIS+, and other kinds of file
lookup, but not all systems have these components installed, so the default is
not to include the relevant code in the binary. All the different kinds of file
and database lookup that Exim supports are implemented as separate code modules
which are included only if the relevant compile-time options are set. In the
case of LDAP, NIS, and NIS+, the settings for \(Local/Makefile)\ are:
.display asis
LOOKUP_LDAP=yes
LOOKUP_NIS=yes
LOOKUP_NISPLUS=yes
.endd
and similar settings apply to the other lookup types. They are all listed in
\(src/EDITME)\. In most cases the relevant include files and interface
libraries need to be installed before compiling Exim.
.index cdb||including support for
However, in the case of cdb, which is included in the binary only if
.display asis
LOOKUP_CDB=yes
.endd
is set, the code is entirely contained within Exim, and no external include
files or libraries are required. When a lookup type is not included in the
binary, attempts to configure Exim to use it cause run time configuration
errors.

.index Perl||including support for
Exim can be linked with an embedded Perl interpreter, allowing Perl
subroutines to be called during string expansion. To enable this facility,
.display asis
EXIM_PERL=perl.o
.endd
must be defined in \(Local/Makefile)\. Details of this facility are given in
chapter ~~CHAPperl.

.index X11 libraries, location of
The location of the X11 libraries is something that varies a lot between
operating systems, and of course there are different versions of X11 to cope
with. Exim itself makes no use of X11, but if you are compiling the Exim
monitor, the X11 libraries must be available.
The following three variables are set in \(OS/Makefile-Default)\:
.display asis
X11=/usr/X11R6
XINCLUDE=-I$(X11)/include
XLFLAGS=-L$(X11)/lib
.endd
These are overridden in some of the operating-system configuration files. For
example, in \(OS/Makefile-SunOS5)\ there is
.display asis
X11=/usr/openwin
XINCLUDE=-I$(X11)/include
XLFLAGS=-L$(X11)/lib -R$(X11)/lib
.endd
If you need to override the default setting for your operating system, place a
definition of all three of these variables into your
\(Local/Makefile-<<ostype>>)\ file.

.index \\EXTRALIBS\\
If you need to add any extra libraries to the link steps, these can be put in a
variable called \\EXTRALIBS\\, which appears in all the link commands, but by
default is not defined. In contrast, \\EXTRALIBS@_EXIM\\ is used only on the
command for linking the main Exim binary, and not for any associated utilities.
.index DBM||libraries, configuration for building
There is also \\DBMLIB\\, which appears in the link commands for binaries that
use DBM functions (see also section ~~SECTdb). Finally, there is
\\EXTRALIBS@_EXIMON\\, which appears only in the link step for the Exim monitor
binary, and which can be used, for example, to include additional X11
libraries.

.index configuration file||editing
The make file copes with rebuilding Exim correctly if any of the configuration
files are edited. However, if an optional configuration file is deleted, it is
necessary to touch the associated non-optional file (that is, \(Local/Makefile)\
or \(Local/eximon.conf)\) before rebuilding.

.section OS-specific header files
.index \(os.h)\
.index building Exim||OS-specific C header files
The \(OS)\ directory contains a number of files with names of the form
\(os.h-<<ostype>>)\. These are system-specific C header files that should not
normally need to be changed. There is a list of macro settings that are
recognized in the file \(OS/os.configuring)\, which should be consulted if you
are porting Exim to a new operating system.


.section Overriding build-time options for the monitor
.index building Eximon||overriding default options
A similar process is used for overriding things when building the Exim monitor,
where the files that are involved are
.display rm
\(OS/eximon.conf-Default)\
\(OS/eximon.conf-)\<<ostype>>
\(Local/eximon.conf)\
\(Local/eximon.conf-)\<<ostype>>
\(Local/eximon.conf-)\<<archtype>>
\(Local/eximon.conf-)\<<ostype>>-<<archtype>>
.endd
.index \(Local/eximon.conf)\
As with Exim itself, the final three files need not exist, and in this case the
\(OS/eximon.conf-<<ostype>>)\ file is also optional. The default values in
\(OS/eximon.conf-Default)\ can be overridden dynamically by setting environment
variables of the same name, preceded by \\EXIMON@_\\. For example, setting
\\EXIMON@_LOG@_DEPTH\\ in the environment overrides the value of
\\LOG@_DEPTH\\ at run time.



.section Installing Exim binaries and scripts
.index installing Exim
.index \\BIN@_DIRECTORY\\
The command \*make install*\ runs the \*exim@_install*\ script with no
arguments. The script copies binaries and utility scripts into the directory
whose name is specified by the \\BIN@_DIRECTORY\\ setting in
\(Local/Makefile)\. 

Exim's run time configuration file is named by the \\CONFIGURE@_FILE\\ setting
.index \\CONFIGURE@_FILE\\
in \(Local/Makefile)\. If this names a single file, and the file does not
exist, the default configuration file \(src/configure.default)\ is copied there
by the installation script. If a run time configuration file already exists, it
is left alone. If \\CONFIGURE@_FILE\\ is a colon-separated list, naming several
alternative files, no default is installed.

.index system aliases file
.index \(/etc/aliases)\
One change is made to the default configuration file when it is installed: the
default configuration contains a router that references a system aliases file.
The path to this file is set to the value specified by
\\SYSTEM@_ALIASES@_FILE\\ in \(Local/Makefile)\ (\(/etc/aliases)\ by default).
If the system aliases file does not exist, the installation script creates it,
and outputs a comment to the user.

The created file contains no aliases, but it does contain comments about the
aliases a site should normally have. Mail aliases have traditionally been
kept in \(/etc/aliases)\. However, some operating systems are now using
\(/etc/mail/aliases)\. You should check if yours is one of these, and change
Exim's configuration if necessary.

The default configuration uses the local host's name as the only local domain,
and is set up to do local deliveries into the shared directory \(/var/mail)\,
running as the local user. System aliases and \(.forward)\ files in users' home
directories are supported, but no NIS or NIS+ support is configured. Domains
other than the name of the local host are routed using the DNS, with delivery
over SMTP.

The install script copies files only if they are newer than the files they are
going to replace. The Exim binary is required to be owned by root and have the
\*setuid*\ bit set,
.index setuid||installing Exim with
for normal configurations. Therefore, you must run \*make install*\ as root so
that it can set up the Exim binary in this way. However, in some special
situations (for example, if a host is doing no local deliveries) it may be
possible to run Exim without making the binary setuid root (see chapter
~~CHAPsecurity for details).

It is possible to install Exim for special purposes (such as building a binary
distribution) in a private part of the file system. You can do this by a
command such as
.display asis
make DESTDIR=/some/directory/ install
.endd
This has the effect of pre-pending the specified directory to all the file 
paths, except the name of the system aliases file that appears in the default 
configuration. (If a default alias file is created, its name \*is*\ modified.)
For backwards compatibility, \\ROOT\\ is used if \\DESTDIR\\ is not set, 
but this usage is deprecated.

.index installing Exim||what is not installed
Running \*make install*\ does not copy the Exim 4 conversion script
\*convert4r4*\, or the \*pcretest*\ test program. You will probably run the
first of these only once (if you are upgrading from Exim 3), and the second
isn't really part of Exim. None of the documentation files in the \(doc)\
directory are copied, except for the info files when you have set
\\INFO@_DIRECTORY\\, as described in section ~~SECTinsinfdoc below.

For the utility programs, old versions are renamed by adding the suffix \(.O)\
to their names. The Exim binary itself, however, is handled differently. It is
installed under a name that includes the version number and the compile number,
for example \(exim-~~version-1)\. The script then arranges for a symbolic link
called \(exim)\ to point to the binary. If you are updating a previous version
of Exim, the script takes care to ensure that the name \(exim)\ is never absent
from the directory (as seen by other processes).

.index installing Exim||testing the script
If you want to see what the \*make install*\ will do before running it for
real, you can pass the \-n-\ option to the installation script by this command:
.display asis
make INSTALL_ARG=-n install
.endd
The contents of the variable \\INSTALL@_ARG\\ are passed to the installation
script. You do not need to be root to run this test. Alternatively, you can run
the installation script directly, but this must be from within the build
directory. For example, from the top-level Exim directory you could use this
command:
.display
(cd build-SunOS5-5.5.1-sparc; ../scripts/exim@_install -n)
.endd

.index installing Exim||install script options
There are two other options that can be supplied to the installation script.
.numberpars $.
\-no@_chown-\ bypasses the call to change the owner of the installed binary
to root, and the call to make it a setuid binary.
.nextp
\-no@_symlink-\ bypasses the setting up of the symbolic link \(exim)\ to the
installed binary.
.endp
\\INSTALL@_ARG\\ can be used to pass these options to the script. For example:
.display asis
make INSTALL_ARG=-no_symlink install
.endd

The installation script can also be given arguments specifying which files are 
to be copied. For example, to install just the Exim binary, and nothing else, 
without creating the symbolic link, you could use:
.display asis
make INSTALL_ARG='-no_symlink exim' install
.endd


.section Installing info documentation
.rset SECTinsinfdoc "~~chapter.~~section"
.index installing Exim||\*info*\ documentation
Not all systems use the GNU \*info*\ system for documentation, and for this
reason, the Texinfo source of Exim's documentation is not included in the main
distribution. Instead it is available separately from the ftp site (see section
~~SECTavail).

If you have defined \\INFO@_DIRECTORY\\ in \(Local/Makefile)\ and the Texinfo
source of the documentation is found in the source tree, running \*make
install*\ automatically builds the info files and installs them.


.section Setting up the spool directory
.index spool directory||creating
When it starts up, Exim tries to create its spool directory if it does not
exist. The Exim uid and gid are used for the owner and group of the spool
directory. Sub-directories are automatically created in the spool directory as
necessary.



.section Testing
.index testing||installation
Having installed Exim, you can check that the run time configuration file is
syntactically valid by running the following command, which assumes that the
Exim binary directory is within your \\PATH\\ environment variable:
.display
exim -bV
.endd
If there are any errors in the configuration file, Exim outputs error messages.
Otherwise it outputs the version number and build date,
the DBM library that is being used, and information about which drivers and 
other optional code modules are included in the binary.
Some simple routing tests can be done by using the address testing option. For
example,
.display
exim -bt <<local username>>
.endd
should verify that it recognizes a local mailbox, and
.display
exim -bt <<remote address>>
.endd
a remote one. Then try getting it to deliver mail, both locally and remotely.
This can be done by passing messages directly to Exim, without going through a
user agent. For example:
.display
exim -v postmaster@@your.domain.example
From: user@@your.domain.example
To: postmaster@@your.domain.example
Subject: Testing Exim

This is a test message.
^D
.endd
The \-v-\ option causes Exim to output some verification of what it is doing.
In this case you should see copies of three log lines, one for the message's
arrival, one for its delivery, and one containing `Completed'.

.index delivery||problems with
If you encounter problems, look at Exim's log files (\*mainlog*\ and
\*paniclog*\) to see if there is any relevant information there. Another source
of information is running Exim with debugging turned on, by specifying the
\-d-\ option. If a message is stuck on Exim's spool, you can force a delivery
with debugging turned on by a command of the form
.display
exim -d -M <<message-id>>
.endd
You must be root or an `admin user' in order to do this. The \-d-\ option
produces rather a lot of output, but you can cut this down to specific areas.
For example, if you use \-d-all+route-\ only the debugging information relevant
to routing is included. (See the \-d-\ option in chapter ~~CHAPcommandline for
more details.)

.index `sticky' bit
.index lock files
One specific problem that has shown up on some sites is the inability to do
local deliveries into a shared mailbox directory, because it does not have the
`sticky bit' set on it. By default, Exim tries to create a lock file before
writing to a mailbox file, and if it cannot create the lock file, the delivery
is deferred. You can get round this either by setting the `sticky bit' on the
directory, or by setting a specific group for local deliveries and allowing
that group to create files in the directory (see the comments above the
\%local@_delivery%\ transport in the default configuration file). Another
approach is to configure Exim not to use lock files, but just to rely on
\*fcntl()*\ locking instead. However, you should do this only if all user
agents also use \*fcntl()*\ locking. For further discussion of locking issues,
see chapter ~~CHAPappendfile.

One thing that cannot be tested on a system that is already running an MTA is
the receipt of incoming SMTP mail on the standard SMTP port. However, the
\-oX-\ option can be used to run an Exim daemon that listens on some other
port, or \*inetd*\ can be used to do this. The \-bh-\ option and the
\*exim@_checkaccess*\ utility can be used to check out policy controls on
incoming SMTP mail.

Testing a new version on a system that is already running Exim can most easily
be done by building a binary with a different \\CONFIGURE@_FILE\\ setting. From
within the run time configuration, all other file and directory names
that Exim uses can be altered, in order to keep it entirely clear of the
production version.

.section Replacing another MTA with Exim
.index replacing another MTA
Building and installing Exim for the first time does not of itself put it in
general use. The name by which the system's MTA is called by mail user agents
is either \(/usr/sbin/sendmail)\, or \(/usr/lib/sendmail)\ (depending on the
operating system), and it is necessary to make this name point to the \*exim*\
binary in order to get the user agents to pass messages to Exim. This is
normally done by renaming any existing file and making \(/usr/sbin/sendmail)\
or \(/usr/lib/sendmail)\
.index symbolic link||to \*exim*\ binary
a symbolic link to the \*exim*\ binary. It is a good idea to remove any setuid
privilege and executable status from the old MTA. It is then necessary to stop
and restart the mailer daemon, if one is running.

.index FreeBSD, MTA indirection
.index \(/etc/mail/mailer.conf)\
Some operating systems have introduced alternative ways of switching MTAs. For
example, if you are running FreeBSD, you need to edit the file
\(/etc/mail/mailer.conf)\ instead of setting up a symbolic link as just
described. A typical example of the contents of this file for running Exim is
as follows:
.display asis
sendmail            /usr/exim/bin/exim
send-mail           /usr/exim/bin/exim
mailq               /usr/exim/bin/exim -bp
newaliases          /usr/bin/true
.endd

Once you have set up the symbolic link, or edited \(/etc/mail/mailer.conf)\,
your Exim installation is `live'. Check it by sending a message from your
favourite user agent.

You should consider what to tell your users about the change of MTA. Exim may
have different capabilities to what was previously running, and there are
various operational differences such as the text of messages produced by
command line options and in bounce messages. If you allow your users to make
use of Exim's filtering capabilities, you should make the document entitled
.if ~~html
[(A HREF="filter.html")]
.fi
\*Exim's interface to mail filtering*\
.if ~~html
[(/A)]
.fi
available to them.


.section Upgrading Exim
.index upgrading Exim
If you are already running Exim on your host, building and installing a new
version automatically makes it available to MUAs, or any other programs that
call the MTA directly. However, if you are running an Exim daemon, you do need
to send it a HUP signal, to make it re-exec itself, and thereby pick up the new
binary. You do not need to stop processing mail in order to install a new
version of Exim.


.section Stopping the Exim daemon on Solaris
.index Solaris||stopping Exim on
The standard command for stopping the mailer daemon on Solaris is
.display
/etc/init.d/sendmail stop
.endd
If \(/usr/lib/sendmail)\ has been turned into a symbolic link, this script
fails to stop Exim because it uses the command \*ps -e*\ and greps the output
for the text `sendmail'; this is not present because the actual program name
(that is, `exim') is given by the \*ps*\ command with these options. A solution
is to replace the line that finds the process id with something like
.display asis
pid=`cat /var/spool/exim/exim-daemon.pid`
.endd
to obtain the daemon's pid directly from the file that Exim saves it in.

Note, however, that stopping the daemon does not `stop Exim'. Messages can 
still be received from local processes, and if automatic delivery is configured 
(the normal case), deliveries will still occur.


.
.
.
.
. ============================================================================
.chapter The Exim command line
.set runningfoot "command line"
.rset CHAPcommandline ~~chapter
.index command line||options
.index options||command line

Exim's command line takes the standard Unix form of a sequence of options,
each starting with a hyphen character, followed by a number of arguments. The
options are compatible with the main options of Sendmail, and there are also
some additional options, some of which are compatible with Smail 3. Certain
combinations of options do not make sense, and provoke an error if used.
The form of the arguments depends on which options are set.

.section Setting options by program name
.index \*mailq*\
If Exim is called under the name \*mailq*\, it behaves as if the option \-bp-\
were present before any other options. 
The \-bp-\ option requests a listing of the contents of the mail queue on the 
standard output.
This feature is for compatibility with some systems that contain a command of
that name in one of the standard libraries, symbolically linked to
\(/usr/sbin/sendmail)\ or \(/usr/lib/sendmail)\.

.index \*rsmtp*\
If Exim is called under the name \*rsmtp*\ it behaves as if the option \-bS-\
were present before any other options, for compatibility with Smail. The \-bS-\
option is used for reading in a number of messages in batched SMTP format.

.index \*rmail*\
If Exim is called under the name \*rmail*\ it behaves as if the \-i-\ and
\-oee-\ options were present before any other options, for compatibility with
Smail. The name \*rmail*\ is used as an interface by some UUCP systems.

.index \*runq*\
.index queue runner
If Exim is called under the name \*runq*\ it behaves as if the option \-q-\ were
present before any other options, for compatibility with Smail. The \-q-\
option causes a single queue runner process to be started.

.index \*newaliases*\
.index alias file||building
.index Sendmail compatibility||calling Exim as \*newaliases*\
If Exim is called under the name \*newaliases*\ it behaves as if the option
\-bi-\ were present before any other options, for compatibility with Sendmail.
This option is used for rebuilding Sendmail's alias file. Exim does not have
the concept of a single alias file, but can be configured to run a given
command if called with the \-bi-\ option.

.section Trusted and admin users
.rset SECTtrustedadmin "~~chapter.~~section"
Some Exim options are available only to \*trusted users*\ and others are
available only to \*admin users*\. In the description below, the phrases `Exim
user' and `Exim group' mean the user and group defined by \\EXIM@_USER\\ and
\\EXIM@_GROUP\\ in \(Local/Makefile)\ or set by the \exim@_user\ and
\exim@_group\ options. These do not necessarily have to use the name `exim'.

.numberpars $.
.index trusted user||definition of
.index user||trusted, definition of
The trusted users are root, the Exim user, any user listed in the
\trusted@_users\ configuration option, and any user whose current group or any
supplementary group is one of those listed in the \trusted@_groups\
configuration option. Note that the Exim group is not automatically trusted.

.index `From' line
.index envelope sender
Trusted users are always permitted to use the \-f-\ option or a leading `From '
line to specify the envelope sender of a message that is passed to Exim through
the local interface (see the \-bm-\ and \-f-\ options below). See the
\untrusted@_set@_sender\ option for a way of permitting non-trusted users to
set envelope senders.
.index ::From:: header line
.index ::Sender:: header line
For a trusted user, there is never any check on the contents of the ::From::
header line, and a ::Sender:: line is never added. Furthermore, any existing
::Sender:: line in incoming local (non-TCP/IP) messages is not removed.

Trusted users may also specify a host name, host address, interface address,
protocol name, ident value, and authentication data when submitting a message
locally. Thus, they are able to insert messages into Exim's queue locally that
have the characteristics of messages received from a remote host. Untrusted
users may in some circumstances use \-f-\, but can never set the other values
that are available to trusted users.
.nextp
.index user||admin, definition of
.index admin user||definition of
The admin users are root, the Exim user, and any user that is a member of the
Exim group or of any group listed in the \admin@_groups\ configuration option.
The current group does not have to be one of these groups.

Admin users are permitted to list the queue, and to carry out certain
operations on messages, for example, to force delivery failures. It is also
necessary to be an admin user in order to see the full information provided by
the Exim monitor, and full debugging output.

By default, the use of the \-M-\, \-q-\, \-R-\, and \-S-\ options to cause Exim
to attempt delivery of messages on its queue is restricted to admin users.
However, this restriction can be relaxed by setting the \prod@_requires@_admin\
option false (that is, specifying \no@_prod@_requires@_admin\).

Similarly, the use of the \-bp-\ option to list all the messages in the queue
is restricted to admin users unless \queue@_list@_requires@_admin\ is set
false.
.endp

\**Warning**\: If you configure your system so that admin users are able to 
edit Exim's configuration file, you are giving those users an easy way of 
getting root. There is further discussion of this issue at the start of chapter 
~~CHAPconf.



.section Command line options
The command options are described in alphabetical order below.

.startoptions

.option @-
.index options||command line, terminating
This is a pseudo-option whose only purpose is to terminate the options and
therefore to cause subsequent command line items to be treated as arguments
rather than options, even if they begin with hyphens.

.option -help
This option causes Exim to output a few sentences stating what it is.
The same output is generated if the Exim binary is called with no options and 
no arguments.

.option B <<type>>
.index 8-bit characters
.index Sendmail compatibility||8-bit characters
This is a Sendmail option for selecting 7 or 8 bit processing. Exim is 8-bit
clean; it ignores this option.

.option bd
.index daemon
.index SMTP listener
.index queue runner
This option runs Exim as a daemon, awaiting incoming SMTP connections. Usually
the \-bd-\ option is combined with the \-q-\<<time>> option, to specify that
the daemon should also initiate periodic queue runs.

The \-bd-\ option can be used only by an admin user. If either of the \-d-\
(debugging) or \-v-\ (verifying) options are set, the daemon does not
disconnect from the controlling terminal. When running this way, it can be
stopped by pressing ctrl-C.

By default, Exim listens for incoming connections to the standard SMTP port on
all the host's running interfaces. However, it is possible to listen on other
ports, on multiple ports, and only on specific interfaces. Chapter
~~CHAPinterfaces contains a description of the options that control this.

.index daemon||process id (pid)
.index pid (process id)||of daemon
When a listening daemon is started without the use of \-oX-\ (that is, without
overriding the normal configuration), it writes its process id to a file called
\(exim-daemon.pid)\ in Exim's spool directory. This location can be overridden
by setting \\PID@_FILE@_PATH\\ in \(Local/Makefile)\. The file is written while
Exim is still running as root.

When \-oX-\ is used on the command line to start a listening daemon, the
process id is not written to the normal pid file path. However, \-oP-\ can be
used to specify a path on the command line if a pid file is required.

.index \\SIGHUP\\
The \\SIGHUP\\ signal can be used to cause the daemon to re-exec itself. This
should be done whenever Exim's configuration file, or any file that is
incorporated into it by means of the \.include\ facility, is changed, and also 
whenever a new version of Exim is installed. It is not necessary to do this
when other files that are referenced from the configuration (for example, alias
files) are changed, because these are reread each time they are used.

.option bdf
This option has the same effect as \-bd-\ except that it never disconnects from
the controlling terminal, even when no debugging is specified.

.option be
.index testing||string expansion
.index expansion||testing
Run Exim in expansion testing mode. Exim discards its root privilege, to
prevent ordinary users from using this mode to read otherwise inaccessible
files. If no arguments are given, Exim runs interactively, prompting for lines
of data. Long expressions can be split over several lines by using backslash
continuations. 
As in Exim's run time configuration, whitespace at the start of continuation
lines is ignored.

Each argument or data line is passed through the string expansion mechanism,
and the result is output. Variable values from the configuration file (for
example, \$qualify@_domain$\) are available, but no message-specific values
(such as \$domain$\) are set, because no message is being processed.

.option bF #<<filename>>
.index system filter||testing
.index testing||system filter
This option is the same as \-bf-\ except that it assumes that the filter being
tested is a system filter. The additional commands that are available only in
system filters are recognized.

.option bf #<<filename>>
.index filter||testing
.index testing||filter file
.index forward file||testing
.index testing||forward file
.index Sieve filter||testing
This option runs Exim in filter testing mode; the file is the filter file to be
tested, and a test message must be supplied on the standard input. If there are
no message-dependent tests in the filter, an empty file can be supplied. If a
system filter file is being tested, \-bF-\ should be used instead of \-bf-\. If
the test file does not begin with 
one of the special lines
.display asis
# Exim filter
# Sieve filter
.endd
it is taken to be a normal \(.forward)\ file, and is tested for validity under
that interpretation. See sections ~~SECTitenonfilred to ~~SECTspecitredli for a 
description of the possible contents of non-filter redirection lists.

The result of an Exim command that uses \-bf-\, provided no errors are
detected, is a list of the actions that Exim would try to take if presented
with the message for real. More details of filter testing are given in the
separate document entitled \*Exim's interfaces to mail filtering*\.

.index `From' line
.index envelope sender
.index \-f-\ option||for filter testing
When testing a filter file, the envelope sender can be set by the \-f-\ option,
or by a `From ' line at the start of the test message. Various parameters that
would normally be taken from the envelope recipient address of the message can
be set by means of additional command line options. These are:
.display rm
.if ~~sys.fancy
.tabset 12em 16em
.else
.tabset 15em 20em
.fi
. The odd alignment here gets it lined up in the man page.
\-bfd-\ $t <<domain>>            $t $rm{default is the qualify domain}
\-bfl-\ $t <<local@_part>>        $t $rm{default is the logged in user}
\-bfp-\ $t <<local@_part@_prefix>> $t $rm{default is null}
\-bfs-\ $t <<local@_part@_suffix>> $t $rm{default is null}
.endd
The local part should always be set to the incoming address with any prefix or
suffix stripped, because that is how it appears to the filter when a message is
actually being delivered.

.option bh #<<IP address>>
.index testing||incoming SMTP
.index SMTP||testing incoming
.index testing||relay control
.index relaying||testing configuration
.index policy control||testing
.index debugging||\-bh-\ option
This option runs a fake SMTP session as if from the given IP address, using the
standard input and output. The IP address may include a port number at the end,
after a full stop. For example:
.display asis
exim -bh 10.9.8.7.1234
exim -bh fe80::a00:20ff:fe86:a061.5678
.endd
Comments as to what is going on are written to the standard error file. These
include lines beginning with `LOG' for anything that would have been logged.
This facility is provided for testing configuration options for incoming 
messages, to make sure they implement the required policy. For example, you can 
test your relay controls using \-bh-\.

.index RFC 1413
\**Warning 1**\: You cannot test features of the configuration that rely on
ident (RFC 1413) callouts. These cannot be done when testing using
\-bh-\ because there is no incoming SMTP connection.

\**Warning 2**\: Address verification callouts (see section ~~SECTcallver) are
also skipped when testing using \-bh-\. If you want these callouts to occur, 
use \-bhc-\ instead.

Messages supplied during the testing session are discarded, and nothing is
written to any of the real log files. There may be pauses when DNS (and other)
lookups are taking place, and of course these may time out. The \-oMi-\ option
can be used to specify a specific IP interface and port if this is important.

The \*exim@_checkaccess*\ utility is a `packaged' version of \-bh-\ whose
output just states whether a given recipient address from a given host is
acceptable or not. See section ~~SECTcheckaccess.

.option bhc #<<IP address>>
This option operates in the same way as \-bh-\, except that address 
verification callouts are performed if required. This includes consulting and 
updating the callout cache database. 

.option bi
.index alias file||building
.index building alias file
.index Sendmail compatibility||\-bi-\ option
Sendmail interprets the \-bi-\ option as a request to rebuild its alias file.
Exim does not have the concept of a single alias file, and so it cannot mimic
this behaviour. However, calls to \(/usr/lib/sendmail)\ with the \-bi-\ option
tend to appear in various scripts such as NIS make files, so the option must be
recognized.

If \-bi-\ is encountered, the command specified by the \bi@_command\
configuration option is run, under the uid and gid of the caller of Exim. If
the \-oA-\ option is used, its value is passed to the command as an argument.
The command set by \bi@_command\ may not contain arguments. The command can use
the \*exim@_dbmbuild*\ utility, or some other means, to rebuild alias files if
this is required. If the \bi@_command\ option is not set, calling Exim with
\-bi-\ is a no-op.

.option bm
.index local message reception
This option runs an Exim receiving process that accepts an incoming,
locally-generated message on the current input. The recipients are given as the
command arguments (except when \-t-\ is also present -- see below). Each
argument can be a comma-separated list of RFC 2822 addresses. This is the
default option for selecting the overall action of an Exim call; it is assumed
if no other conflicting option is present.

If any addresses in the message are unqualified (have no domain), they are
qualified by the values of the \qualify@_domain\ or \qualify@_recipient\
options, as appropriate. The \-bnq-\ option (see below) provides a way of
suppressing this for special cases.

Policy checks on the contents of local messages can be enforced by means of the 
non-SMTP ACL. See chapter ~~CHAPACL for details.
.index return code||for \-bm-\
The return code is zero if the message is successfully accepted. Otherwise, the
action is controlled by the \-oe$it{x}-\ option setting -- see below.

.index message||format
.index format||message
.index `From' line
.index UUCP||`From' line
.index Sendmail compatibility||`From' line
The format of the message must be as defined in RFC 2822, except that, for
compatibility with Sendmail and Smail, a line in one of the forms
.display
From sender Fri Jan  5 12:55 GMT 1997
From sender Fri, 5 Jan 97 12:55:01
.endd
(with the weekday optional, and possibly with additional text after the date)
is permitted to appear at the start of the message. There appears to be no
authoritative specification of the format of this line. Exim recognizes it by
matching against the regular expression defined by the \uucp@_from@_pattern\
option, which can be changed if necessary. 
.index \-f-\ option||overriding `From' line
The specified sender is treated as if it were given as the argument to the
\-f-\ option, but if a \-f-\ option is also present, its argument is used in
preference to the address taken from the message. The caller of Exim must be a
trusted user for the sender of a message to be set in this way.

.option bnq
.index address||qualification, suppressing
By default, Exim automatically qualifies unqualified addresses (those
without domains) that appear in messages that are submitted locally (that
is, not over TCP/IP). This qualification applies both to addresses in
envelopes, and addresses in header lines. Sender addresses are qualified using 
\qualify@_domain\, and recipient addresses using \qualify@_recipient\ (which 
defaults to the value of \qualify@_domain\).

Sometimes, qualification is not wanted. For example, if \-bS-\ (batch SMTP) is
being used to re-submit messages that originally came from remote hosts after
content scanning, you probably do not want to qualify unqualified addresses in
header lines. (Such lines will be present only if you have not enabled a header
syntax check in the appropriate ACL.)

The \-bnq-\ option suppresses all qualification of unqualified addresses in
messages that originate on the local host. When this is used, unqualified
addresses in the envelope provoke errors (causing message rejection) and
unqualified addresses in header lines are left alone.


.option bP
.index configuration options, extracting
.index options||configuration, extracting
If this option is given with no arguments, it causes the values of all Exim's
main configuration options to be written to the standard output. The values
of one or more specific options can be requested by giving their names as
arguments, for example:
.display
exim -bP qualify@_domain hold@_domains
.endd
However, any option setting that is preceded by the word `hide' in the
configuration file is not shown in full, except to an admin user. For other
users, the output is as in this example:
.display asis
mysql_servers = <value not displayable>
.endd
If \configure@_file\ is given as an argument, the name of the run time
configuration file is output.
If a list of configuration files was supplied, the value that is output here 
is the name of the file that was actually used.

.index daemon||process id (pid)
.index pid (process id)||of daemon
If \log__file__path\ or \pid@_file@_path\ are given, the names of the
directories where log files and daemon pid files are written are output,
respectively. If these values are unset, log files are written in a
sub-directory of the spool directory called \log\, and the pid file is written
directly into the spool directory.

If \-bP-\ is followed by a name preceded by \"+"\, for example,
.display asis
exim -bP +local_domains
.endd
it searches for a matching named list of any type (domain, host, address, or
local part) and outputs what it finds.

.index options||router, extracting
.index options||transport, extracting
If one of the words \router\, \transport\, or \authenticator\ is given,
followed by the name of an appropriate driver instance, the option settings for
that driver are output. For example:
.display
exim -bP transport local@_delivery
.endd
The generic driver options are output first, followed by the driver's private
options. A list of the names of drivers of a particular type can be obtained by
using one of the words \router@_list\, \transport@_list\, or
\authenticator@_list\, and a complete list of all drivers with their option
settings can be obtained by using \routers\, \transports\, or \authenticators\.


.option bp
.index queue||listing messages on
.index listing||messages on the queue
This option requests a listing of the contents of the mail queue on the
standard output. If the \-bp-\ option is followed by a list of message ids,
just those messages are listed. By default, this option can be used only by an
admin user. However, the \queue__list__requires__admin\ option can be set false
to allow any user to see the queue.

Each message on the queue is displayed as in the following example:
.display
25m  2.9K 0t5C6f-0000c8-00 <alice@@wonderland.fict.example>
          red.king@@looking-glass.fict.example
          <<other addresses>>
.endd
.index message||size in queue listing
.index size||of message
The first line contains the length of time the message has been on the queue
(in this case 25 minutes), the size of the message (2.9K), the unique local
identifier for the message, and the message sender, as contained in the
envelope. For bounce messages, the sender address is empty, and appears as
`<>'. If the message was submitted locally by an untrusted user who overrode
the default sender address, the user's login name is shown in parentheses
before the sender address.
.index frozen messages||in queue listing
If the message is frozen (attempts to deliver it are suspended) then the text
`$*$$*$$*$ frozen $*$$*$$*$' is displayed at the end of this line.

The recipients of the message (taken from the envelope, not the headers) are
displayed on subsequent lines. Those addresses to which the message has already
been delivered are marked with the letter D. If an original address gets
expanded into several addresses via an alias or forward file, the original is
displayed with a D only when deliveries for all of its child addresses are
complete.


.option bpa
This option operates like \-bp-\, but in addition it shows delivered addresses
that were generated from the original top level address(es) in each message by
alias or forwarding operations. These addresses are flagged with `+D' instead
of just `D'.


.option bpc
.index queue||count of messages on
This option counts the number of messages on the queue, and writes the total
to the standard output. It is restricted to admin users, unless
\queue__list__requires__admin\ is set false.


.option bpr
This option operates like \-bp-\, but the output is not sorted into
chronological order of message arrival. This can speed it up when there are
lots of messages on the queue, and is particularly useful if the output is
going to be post-processed in a way that doesn't need the sorting.

.option bpra
This option is a combination of \-bpr-\ and \-bpa-\.

.option bpru
This option is a combination of \-bpr-\ and \-bpu-\.


.option bpu
This option operates like \-bp-\ but shows only undelivered top-level addresses
for each message displayed. Addresses generated by aliasing or forwarding are
not shown, unless the message was deferred after processing by a router with
the \one@_time\ option set.


.option brt
.index testing||retry configuration
.index retry||configuration testing
This option is for testing retry rules, and it must be followed by up to three
arguments. It causes Exim to look for a retry rule that matches the values
and to write it to the standard output. For example:
.display asis
exim -brt bach.comp.mus.example
Retry rule: *.comp.mus.example  F,2h,15m; F,4d,30m;
.endd
See chapter ~~CHAPretry for a description of Exim's retry rules. The first
argument, which is required, can be a complete address in the form
\*local@_part@@domain*\, or it can be just a domain name. The second argument is
an optional second domain name; if no retry rule is found for the first
argument, the second is tried. This ties in with Exim's behaviour when looking
for retry rules for remote hosts -- if no rule is found that matches the host,
one that matches the mail domain is sought. The final argument is the name of a
specific delivery error, as used in setting up retry rules, for example
`quota@_3d'.

.option brw
.index testing||rewriting
.index rewriting||testing
This option is for testing address rewriting rules, and it must be followed by
a single argument, consisting of either a local part without a domain, or a
complete address with a fully qualified domain. Exim outputs how this address
would be rewritten for each possible place it might appear. See chapter
~~CHAPrewrite for further details.

.option bS
.index SMTP||batched incoming
.index batched SMTP input
This option is used for batched SMTP input, which is an alternative interface
for non-interactive local message submission. A number of messages can be
submitted in a single run. However, despite its name, this is not really SMTP
input. Exim reads each message's envelope from SMTP commands on the standard
input, but generates no responses. If the caller is trusted, or
\untrusted@_set@_sender\ is set, the senders in the SMTP \\MAIL\\ commands are
believed; otherwise the sender is always the caller of Exim.

The message itself is read from the standard input, in SMTP format (leading
dots doubled), terminated by a line containing just a single dot. An error is
provoked if the terminating dot is missing. A further message may then follow.

As for other local message submissions, the contents of incoming batch SMTP
messages can be checked using the non-SMTP ACL (see chapter ~~CHAPACL).
Unqualified addresses are automatically qualified using \qualify@_domain\ and
\qualify@_recipient\, as appropriate, unless the \-bnq-\ option is used.

Some other SMTP commands are recognized in the input. \\HELO\\ and \\EHLO\\ act
as \\RSET\\; \\VRFY\\, \\EXPN\\, \\ETRN\\, and \\HELP\\ act as \\NOOP\\;
\\QUIT\\ quits, ignoring the rest of the standard input.

If any error is encountered, reports are written to the standard output and
error streams, and Exim gives up immediately.
.index return code||for \-bS-\
The return code is 0 if no error was detected; it is 1 if one or more messages
were accepted before the error was detected; otherwise it is 2.

More details of input using batched SMTP are given in section
~~SECTincomingbatchedSMTP.

.option bs
.index SMTP||local input
.index local SMTP input
This option causes Exim to accept one or more messages by reading SMTP commands
on the standard input, and producing SMTP replies on the standard output. SMTP
policy controls, as defined in ACLs (see chapter ~~CHAPACL) are applied. 

Some user agents use this interface as a way of passing locally-generated
messages to the MTA.
.index sender||source of
In this usage, if the caller of Exim is trusted, or \untrusted@_set@_sender\ is
set, the senders of messages are taken from the SMTP \\MAIL\\ commands.
Otherwise the content of these commands is ignored and the sender is set up as
the calling user. Unqualified addresses are automatically qualified using
\qualify@_domain\ and \qualify@_recipient\, as appropriate, unless the \-bnq-\
option is used.

.index inetd
The \-bs-\ option is also used to run Exim from \*inetd*\, as an alternative to
using a listening daemon. Exim can distinguish the two cases by checking
whether the standard input is a TCP/IP socket. When Exim is called from 
\*inetd*\, the source of the mail is assumed to be remote, and the comments 
above concerning senders and qualification do not apply. In this situation, 
Exim behaves in exactly the same way as it does when receiving a message via 
the listening daemon.

.option bt
.index testing||addresses
.index address||testing
This option runs Exim in address testing mode, in which each argument is taken
as an address to be tested for deliverability. The results are written to the
standard output. 
If a test fails, and the caller is not an admin user, no details of the 
failure are output, because these might contain sensitive information such as 
usernames and passwords for database lookups.

If no arguments are given, Exim runs in an interactive manner, prompting with a
right angle bracket for addresses to be tested. Each address is handled as if
it were the recipient address of a message (compare the \-bv-\ option). It is
passed to the routers and the result is written to the standard output.
However, any router that has \no@_address@_test\ set is bypassed. This can 
make \-bt-\ easier to use for genuine routing tests if your first router passes
everything to a scanner program.

.index return code||for \-bt-\
The return code is 2 if any address failed outright; it is 1 if no address
failed outright but at least one could not be resolved for some reason. Return
code 0 is given only when all addresses succeed.

\**Warning**\: \-bt-\ can only do relatively simple testing. If any of the
routers in the configuration makes any tests on the sender address of a
message, 
.index \-f-\ option||for address testing
you can use the \-f-\ option to set an appropriate sender when running
\-bt-\ tests. Without it, the sender is assumed to be the calling user at the
default qualifying domain. However, if you have set up (for example) routers
whose behaviour depends on the contents of an incoming message, you cannot test
those conditions using \-bt-\. The \-N-\ option provides a possible way of
doing such tests.

.option bV
.index version number of Exim, verifying
This option causes Exim to write the current version number, compilation
number, and compilation date of the \*exim*\ binary to the standard output.
It also lists the DBM library this is being used, the optional modules (such as
specific lookup types), the drivers that are included in the binary, and the
name of the run time configuration file that is in use.

.option bv
.index verifying||address, using \-bv-\
.index address||verification
This option runs Exim in address verification mode, in which each argument is
taken as an address to be verified. During normal operation, verification
happens mostly as a consequence processing a \verify\ condition in an ACL (see
chapter ~~CHAPACL). If you want to test an entire ACL, see the \-bh-\ option.

If verification fails, and the caller is not an admin user, no details of the
failure are output, because these might contain sensitive information such as
usernames and passwords for database lookups.

If no arguments are given, Exim runs in an interactive manner, prompting with a
right angle bracket for addresses to be verified. Verification differs from
address testing (the \-bt-\ option) in that routers that have \no@_verify\ set
are skipped, and if the address is accepted by a router that has \fail@_verify\
set, verification fails. The address is verified as a recipient if \-bv-\ is
used; to test verification for a sender address, \-bvs-\ should be used.

If the \-v-\ option is not set, the output consists of a single line for each
address, stating whether it was verified or not, and giving a reason in the
latter case. Otherwise, more details are given of how the address has been
handled, and in the case of address redirection, all the generated addresses
are also considered. Without \-v-\, generating more than one address by
redirection causes verification to end sucessfully.

.index return code||for \-bv-\
The return code is 2 if any address failed outright; it is 1 if no address
failed outright but at least one could not be resolved for some reason. Return
code 0 is given only when all addresses succeed.

If any of the routers in the configuration makes any tests on the sender
address of a message, you should use the \-f-\ option to set an appropriate
sender when running \-bv-\ tests. Without it, the sender is assumed to be the
calling user at the default qualifying domain.

.option bvs
This option acts like \-bv-\, but verifies the address as a sender rather
than a recipient address. This affects any rewriting and qualification that
might happen.

.option C #<<filelist>>
.index configuration file||alternate
.index \\CONFIGURE@_FILE\\
.index alternate configuration file
This option causes Exim to find the run time configuration file from the given
list instead of from the list specified by the \\CONFIGURE@_FILE\\
compile-time setting. Usually, the list will consist of just a single file
name, but it can be a colon-separated list of names. In this case, the first
file that exists is used. Failure to open an existing file stops Exim from
proceeding any further along the list, and an error is generated.

When this option is used by a caller other than root or the Exim user,
and the list is different from the compiled-in list, Exim gives up
its root privilege immediately, and runs with the real and effective uid and
gid set to those of the caller.
However, if \\ALT@_CONFIG@_ROOT@_ONLY\\ is defined in \(Local/Makefile)\, root
privilege is retained for \-C-\ only if the caller of Exim is root.
This option is not set by default.

Setting \\ALT@_CONFIG@_ROOT@_ONLY\\ locks out the possibility of testing a
configuration using \-C-\ right through message reception and delivery, even if
the caller is root. The reception works, but by that time, Exim is running as
the Exim user, so when it re-execs to regain privilege for the delivery, the
use of \-C-\ causes privilege to be lost. However, root can test reception and
delivery using two separate commands (one to put a message on the queue, using 
\-odq-\, and another to do the delivery, using \-M-\).

If \\ALT@_CONFIG@_PREFIX\\ is defined \(in Local/Makefile)\, it specifies a
prefix string with which any file named in a \-C-\ command line option
must start. In addition, the file name must not contain the sequence \"/../"\.
However, if the value of the \-C-\ option is identical to the value of
\\CONFIGURE@_FILE\\ in \(Local/Makefile)\, Exim ignores \-C-\ and proceeds as
usual. There is no default setting for \\ALT@_CONFIG@_PREFIX\\; when it is 
unset, any file name can be used with \-C-\.

\\ALT@_CONFIG@_PREFIX\\ can be used to confine alternative configuration files
to a directory to which only root has access. This prevents someone who has
broken into the Exim account from running a privileged Exim with an arbitrary
configuration file.

The \-C-\ facility is useful for ensuring that configuration files are
syntactically correct, but cannot be used for test deliveries, unless the
caller is privileged, or unless it is an exotic configuration that does not
require privilege. No check is made on the owner or group of the files
specified by this option.

.option D <<macro>>=<<value>>
.index macro||setting on command line
This option can be used to override macro definitions in the configuration file
(see section ~~SECTmacrodefs). However, like \-C-\, if it is used by an
unprivileged caller, it causes Exim to give up its root privilege. 
If \\DISABLE@_D@_OPTION\\ is defined in \(Local/Makefile)\, the use of \-D-\ is
completely disabled, and its use causes an immediate error exit.

The entire option (including equals sign if present) must all be within one
command line item. \-D-\ can be used to set the value of a macro to the empty 
string, in which case the equals sign is optional. These two commands are 
synonymous:
.display asis
exim -DABC  ...
exim -DABC= ...
.endd
To include spaces in a macro definition item, quotes must be used. If you use 
quotes, spaces are permitted around the macro name and the equals sign. For 
example:
.display asis
exim '-D ABC = something' ...
.endd
\-D-\ may be repeated up to 10 times on a command line.

.option d <<debug options>>
.index debugging||list of selectors
.index debugging||\-d-\ option
This option causes debugging information to be written to the standard
error stream. It is restricted to admin users because debugging output may show
database queries that contain password information. Also, the details of users'
filter files should be protected. When \-d-\ is used, \-v-\ is assumed. If
\-d-\ is given on its own, a lot of standard debugging data is output. This can
be reduced, or increased to include some more rarely needed information, by
following \-d-\ with a string made up of names preceded by plus or minus
characters. These add or remove sets of debugging data, respectively. For
example, \-d+filter-\ adds filter debugging, whereas \-d-all+filter-\ selects
only filter debugging. The available debugging categories are:
.display flow
.tabs 21
.
. The odd formatting of the lines below is deliberate. It does not affect the
. SGCAL output, but by putting in the space it keeps things aligned in the man
. page that is automatically generated from this text.
.
acl           $t $rm{ACL interpretation}
auth          $t $rm{authenticators}
deliver       $t $rm{general delivery logic}
dns           $t $rm{DNS lookups (see also resolver)}
dnsbl         $t $rm{DNS black list (aka RBL) code}
exec          $t $rm{arguments for \execv@(@)\ calls}
expand        $t $rm{detailed debugging for string expansions}
filter        $t $rm{filter handling}
hints@_lookup  $t $rm{hints data lookups}
host@_lookup   $t $rm{all types of name-to-IP address handling}
ident         $t $rm{ident lookup}
interface     $t $rm{lists of local interfaces}
lists         $t $rm{matching things in lists}
load          $t $rm{system load checks}
local@_scan    $t $rm{can be used by \*local@_scan()*\ (see chapter ~~CHAPlocalscan)} 
lookup        $t $rm{general lookup code and all lookups}
memory        $t $rm{memory handling}
pid           $t $rm{add pid to debug output lines}
process@_info  $t $rm{setting info for the process log}
queue@_run     $t $rm{queue runs}
receive       $t $rm{general message reception logic}
resolver      $t $rm{turn on the DNS resolver's debugging output}
retry         $t $rm{retry handling}
rewrite       $t $rm{address rewriting}
route         $t $rm{address routing}
timestamp     $t $rm{add timestamp to debug output lines}
tls           $t $rm{TLS logic}
transport     $t $rm{transports}
uid           $t $rm{changes of uid/gid and looking up uid/gid}
verify        $t $rm{address verification logic}

all           $t $rm{all of the above, and also \-v-\}
.endd
.em
.index resolver, debugging output
.index DNS||resolver, debugging output
The \"resolver"\ option produces output only if the DNS resolver was compiled 
with \\DEBUG\\ enabled. This is not the case in some operating systems. Also,
unfortunately, debugging output from the DNS resolver is written to stdout
rather than stderr.
.nem

The default (\-d-\ with no argument) omits \"expand"\, \"filter"\,
\"interface"\, \"load"\, \"memory"\, \"pid"\, \"resolver"\, and \"timestamp"\.
However, the \"pid"\ selector is forced when debugging is turned on for a
daemon, which then passes it on to any re-executed Exims. Exim also
automatically adds the pid to debug lines when several remote deliveries are
run in parallel.

The \"timestamp"\ selector causes the current time to be inserted at the start
of all debug output lines. This can be useful when trying to track down delays
in processing.

If the \debug@_print\ option is set in any driver, it produces output whenever
any debugging is selected, or if \-v-\ is used.

.option dropcr
This is an obsolete option that is now a no-op. It used to affect the way Exim 
handled CR and LF characters in incoming messages. What happens now is 
described in section ~~SECTlineendings.


.option E
.index bounce message||generating
This option specifies that an incoming message is a locally-generated delivery
failure report. It is used internally by Exim when handling delivery failures
and is not intended for external use. Its only effect is to stop Exim
generating certain messages to the postmaster, as otherwise message cascades
could occur in some situations. As part of the same option, a message id may
follow the characters \-E-\. If it does, the log entry for the receipt of the
new message contains the id, following `R=', as a cross-reference.

.option e$it{x}
There are a number of Sendmail options starting with \-oe-\ which seem to be
called by various programs without the leading \o\ in the option. For example,
the \vacation\ program uses \-eq-\. Exim treats all options of the form
\-e$it{x}-\ as synonymous with the corresponding \-oe$it{x}-\ options.

.option F #<<string>>
.index sender||name
.index name||of sender
This option sets the sender's full name for use when a locally-generated
message is being accepted. In the absence of this option, the user's \*gecos*\
entry from the password data is used. As users are generally permitted to alter
their \*gecos*\ entries, no security considerations are involved. White space
between \-F-\ and the <<string>> is optional.

.option f #<<address>>
.index sender||address
.index address||sender
.index trusted user
.index envelope sender
.index user||trusted
This option sets the address of the envelope sender of a locally-generated
message (also known as the return path). The option can normally be used only
by a trusted user, but \untrusted@_set@_sender\ can be set to allow untrusted
users to use it. In the absence of \-f-\, or if the caller is not allowed to
use it, the sender of a local message is set to the caller's login name at the
default qualify domain.

There is one exception to the restriction on the use of \-f-\: an empty sender 
can be specified by any user, to create a message that can never provoke a
bounce. An empty sender can be specified either as an empty string, or as a
pair of angle brackets with nothing between them, as in these examples of shell 
commands:
.display asis
exim -f '<>' user@domain
exim -f "" user@domain
.endd
In addition, the use of \-f-\ is not restricted when testing a filter file with
\-bf-\ or when testing or verifying addresses using the \-bt-\ or \-bv-\
options.

Allowing untrusted users to change the sender address does not of itself make
it possible to send anonymous mail. Exim still checks that the ::From:: header
refers to the local user, and if it does not, it adds a ::Sender:: header,
though this can be overridden by setting \no@_local@_from@_check\.

.index `From' line
White space between \-f-\ and the <<address>> is optional
(that is, they can be given as two arguments or one combined argument).
The sender of a locally-generated message can also be set (when permitted) by
an initial `From ' line in the message -- see the description of \-bm-\ above
-- but if \-f-\ is also present, it overrides `From'.

.option G
.index Sendmail compatibility||\-G-\ option ignored
This is a Sendmail option which is ignored by Exim.

.option h #<<number>>
.index Sendmail compatibility||\-h-\ option ignored
This option is accepted for compatibility with Sendmail, but has no effect. (In
Sendmail it overrides the `hop count' obtained by counting ::Received::
headers.)

.option i
.index Solaris||\*mail*\ command
.index dot||in incoming, non-SMTP message
This option, which has the same effect as \-oi-\, specifies that a dot on a
line by itself should not terminate an incoming, non-SMTP message. I can find
no documentation for this option in Solaris 2.4 Sendmail, but the \*mailx*\
command in Solaris 2.4 uses it. See also \-ti-\.

.option M #<<message id>>#<<message id>> ...
.index forcing delivery
.index delivery||forcing attempt
.index frozen messages||forcing delivery
This option requests Exim to run a delivery attempt on each message in turn. If
any of the messages are frozen, they are automatically thawed before the
delivery attempt. The settings of \queue@_domains\, \queue@_smtp@_domains\, and
\hold@_domains\ are ignored. 
.index hints database||overriding retry hints
Retry hints for any of the addresses are
overridden -- Exim tries to deliver even if the normal retry time has not yet
been reached. This option requires the caller to be an admin user. However,
there is an option called \prod@_requires@_admin\ which can be set false to
relax this restriction (and also the same requirement for the \-q-\, \-R-\, and
\-S-\ options).


.option Mar #<<message id>>#<<address>>#<<address>> ...
.index message||adding recipients
.index recipient||adding
This option requests Exim to add the addresses to the list of recipients of the
message (`ar' for `add recipients'). The first argument must be a message id,
and the remaining ones must be email addresses. However, if the message is
active (in the middle of a delivery attempt), it is not altered. This option
can be used only by an admin user.

.index SMTP||passed connection
.index SMTP||multiple deliveries
.index multiple SMTP deliveries
.option MC #<<transport>>#<<hostname>>#<<sequence number>>#<<message id>>
This option is not intended for use by external callers. It is used internally
by Exim to invoke another instance of itself to deliver a waiting message using
an existing SMTP connection, which is passed as the standard input. Details are
given in chapter ~~CHAPSMTP. This must be the final option, and the caller must
be root or the Exim user in order to use it.

.option MCA
This option is not intended for use by external callers. It is used internally
by Exim in conjunction with the \-MC-\ option. It signifies that the connection
to the remote host has been authenticated.

.option MCP
This option is not intended for use by external callers. It is used internally 
by Exim in conjunction with the \-MC-\ option. It signifies that the server to 
which Exim is connected supports pipelining.

.option MCQ #<<process id>> <<pipe fd>>
This option is not intended for use by external callers. It is used internally
by Exim in conjunction with the \-MC-\ option when the original delivery was
started by a queue runner. It passes on the process id of the queue runner,
together with the file descriptor number of an open pipe. Closure of the pipe
signals the final completion of the sequence of processes that are passing
messages through the same SMTP connection.

.option MCS
This option is not intended for use by external callers. It is used internally
by Exim in conjunction with the \-MC-\ option, and passes on the fact that the
SMTP \\SIZE\\ option should be used on messages delivered down the existing
connection.

.option MCT
This option is not intended for use by external callers. It is used internally
by Exim in conjunction with the \-MC-\ option, and passes on the fact that the
host to which Exim is connected supports TLS encryption.

.option Mc #<<message id>>#<<message id>> ...
.index hints database||not overridden by \-Mc-\
.index delivery||manually started, not forced
This option requests Exim to run a delivery attempt on each message in turn,
but unlike the \-M-\ option, it does check for retry hints, and respects any
that are found. This option is not very useful to external callers. It is
provided mainly for internal use by Exim when it needs to re-invoke itself in
order to regain root privilege for a delivery (see chapter ~~CHAPsecurity).
However, \-Mc-\ can be useful when testing, in order to run a delivery that
respects retry times and other options such as \hold@_domains\ that are
overridden when \-M-\ is used. Such a delivery does not count as a queue run.
If you want to run a specific delivery as if in a queue run, you should use
\-q-\ with a message id argument. A distinction between queue run deliveries
and other deliveries is made in one or two places.

.option Mes #<<message id>>#<<address>>
.index message||changing sender
.index sender||changing
This option requests Exim to change the sender address in the message to the
given address, which must be a fully qualified address or `<>' (`es' for `edit
sender'). There must be exactly two arguments. The first argument must be a
message id, and the second one an email address. However, if the message is
active (in the middle of a delivery attempt), its status is not altered. This
option can be used only by an admin user.

.option Mf #<<message id>>#<<message id>> ...
.index freezing messages
.index message||manually freezing
This option requests Exim to mark each listed message as `frozen'. This
prevents any delivery attempts taking place until the message is `thawed',
either manually or as a result of the \auto@_thaw\ configuration option.
However, if any of the messages are active (in the middle of a delivery
attempt), their status is not altered. This option can be used only by an admin
user.

.option Mg #<<message id>>#<<message id>> ...
.index giving up on messages
.index message||abandoning delivery attempts
.index delivery||abandoning further attempts
This option requests Exim to give up trying to deliver the listed messages,
including any that are frozen. However, if any of the messages are active,
their status is not altered. 
For non-bounce messages, a delivery error message is sent to the sender,
containing the text `cancelled by administrator'. Bounce messages are just
discarded.
This option can be used only by an admin user.

.option Mmad #<<message id>>#<<message id>> ...
.index delivery||cancelling all
This option requests Exim to mark all the recipient addresses in the messages
as already delivered (`mad' for `mark all delivered'). However, if any message
is active (in the middle of a delivery attempt), its status is not altered.
This option can be used only by an admin user.

.option Mmd #<<message id>>#<<address>>#<<address>> ...
.index delivery||cancelling by address
.index recipient||removing
.index removing recipients
This option requests Exim to mark the given addresses as already delivered
(`md' for `mark delivered'). The first argument must be a message id, and the
remaining ones must be email addresses. These are matched to recipient
addresses in the message in a case-sensitive manner. If the message is active
(in the middle of a delivery attempt), its status is not altered. This option
can be used only by an admin user.

.option Mrm #<<message id>>#<<message id>> ...
.index removing messages
.index abandoning mail
.index message||manually discarding
This option requests Exim to remove the given messages from the queue. No
bounce messages are sent; each message is simply forgotten. However, if any of
the messages are active, their status is not altered. This option can be used
only by an admin user or by the user who originally caused the message to be
placed on the queue.

.option Mt #<<message id>>#<<message id>> ...
.index thawing messages
.index unfreezing messages
.index frozen messages||thawing
.index message||thawing frozen
This option requests Exim to `thaw' any of the listed messages that are
`frozen', so that delivery attempts can resume. However, if any of the messages
are active, their status is not altered. This option can be used only by an
admin user.

.option Mvb #<<message id>>
.index listing||message body
.index message||listing body of
This option causes the contents of the message body (-D) spool file to be
written to the standard output. This option can be used only by an admin user.

.option Mvh #<<message id>>
.index listing||message headers
.index header lines||listing
.index message||listing header lines
This option causes the contents of the message headers (-H) spool file to be
written to the standard output. This option can be used only by an admin user.

.option Mvl #<<message id>>
.index listing||message log
.index message||listing message log
This option causes the contents of the message log spool file to be written to
the standard output. This option can be used only by an admin user.

.option m
This is apparently a synonym for \-om-\ that is accepted by Sendmail, so Exim
treats it that way too.

.option N
.index debugging||\-N-\ option
.index debugging||suppressing delivery
This is a debugging option that inhibits delivery of a message at the transport
level. It implies \-v-\. Exim goes through many of the motions of delivery --
it just doesn't actually transport the message, but instead behaves as if it
had successfully done so. However, it does not make any updates to the retry
database, and the log entries for deliveries are flagged with `$*$>' rather
than `=>'.

Because \-N-\ discards any message to which it applies, only root or the Exim
user are allowed to use it with \-bd-\, \-q-\, \-R-\ or \-M-\. In other words,
an ordinary user can use it only when supplying an incoming message to which it
will apply. Although transportation never fails when \-N-\ is set, an address
may be deferred because of a configuration problem on a transport, or a routing
problem. Once \-N-\ has been used for a delivery attempt, it sticks to the
message, and applies to any subsequent delivery attempts that may happen for
that message.

.option n
.index Sendmail compatibility||\-n-\ option ignored
This option is interpreted by Sendmail to mean `no aliasing'. It is ignored by
Exim.

.option O #<<data>>
This option is interpreted by Sendmail to mean `set option`. It is ignored by 
Exim.

.option oA #<<file name>>
.index Sendmail compatibility||\-oA-\ option
This option is used by Sendmail in conjunction with \-bi-\ to specify an
alternative alias file name. Exim handles \-bi-\ differently; see the
description above.

.index SMTP||passed connection
.option oB #<<n>>
.index SMTP||multiple deliveries
.index multiple SMTP deliveries
This is a debugging option which limits the maximum number of messages that can
be delivered down one SMTP connection, overriding the value set in any \%smtp%\
transport. If <<n>> is omitted, the limit is set to 1.

.option odb
.index background delivery
.index delivery||in the background
This option applies to all modes in which Exim accepts incoming messages,
including the listening daemon. It requests `background' delivery of such
messages, which means that the accepting process automatically starts delivery
process for each message received, but does not wait for the delivery process
to complete. This is the default action if none of the \-od-\ options are
present. 

If one of the queueing options in the configuration file
(\queue@_only\ or \queue@_only@_file\, for example) is in effect, \-odb-\
overrides it if \queue@_only@_override\ is set true, which is the default
setting. If \queue@_only@_override\ is set false, \-odb-\ has no effect.

.option odf
.index foreground delivery
.index delivery||in the foreground
This option requests `foreground' (synchronous) delivery when Exim has accepted
a locally-generated message. (For the daemon it is exactly the same as
\-odb-\.) A delivery process is automatically started to deliver the
message, and Exim waits for it to complete before proceeding.
However, like \-odb-\, this option has no effect if \queue@_only@_override\ is 
false and one of the queueing options in the configuration file is in effect.

.option odi
This option is synonymous with \-odf-\. It is provided for compatibility with
Sendmail.

.option odq
.index non-immediate delivery
.index delivery||suppressing immediate
.index queueing incoming messages
This option applies to all modes in which Exim accepts incoming messages,
including the listening daemon. It specifies that the accepting process should
not automatically start a delivery process for each message received. Messages
are placed on the queue, and remain there until a subsequent queue runner
process encounters them.
There are several configuration options (such as \queue@_only\) that can be
used to queue incoming messages under certain conditions. This option overrides
all of them and also \-odqs-\. It always forces queueing.

.option odqs
.index SMTP||delaying delivery
This option is a hybrid between \-odb-\/\-odi-\ and \-odq-\. 
However, like \-odb-\ and \-odi-\, this option has no effect if
\queue@_only@_override\ is false and one of the queueing options in the
configuration file is in effect.

When \-odqs-\ does operate, a delivery process is started for each incoming
message, in the background by default, but in the foreground if \-odi-\ is also
present.
The recipient addresses are routed, and local deliveries are done in the normal
way. However, if any SMTP deliveries are required, they are not done at this
time, so the message remains on the queue until a subsequent queue runner
process encounters it. Because routing was done, Exim knows which messages are
waiting for which hosts, and so a number of messages for the same host can be
sent in a single SMTP connection. The \queue@_smtp@_domains\ configuration
option has the same effect for specific domains. See also the \-qq-\ option.

.option oee
.index error||reporting
If an error is detected while a non-SMTP message is being received (for
example, a malformed address), the error is reported to the sender in a mail
message.
.index return code||for \-oee-\
Provided this error message is successfully sent, the Exim receiving process
exits with a return code of zero. If not, the return code is 2 if the problem
is that the original message has no recipients, or 1 any other error. This is
the default \-oe$it{x}-\ option if Exim is called as \*rmail*\.

.option oem
.index error||reporting
.index return code||for \-oem-\
This is the same as \-oee-\, except that Exim always exits with a non-zero
return code, whether or not the error message was successfully sent.
This is the default \-oe$it{x}-\ option, unless Exim is called as \*rmail*\.

.option oep
.index error||reporting
If an error is detected while a non-SMTP message is being received, the
error is reported by writing a message to the standard error file (stderr).
.index return code||for \-oep-\
The return code is 1 for all errors.

.option oeq
.index error||reporting
This option is supported for compatibility with Sendmail, but has the same
effect as \-oep-\.

.option oew
.index error||reporting
This option is supported for compatibility with Sendmail, but has the same
effect as \-oem-\.

.option oi
.index dot||in incoming, non-SMTP message
This option, which has the same effect as \-i-\, specifies that a dot on a line
by itself should not terminate an incoming, non-SMTP message.
.em
Otherwise, a single dot does terminate, though Exim does no special processing 
for other lines that start with a dot.
.nem
This option is set by default if Exim is called as \*rmail*\. See also \-ti-\.

.option oitrue
This option is treated as synonymous with \-oi-\.

.option oMa #<<host address>>
.index sender||host address, specifying for local message
A number of options starting with \-oM-\ can be used to set values associated
with remote hosts on locally-submitted messages (that is, messages not received
over TCP/IP). These options can be used by any caller in conjunction with the
\-bh-\, 
\-be-\,
\-bf-\, \-bF-\, \-bt-\, or \-bv-\ testing options. In other circumstances, they
are ignored unless the caller is trusted.

The \-oMa-\ option sets the sender host address. This may include a port number
at the end, after a full stop (period). For example:
.display asis
exim -bs -oMa 10.9.8.7.1234
.endd
An alternative syntax is to enclose the IP address in square brackets, followed
by a colon and the port number:
.display asis
exim -bs -oMa [10.9.8.7]:1234
.endd
The IP address is placed in the \$sender@_host@_address$\ variable, and the
port, if present, in \$sender@_host@_port$\.

.option oMaa #<<name>>
.index authentication||name, specifying for local message
See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMaa-\
option sets the value of \$sender@_host@_authenticated$\ (the authenticator
name). See chapter ~~CHAPSMTPAUTH for a discussion of SMTP authentication.

.option oMai #<<string>>
.index authentication||id, specifying for local message
See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMai-\
option sets the 
value of \$authenticated@_id$\ (the id that was authenticated).
This overrides the default value (the caller's login id) for messages from
local sources. See chapter ~~CHAPSMTPAUTH for a discussion of authenticated
ids.

.option oMas #<<address>>
.index authentication||sender, specifying for local message
See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMas-\
option sets the authenticated sender value
in \$authenticated@_sender$\. 
It overrides the sender address that is created from the caller's login id for
messages from local sources. See chapter ~~CHAPSMTPAUTH for a discussion of
authenticated senders.

.option oMi #<<interface address>>
.index interface||address, specifying for local message
See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMi-\
option sets the IP interface address value. A port number may be included,
using the same syntax as for \-oMa-\.
The interface address is placed in \$interface@_address$\ and the port number, 
if present, in \$interface@_port$\.

.option oMr #<<protocol name>>
.index protocol||incoming, specifying for local message
See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMr-\
option sets the received protocol value
in \$received@_protocol$\. 
However, this applies only when \-bs-\ is not used. For interactive SMTP input,
the protocol is determined by whether \\EHLO\\ or \\HELO\\ is used, and is
always either `local-esmtp' or `local-smtp'. For \-bS-\ (batch SMTP) however,
the protocol can be set by \-oMr-\.

.option oMs #<<host name>>
.index sender||host name, specifying for local message
See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMs-\
option sets the sender host name 
in \$sender@_host@_name$\. When this option is present, Exim does not attempt 
to look up a host name from an IP address; it uses the name it is given.

.option oMt #<<ident string>>
.index sender||ident string, specifying for local message
See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMt-\
option sets the sender ident value
in \$sender@_ident$\. 
The default setting for local callers is the login id of the calling process.

.option om
.index Sendmail compatibility||\-om-\ option ignored
In Sendmail, this option means `me too', indicating that the sender of a
message should receive a copy of the message if the sender appears in an alias
expansion. Exim always does this, so the option does nothing.

.option oo
.index Sendmail compatibility||\-oo-\ option ignored
This option is ignored. In Sendmail it specifies `old style headers', whatever
that means.

.option oP #<<path>>
.index pid (process id)||of daemon
.index daemon||process id (pid)
This option is useful only in conjunction with \-bd-\ or \-q-\ with a time 
value. The option specifies the file to which the process id of the daemon is
written. When \-oX-\ is used with \-bd-\, or when \-q-\ with a time is used
without \-bd-\, this is the only way of causing Exim to write a pid file,
because in those cases, the normal pid file is not used.

.option or #<<time>>
.index timeout||for non-SMTP input
This option sets a timeout value for incoming non-SMTP messages. If it is not
set, Exim will wait forever for the standard input. The value can also be set
by the \receive@_timeout\ option. The format used for specifying times is
described in section ~~SECTtimeformat.

.option os #<<time>>
.index timeout||for SMTP input
.index SMTP||timeout, input
This option sets a timeout value for incoming SMTP messages. The timeout
applies to each SMTP command and block of data. The value can also be set by
the \smtp@_receive@_timeout\ option; it defaults to 5 minutes. The format used
for specifying times is described in section ~~SECTtimeformat.

.option ov
This option has exactly the same effect as \-v-\.

.option oX #<<number or string>>
.index TCP/IP||setting listening ports
.index TCP/IP||setting listening interfaces
.index port||receiving TCP/IP
This option is relevant only when the \-bd-\ (start listening daemon) option is
also given. It controls which ports and interfaces the daemon uses. Details of
the syntax, and how it interacts with configuration file options, are given in
chapter ~~CHAPinterfaces. When \-oX-\ is used to start a daemon, no pid file is
written unless \-oP-\ is also present to specify a pid file name.

.option pd
.index Perl||starting the interpreter
This option applies when an embedded Perl interpreter is linked with Exim (see
chapter ~~CHAPperl). It overrides the setting of the \perl@_at@_start\ option,
forcing the starting of the interpreter to be delayed until it is needed.

.option ps
.index Perl||starting the interpreter
This option applies when an embedded Perl interpreter is linked with Exim (see
chapter ~~CHAPperl). It overrides the setting of the \perl@_at@_start\ option,
forcing the starting of the interpreter to occur as soon as Exim is started.

.em
.option p<<rval>>:<<sval>>
For compatibility with Sendmail, this option
is equivalent to
.display 
-oMr <<rval>> -oMs <<sval>>
.endd
It sets the incoming protocol and host name (for trusted callers). The
host name and its colon can be omitted when only the protocol is to be set.
Note the Exim already has two private options, \-pd-\ and \-ps-\, that refer to
embedded Perl. It is therefore impossible to set a protocol value of \"p"\ or
\"s"\ using this option (but that does not seem a real limitation).
.nem

.option q
.index queue runner||starting manually
This option is normally restricted to admin users. However, there is a
configuration option called \prod@_requires@_admin\ which can be set false to
relax this restriction (and also the same requirement for the \-M-\, \-R-\, and
\-S-\ options).

.index queue runner||description of operation
The \-q-\ option starts one queue runner process. This scans the queue of
waiting messages, and runs a delivery process for each one in turn. It waits
for each delivery process to finish before starting the next one. A delivery
process may not actually do any deliveries if the retry times for the addresses
have not been reached. Use \-qf-\ (see below) if you want to override this.
.index SMTP||passed connection
.index SMTP||multiple deliveries
.index multiple SMTP deliveries
If the delivery process spawns other processes to deliver other messages down
passed SMTP connections, the queue runner waits for these to finish before
proceeding.

When all the queued messages have been considered, the original queue runner
process terminates. In other words, a single pass is made over the waiting
mail, one message at a time. Use \-q-\ with a time (see below) if you want this
to be repeated periodically.

Exim processes the waiting messages in an unpredictable order. It isn't very
random, but it is likely to be different each time, which is all that matters.
If one particular message screws up a remote MTA, other messages to the same
MTA have a chance of getting through if they get tried first.

It is possible to cause the messages to be processed in lexical message id
order, which is essentially the order in which they arrived, by setting the
\queue@_run@_in@_order\ option, but this is not recommended for normal use.

.option q <<qflags>>
The \-q-\ option may be followed by one or more flag letters that change its
behaviour. They are all optional, but if more than one is present, they must
appear in the correct order. Each flag is described in a separate item below.

.option qq...
.index queue||double scanning
.index queue||routing
.index routing||whole queue before delivery
An option starting with \-qq-\ requests a two-stage queue run. In the first
stage, the queue is scanned as if the \queue@_smtp@_domains\ option matched
every domain. Addresses are routed, local deliveries happen, but no remote
transports are run. 
.index hints database||remembering routing
The hints database that remembers which messages are
waiting for specific hosts is updated, as if delivery to those hosts had been
deferred. After this is complete, a second, normal queue scan happens, with
routing and delivery taking place as normal. Messages that are routed to the
same host should mostly be delivered down a single SMTP
.index SMTP||passed connection
.index SMTP||multiple deliveries
.index multiple SMTP deliveries
connection because of the hints that were set up during the first queue scan.
This option may be useful for hosts that are connected to the Internet
intermittently.

.option q[q]i...
.index queue||initial delivery
If the \*i*\ flag is present, the queue runner runs delivery processes only for
those messages that haven't previously been tried. (\*i*\ stands for `initial
delivery'.) This can be helpful if you are putting messages on the queue using
\-odq-\ and want a queue runner just to process the new messages.

.option q[q][i]f...
.index queue||forcing delivery 
.index delivery||forcing in queue run
If one \*f*\ flag is present, a delivery attempt is forced for each non-frozen
message, whereas without \f\ only those non-frozen addresses that have passed
their retry times are tried.

.option q[q][i]ff...
.index frozen messages||forcing delivery
If \*ff*\ is present, a delivery attempt is forced for every message, whether
frozen or not.

.option q[q][i][f[f]]l
.index queue||local deliveries only
The \*l*\ (the letter `ell') flag specifies that only local deliveries are to be
done. If a message requires any remote deliveries, it remains on the queue for
later delivery.

.option q <<qflags>>#<<start id>>#<<end id>>
.index queue||delivering specific messages
When scanning the queue, Exim can be made to skip over messages whose ids are
lexically less than a given value by following the \-q-\ option with a starting
message id. For example:
.display
exim -q 0t5C6f-0000c8-00
.endd
Messages that arrived earlier than \"0t5C6f-0000c8-00"\ are not inspected. If a
second message id is given, messages whose ids are lexically greater than it
are also skipped. If the same id is given twice, for example,
.display
exim -q 0t5C6f-0000c8-00 0t5C6f-0000c8-00
.endd
just one delivery process is started, for that message. This differs from \-M-\
in that retry data is respected, and it also differs from \-Mc-\ in that it
counts as a delivery from a queue run. Note that the selection mechanism does
not affect the order in which the messages are scanned. There are also other
ways of selecting specific sets of messages for delivery in a queue run -- see
\-R-\ and \-S-\.

.option q <<qflags>><<time>>
.index queue runner||starting periodically
.index periodic queue running
When a time value is present, the \-q-\ option causes Exim to run as a daemon,
starting a queue runner process at intervals specified by the given time value
(whose format is described in section ~~SECTtimeformat). This form of the \-q-\
option is commonly combined with the \-bd-\ option, in which case a single
daemon process handles both functions. A common way of starting up a combined
daemon at system boot time is to use a command such as
.display
/usr/exim/bin/exim -bd -q30m
.endd
Such a daemon listens for incoming SMTP calls, and also starts a queue runner
process every 30 minutes.

When a daemon is started by \-q-\ with a time value, but without \-bd-\, no pid 
file is written unless one is explicitly requested by the \-oP-\ option.

.option qR <<rsflags>>#<<string>>
This option is synonymous with \-R-\. It is provided for Sendmail
compatibility.

.option qS <<rsflags>>#<<string>>
This option is synonymous with \-S-\.

.option R <<rsflags>>#<<string>>
.index queue runner||for specific recipients
.index delivery||to given domain
.index domain||delivery to
The <<rsflags>> may be empty, in which case the white space before the string
is optional, unless the string is \*f*\, \*ff*\, \*r*\, \*rf*\, or \*rff*\,
which are the possible values for <<rsflags>>. White space is required if
<<rsflags>> is not empty.

This option is similar to \-q-\ with no time value, that is, it causes Exim to
perform a single queue run, except that, when scanning the messages on the
queue, Exim processes only those that have at least one undelivered recipient
address containing the given string, which is checked in a case-independent
way. If the <<rsflags>> start with \*r*\, <<string>> is interpreted as a regular
expression; otherwise it is a literal string.

Once a message is selected, all its addresses are processed. For the first
selected message, Exim overrides any retry information and forces a delivery
attempt for each undelivered address. This means that if delivery of any
address in the first message is successful, any existing retry information is
deleted, and so delivery attempts for that address in subsequently selected
messages (which are processed without forcing) will run. However, if delivery
of any address does not succeed, the retry information is updated, and in
subsequently selected messages, the failing address will be skipped.

If the <<rsflags>> contain \*f*\ or \*ff*\, the delivery forcing applies to all
selected messages, not just the first;
.index frozen messages||forcing delivery
frozen messages are included when \*ff*\ is present.

The \-R-\ option makes it straightforward to initiate delivery of all messages
to a given domain after a host has been down for some time. When the SMTP
command \\ETRN\\ is accepted by its ACL (see chapter ~~CHAPACL), its default
effect is to run Exim with the \-R-\ option, but it can be configured to run an
arbitrary command instead.

.option r
This is a documented (for Sendmail) obsolete alternative name for \-f-\.

.index delivery||from given sender
.option S <<rsflags>>#<<string>>
.index queue runner||for specific senders
This option acts like \-R-\ except that it checks the string against each
message's sender instead of against the recipients. If \-R-\ is also set, both
conditions must be met for a message to be selected. If either of the options
has \*f*\ or \*ff*\ in its flags, the associated action is taken.

.em
.option Tqt#<<times>>
This an option that is exclusively for use by the Exim testing suite.
It is not recognized when Exim is run normally. It allows for the setting up
of explicit `queue times' so that various warning/retry features can be 
tested. 
.nem                                           

.option t
.index recipient||extracting from header lines
.index ::Bcc:: header line
.index ::Cc:: header line
.index ::To:: header line
When Exim is receiving a locally-generated, non-SMTP message on its standard
input, the \-t-\ option causes the recipients of the message to be obtained
from the ::To::, ::Cc::, and ::Bcc:: header lines in the message instead of from
the command arguments. The addresses are extracted before any rewriting takes
place.

.index Sendmail compatibility||\-t-\ option
If the command has any arguments, they specify addresses to which the message
is $it{not} to be delivered. That is, the argument addresses are removed from
the recipients list obtained from the headers. This is compatible with Smail 3
and in accordance with the documented behaviour of several versions of
Sendmail, as described in man pages on a number of operating systems (e.g.
Solaris 8, IRIX 6.5, HP-UX 11). However, some versions of Sendmail $it{add}
argument addresses to those obtained from the headers, and the O'Reilly
Sendmail book documents it that way. Exim can be made to add argument addresses
instead of subtracting them by setting the option
\extract__addresses__remove__arguments\ false.

If a ::Bcc:: header line is present, it is removed from the message unless
there is no ::To:: or ::Cc::, in which case a ::Bcc:: line with no data is
created. This is necessary for conformity with the original RFC 822 standard;
the requirement has been removed in RFC 2822, but that is still very new.

.index \Resent@-\ header lines||with \-t-\
If there are any \Resent@-\ header lines in the message, Exim extracts 
recipients from all ::Resent-To::, ::Resent-Cc::, and ::Resent-Bcc:: header
lines instead of from ::To::, ::Cc::, and ::Bcc::. This is for compatibility 
with Sendmail and other MTAs. (Prior to release 4.20, Exim gave an error if 
\-t-\ was used in conjunction with \Resent@-\ header lines.)

RFC 2822 talks about different sets of \Resent@-\ header lines (for when a
message is resent several times). The RFC also specifies that they should be
added at the front of the message, and separated by ::Received:: lines. It is
not at all clear how \-t-\ should operate in the present of multiple sets,
nor indeed exactly what constitutes a `set'.
In practice, it seems that MUAs do not follow the RFC. The \Resent@-\ lines are
often added at the end of the header, and if a message is resent more than
once, it is common for the original set of \Resent@-\ headers to be renamed as
\X-Resent@-\ when a new set is added. This removes any possible ambiguity.

.option ti
This option is exactly equivalent to \-t-\ \-i-\. It is provided for 
compatibility with Sendmail.

.option tls-on-connect
.index TLS||use without STARTTLS
.index TLS||automatic start
This option is available when Exim is compiled with TLS support. It makes it
possible to support legacy clients that do not support the \\STARTTLS\\
command, but instead expect to start up a TLS session as soon as a connection
to the server is established. These clients use a special port (usually called
the `ssmtp' port) instead of the normal SMTP port 25. The \-tls-on-connect-\
option can be used to run Exim in this way from \*inetd*\, and it can also be
used to run a special daemon that operates in this manner (use \-oX-\ to
specify the port). However, although it is possible to run one daemon that
listens on several ports, it is not possible to have some of them operate one
way and some the other. With only a few clients that need the legacy support, a
convenient approach is to use a daemon for normal SMTP (with or without
\\STARTTLS\\) and \*inetd*\ with \-tls-on-connect-\ for the legacy clients.

.option U
.index Sendmail compatibility||\-U-\ option ignored
Sendmail uses this option for `initial message submission', and its
documentation states that in future releases, it may complain about
syntactically invalid messages rather than fixing them when this flag is not
set. Exim ignores this option.

.option v
This option causes Exim to write information to the standard error stream,
describing what it is doing. In particular, it shows the log lines for
receiving and delivering a message, and if an SMTP connection is made, the SMTP
dialogue is shown. Some of the log lines shown may not actually be written to
the log if the setting of \log@_selector\ discards them. Any relevant selectors
are shown with each log line. If none are shown, the logging is unconditional.

.option x
AIX uses \-x-\ for a private purpose (`mail from a local mail program has
National Language Support extended characters in the body of the mail item').
It sets \-x-\ when calling the MTA from its \mail\ command. Exim ignores this
option.

.endoptions



.
.
.
.
. ============================================================================
.chapter The Exim run time configuration file
.set runningfoot "configuration file"
.rset CHAPconf ~~chapter

.index run time configuration
.index configuration file||general description
.index \\CONFIGURE@_FILE\\
Exim uses a single run time configuration file that is read whenever an Exim
binary is executed. Note that in normal operation, this happens frequently,
because Exim is designed to operate in a distributed manner, without central 
control.

The name of the configuration file is compiled into the binary for security
reasons, and is specified by the \\CONFIGURE@_FILE\\ compilation option. In
most configurations, this specifies a single file. However, it is permitted to
give a colon-separated list of file names, in which case Exim uses the first
existing file in the list.

.index \\EXIM@_USER\\
.index \\EXIM@_GROUP\\
.index configuration file||ownership
.index ownership||configuration file
The run time configuration file must be owned by root or by the user that
is specified at compile time by the \\EXIM@_USER\\ option, 
.em
or by the user that is specified at compile time by the \\CONFIGURE@_OWNER\\ 
option (if set).
.nem
The configuration file must not be world-writeable or group-writeable, unless
its group is the one specified at compile time by the \\EXIM@_GROUP\\ option.

\**Warning**\: In a conventional configuration, where the Exim binary is setuid 
to root, anybody who is able to edit the run time configuration file has an 
easy way to run commands as root. If you make your mail administrators members 
of the Exim group, but do not trust them with root, make sure that the run time 
configuration is not group writeable.


A default configuration file, which will work correctly in simple situations,
is provided in the file \(src/configure.default)\. 
If \\CONFIGURE@_FILE\\ defines just one file name, the installation process
copies the default configuration to a new file of that name if it did not
previously exist. If \\CONFIGURE@_FILE\\ is a list, no default is automatically
installed. Chapter ~~CHAPdefconfil is a `walk-through' discussion of the
default configuration.

.index configuration file||errors in
.index error||in configuration file
.index return code||for bad configuration
If a syntax error is detected while reading the configuration file, Exim
writes a message on the standard error, and exits with a non-zero return code.
The message is also written to the panic log.


.section Using a different configuration file
.index configuration file||alternate
A one-off alternate configuration can be specified by the \-C-\ command line
option, which may specify a single file or a list of files. However, when \-C-\
is used, Exim gives up its root privilege, unless called by root or the Exim
user (or unless the argument for \-C-\ is identical to the built-in value from 
\\CONFIGURE@_FILE\\). \-C-\ is useful mainly for checking the syntax of
configuration files before installing them. No owner or group checks are done
on a configuration file specified by \-C-\.

The privileged use of \-C-\ by the Exim user can be locked out by setting
\\ALT@_CONFIG@_ROOT@_ONLY\\ in \(Local/Makefile)\ when building Exim. However,
if you do this, you also lock out the possibility of testing a
configuration using \-C-\ right through message reception and delivery, even if
the caller is root. The reception works, but by that time, Exim is running as
the Exim user, so when it re-execs to regain privilege for the delivery, the
use of \-C-\ causes privilege to be lost. However, root can test reception and
delivery using two separate commands (one to put a message on the queue, using 
\-odq-\, and another to do the delivery, using \-M-\).

If \\ALT@_CONFIG@_PREFIX\\ is defined \(in Local/Makefile)\, it specifies a
prefix string with which any file named in a \-C-\ command line option must
start. In addition, the file name must not contain the sequence \"/../"\. There
is no default setting for \\ALT@_CONFIG@_PREFIX\\; when it is unset, any file
name can be used with \-C-\.

One-off changes to a configuration can be specified by the \-D-\ command line
option, which defines and overrides values for macros used inside the 
configuration file. However, like \-C-\, the use of this option by a
non-privileged user causes Exim to discard its root privilege.
If \\DISABLE@_D@_OPTION\\ is defined in \(Local/Makefile)\, the use of \-D-\ is
completely disabled, and its use causes an immediate error exit.

Some sites may wish to use the same Exim binary on different machines that
share a file system, but to use different configuration files on each machine.
If \\CONFIGURE@_FILE@_USE@_NODE\\ is defined in \(Local/Makefile)\, Exim first
looks for a file whose name is the configuration file name followed by a dot
and the machine's node name, as obtained from the \*uname()*\ function. If this
file does not exist, the standard name is tried. This processing occurs for 
each file name in the list given by \\CONFIGURE@_FILE\\ or \-C-\.

In some esoteric situations different versions of Exim may be run under
different effective uids and the \\CONFIGURE@_FILE@_USE@_EUID\\ is defined to
help with this. See the comments in \(src/EDITME)\ for details.


.section Configuration file format
.rset SECTconffilfor "~~chapter.~~section"
.index configuration file||format of
.index format||configuration file
Exim's configuration file is divided into a number of different parts. General
option settings must always appear at the start of the file. The other parts
are all optional, and may appear in any order. Each part other than the first
is introduced by the word `begin' followed by the name of the part. The
optional parts are:

.numberpars $.
\*ACL*\: Access control lists for controlling incoming SMTP mail.
.nextp
.index \\AUTH\\||configuration
\*authenticators*\: Configuration settings for the authenticator drivers. These
are concerned with the SMTP \\AUTH\\ command (see chapter ~~CHAPSMTPAUTH).
.nextp
\*routers*\: Configuration settings for the router drivers. Routers process
addresses and determine how the message is to be delivered.
.nextp
\*transports*\: Configuration settings for the transport drivers. Transports
define mechanisms for copying messages to destinations.
.nextp
\*retry*\: Retry rules, for use when a message cannot be immediately delivered.
.nextp
\*rewrite*\: Global address rewriting rules, for use when a message arrives and
when new addresses are generated during delivery.
.nextp
\*local@_scan*\: Private options for the \*local@_scan()*\ function. If you
want to use this feature, you must set
.display asis
LOCAL_SCAN_HAS_OPTIONS=yes
.endd
in \(Local/Makefile)\ before building Exim. Full details of the 
\*local@_scan()*\ facility are given in chapter ~~CHAPlocalscan.
.endp
Blank lines in the file, and lines starting with a @# character (ignoring
leading white space) are treated as comments and are ignored. \**Note**\: a
@# character other than at the beginning of a line is not treated specially,
and does not introduce a comment.

Any non-comment line can be continued by ending it with a backslash. Trailing
white space after the backslash is ignored, and leading white space at the
start of continuation lines is also ignored. 
Comment lines beginning with @# (but not empty lines) may appear in the middle
of a sequence of continuation lines.

A convenient way to create a configuration file is to start from the
default, which is supplied in \(src/configure.default)\, and add, delete, or
change settings as required.

The ACLs, retry rules, and rewriting rules have their own syntax which is
described in chapters ~~CHAPACL, ~~CHAPretry, and ~~CHAPrewrite, respectively.
The other parts of the configuration file have some syntactic items in common,
and these are described below, from section ~~SECTcos onwards. Before that, the
inclusion, macro, and conditional facilities are described.


.section File inclusions in the configuration file
.index inclusions in configuration file
.index configuration file||including other files
.index .include in configuration file
.index .include@_if@_exists in configuration file
You can include other files inside Exim's run time configuration file by
using this syntax:
.display
@.include <<file name>>
.endd
or
.display
@.include@_if@_exists <<file name>>
.endd
on a line by itself. Double quotes round the file name are optional. If you use 
the first form, a configuration error occurs if the file does not exist; the 
second form does nothing for non-existent files.

Includes may be nested to any depth, but remember that Exim reads its
configuration file often, so it is a good idea to keep them to a minimum.
If you change the contents of an included file, you must HUP the daemon,
because an included file is read only when the configuration itself is read.

The processing of inclusions happens early, at a physical line level, so, like
comment lines, an inclusion can be used in the middle of an option setting,
for example:
.display asis
hosts_lookup = a.b.c \
               .include /some/file
.endd
Include processing happens 
after 
macro processing (see below). Its effect is to process the lines of the file as
if they occurred inline where the inclusion appears.


.section Macros in the configuration file
.rset SECTmacrodefs "~~chapter.~~section"
.index macro||description of
.index configuration file||macros
If a line in the main part of the configuration (that is, before the first
`begin' line) begins with an upper case letter, it is taken as a macro
definition, and must be of the form
.display
<<name>> = <<rest of line>>
.endd
The name must consist of letters, digits, and underscores, and need not all be
in upper case, though that is recommended. The rest of the line, including any
continuations, is the replacement text, and has leading and trailing white
space removed. Quotes are not removed. The replacement text can never end with
a backslash character, but this doesn't seem to be a serious limitation.

Once a macro is defined, all subsequent lines in the file (and any included
files) are scanned for the macro name; if there are several macros, the line is
scanned for each in turn, in the order in which they are defined. The
replacement text is not re-scanned for the current macro, though it is scanned
for subsequently defined macros. For this reason, a macro name may not contain
the name of a previously defined macro as a substring. You could, for example,
define
.display asis
ABCD_XYZ = <<something>>
ABCD = <<something else>>
.endd
but putting the definitions in the opposite order would provoke a configuration
error.

Macro expansion is applied to individual lines from the file, before checking
for line continuation or file inclusion (see below). If a line consists solely
of a macro name, and the expansion of the macro is empty, the line is ignored.
A macro at the start of a line may turn the line into a comment line or a
\".include"\ line.

As an example of macro usage, consider a configuration where aliases are looked
up in a MySQL database. It helps to keep the file less cluttered if long
strings such as SQL statements are defined separately as macros, for example:
.display asis
ALIAS_QUERY = select mailbox from user where \
              login=${quote_mysql:$local_part};
.endd
This can then be used in a \%redirect%\ router setting like this:
.display asis
data = ${lookup mysql{ALIAS_QUERY}}
.endd
In earlier versions of Exim macros were sometimes used for domain, host, or
address lists. In Exim 4 these are handled better by named lists -- see section
~~SECTnamedlists.

Macros in the configuration file can be overridden by the \-D-\ command line
option, but Exim gives up its root privilege when \-D-\ is used, unless called
by root or the Exim user.


.section Conditional skips in the configuration file
.index configuration file||conditional skips
.index .ifdef
You can use the directives \".ifdef"\, \".ifndef"\, \".elifdef"\,
\".elifndef"\, \".else"\, and \".endif"\ to dynamically include or exclude 
portions of the configuration file. The processing happens whenever the file is 
read (that is, when an Exim binary starts to run). 

The implementation is very simple. Instances of the first four directives must
be followed by text that includes the names of one or macros. The condition
that is tested is whether or not any macro substitution has taken place in the
line. Thus:
.display
@.ifdef AAA
message@_size@_limit = 50M
@.else
message@_size@_limit = 100M
@.endif
.endd
sets a message size limit of 50M if the macro \"AAA"\ is defined, and 100M
otherwise. If there is more than one macro named on the line, the condition
is true if any of them are defined. That is, it is an `or' condition. To
obtain an `and' condition, you need to use nested \".ifdef"\s.

Although you can use a macro expansion to generate one of these directives,
it is not very useful, because the condition `there was a macro substitution
in this line' will always be true.

Text following \".else"\ and \".endif"\ is ignored, and can be used as comment
to clarify complicated nestings.


.section Common option syntax
.rset SECTcos "~~chapter.~~section"
.index common option syntax
.index syntax of common options
.index configuration file||common option syntax
For the main set of options, driver options, and \*local@_scan()*\ options,
each setting is on a line by itself, and starts with a name consisting of
lower-case letters and underscores. Many options require a data value, and in
these cases the name must be followed by an equals sign (with optional white
space) and then the value. For example:
.display asis
qualify_domain = mydomain.example.com
.endd
Some option settings may contain sensitive data, for example, passwords for
accessing databases. To stop non-admin users from using the \-bP-\ command line
option to read these values, you can precede the option settings with the word
`hide'. For example:
.display asis
hide mysql_servers = localhost/users/admin/secret-password
.endd
For non-admin users, such options are displayed like this:
.display asis
mysql_servers = <value not displayable>
.endd
If `hide' is used on a driver option, it hides the value of that option on all
instances of the same driver.

The following sections describe the syntax used for the different data types
that are found in option settings.

.section Boolean options
.index format||boolean
.index boolean configuration values
Options whose type is given as boolean are on/off switches. There are two
different ways of specifying such options: with and without a data value. If
the option name is specified on its own without data, the switch is turned on;
if it is preceded by `no@_' or `not@_' the switch is turned off. However,
boolean options may optionally be followed by an equals sign and one of the
words `true', `false', `yes', or `no', as an alternative syntax. For example,
the following two settings have exactly the same effect:
.display asis
queue_only
queue_only = true
.endd
The following two lines also have the same (opposite) effect:
.display asis
no_queue_only
queue_only = false
.endd
You can use whichever syntax you prefer.



.section Integer values
.index integer configuration values
.index format||integer
If an integer data item starts with the characters `0x', the remainder of it
is interpreted as a hexadecimal number. Otherwise, it is treated as octal if it
starts with the digit 0, and decimal if not. If an integer value is followed by
the letter K, it is multiplied by 1024; if it is followed by the letter M, it
is multiplied by 1024x1024.

When the values of integer option settings are output, values which are an
exact multiple of 1024 or 1024x1024 are 
sometimes, but not always,
printed using the letters K and M. The printing style is independent of the
actual input format that was used.

.section Octal integer values
.index integer format
.index format||octal integer
The value of an option specified as an octal integer is always interpreted in
octal, whether or not it starts with the digit zero. Such options are always
output in octal.


.section Fixed point number values
.index fixed point configuration values
.index format||fixed point
A fixed point number consists of a decimal integer, optionally followed by a
decimal point and up to three further digits.


.section Time interval values
.index time interval||specifying in configuration
.index format||time interval
.rset SECTtimeformat "~~chapter.~~section"
A time interval is specified as a sequence of numbers, each followed by one of
the following letters, with no intervening white space:
.display rm
.tabs 5
\s\  $t seconds
\m\  $t minutes
\h\  $t hours
\d\  $t days
\w\  $t weeks
.endd
For example, `3h50m' specifies 3 hours and 50 minutes. The values of time
intervals are output in the same format.
Exim does not restrict the values; it is perfectly acceptable, for example, to 
specify `90m' instead of `1h30m'.


.section String values
.index string||format of configuration values
.index format||string
.rset SECTstrings "~~chapter.~~section"
If a string data item does not start with a double-quote character, it is taken
as consisting of the remainder of the line plus any continuation lines,
starting at the first character after any leading white space, with trailing
white space characters removed, and with no interpretation of the characters in
the string. Because Exim removes comment lines (those beginning with @#) at an
early stage, they can appear in the middle of a multi-line string. The
following settings are therefore equivalent:
.display asis
trusted_users = uucp:mail

trusted_users = uucp:\
                # This comment line is ignored
                mail
.endd
.index string||quoted
.index escape characters in quoted strings
If a string does start with a double-quote, it must end with a closing
double-quote, and any backslash characters other than those used for line
continuation are interpreted as escape characters, as follows:
.display
.tabs 15
@\@\   $t $rm{single backslash}
@\n    $t $rm{newline}
@\r    $t $rm{carriage return}
@\t    $t $rm{tab}
@\<<octal digits>> $t $rm{up to 3 octal digits specify one character}
@\x<<hex digits>>  $t $rm{up to 2 hexadecimal digits specify one character}
.endd
If a backslash is followed by some other character, including a double-quote
character, that character replaces the pair.

Quoting is necessary only if you want to make use of the backslash escapes to
insert special characters, or if you need to specify a value with leading or
trailing spaces. These cases are rare, so quoting is almost never needed in
current versions of Exim. In versions of Exim before 3.14, quoting was required
in order to continue lines, so you may come across older configuration files
and examples that apparently quote unnecessarily.

.section Expanded strings
.index string||expansion, definition of
.index expansion||definition of
Some strings in the configuration file are subjected to \*string expansion*\,
by which means various parts of the string may be changed according to the
circumstances (see chapter ~~CHAPexpand). The input syntax for such strings is
as just described; in particular, the handling of backslashes in quoted strings
is done as part of the input process, before expansion takes place. However,
backslash is also an escape character for the expander, so any backslashes that
are required for that reason must be doubled if they are within a quoted
configuration string.

.section User and group names
.index user name||format of
.index format||user name
.index group||name format
.index format||group name
User and group names are specified as strings, using the syntax described
above, but the strings are interpreted specially. A user or group name must
either consist entirely of digits, or be a name that can be looked up using the
\*getpwnam()*\ or \*getgrnam()*\ function, as appropriate.

.section List construction
.index list||syntax of in configuration
.index format||list item in configuration
.index string list, definition
.rset SECTlistconstruct "~~chapter.~~section"
The data for some configuration options is a colon-separated list of items. 
Many of these options are shown with type `string list' in the descriptions
later in this document. Others are listed as `domain list', `host list', 
`address list', or `local part list'. Syntactically, they are all the same; 
however, those other than `string list' are subject to particular kinds of
interpretation, as described in chapter ~~CHAPdomhosaddlists.

In all these cases, the entire list is treated as a single string as far as the
input syntax is concerned. The \trusted@_users\ setting in section
~~SECTstrings above is an example. If a colon is actually needed in an item in
a list, it must be entered as two colons. Leading and trailing white space on
each item in a list is ignored. This makes it possible to include items that
start with a colon, and in particular, certain forms of IPv6 address. For
example, the list
.display asis
local_interfaces = 127.0.0.1 : ::::1
.endd
contains two IP addresses, the IPv4 address 127.0.0.1 and the IPv6 address
@:@:1. IPv6 addresses are going to become more and more common as the new
protocol gets more widely deployed.
.index list||separator, changing
.index IPv6||addresses in lists
Doubling their colons is an unwelcome chore, so a mechanism was introduced to
allow the separator character to be changed. If a list begins with a left angle
bracket, followed by any punctuation character, that character is used instead
of colon as the list separator. For example, the list above can be rewritten to
use a semicolon separator like this:
.display asis
local_interfaces = <; 127.0.0.1 ; ::1
.endd
This facility applies to all lists, with the exception of the list in
\log@_file@_path\. It is recommended that the use of non-colon separators be
confined to circumstances where they really are needed.


.section Format of driver configurations
.rset SECTfordricon "~~chapter.~~section"
.index drivers||configuration format
There are separate parts in the configuration for defining routers, transports,
and authenticators. In each part, you are defining a number of driver
instances, each with its own set of options. Each driver instance is defined by
a sequence of lines like this:
.display
<<instance name>>:
  <<option>>
  ...
  <<option>>
.endd
In the following example, the instance name is \%localuser%\, and it is
followed by three options settings:
.display asis
localuser:
  driver = accept
  check_local_user
  transport = local_delivery
.endd
For each driver instance, you specify which Exim code module it uses -- by the 
setting of the \driver\ option -- and (optionally) some configuration settings.
For example, in the case of transports, if you want a transport to deliver with
SMTP you would use the \%smtp%\ driver; if you want to deliver to a local file
you would use the \%appendfile%\ driver. Each of the drivers is described in
detail in its own separate chapter later in this manual.

You can have several routers, transports, or authenticators that are based on
the same underlying driver (each must have a different name).

The order in which routers are defined is important, because addresses are
passed to individual routers one by one, in order. The order in which
transports are defined does not matter at all. The order in which
authenticators are defined is used only when Exim, as a client, is searching
them to find one that matches an authentication mechanism offered by the
server.

.index generic options
.index options||generic, definition of
Within a driver instance definition, there are two kinds of option:
$it{generic} and $it{private}. The generic options are those that apply to all
drivers of the same type (that is, all routers, all transports or all
authenticators).
The \driver\ option is a generic option that must appear in every definition.
.index private options
The private options are special for each driver, and none need appear, because
they all have default values.

The options may appear in any order, except that the \driver\ option must
precede any private options, since these depend on the particular driver. For
this reason, it is recommended that \driver\ always be the first option.

Driver instance names, which are used for reference in log entries and
elsewhere, can be any sequence of letters, digits, and underscores (starting
with a letter) and must be unique among drivers of the same type. A router and
a transport (for example) can each have the same name, but no two router
instances can have the same name. The name of a driver instance should not be
confused with the name of the underlying driver module. For example, the
configuration lines:
.display asis
remote_smtp:
  driver = smtp
.endd
create an instance of the \%smtp%\ transport driver whose name is
\%remote@_smtp%\. The same driver code can be used more than once, with
different instance names and different option settings each time. A second
instance of the \%smtp%\ transport, with different options, might be defined
thus:
.display asis
special_smtp:
  driver = smtp
  port = 1234
  command_timeout = 10s
.endd
The names \%remote@_smtp%\ and \%special@_smtp%\ would be used to reference
these transport instances from routers, and these names would appear in log
lines.

Comment lines may be present in the middle of driver specifications. The full
list of option settings for any particular driver instance, including all the
defaulted values, can be extracted by making use of the \-bP-\ command line
option.






.
.
.
.
. ============================================================================
.chapter The default configuration file
.set runningfoot "default configuration"
.rset CHAPdefconfil "~~chapter"
.index configuration file||default, `walk through'
.index default||configuration file `walk through'
The default configuration file supplied with Exim as \(src/configure.default)\
is sufficient for a host with simple mail requirements. As an introduction to
the way Exim is configured, this chapter `walks through' the default
configuration, giving brief explanations of the settings. Detailed descriptions
of the options are given in subsequent chapters. The default configuration file
itself contains extensive comments about ways you might want to modify the
initial settings. However, note that there are many options that are not
mentioned at all in the default configuration.


.section Main configuration settings
The main (global) configuration option settings must always come first in the
file. The first thing you'll see in the file, after some initial comments, is
the line
.display asis
# primary_hostname =
.endd
This is a commented-out setting of the \primary@_hostname\ option. Exim needs
to know the official, fully qualified name of your host, and this is where you
can specify it. However, in most cases you do not need to set this option. When
it is unset, Exim uses the \*uname()*\ system function to obtain the host name.

The first three non-comment configuration lines are as follows:
.display asis
domainlist local_domains = @
domainlist relay_to_domains =
hostlist   relay_from_hosts = 127.0.0.1
.endd
These are not, in fact, option settings. They are definitions of two named
domain lists and one named host list. Exim allows you to give names to lists of
domains, hosts, and email addresses, in order to make it easier to manage the
configuration file (see section ~~SECTnamedlists).

The first line defines a domain list called \*local@_domains*\; this is used
later in the configuration to identify domains that are to be delivered
on the local host. 
.index @@ in a domain list
There is just one item in this list, the string `@@'. This is a special form of
entry which means `the name of the local host'. Thus, if the local host is
called \*a.host.example*\, mail to \*any.user@@a.host.example*\ is expected to
be delivered locally. Because the local host's name is referenced indirectly,
the same configuration file can be used on different hosts.

The second line defines a domain list called \*relay@_to@_domains*\, but the
list itself is empty. Later in the configuration we will come to the part that
controls mail relaying through the local host; it allows relaying to any
domains in this list. By default, therefore, no relaying on the basis of a mail
domain is permitted.

The third line defines a host list called \*relay@_from@_hosts*\. This list is
used later in the configuration to permit relaying from any host or IP address
that matches the list. The default contains just the IP address of the IPv4
loopback interface, which means that processes on the local host are able to
submit mail for relaying by sending it over TCP/IP to that interface. No other
hosts are permitted to submit messages for relaying.

Just to be sure there's no misunderstanding: at this point in the configuration
we aren't actually setting up any controls. We are just defining some domains
and hosts that will be used in the controls that are specified later.

The next configuration line is a genuine option setting:
.display asis
acl_smtp_rcpt = acl_check_rcpt
.endd
This option specifies an \*Access Control List*\ (ACL) which is to be used
during an incoming SMTP session for every recipient of a message (every 
\\RCPT\\ command). The name of the list is \*acl@_check@_rcpt*\, and we will
come to its definition below, in the ACL section of the configuration. ACLs
control which recipients are accepted for an incoming message -- if a
configuration does not provide an ACL to check recipients, no SMTP mail can be
accepted.

Two commented-out options settings are next:
.display asis
# qualify_domain =
# qualify_recipient =
.endd
The first of these specifies a domain that Exim uses when it constructs a
complete email address from a local login name. This is often needed when Exim
receives a message from a local process. If you do not set \qualify@_domain\,
the value of \primary@_hostname\ is used. If you set both of these options, you
can have different qualification domains for sender and recipient addresses. If
you set only the first one, its value is used in both cases.

.index domain literal||recognizing format
The following line must be uncommented if you want Exim to recognize
addresses of the form \*user@@[10.11.12.13]*\ that is, with a `domain literal'
(an IP address) instead of a named domain.
.display asis
# allow_domain_literals
.endd
.em
The RFCs still require this form, but many people think that in the modern
Internet it makes little sense to permit mail to be sent to specific hosts by
quoting their IP addresses. This ancient format has been used by people who
try to abuse hosts by using them for unwanted relaying. However, some
people believe there are circumstances (for example, messages addressed to 
\*postmaster*\) where domain literals are still useful.
.nem

The next configuration line is a kind of trigger guard:
.display asis
never_users = root
.endd
It specifies that no delivery must ever be run as the root user. The normal
convention is to set up \*root*\ as an alias for the system administrator. This
setting is a guard against slips in the configuration.
The list of users specified by \never@_users\ is not, however, the complete
list; the build-time configuration in \(Local/Makefile)\ has an option called
\\FIXED@_NEVER@_USERS\\ specifying a list that cannot be overridden. The
contents of \never@_users\ are added to this list. By default 
\\FIXED@_NEVER@_USERS\\ also specifies root.

When a remote host connects to Exim in order to send mail, the only information
Exim has about the host's identity is its IP address. The next configuration
line,
.display asis
host_lookup = *
.endd
specifies that Exim should do a reverse DNS lookup on all incoming connections,
in order to get a host name. This improves the quality of the logging
information, but if you feel it is too expensive, you can remove it entirely,
or restrict the lookup to hosts on `nearby' networks.
Note that it is not always possible to find a host name from an IP address, 
because not all DNS reverse zones are maintained, and sometimes DNS servers are
unreachable.

The next two lines are concerned with \*ident*\ callbacks, as defined by RFC
1413 (hence their names):
.display asis
rfc1413_hosts = *
rfc1413_query_timeout = 30s
.endd
These settings cause Exim to make ident callbacks for all incoming SMTP calls.
You can limit the hosts to which these calls are made, or change the timeout
that is used. If you set the timeout to zero, all ident calls are disabled.
Although they are cheap and can provide useful information for tracing problem
messages, some hosts and firewalls have problems with ident calls. This can
result in a timeout instead of an immediate refused connection, leading to
delays on starting up an incoming SMTP session.

When Exim receives messages over SMTP connections, it expects all addresses to
be fully qualified with a domain, as required by the SMTP definition. However,
if you are running a server to which simple clients submit messages, you may
find that they send unqualified addresses. The two commented-out options:
.display asis
# sender_unqualified_hosts =
# recipient_unqualified_hosts =
.endd
show how you can specify hosts that are permitted to send unqualified sender
and recipient addresses, respectively.

The \percent@_hack@_domains\ option is also commented out:
.display asis
# percent_hack_domains =
.endd
It provides a list of domains for which the `percent hack' is to operate. This
is an almost obsolete form of explicit email routing. If you do not know
anything about it, you can safely ignore this topic.

The last two settings in the main part of the default configuration are
concerned with messages that have been `frozen' on Exim's queue. When a message
is frozen, Exim no longer continues to try to deliver it. Freezing occurs when
a bounce message encounters a permanent failure because the sender address of
the original message that caused the bounce is invalid, so the bounce cannot be
delivered. This is probably the most common case, but there are also other
conditions that cause freezing, and frozen messages are not always bounce
messages.
.display asis
ignore_bounce_errors_after = 2d
timeout_frozen_after = 7d
.endd
The first of these options specifies that failing bounce messages are to be
discarded after 2 days on the queue. The second specifies that any frozen
message (whether a bounce message or not) is to be timed out (and discarded)
after a week. In this configuration, the first setting ensures that no failing
bounce message ever lasts a week.


.section ACL configuration
.index default||ACLs
.index ~~ACL||default configuration
In the default configuration, the ACL section follows the main configuration.
It starts with the line
.display asis
begin acl
.endd
and it contains the definition of one ACL called \*acl@_check@_rcpt*\ that was
referenced in the setting of \acl@_smtp@_rcpt\ above.
.index \\RCPT\\||ACL for
This ACL is used for every \\RCPT\\ command in an incoming SMTP message. Each
\\RCPT\\ command specifies one of the message's recipients. The ACL statements
are considered in order, until the recipient address is either accepted or
rejected. The \\RCPT\\ command is then accepted or rejected, according to the
result of the ACL processing.
.display asis
acl_check_rcpt:
.endd
This line, consisting of a name terminated by a colon, marks the start of the
ACL, and names it.
.display asis
accept  hosts = :
.endd
This ACL statement accepts the recipient if the sending host matches the list.
But what does that strange list mean? It doesn't actually contain any host
names or IP addresses. The presence of the colon puts an empty item in the
list; Exim matches this only if the incoming message didn't come from a remote
host. The colon is important. Without it, the list itself is empty, and can
never match anything.

What this statement is doing is to accept unconditionally all recipients in
messages that are submitted by SMTP from local processes using the standard
input and output (that is, not using TCP/IP). A number of MUAs operate in this
manner.
.display asis
deny    domains       = +local_domains
        local_parts   = ^[.] : ^.*[@%!/|]

deny    domains       = !+local_domains
        local_parts   = ^[./|] : ^.*[@%!] : ^.*/\\.\\./
.endd         
These statements are concerned with local parts that contain any of the 
characters `@@', `%', `!', `/', `|', or dots in unusual places. Although these
characters are entirely legal in local parts (in the case of `@@' and leading
dots, only if correctly quoted), they do not commonly occur in Internet mail
addresses.

The first three have in the past been associated with explicitly routed
addresses (percent is still sometimes used -- see the \percent@_hack@_domains\
option). Addresses containing these characters are regularly tried by spammers
in an attempt to bypass relaying restrictions, and also by open relay testing
programs. Unless you really need them it is safest to reject these characters
at this early stage. This configuration is heavy-handed in rejecting these
characters for all messages it accepts from remote hosts. This is a deliberate
policy of being as safe as possible.

The first rule above is stricter, and is applied to messages that are addressed
to one of the local domains handled by this host. This is implemented by the
first condition, which restricts it to domains that are listed in the
\*local@_domains*\ domain list. The `+' character is used to indicate a
reference to a named list. In this configuration, there is just one domain in
\*local@_domains*\, but in general there may be many.

The second condition on the first statement uses two regular expressions to
block local parts that begin with a dot or contain `@@', `%', `!', `/', or `|'.
If you have local accounts that include these characters, you will have to
modify this rule.

Empty components (two dots in a row) are not valid in RFC 2822, but Exim
allows them because they have been encountered in practice. (Consider local
parts constructed as `first-initial.second-initial.family-name' when applied to
someone like the author of Exim, who has no second initial.) However, a local
part starting with a dot or containing `/../' can cause trouble if it is used
as part of a file name (for example, for a mailing list). This is also true for
local parts that contain slashes. A pipe symbol can also be troublesome if the
local part is incorporated unthinkingly into a shell command line.

The second rule above applies to all other domains, and is less strict. This
allows your own users to send outgoing messages to sites that use slashes
and vertical bars in their local parts. It blocks local parts that begin
with a dot, slash, or vertical bar, but allows these characters within the
local part. However, the sequence `/../' is barred. The use of `@@', `%', and
`!' is blocked, as before. The motivation here is to prevent your users (or
your users' viruses) from mounting certain kinds of attack on remote sites.

.display asis
accept  local_parts   = postmaster
        domains       = +local_domains
.endd
This statement, which has two conditions, accepts an incoming address if the
local part is \*postmaster*\ and the domain is one of those listed in the
\*local@_domains*\ domain list. The `+' character is used to indicate a
reference to a named list. In this configuration, there is just one domain in
\*local@_domains*\, but in general there may be many.

The presence of this statement means that mail to postmaster is never blocked
by any of the subsequent tests. This can be helpful while sorting out problems
in cases where the subsequent tests are incorrectly denying access.
.display asis
require verify        = sender
.endd
This statement requires the sender address to be verified before any subsequent
ACL statement can be used. If verification fails, the incoming recipient
address is refused. Verification consists of trying to route the address, to
see if a 
bounce 
message could be delivered to it. In the case of remote addresses, basic
verification checks only the domain, but \*callouts*\ can be used for more
verification if required. Section ~~SECTaddressverification discusses the
details of address verification.

.display asis
# deny    message       = rejected because $sender_host_address is \
#                         in a black list at $dnslist_domain\n\
#                         $dnslist_text
#         dnslists      = black.list.example
#
# warn    message       = X-Warning: $sender_host_address is \
#                         in a black list at $dnslist_domain
#         log_message   = found in $dnslist_domain
#         dnslists      = black.list.example
.endd
These commented-out lines are examples of how you could configure Exim to check
sending hosts against a DNS black list. The first statement rejects messages
from blacklisted hosts, whereas the second merely inserts a warning header
line.

.display asis
accept  domains       = +local_domains
        endpass
        message       = unknown user
        verify        = recipient
.endd
This statement accepts the incoming recipient address if its domain is one of
the local domains, but only if the address can be verified. Verification of
local addresses normally checks both the local part and the domain. The
\endpass\ line needs some explanation: if the condition above \endpass\ fails,
that is, if the address is not in a local domain, control is passed to the next
ACL statement. However, if the condition below \endpass\ fails, that is, if a
recipient in a local domain cannot be verified, access is denied and the
recipient is rejected.
.index customizing||ACL failure message
The \message\ modifier provides a customized error message for the failure.
.display asis
accept  domains       = +relay_to_domains
        endpass
        message       = unrouteable address
        verify        = recipient
.endd
This statement accepts the incoming recipient address if its domain is one of
the domains for which this host is a relay, but again, only if the address can
be verified.
.display asis
accept  hosts         = +relay_from_hosts
.endd
Control reaches this statement only if the recipient's domain is neither a
local domain, nor a relay domain. The statement accepts the address if the
message is coming from one of the hosts that are defined as being allowed to
relay through this host. Recipient verification is omitted here, because in
many cases the clients are dumb MUAs that do not cope well with SMTP error
responses. If you are actually relaying out from MTAs, you should probably add
recipient verification here.
.display asis
accept  authenticated = *
.endd
Control reaches here for attempts to relay to arbitrary domains from arbitrary
hosts. The statement accepts the address only if the client host has
authenticated itself. The default configuration does not define any
authenticators, which means that no client can in fact authenticate. You will
need to add authenticator definitions if you want to make use of this ACL
statement.
.display asis
deny    message       = relay not permitted
.endd
The final statement denies access, giving a specific error message. Reaching
the end of the ACL also causes access to be denied, but with the generic
message `administrative prohibition'.


.section Router configuration
.index default||routers
.index routers||default
The router configuration comes next in the default configuration, introduced
by the line
.display asis
begin routers
.endd
Routers are the modules in Exim that make decisions about where to send
messages. An address is passed to each router in turn, until it is either
accepted, or failed. This means that the order in which you define the routers
matters. Each router is fully described in its own chapter later in this
manual. Here we give only brief overviews.

.index domain literal||default router
.display asis
# domain_literal:
#   driver = ipliteral
#   domains = !+local_domains
#   transport = remote_smtp
.endd
This router is commented out because the majority of sites do not want to
support domain literal addresses (those of the form \*user@@[10.9.8.7]*\). If
you uncomment this router, you also need to uncomment the setting of
\allow@_domain@_literals\ in the main part of the configuration.

.display asis
dnslookup:
  driver = dnslookup
  domains = ! +local_domains
  transport = remote_smtp
.newline
  ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
.newline
  no_more
.endd
The first uncommented router handles addresses that do not involve any local
domains. This is specified by the line
.display asis
domains = ! +local_domains
.endd
The \domains\ option lists the domains to which this router applies, but the
exclamation mark is a negation sign, so the router is used only for domains
that are not in the domain list called \*local@_domains*\ (which was defined at
the start of the configuration). The plus sign before \*local@_domains*\
indicates that it is referring to a named list. Addresses in other domains are
passed on to the following routers.

The name of the router driver is \%dnslookup%\,
and is specified by the \driver\ option. Do not be confused by the fact that
the name of this router instance is the same as the name of the driver. The 
instance name is arbitrary, but the name set in the \driver\ option must be one 
of the driver modules that is in the Exim binary.

The \%dnslookup%\ router routes addresses by looking up their domains in the
DNS in order to obtain a list of hosts to which the address is routed. If the
router succeeds, the address is queued for the \%remote@_smtp%\ transport, as
specified by the \transport\ option. If the router does not find the domain in
the DNS, no further routers are tried because of the \no@_more\ setting, so the
address fails and is bounced.

The \ignore@_target@_hosts\ option specifies a list of IP addresses that are to
be entirely ignored. This option is present because a number of cases have been
encountered where MX records in the DNS point to host names 
whose IP addresses are 0.0.0.0 or are in the 127 subnet (typically 127.0.0.1).
Completely ignoring these IP addresses causes Exim to fail to route the
email address, so it bounces. Otherwise, Exim would log a routing problem, and
continue to try to deliver the message periodically until the address timed
out.
.display asis
system_aliases:
  driver = redirect
  allow_fail
  allow_defer
  data = ${lookup{$local_part}lsearch{/etc/aliases}}
# user = exim
  file_transport = address_file
  pipe_transport = address_pipe
.endd
Control reaches this and subsequent routers only for addresses in the local
domains. This router checks to see whether the local part is defined as an
alias in the \(/etc/aliases)\ file, and if so, redirects it according to the
data that it looks up from that file. If no data is found for the local part,
the value of the \data\ option is empty, causing the address to be passed to
the next router.

\(/etc/aliases)\ is a conventional name for the system aliases file that is 
often used. That is why it is referenced by from the default configuration 
file. However, you can change this by setting \\SYSTEM@_ALIASES@_FILE\\ in
\(Local/Makefile)\ before building Exim.

.display asis
userforward:
  driver = redirect
  check_local_user
  file = $home/.forward
  no_verify
  no_expn
  check_ancestor
# allow_filter
  file_transport = address_file
  pipe_transport = address_pipe
  reply_transport = address_reply
.endd
This is the most complicated router in the default configuration. It is another
redirection router, but this time it is looking for forwarding data set up by
individual users. The \check@_local@_user\ setting means that the first thing it
does is to check that the local part of the address is the login name of a
local user. If it is not, the router is skipped. When a local user is found,
the file called \(.forward)\ in the user's home directory is consulted. If it
does not exist, or is empty, the router declines. Otherwise, the contents of
\(.forward)\ are interpreted as redirection data (see chapter ~~CHAPredirect 
for more details).

.index Sieve filter||enabling in default router
Traditional \(.forward)\ files contain just a list of addresses, pipes, or
files. Exim supports this by default. However, if \allow@_filter\ is set (it is
commented out by default), the contents of the file are interpreted as a set of
Exim or Sieve filtering instructions, provided the file begins with `@#Exim
filter' or `@#Sieve filter', respectively. User filtering is discussed in the
separate document entitled \*Exim's interfaces to mail filtering*\.

The \no@_verify\ and \no@_expn\ options mean that this router is skipped when
verifying addresses, or when running as a consequence of an SMTP \\EXPN\\
command. 
There are two reasons for doing this:
.numberpars
Whether or not a local user has a \(.forward)\ file is not really relevant when 
checking an address for validity; it makes sense not to waste resources doing
unnecessary work.
.nextp
More importantly, when Exim is verifying addresses or handling an \\EXPN\\ 
command during an SMTP session, it is running as the Exim user, not as root. 
The group is the Exim group, and no additional groups are set up.
It may therefore not be possible for Exim to read users' \(.forward)\ files at
this time.
.endp

The setting of \check@_ancestor\ prevents the router from generating a new
address that is the same as any previous address that was redirected. (This
works round a problem concerning a bad interaction between aliasing and
forwarding -- see section ~~SECTredlocmai).

The final three option settings specify the transports that are to be used when
forwarding generates a direct delivery to a file, or to a pipe, or sets up an
auto-reply, respectively. For example, if a \(.forward)\ file contains
.display asis
a.nother@elsewhere.example, /home/spqr/archive
.endd
the delivery to \(/home/spqr/archive)\ is done by running the \address@_file\
transport.
.display asis
localuser:
  driver = accept
  check_local_user
  transport = local_delivery
.endd
The final router sets up delivery into local mailboxes, provided that the local
part is the name of a local login, by accepting the address and queuing it for
the \%local@_delivery%\ transport. Otherwise, we have reached the end of the
routers, so the address is bounced.


.section Transport configuration
.index default||transports
.index transports||default
Transports define mechanisms for actually delivering messages. They operate
only when referenced from routers, so the order in which they are defined does
not matter. The transports section of the configuration starts with
.display asis
begin transports
.endd
One remote transport and four local transports are defined.
.display asis
remote_smtp:
  driver = smtp
.endd
This transport is used for delivering messages over SMTP connections. All its
options are defaulted. The list of remote hosts comes from the router.
.display asis
local_delivery:
  driver = appendfile
  file = /var/mail/$local_part
  delivery_date_add
  envelope_to_add
  return_path_add
# group = mail
# mode = 0660
.endd
This \%appendfile%\ transport is used for local delivery to user mailboxes in
traditional BSD mailbox format. By default it runs under the uid and gid of the
local user, which requires the sticky bit to be set on the \(/var/mail)\
directory. Some systems use the alternative approach of running mail deliveries
under a particular group instead of using the sticky bit. The commented options
show how this can be done.

Exim adds three headers to the message as it delivers it: ::Delivery-date::,
::Envelope-to:: and ::Return-path::. This action is requested by the three
similarly-named options above.
.display asis
address_pipe:
  driver = pipe
  return_output
.endd
This transport is used for handling deliveries to pipes that are generated by
redirection (aliasing or users' \(.forward)\ files). The \return@_output\
option specifies that any output generated by the pipe is to be returned to the
sender.
.display asis
address_file:
  driver = appendfile
  delivery_date_add
  envelope_to_add
  return_path_add
.endd
This transport is used for handling deliveries to files that are generated by
redirection. The name of the file is not specified in this instance of
\%appendfile%\, because it comes from the \%redirect%\ router.
.display asis
address_reply:
  driver = autoreply
.endd
This transport is used for handling automatic replies generated by users'
filter files.


.section Default retry rule
.index retry||default rule
.index default||retry rule
The retry section of the configuration file contains rules which affect the way
Exim retries deliveries that cannot be completed at the first attempt. It is
introduced by the line
.display asis
begin retry
.endd
In the default configuration, there is just one rule, which applies to all
errors:
.display asis
*   *   F,2h,15m; G,16h,1h,1.5; F,4d,6h
.endd
This causes any temporarily failing address to be retried every 15 minutes for
2 hours, then at intervals starting at one hour and increasing by a factor of
1.5 until 16 hours have passed, then every 6 hours up to 4 days. If an address
is not delivered after 4 days of failure, it is bounced.


.section Rewriting configuration
The rewriting section of the configuration, introduced by
.display asis
begin rewrite
.endd
contains rules for rewriting addresses in messages as they arrive. There are no
rewriting rules in the default configuration file.


.section Authenticators configuration
.index \\AUTH\\||configuration
The authenticators section of the configuration, introduced by
.display asis
begin authenticators
.endd
defines mechanisms for the use of the SMTP \\AUTH\\ command. No authenticators
are specified in the default configuration file.



.
.
.
.
. ============================================================================
.chapter Regular expressions
.set runningfoot "regular expressions"
.rset CHAPregexp ~~chapter

.index regular expressions||library
.index PCRE
Exim supports the use of regular expressions in many of its options. It
uses the PCRE regular expression library; this provides regular expression
matching that is compatible with Perl 5. The syntax and semantics of
regular expressions is discussed in many Perl reference books, and also in
Jeffrey Friedl's
.if ~~html
[(A HREF="http://www.oreilly.com/catalog/regex/")]
.fi
$it{Mastering Regular Expressions}
.if ~~html
[(/A)]
.fi
(O'Reilly, ISBN 0-596-00289-0).

The documentation for the syntax and semantics of the regular expressions that 
are supported by PCRE is included in plain text in the file
\(doc/pcrepattern.txt)\ in the Exim distribution, and also in the HTML
tarbundle of Exim documentation, and as an appendix to the
.if ~~html
[(A HREF="http://www.uit.co.uk/exim-book/")]
.fi
Exim book.
.if ~~html
[(/A)]
.fi
It describes in detail the features of the regular expressions that PCRE
supports, so no further description is included here. The PCRE functions are
called from Exim using the default option settings (that is, with no PCRE
options set), except that the \\PCRE@_CASELESS\\ option is set when the
matching is required to be case-insensitive.

.em
In most cases, when a regular expression is required in an Exim configuration, 
it has to start with a circumflex, in order to distinguish it from plain text 
or an `ends with' wildcard. In this example of a configuration setting, the
second item in the colon-separated list is a regular expression.
.display asis
domains = a.b.c : ^\\d{3} : *.y.z : ...
.endd
The doubling of the backslash is required because of string expansion that
precedes interpretation -- see section ~~SECTlittext for more discussion of
this issue, and a way of avoiding the need for doubling backslashes. The
regular expression that is eventually used in this example contains just one
backslash. The circumflex is included in the regular expression, and has the
normal effect of `anchoring' it to the start of the string that is being
matched.

There are, however, two cases where a circumflex is not required for the 
recognition of a regular expression: these are the \match\ condition in a
string expansion, and the \matches\ condition in an Exim filter file. In these
cases, the relevant string is always treated as a regular expression; if it
does not start with a circumflex, the expression is not anchored, and can match
anywhere in the subject string.

In all cases, if you want a regular expression to match at the end of a string, 
you must code the @$ metacharacter to indicate this. For example:
.display asis
domains = ^\\d{3}\\.example
.endd
matches the domain \*123.example*\, but it also matches \*123.example.com*\. 
You need to use:
.display asis
domains = ^\\d{3}\\.example\$
.endd
if you want \*example*\ to be the top-level domain. (The backslash before the
@$ is another artefact of string expansion.)
.nem


.section Testing regular expressions
.index testing||regular expressions
.index regular expressions||testing
.index \*pcretest*\
A program called \*pcretest*\ forms part of the PCRE distribution and is built
with PCRE during the process of building Exim. It is primarily intended for
testing PCRE itself, but it can also be used for experimenting with regular
expressions. After building Exim, the binary can be found in the build
directory (it is not installed anywhere automatically). There is documentation
of various options in \(doc/pcretest.txt)\, but for simple testing, none are
needed. This is the output of a sample run of \*pcretest*\:
.display
  re> $cb{/^([^@@]+)@@.+@\.(ac|edu)@\.(?!kr)[a-z]@{2@}@$/}
data> $cb{x@@y.ac.uk}
 0: x@@y.ac.uk
 1: x
 2: ac
data> $cb{x@@y.ac.kr}
No match
data> $cb{x@@y.edu.com}
No match
data> $cb{x@@y.edu.co}
 0: x@@y.edu.co
 1: x
 2: edu
.endd
.if ~~sys.fancy
Input typed by the user is shown in bold face.
.fi
After the `re>' prompt, a regular expression enclosed in delimiters is
expected. If this compiles without error, `data>' prompts are given for strings
against which the expression is matched. An empty data line causes a new
regular expression to be read. If the match is successful, the captured
substring values (that is, what would be in the variables \$0$\, \$1$\, \$2$\,
etc.) are shown. The above example tests for an email address whose domain ends
with either `ac' or `edu' followed by a two-character top-level domain that is
not `kr'. The local part is captured in \$1$\ and the `ac' or `edu' in \$2$\.






.
.
.
.
. ============================================================================
.chapter File and database lookups
.set runningfoot "file/database lookups"
.rset CHAPfdlookup "~~chapter"
.index file||lookup
.index database lookups
.index lookup||description of
Exim can be configured to look up data in files or databases as it processes
messages. Two different kinds of syntax are used:
.numberpars
A string that is to be expanded may contain explicit lookup requests. These
cause parts of the string to be replaced by data that is obtained from the 
lookup. 
.nextp
Lists of domains, hosts, and email addresses can contain lookup requests as a
way of avoiding excessively long linear lists. In this case, the data that is
returned by the lookup is often (but not always) discarded; whether the lookup
succeeds or fails is what really counts. These kinds of list are described in
chapter ~~CHAPdomhosaddlists.
.endp
It is easy to confuse the two different kinds of lookup, especially as the
lists that may contain the second kind are always expanded before being
processed as lists. Therefore, they may also contain lookups of the first kind. 
Be careful to distinguish between the following two examples:
.display asis
domains = ${lookup{$sender_host_address}lsearch{/some/file}}
domains = lsearch;/some/file
.endd
The first uses a string expansion, the result of which must be a domain list.
String expansions are described in detail in chapter ~~CHAPexpand. The
expansion takes place first, and the file that is searched could contain lines
like this:
.display asis
192.168.3.4: domain1 : domain2 : ...
192.168.1.9: domain3 : domain4 : ...
.endd
Thus, the result of the expansion is a list of domains (and possibly other 
types of item that are allowed in domain lists).

In the second case, the lookup is a single item in a domain list. It causes 
Exim to use a lookup to see if the domain that is being processed can be found
in the file. The file could contains lines like this:
.display asis
domain1: 
domain2:
.endd
Any data that follows the keys is not relevant when checking that the domain 
matches the list item.

It is possible to use both kinds of lookup at once. Consider a file containing 
lines like this:
.display asis
192.168.5.6: lsearch;/another/file
.endd
If the value of \$sender@_host@_address$\ is 192.168.5.6, expansion of the 
first \domains\ setting above generates the second setting, which therefore 
causes a second lookup to occur.

The rest of this chapter describes the different lookup types that are
available. Any of them can be used in either of the circumstances described
above. The syntax requirements for the two cases are described in chapters 
~~CHAPexpand and ~~CHAPdomhosaddlists, respectively.

.section Lookup types
.index lookup||types of
.index single-key lookup||definition of
Two different styles of data lookup are implemented:
.numberpars $.
The \*single-key*\ style requires the specification of a file in which to look,
and a single key to search for. The lookup type determines how the file is
searched.
.nextp
.index query-style lookup||definition of
The \*query*\ style accepts a generalized database query.
No particular key value is assumed by Exim for query-style lookups. You can
use whichever Exim variable(s) you need to construct the database query.
.endp
The code for each lookup type is in a separate source file that is included in
the binary of Exim only if the corresponding compile-time option is set. The
default settings in \(src/EDITME)\ are:
.display asis
LOOKUP_DBM=yes
LOOKUP_LSEARCH=yes
.endd
which means that only linear searching and DBM lookups are included by default.
For some types of lookup (e.g. SQL databases), you need to install appropriate
libraries and header files before building Exim.



.section Single-key lookup types
.rset SECTsinglekeylookups "~~chapter.~~section"
.index lookup||single-key types
.index single-key lookup||list of types
The following single-key lookup types are implemented:
.numberpars $.
.index cdb||description of
.index lookup||cdb
.index binary zero||in lookup key
\%cdb%\: The given file is searched as a Constant DataBase file, using the key
string without a terminating binary zero. The cdb format is designed for
indexed files that are read frequently and never updated, except by total
re-creation. As such, it is particulary suitable for large files containing
aliases or other indexed data referenced by an MTA. Information about cdb can
be found in several places:
.display rm
\?http://www.pobox.com/@~djb/cdb.html?\
\?ftp://ftp.corpit.ru/pub/tinycdb/?\
\?http://packages.debian.org/stable/utils/freecdb.html?\
.endd
A cdb distribution is not needed in order to build Exim with cdb support,
because the code for reading cdb files is included directly in Exim itself.
However, no means of building or testing cdb files is provided with Exim, so
you need to obtain a cdb distribution in order to do this.
.nextp
.index DBM||lookup type
.index lookup||dbm
.index binary zero||in lookup key
\%dbm%\: Calls to DBM library functions are used to extract data from the given
DBM file by looking up the record with the given key. A terminating binary
zero is included in the key that is passed to the DBM library. See section
~~SECTdb for a discussion of DBM libraries.
.index Berkeley DB library||file format
For all versions of Berkeley DB, Exim uses the \\DB@_HASH\\ style of database 
when building DBM files using the \exim@_dbmbuild\ utility. However, when using 
Berkeley DB versions 3 or 4, it opens existing databases for reading with the
\\DB@_UNKNOWN\\ option. This enables it to handle any of the types of database
that the library supports, and can be useful for accessing DBM files created by 
other applications. (For earlier DB versions, \\DB@_HASH\\ is always used.)

.nextp
.index lookup||dbmnz
.index lookup||dbm, terminating zero
.index binary zero||in lookup key
.index Courier
.index \(/etc/userdbshadow.dat)\
.index dmbnz lookup type
\%dbmnz%\: This is the same as \%dbm%\, except that a terminating binary zero
is not included in the key that is passed to the DBM library. You may need this
if you want to look up data in files that are created by or shared with some
other application that does not use terminating zeros. For example, you need to
use \%dbmnz%\ rather than \%dbm%\ if you want to authenticate incoming SMTP
calls using the passwords from Courier's \(/etc/userdbshadow.dat)\ file. Exim's
utility program for creating DBM files (\*exim@_dbmbuild*\) includes the zeros
by default, but has an option to omit them (see section ~~SECTdbmbuild).
.nextp
.index lookup||dsearch
.index dsearch lookup type
\%dsearch%\: The given file must be a directory; this is searched for a file
whose name is the key. The key may not contain any forward slash characters.
The result of a successful lookup is the name of the file. An example of how
this lookup can be used to support virtual domains is given in section
~~SECTvirtualdomains.
.nextp
.index lookup||iplsearch
.index iplsearch lookup type
.em
\%iplsearch%\: The given file is a text file containing keys and data. A key is
terminated by a colon or white space or the end of the line. The keys in the
file must be IP addresses, or IP addresses with CIDR masks. Keys that involve
IPv6 addresses must be enclosed in quotes to prevent the first internal colon
being interpreted as a key terminator. For example:
.display asis
1.2.3.4:           data for 1.2.3.4
192.168.0.0/16     data for 192.168.0.0/16
"abcd::cdab":      data for abcd::cdab
"abcd:abcd::/32"   data for abcd:abcd::/32
.endd
The key for an \%iplsearch%\ lookup must be an IP address (without a mask). The
file is searched linearly, using the CIDR masks where present, until a matching
key is found. The first key that matches is used; there is no attempt to find a
`best' match. Apart from the way the keys are matched, the processing for 
\%iplsearch%\ is the same as for \%lsearch%\.

\**Warning 1**\: Unlike most other single-key lookup types, a file of data for
\%iplsearch%\ can \*not*\ be turned into a DBM or cdb file, because those
lookup types support only literal keys.

\**Warning 2**\: In a host list, you must always use \%net-iplsearch%\ so that 
the implicit key is the host's IP address rather than its name (see section
~~SECThoslispatsikey).
.nem

.nextp
.index linear search
.index lookup||lsearch
.index lsearch lookup type
\%lsearch%\: The given file is a text file that is searched linearly for a
line beginning with the search key, terminated by a colon or white space or the
end of the line. The first occurrence that is found in the file is used. White
space between the key and the colon is permitted. The remainder of the line,
with leading and trailing white space removed, is the data. This can be
continued onto subsequent lines by starting them with any amount of white
space, but only a single space character is included in the data at such a
junction. If the data begins with a colon, the key must be terminated by a
colon, for example:
.display
baduser:  :fail:
.endd
Empty lines and lines beginning with @# are ignored, even if they occur in the
middle of an item. This is the traditional textual format of alias files. Note
that the keys in an \%lsearch%\ file are literal strings. There is no
wildcarding of any kind.

.index lookup||lsearch, colons in keys
In most \%lsearch%\ files, keys are not required to contain colons 
.em
or @# characters, or
.nem
whitespace. However, if you need this feature, it is available. If a key begins
with a doublequote character, it is terminated only by a matching quote (or end
of line), and the normal escaping rules apply to its contents (see section
~~SECTstrings). An optional colon is permitted after quoted keys (exactly as
for unquoted keys). There is no special handling of quotes for the data part of
an \%lsearch%\ line.
.nextp
.index NIS lookup type
.index lookup||NIS
.index binary zero||in lookup key
\%nis%\: The given file is the name of a NIS map, and a NIS lookup is done with
the given key, without a terminating binary zero. There is a variant called
\%nis0%\ which does include the terminating binary zero in the key. This is
reportedly needed for Sun-style alias files. Exim does not recognize NIS
aliases; the full map names must be used.
.nextp
.index wildlsearch lookup type
.index lookup||wildlsearch
.index nwildlsearch lookup type
.index lookup||nwildlsearch
\%wildlsearch%\ or \%nwildlsearch%\: These search a file linearly, like
\%lsearch%\, but instead of being interpreted as a literal string, each key may
be wildcarded. The difference between these two lookup types is that for
\%wildlsearch%\, each key in the file is string-expanded before being used, 
whereas for \%nwildlsearch%\, no expansion takes place.

Like \%lsearch%\, the testing is done case-insensitively. The following forms
of wildcard are recognized:
.numberpars "$*$"
The string may begin with an asterisk to mean `begins with'. For example:
.display asis
*.a.b.c       data for anything.a.b.c
*fish         data for anythingfish
.endd
.nextp
The string may begin with a circumflex to indicate a regular expression. For
example, for \%wildlsearch%\:
.display asis
^\N\d+\.a\.b\N    data for <digits>.a.b
.endd
Note the use of \"@\N"\ to disable expansion of the contents of the regular 
expression. If you are using \%nwildlsearch%\, where the keys are not 
string-expanded, the equivalent entry is:
.display asis
^\d+\.a\.b        data for <digits>.a.b
.endd

If the regular expression contains white space or colon characters, you must
either quote it (see \%lsearch%\ above), or represent these characters in other
ways. For example, \"@\s"\ can be used for white space and \"@\x3A"\ for a
colon. This may be easier than quoting, because if you quote, you have to
escape all the backslashes inside the quotes.
.nextp
Although I cannot see it being of much use, the general matching function
that is used to implement 
\%(n)wildlsearch%\ 
means that the string may begin with a lookup name terminated by a semicolon,
and followed by lookup data. For example:
.display asis
cdb;/some/file  data for keys that match the file
.endd
The data that is obtained from the nested lookup is discarded.
.endp
Keys that do not match any of these patterns are interpreted literally. The
continuation rules for the data are the same as for \%lsearch%\, and keys may
be followed by optional colons.

\**Warning**\: Unlike most other single-key lookup types, a file of data for
\%(n)wildlsearch%\ can \*not*\ be turned into a DBM or cdb file, because those
lookup types support only literal keys.
.endp

.section Query-style lookup types
.index lookup||query-style types
.index query-style lookup||list of types
The supported query-style lookup types are listed below. Further details about 
many of them are given in later sections.
.numberpars $.
.index DNS||as a lookup type
.index lookup||DNS
\%dnsdb%\: This does a DNS search for a record whose domain name is the supplied
query. The resulting data is the contents of the record. See section
~~SECTdnsdb.
.nextp
.index Interbase lookup type
.index lookup||Interbase
\%ibase%\: This does a lookup in an Interbase database.
.nextp
.index LDAP||lookup type
.index lookup||LDAP
\%ldap%\: This does an LDAP lookup using a query in the form of a URL, and
returns attributes from a single entry. There is a variant called \%ldapm%\
that permits values from multiple entries to be returned. A third variant
called \%ldapdn%\ returns the Distinguished Name of a single entry instead of
any attribute values. See section ~~SECTldap.
.nextp
.index MySQL||lookup type
.index lookup||MySQL
\%mysql%\: The format of the query is an SQL statement that is passed to a MySQL
database. See section ~~SECTsql.
.nextp
.index NIS@+ lookup type
.index lookup||NIS+
\%nisplus%\: This does a NIS+ lookup using a query that can specify the name of
the field to be returned. See section ~~SECTnisplus.
.nextp
.index Oracle||lookup type
.index lookup||Oracle
\%oracle%\: The format of the query is an SQL statement that is passed to an
Oracle database. See section ~~SECTsql.
.nextp
.index lookup||passwd
.index passwd lookup type
\%passwd%\ is a query-style lookup with queries that are just user names. The
lookup calls \*getpwnam()*\ to interrogate the system password data, and on
success, the result string is the same as you would get from an \%lsearch%\
lookup on a traditional \(/etc/passwd file)\, though with \"*"\ for the
password value. For example:
.display asis
*:42:42:King Rat:/home/kr:/bin/bash
.endd
.nextp
.index PostgreSQL lookup type
.index lookup||PostgreSQL
\%pgsql%\: The format of the query is an SQL statement that is passed to a
PostgreSQL database. See section ~~SECTsql.
.nextp
\%testdb%\: This is a lookup type that is used for testing Exim. It is
not likely to be useful in normal operation.
.nextp
.index whoson lookup type
.index lookup||whoson
\%whoson%\: \*Whoson*\ (\?http://whoson.sourceforge.net?\) is a proposed
Internet protocol that allows Internet server programs to check whether a
particular (dynamically allocated) IP address is currently allocated to a known
(trusted) user and, optionally, to obtain the identity of the said user. In
Exim, this can be used to implement `POP before SMTP' checking using ACL
statements such as
.display asis
require condition = \
  ${lookup whoson {$sender_host_address}{yes}{no}}
.endd
The query consists of a single IP address. The value returned is the name of
the authenticated user.
.endp

.section Temporary errors in lookups
.index lookup||temporary error in
Lookup functions can return temporary error codes if the lookup cannot be
completed. For example, a NIS or LDAP database might be unavailable. For this
reason, it is not advisable to use a lookup that might do this for critical
options such as a list of local domains.

When a lookup cannot be completed in a router or transport, delivery
of the message (to the relevant address) is deferred, as for any other
temporary error. In other circumstances Exim may assume the lookup has failed,
or may give up altogether.


.section Default values in single-key lookups
.rset SECTdefaultvaluelookups "~~chapter.~~section"
.index wildcard lookups
.index lookup||default values
.index lookup||wildcard
.index lookup||$*$ added to type
.index default||in single-key lookups
In this context, a `default value' is a value specified by the administrator
that is to be used if a lookup fails.

If `$*$' is added to a single-key lookup type (for example, \lsearch$*$\) and
the initial lookup fails, the key `$*$' is looked up in the file to provide
a default value. See also the section on partial matching below.

.index @*@@ with single-key lookup
.index lookup||$*$@@ added to type
.index alias file||per-domain default
Alternatively, if `$*$@@' is added to a single-key lookup type (for example
\dbm$*$@@\) then, if the initial lookup fails and the key contains an @@
character, a second lookup is done with everything before the last @@ replaced
by $*$. This makes it possible to provide per-domain defaults in alias files
that include the domains in the keys. If the second lookup fails (or doesn't
take place because there is no @@ in the key), `$*$' is looked up.
For example, a \%redirect%\ router might contain:
.display asis
data = ${lookup{$local_part@$domain}lsearch*@{/etc/mixed-aliases}}
.endd
Suppose the address that is being processed is \*jane@@eyre.example*\. Exim 
looks up these keys, in this order:
.display asis
jane@eyre.example
*@eyre.example
*
.endd
The data is taken from whichever key it finds first. \**Note**\: in an 
\%lsearch%\ file, this does not mean the first of these keys in the file. A 
complete scan is done for each key, and only if it is not found at all does 
Exim move on to try the next key.


.section Partial matching in single-key lookups
.rset SECTpartiallookup "~~chapter.~~section"
.index partial matching
.index wildcard lookups
.index lookup||partial matching
.index lookup||wildcard
.index asterisk||in search type
The normal operation of a single-key lookup is to search the file for an exact
match with the given key. However, in a number of situations where domains are
being looked up, it is useful to be able to do partial matching. In this case,
information in the file that has a key starting with `$*$.' is matched by any
domain that ends with the components that follow the full stop. For example, if
a key in a DBM file is
.display
*.dates.fict.example
.endd
then when partial matching is enabled this is matched by (amongst others)
\*2001.dates.fict.example*\ and \*1984.dates.fict.example*\. It is also matched
by \*dates.fict.example*\, if that does not appear as a separate key in the
file.

\**Note**\: Partial matching is not available for query-style lookups. It is 
also not available for any lookup items in address lists (see section
~~SECTaddresslist).

Partial matching is implemented by doing a series of separate lookups using
keys constructed by modifying the original subject key. This means that it can
be used with any of the single-key lookup types, provided that
partial matching keys 
beginning with a special prefix (default `$*$.') are included in the data file.
Keys in the file that do not begin with the prefix are matched only by
unmodified subject keys when partial matching is in use.

Partial matching is requested by adding the string `partial-' to the front of
the name of a single-key lookup type, for example, \partial-dbm\. When this is
done, the subject key is first looked up unmodified; if that fails, `$*$.'
is added at the start of the subject key, and it is looked up again. If that
fails, further lookups are tried with dot-separated components removed
from the start of the subject key, one-by-one, and `$*$.' added on the front of
what remains.

A minimum number of two non-$*$ components are required. This can be adjusted
by including a number before the hyphen in the search type. For example,
\partial3-lsearch\ specifies a minimum of three non-$*$ components in the
modified keys. Omitting the number is equivalent to `partial2-'. If the subject
key is \*2250.dates.fict.example*\ then the following keys are looked up when
the minimum number of non-$*$ components is two:
.display asis
2250.dates.fict.example
*.2250.dates.fict.example
*.dates.fict.example
*.fict.example
.endd
As soon as one key in the sequence is successfully looked up, the lookup
finishes. 

.index lookup||partial matching, changing prefix
.index prefix||for partial matching
The use of `$*$.' as the partial matching prefix is a default that can be 
changed. The motivation for this feature is to allow Exim to operate with file
formats that are used by other MTAs. A different prefix can be supplied in
parentheses instead of the hyphen after `partial'. For example:
.display asis
domains = partial(.)lsearch;/some/file
.endd
In this example, if the domain is \*a.b.c*\, the sequence of lookups is
\"a.b.c"\, \".a.b.c"\, and \".b.c"\ (the default minimum of 2 non-wild 
components is unchanged). The prefix may consist of any punctuation characters
other than a closing parenthesis. It may be empty, for example:
.display asis
domains = partial1()cdb;/some/file
.endd
For this example, if the domain is \*a.b.c*\, the sequence of lookups is
\"a.b.c"\, \"b.c"\, and \"c"\.

If `partial0' is specified, what happens at the end (when the lookup with just
one non-wild component has failed, and the original key is shortened right down
to the null string) depends on the prefix:
.numberpars $.
If the prefix has zero length, the whole lookup fails.
.nextp
If the prefix has length 1, a lookup for just the prefix is done. For
example, the final lookup for `partial0(.)' is for \"."\ alone.
.nextp
Otherwise, if the prefix ends in a dot, the dot is removed, and the
remainder is looked up. With the default prefix, therefore, the final lookup is 
for `$*$' on its own.
.nextp
Otherwise, the whole prefix is looked up.
.endp

If the search type ends in `$*$' or `$*$@@' (see section
~~SECTdefaultvaluelookups above), the search for an ultimate default that this
implies happens after all partial lookups have failed. If `partial0' is
specified, adding `$*$' to the search type has no effect with the default
prefix, because the `$*$' key is already included in the sequence of partial
lookups. However, there might be a use for lookup types such as
`partial0(.)lsearch$*$'.

The use of `$*$' in lookup partial matching differs from its use as a wildcard
in domain lists and the like. Partial matching works only in terms of
dot-separated components; a key such as \"*fict.example"\
in a database file is useless, because the asterisk in a partial matching
subject key is always followed by a dot.



.section Lookup caching
.index lookup||caching 
.index caching||lookup data
An Exim process
caches the most recent lookup result on a per-file basis for single-key
lookup types, and keeps the relevant files open. In some types of configuration
this can lead to many files being kept open for messages with many recipients.
To avoid hitting the operating system limit on the number of simultaneously
open files, Exim closes the least recently used file when it needs to open more
files than its own internal limit, which can be changed via the
\lookup@_open@_max\ option.

For query-style lookups, a single data cache per lookup type is kept. The files
are closed and the caches flushed at strategic points during delivery -- for
example, after all routing is complete.


.section Quoting lookup data
.index lookup||quoting
.index quoting||in lookups
When data from an incoming message is included in a query-style lookup, there
is the possibility of special characters in the data messing up the syntax of
the query. For example, a NIS+ query that contains
.display asis
[name=$local_part]
.endd
will be broken if the local part happens to contain a closing square bracket.
For NIS+, data can be enclosed in double quotes like this:
.display asis
[name="$local_part"]
.endd
but this still leaves the problem of a double quote in the data. The rule for
NIS+ is that double quotes must be doubled. Other lookup types have different
rules, and to cope with the differing requirements, an expansion operator
of the following form is provided:
.display
@$@{quote@_<<lookup-type>>:<<string>>@}
.endd
For example, the safest way to write the NIS+ query is
.display asis
[name="${quote_nisplus:$local_part}"]
.endd
See chapter ~~CHAPexpand for full coverage of string expansions. The quote
operator can be used for all lookup types, but has no effect for single-key
lookups, since no quoting is ever needed in their key strings.



.section More about dnsdb
.rset SECTdnsdb "~~chapter.~~section"
.index dnsdb lookup
.index lookup||dnsdb
.index DNS||as a lookup type
The \%dnsdb%\ lookup type uses the DNS as its database. A query consists of a
record type and a domain name, separated by an equals sign. For example, an
expansion string could contain:
.display asis
${lookup dnsdb{mx=a.b.example}{$value}fail}
.endd
.em
The supported record types are A, CNAME, MX, NS, PTR, SRV, and TXT, 
.nem
and, when Exim is compiled with IPv6 support, AAAA (and A6 if that is also
configured). If no type is given, TXT is assumed. When the type is PTR, the
address should be given as normal; it is converted to the necessary inverted
format internally. For example:
.display asis
${lookup dnsdb{ptr=192.168.4.5}{$value}fail}
.endd

.index MX record||in \%dnsdb%\ lookup
For MX records, both the preference value and the host name are returned,
separated by a space. 
.em
.index SRV record||in \%dnsdb%\ lookup
For SRV records, the priority, weight, port, and host name are returned, 
separated by spaces. For any record type,
.nem
if multiple records are found (or, for A6 lookups, if a single record leads to
multiple addresses), the data is returned as a concatenation, separated by
newlines. The order, of course, depends on the DNS resolver.




.section More about LDAP
.rset SECTldap "~~chapter.~~section"
.index LDAP lookup
.index lookup||LDAP
.index Solaris||LDAP
The original LDAP implementation came from the University of Michigan; this has
become `Open LDAP', and there are now two different releases. Another
implementation comes from Netscape, and Solaris 7 and subsequent releases
contain inbuilt LDAP support. Unfortunately, though these are all compatible at
the lookup function level, their error handling is different. For this reason
it is necessary to set a compile-time variable when building Exim with LDAP, to
indicate which LDAP library is in use. One of the following should appear in
your \(Local/Makefile)\:
.display asis
LDAP_LIB_TYPE=UMICHIGAN
LDAP_LIB_TYPE=OPENLDAP1
LDAP_LIB_TYPE=OPENLDAP2
LDAP_LIB_TYPE=NETSCAPE
LDAP_LIB_TYPE=SOLARIS
.endd
If \\LDAP@_LIB@_TYPE\\ is not set, Exim assumes \"OPENLDAP1"\, which has the
same interface as the University of Michigan version.

There are three LDAP lookup types in Exim. These behave slightly differently in
the way they handle the results of a query:
.numberpars $.
\%ldap%\ requires the result to contain just one entry; if there are more, it
gives an error.
.nextp
\%ldapdn%\ also requires the result to contain just one entry, but it is the
Distinguished Name that is returned rather than any attribute values.
.nextp
\%ldapm%\ permits the result to contain more than one entry; the attributes from
all of them are returned.
.endp

For \%ldap%\ and \%ldapm%\, if a query finds only entries with no attributes,
Exim behaves as if the entry did not exist, and the lookup fails. The format of
the data returned by a successful lookup is described in the next section.
First we explain how LDAP queries are coded.

.section Format of LDAP queries
.rset SECTforldaque "~~chapter.~~section"
.index LDAP||query format
An LDAP query takes the form of a URL as defined in RFC 2255. For example, in
the configuration of a \%redirect%\ router one might have this setting:
.display asis
data = ${lookup ldap \
  {ldap:///cn=$local_part,o=University%20of%20Cambridge,\
  c=UK?mailbox?base?}}
.endd
.index LDAP||with TLS
The URL may begin with \"ldap"\ or \"ldaps"\ if your LDAP library supports
secure (encrypted) LDAP connections. The second of these ensures that an
encrypted TLS connection is used.

.section LDAP quoting
.index LDAP||quoting
Two levels of quoting are required in LDAP queries, the first for LDAP itself
and the second because the LDAP query is represented as a URL. Furthermore,
within an LDAP query, two different kinds of quoting are required. For this 
reason, there are two different LDAP-specific quoting operators.

The \quote@_ldap\ operator is designed for use on strings that are part of
filter specifications. Conceptually, it first does the following conversions on
the string:
.display asis
*   =>   \2A
(   =>   \28
)   =>   \29
\   =>   \5C
.endd
in accordance with RFC 2254. The resulting string is then quoted according
to the rules for URLs, that is, all characters except
.display asis
! $ ' - . _ ( ) * +
.endd
are converted to their hex values, preceded by a percent sign. For example:
.display asis
${quote_ldap: a(bc)*, a<yz>; }
.endd
yields
.display asis
%20a%5C28bc%5C29%5C2A%2C%20a%3Cyz%3E%3B%20
.endd
Removing the URL quoting, this is (with a leading and a trailing space):
.display asis
a\28bc\29\2A, a<yz>;
.endd

The \quote@_ldap@_dn\ operator is designed for use on strings that are part of
base DN specifications in queries. Conceptually, it first converts the string
by inserting a backslash in front of any of the following characters:
.display asis
, + " \ < > ;
.endd
It also inserts a backslash before any leading spaces or @# characters, and
before any trailing spaces. (These rules are in RFC 2253.) The resulting string
is then quoted according to the rules for URLs. For example:
.display asis
${quote_ldap_dn: a(bc)*, a<yz>; } 
.endd
yields
.display asis
%5C%20a(bc)*%5C%2C%20a%5C%3Cyz%5C%3E%5C%3B%5C%20
.endd
Removing the URL quoting, this is (with a trailing space):
.display asis
\ a(bc)*\, a\<yz\>\;\
.endd
There are some further comments about quoting in the section on LDAP 
authentication below.

.section LDAP connections
.index LDAP||connections
The connection to an LDAP server may either be over TCP/IP, or, when OpenLDAP
is in use, via a Unix domain socket. The example given above does not specify
an LDAP server. A server that is reached by TCP/IP can be specified in a query
by starting it with
.display
ldap://<<hostname>>:<<port>>/...
.endd
If the port (and preceding colon) are omitted, the standard LDAP port (389) is
used. When no server is specified in a query, a list of default servers is
taken from the \ldap@_default@_servers\ configuration option. This supplies a
colon-separated list of servers which are tried in turn until one successfully
handles a query, or there is a serious error. Successful handling either
returns the requested data, or indicates that it does not exist. Serious errors
are syntactical, or multiple values when only a single value is expected.
Errors which cause the next server to be tried are connection failures, bind
failures, and timeouts.

For each server name in the list, a port number can be given. The standard way
of specifing a host and port is to use a colon separator (RFC 1738). Because
\ldap@_default@_servers\ is a colon-separated list, such colons have to be
doubled. For example
.display asis
ldap_default_servers = ldap1.example.com::145:ldap2.example.com
.endd
If \ldap@_default@_servers\ is unset, a URL with no server name is passed
to the LDAP library with no server name, and the library's default (normally
the local host) is used.

If you are using the OpenLDAP library, you can connect to an LDAP server using
a Unix domain socket instead of a TCP/IP connection. This is specified by using
\"ldapi"\ instead of \"ldap"\ in LDAP queries. What follows here applies only
to OpenLDAP. If Exim is compiled with a different LDAP library, this feature is
not available.

For this type of connection, instead of a host name for the server, a pathname
for the socket is required, and the port number is not relevant. The pathname
can be specified either as an item in \ldap@_default@_servers\, or inline in
the query. In the former case, you can have settings such as
.display asis
ldap_default_servers = /tmp/ldap.sock : backup.ldap.your.domain
.endd
When the pathname is given in the query, you have to escape the slashes as
\"%2F"\ to fit in with the LDAP URL syntax. For example:
.display asis
${lookup ldap {ldapi://%2Ftmp%2Fldap.sock/o=...
.endd
When Exim processes an LDAP lookup and finds that the `hostname' is really
a pathname, it uses the Unix domain socket code, even if the query actually
specifies \"ldap"\ or \"ldaps"\. In particular, no encryption is used for a
socket connection. This behaviour means that you can use a setting of
\ldap@_default@_servers\ such as in the example above with traditional \"ldap"\
or \"ldaps"\ queries, and it will work. First, Exim tries a connection via
the Unix domain socket; if that fails, it tries a TCP/IP connection to the
backup host.

If an explicit \"ldapi"\ type is given in a query when a host name is
specified, an error is diagnosed. However, if there are more items in
\ldap@_default@_servers\, they are tried. In other words:
.numberpars $.
Using a pathname with \"ldap"\ or \"ldaps"\ forces the use of the Unix domain
interface.
.nextp
Using \"ldapi"\ with a host name causes an error. 
.endp

Using \"ldapi"\ with no host or path in the query, and no setting of
\ldap@_default@_servers\, does whatever the library does by default.


.section LDAP authentication and control information
.index LDAP||authentication
The LDAP URL syntax provides no way of passing authentication and other control
information to the server. To make this possible, the URL in an LDAP query may
be preceded by any number of `<<name>>=<<value>>' settings, separated by
spaces. If a value contains spaces it must be enclosed in double quotes, and
when double quotes are used, backslash is interpreted in the usual way inside
them. 

The following names are recognized:
.display
CONNECT     $rm{set a connection timeout}
.newline
DEREFERENCE $rm{set the dereferencing parameter}
USER        $rm{set the DN, for authenticating the LDAP bind}
PASS        $rm{set the password, likewise}
SIZE        $rm{set the limit for the number of entries returned}
TIME        $rm{set the maximum waiting time for a query}
.endd
The value of the \\DEREFERENCE\\ parameter must be one of the words `never', 
`searching', `finding', or `always'.

Here is an example of an LDAP query in an Exim lookup that uses some of these
values. This is a single line, folded for ease of reading:
.display asis
.indent 0
${lookup ldap
  {user="cn=manager,o=University of Cambridge,c=UK" pass=secret
  ldap:///o=University%20of%20Cambridge,c=UK?sn?sub?(cn=foo)}
  {$value}fail}
.endd
The encoding of spaces as %20 is a URL thing which should not be done for any
of the auxiliary data. Exim configuration settings that include lookups which
contain password information should be preceded by `hide' to prevent non-admin
users from using the \-bP-\ option to see their values.

The auxiliary data items may be given in any order. The default is no
connection timeout (the system timeout is used), no user or password, no limit
on the number of entries returned, and no time limit on queries.

The time limit for connection is given in seconds; zero means use the default.
This facility is available in Netscape SDK 4.1; it may not be available in
other LDAP implementations. Exim uses the given value if
\\LDAP@_X@_OPT@_CONNECT@_TIMEOUT\\ is defined in the LDAP headers.

When a DN is quoted in the \\USER=\\ setting for LDAP authentication, Exim
removes any URL quoting that it may contain before passing it LDAP. Apparently
some libraries do this for themselves, but some do not. Removing the URL
quoting has two advantages:
.numberpars $.
It makes it possible to use the same \quote@_ldap@_dn\ expansion for \\USER=\\
DNs as with DNs inside actual queries.
.nextp
It permits spaces inside \\USER=\\ DNs. 
.endp
For example, a setting such as
.display asis
USER=cn=${quote_ldap_dn:$1}
.endd
should work even if \$1$\ contains spaces.

Expanded data for the \\PASS=\\ value should be quoted using the \quote\ 
expansion operator, rather than the LDAP quote operators. The only reason this 
field needs quoting is to ensure that it conforms to the Exim syntax, which 
does not allow unquoted spaces. For example:
.display asis
PASS=${quote:$3}
.endd

The LDAP authentication mechanism can be used to check passwords as part of
SMTP authentication. See the \ldapauth\ expansion string condition in chapter
~~CHAPexpand.


.section Format of data returned by LDAP
.index LDAP||returned data formats
The \%ldapdn%\ lookup type returns the Distinguished Name from a single entry as
a sequence of values, for example
.display asis
cn=manager, o=University of Cambridge, c=UK
.endd

The \%ldap%\ lookup type generates an error if more than one entry matches the
search filter, whereas \%ldapm%\ permits this case, and inserts a newline in the
result between the data from different entries. It is possible for multiple
values to be returned for both \%ldap%\ and \%ldapm%\, but in the former case you
know that whatever values are returned all came from a single entry in the
directory.

In the common case where you specify a single attribute in your LDAP query, the
result is not quoted, and does not contain the attribute name. If the attribute
has multiple values, they are separated by commas.

If you specify multiple attributes, the result contains space-separated, quoted
strings, each preceded by the attribute name and an equals sign. Within the
quotes, the quote character, backslash, and newline are escaped with
backslashes, and commas are used to separate multiple values for the attribute.
Apart from the escaping, the string within quotes takes the same form as the
output when a single attribute is requested. Specifying no attributes is the
same as specifying all of an entry's attributes.

Here are some examples of the output format. The first line of each pair is an
LDAP query, and the second is the data that is returned. The attribute called
\attr1\ has two values, whereas \attr2\ has only one value:
.display asis
ldap:///o=base?attr1?sub?(uid=fred)
value1.1, value1.2

ldap:///o=base?attr2?sub?(uid=fred)
value two

ldap:///o=base?attr1,attr2?sub?(uid=fred)
attr1="value1.1, value1.2" attr2="value two"

ldap:///o=base??sub?(uid=fred)
objectClass="top" attr1="value1.1, value1.2" attr2="value two"
.endd
The \extract\ operator in string expansions can be used to pick out individual
fields from data that consists of $it{key}=$it{value} pairs. You can make use
of Exim's \-be-\ option to run expansion tests and thereby check the results of
LDAP lookups.



.section More about NIS+
.rset SECTnisplus "~~chapter.~~section"
.index NIS@+ lookup type
.index lookup||NIS+
NIS+ queries consist of a NIS+ \*indexed name*\ followed by an optional colon
and field name. If this is given, the result of a successful query is the
contents of the named field; otherwise the result consists of a concatenation
of \*field-name=field-value*\ pairs, separated by spaces. Empty values and
values containing spaces are quoted. For example, the query
.display asis
[name=mg1456],passwd.org_dir
.endd
might return the string
.display asis
name=mg1456 passwd="" uid=999 gid=999 gcos="Martin Guerre"
home=/home/mg1456 shell=/bin/bash shadow=""
.endd
(split over two lines here to fit on the page), whereas
.display asis
[name=mg1456],passwd.org_dir:gcos
.endd
would just return
.display asis
Martin Guerre
.endd
with no quotes. A NIS+ lookup fails if NIS+ returns more than one table entry
for the given indexed key. The effect of the \quote@_nisplus\ expansion
operator is to double any quote characters within the text.


.section More about MySQL, PostgreSQL, Oracle, and Interbase
.rset SECTsql "~~chapter.~~section"
.index MySQL||lookup type
.index PostgreSQL lookup type
.index lookup||MySQL
.index lookup||PostgreSQL
.index Oracle||lookup type
.index lookup||Oracle
.index Interbase lookup type
.index lookup||Interbase
If any MySQL, PostgreSQL, Oracle, or Interbase lookups are used, the
\mysql@_servers\, \pgsql@_servers\, \oracle@_servers\, or \ibase@_servers\
option (as appropriate) must be set to a colon-separated list of server
information. Each item in the list is a slash-separated list of four items:
host name, database name, user name, and password. In the case of Oracle, the
host name field is used for the `service name', and the database name field is
not used and should be empty. For example:
.display asis
hide oracle_servers = oracle.plc.example//ph10/abcdwxyz
.endd
Because password data is sensitive, you should always precede the setting with
`hide', to prevent non-admin users from obtaining the setting via the \-bP-\
option. Here is an example where two MySQL servers are listed:
.display asis
hide mysql_servers = localhost/users/root/secret:\
                     otherhost/users/root/othersecret
.endd
For MySQL and PostgreSQL, a host may be specified as <<name>>:<<port>> but
because this is a colon-separated list, the colon has to be doubled.

For each query, these parameter groups are tried in order until a connection
and a query succeeds. Queries for these databases are SQL statements, so an
example might be
.display asis
.indent 0
${lookup mysql{select mailbox from users where id='ph10'}{$value}fail}
.endd
If the result of the query contains more than one field, the data for
each field in the row is returned, preceded by its name, so the result
of
.display asis
.indent 0
${lookup pgsql{select home,name from users where id='ph10'}{$value}}
.endd
might be
.display asis
home=/home/ph10 name="Philip Hazel"
.endd
Values containing spaces and empty values are double quoted, with embedded
quotes escaped by a backslash.

If the result of the query contains just one field, the value is passed back
verbatim, without a field name, for example:
.display asis
Philip Hazel
.endd
If the result of the query yields more than one row, it is all concatenated,
with a newline between the data for each row.

The \quote@_mysql\, \quote@_pgsql\, and \quote@_oracle\ expansion operators
convert newline, tab, carriage return, and backspace to @\n, @\t, @\r, and @\b
respectively, and the characters single-quote, double-quote, and backslash
itself are escaped with backslashes. The \quote@_pgsql\ expansion operator, in
addition, escapes the percent and underscore characters. This cannot be done
for MySQL because these escapes are not recognized in contexts where these
characters are not special.


.section Special MySQL features
For MySQL, an empty host name or the use of `localhost' in \mysql@_servers\
causes a connection to the server on the local host by means of a Unix domain
socket. An alternate socket can be specified in parentheses. The full syntax of
each item in \mysql@_servers\ is:
.display
<<hostname>>@:@:<<port>>(<<socket name>>)/<<database>>/<<user>>/<<password>>
.endd
Any of the three sub-parts of the first field can be omitted. For normal use on
the local host it can be left blank or set to just `localhost'.

No database need be supplied -- but if it is absent here, it must be given in
the queries.

If a MySQL query is issued that does not request any data (an insert, update,
or delete command), the result of the lookup is the number of rows affected.



.section Special PostgreSQL features
PostgreSQL lookups can also use Unix domain socket connections to the database.
This is usually faster and costs less CPU time than a TCP/IP connection.
However it can be used only if the mail server runs on the same machine as the
database server. A configuration line for PostgreSQL via Unix domain sockets
looks like this:
.display asis
hide pgsql_servers = (/tmp/.s.PGSQL.5432)/db/user/password : ...
.endd
In other words, instead of supplying a host name, a path to the socket is
given. The path name is enclosed in parentheses so that its slashes aren't
visually confused with the delimiters for the other server parameters.

If a PostgreSQL query is issued that does not request any data (an insert,
update, or delete command), the result of the lookup is the number of rows
affected.




.
.
.
.
. ============================================================================
.chapter Domain, host, address, and local part lists
.set runningfoot "domain, host, and address lists"
.rset CHAPdomhosaddlists "~~chapter"
.index list||of domains, hosts, etc.
A number of Exim configuration options contain lists of domains, hosts,
email addresses, or local parts. For example, the \hold@_domains\ option
contains a list of domains whose delivery is currently suspended. These lists
are also used as data in ACL statements (see chapter ~~CHAPACL).

Each item in one of these lists is a pattern to be matched against a domain,
host, email address, or local part, respectively. In the sections below, the
different types of pattern for each case are described, but first we cover some
general facilities that apply to all four kinds of list.


.section Expansion of lists
.index expansion||of lists
Each list is expanded as a single string before it is used. If the expansion is
forced to fail, Exim behaves as if the item it is testing (domain, host,
address, or local part) is not in the list. Other expansion failures cause
temporary errors.

If an item in a list is a regular expression, backslashes, dollars and possibly
other special characters in the expression must be protected against
misinterpretation by the string expander. The easiest way to do this is to use
the \"@\N"\ expansion feature to indicate that the contents of the regular
expression should not be expanded. For example, in an ACL you might have:
.display asis
deny senders = \N^\d{8}\w@.*\.baddomain\.example$\N :
               ${lookup{$domain}lsearch{/badsenders/bydomain}}
.endd
The first item is a regular expression that is protected from expansion by
\"@\N"\, whereas the second uses the expansion to obtain a list of unwanted
senders based on the receiving domain.

After expansion, the list is split up into separate items for matching.
Normally, colon is used as the separator character, but this can be varied if
necessary, as described in section ~~SECTlistconstruct.


.section Negated items in lists
.index list||negation
.index negation in lists
Items in a list may be positive or negative. Negative items are indicated by a
leading exclamation mark, which may be followed by optional white space. A list
defines a set of items (domains, etc). When Exim processes one of these lists,
it is trying to find out whether a domain, host, address, or local part
(respectively) is in the set that is defined by the list. It works like this:

The list is scanned from left to right. If a positive item is matched, the
subject that is being checked is in the set; if a negative item is matched, the
subject is not in the set. If the end of the list is reached without the
subject having matched any of the patterns, it is in the set if the last item
was a negative one, but not if it was a positive one. For example, the list in
.display asis
domainlist relay_domains = !a.b.c : *.b.c
.endd
matches any domain ending in \*.b.c*\ except for \*a.b.c*\. Domains that match
neither \*a.b.c*\ nor \*@*.b.c*\ do not match, because the last item in the
list is positive. However, if the setting were
.display asis
domainlist relay_domains = !a.b.c
.endd
then all domains other than \*a.b.c*\ would match because the last item in the
list is negative. In other words, a list that ends with a negative item behaves
as if it had an extra item \":*"\ on the end.

Another way of thinking about positive and negative items in lists is to read 
the connector as `or' after a positive item and as `and' after a negative 
item. 


.section File names in lists
.rset SECTfilnamlis "~~chapter.~~section"
.index list||file name in
If an item in a domain, host, address, or local part list is an absolute file
name (beginning with a slash character), each line of the file is read and
processed as if it were an independent item in the list, except that further
file names are not allowed,
and no expansion of the data from the file takes place.
Empty lines in the file are ignored, and the file may also contain comment
lines:
.numberpars $.
For domain and host lists, if a @# character appears anywhere in a line of the
file, it and all following characters are ignored.
.nextp
Because local parts may legitimately contain @# characters, a comment in an
address list or local part list file is recognized only if @# is preceded by
white space or the start of the line. For example:
.display asis
not#comment@x.y.z   # but this is a comment
.endd
.endp
Putting a file name in a list has the same effect as inserting each line of the
file as an item in the list (blank lines and comments excepted). However, there
is one important difference: the file is read each time the list is processed,
so if its contents vary over time, Exim's behaviour changes.

If a file name is preceded by an exclamation mark, the sense of any match
within the file is inverted. For example, if
.display asis
hold_domains = !/etc/nohold-domains
.endd
and the file contains the lines
.display asis
!a.b.c
*.b.c
.endd
then \*a.b.c*\ is in the set of domains defined by \hold@_domains\, whereas any
domain matching \"*.b.c"\ is not.


.section An lsearch file is not an out-of-line list
As will be described in the sections that follow, lookups can be used in lists
to provide indexed methods of checking list membership. There has been some
confusion about the way \%lsearch%\ lookups work in lists. Because
an \%lsearch%\ file contains plain text and is scanned sequentially, it is
sometimes thought that it is allowed to contain wild cards and other kinds of
non-constant pattern. This is not the case. The keys in an \%lsearch%\ file are
always fixed strings, just as for any other single-key lookup type.

If you want to use a file to contain wild-card patterns that form part of a 
list, just give the file name on its own, without a search type, as described
in the previous section.



.section Named lists
.rset SECTnamedlists "~~chapter.~~section"
.index named lists
.index list||named
A list of domains, hosts, email addresses, or local parts can be given a name
which is then used to refer to the list elsewhere in the configuration. This is
particularly convenient if the same list is required in several different
places. It also allows lists to be given meaningful names, which can improve
the readability of the configuration. For example, it is conventional to define
a domain list called \*local@_domains*\ for all the domains that are handled
locally on a host, using a configuration line such as
.display asis
domainlist local_domains = localhost:my.dom.example
.endd
Named lists are referenced by giving their name preceded by a plus sign, so,
for example, a router that is intended to handle local domains would be
configured with the line
.display asis
domains = +local_domains
.endd
The first router in a configuration is often one that handles all domains
except the local ones, using a configuration with a negated item like this:
.display asis
dnslookup:
  driver = dnslookup
  domains = ! +local_domains
  transport = remote_smtp
  no_more
.endd
The four kinds of named list are created by configuration lines starting with
the words \domainlist\, \hostlist\, \addresslist\, or \localpartlist\,
respectively. Then there follows the name that you are defining, followed by an
equals sign and the list itself. For example:
.display asis
hostlist    relay_hosts = 192.168.23.0/24 : my.friend.example
addresslist bad_senders = cdb;/etc/badsenders
.endd
A named list may refer to other named lists:
.display asis
domainlist  dom1 = first.example : second.example
domainlist  dom2 = +dom1 : third.example
domainlist  dom3 = fourth.example : +dom2 : fifth.example
.endd

\**Warning**\: If the last item in a referenced list is a negative one, the
effect may not be what you intended, because the negation does not propagate
out to the higher level. For example, consider:
.display asis
domainlist  dom1 = !a.b
domainlist  dom2 = +dom1 : *.b
.endd
The second list specifies `either in the \dom1\ list or \*@*.b*\'. The first
list specifies just `not \*a.b*\', so the domain \*x.y*\ matches it. That means
it matches the second list as well. The effect is not the same as
.display asis
domainlist  dom2 = !a.b : *.b
.endd
where \*x.y*\ does not match. It's best to avoid negation altogether in 
referenced lists if you can.

Named lists may have a performance advantage. When Exim is routing an
address or checking an incoming message, it caches the result of tests on named
lists. So, if you have a setting such as
.display asis
domains = +local_domains
.endd
on several of your routers
or in several ACL statements, 
the actual test is done only for the first one. However, the caching works only
if there are no expansions within the list itself or any sublists that it
references. In other words, caching happens only for lists that are known to be
the same each time they are referenced.

By default, there may be up to 16 named lists of each type. This limit can be
extended by changing a compile-time variable. The use of domain and host lists
is recommended for concepts such as local domains, relay domains, and relay
hosts. The default configuration is set up like this.


.section Named lists compared with macros
.index list||named compared with macro
.index macro||compared with named list
At first sight, named lists might seem to be no different from macros in the
configuration file. However, macros are just textual substitutions. If you
write
.display asis
ALIST = host1 : host2
auth_advertise_hosts = !ALIST
.endd
it probably won't do what you want, because that is exactly the same as
.display asis
auth_advertise_hosts = !host1 : host2
.endd
Notice that the second host name is not negated. However, if you use a host
list, and write
.display asis
hostlist alist = host1 : host2
auth_advertise_hosts = ! +alist
.endd
the negation applies to the whole list, and so that is equivalent to
.display asis
auth_advertise_hosts = !host1 : !host2
.endd


.em 
.section Named list caching
.index list||caching of named
.index caching||named lists
While processing a message, Exim caches the result of checking a named list if
it is sure that the list is the same each time. In practice, this means that
the cache operates only if the list contains no @$ characters, which guarantees
that it will not change when it is expanded. Sometimes, however, you may have
an expanded list that you know will be the same each time within a given
message. For example:
.display asis
domainlist special_domains = \
           ${lookup{$sender_host_address}cdb{/some/file}}
.endd
This provides a list of domains that depends only on the sending host's IP
address. If this domain list is referenced a number of times (for example,
in several ACL lines, or in several routers) the result of the check is not
cached by default, because Exim does not know that it is going to be the
same list each time.

By appending \"@_cache"\ to \"domainlist"\ you can tell Exim to go ahead and
cache the result anyway. For example:
.display asis
domainlist_cache special_domains = ${lookup{...
.endd
If you do this, you should be absolutely sure that caching is going to do
the right thing in all cases. When in doubt, leave it out.
.nem


.section Domain lists
.rset SECTdomainlist "~~chapter.~~section"
.index domain list||patterns for
.index list||domain list
Domain lists contain patterns that are to be matched against a mail domain.
The following types of item may appear in domain lists:
.numberpars $.
.index primary host name
.index host||name, matched in domain list 
.index \primary@_hostname\
.index domain list||matching primary host name
.index @@ in a domain list
If a pattern consists of a single @@ character, it matches the local host name,
as set by the \primary@_hostname\ option (or defaulted). This makes it possible
to use the same configuration file on several different hosts that differ only
in their names.
.nextp
.index @@[] in a domain list
.index domain list||matching local IP interfaces
.index domain literal
If a pattern consists of the string \"@@[]"\ it matches any local IP interface
address, enclosed in square brackets, as in an email address that contains a
domain literal. 
.em
In today's Internet, the use of domain literals is controversial.
.nem
.nextp
.index @@mx@_any
.index @@mx@_primary
.index @@mx@_secondary
.index domain list||matching MX pointers to local host
If a pattern consists of the string \"@@mx@_any"\ it matches any domain that
has an MX record pointing to the local host or to any host that is listed in
.index \hosts@_treat@_as@_local\
\hosts@_treat@_as@_local\. The items \"@@mx@_primary"\ and \"@@mx@_secondary"\
are similar, except that the first matches only when a primary MX target is the
local host, and the second only when no primary MX target is the local host,
but a secondary MX target is. `Primary' means an MX record with the lowest
preference value -- there may of course be more than one of them.

.em
The MX lookup that takes place when matching a pattern of this type is 
performed with the resolver options for widening names turned off. Thus, for 
example, a single-component domain will \*not*\ be expanded by adding the 
resolver's default domain. See the \qualify@_single\ and \search@_parents\ 
options of the \%dnslookup%\ router for a discussion of domain widening.

Sometimes you may want to ignore certain IP addresses when using one of these
patterns. You can specify this by following the pattern with \"/ignore=<<ip
list>>"\, where <<ip list>> is a list of IP addresses. These addresses are
ignored when processing the pattern (compare the \ignore@_target@_hosts\ option 
on a router). For example:
.display asis
domains = @mx_any/ignore=127.0.0.1
.endd
This example matches any domain that has an MX record pointing to one of
the local host's IP addresses other than 127.0.0.1.

The list of IP addresses is in fact processed by the same code that processes 
host lists, so it may contain CIDR-coded network specifications and it may also 
contain negative items.

Because the list of IP addresses is a sublist within a domain list, you have to
be careful about delimiters if there is more than one address. Like any other
list, the default delimiter can be changed. Thus, you might have:
.display asis
domains = @mx_any/ignore=<;127.0.0.1;0.0.0.0 : \
          an.other.domain : ...
.endd
so that the sublist uses semicolons for delimiters. When IPv6 addresses are
involved, it is easiest to change the delimiter for the main list as well:
.display asis
domains = <? @mx_any/ignore=<;127.0.0.1;::1 ? \
          an.other.domain ? ...
.endd
.nem

.nextp
.index asterisk||in domain list
.index domain list||asterisk in
.index domain list||matching `ends with'
If a pattern starts with an asterisk, the remaining characters of the pattern
are compared with the terminating characters of the domain. The use of `$*$' in
domain lists differs from its use in partial matching lookups. In a domain
list, the character following the asterisk need not be a dot, whereas partial
matching works only in terms of dot-separated components. For example, a domain
list item such as \"*key.ex"\ matches \*donkey.ex*\ as well as
\*cipher.key.ex*\.
.nextp
.index regular expressions||in domain list
.index domain list||matching regular expression
If a pattern starts with a circumflex character, it is treated as a regular
expression, and matched against the domain using a regular expression matching
function. The circumflex is treated as part of the regular expression.
References to descriptions of the syntax of regular expressions are given in
chapter ~~CHAPregexp.

\**Warning**\: Because domain lists are expanded before being processed, you
must escape any backslash and dollar characters in the regular expression, or
use the special \"@\N"\ sequence (see chapter ~~CHAPexpand) to specify that it
is not to be expanded (unless you really do want to build a regular expression
by expansion, of course).
.nextp
.index lookup||in domain list
.index domain list||matching by lookup
If a pattern starts with the name of a single-key lookup type followed by a
semicolon (for example, `dbm;' or `lsearch;'), the remainder of the pattern
must be a file name in a suitable format for the lookup type. For example, for
`cdb;' it must be an absolute path:
.display asis
domains = cdb;/etc/mail/local_domains.cdb
.endd
The appropriate type of lookup is done on the file using the domain name as the
key. In most cases, the data that is looked up is not used; Exim is interested
only in whether or not the key is present in the file. However, when a lookup
is used for the \domains\ option on a router
or a \domains\ condition in an ACL statement, the data is preserved in the
\$domain@_data$\ variable and can be referred to in other router options or
other statements in the same ACL.
.nextp
Any of the single-key lookup type names may be preceded by `partial<<n>>-',
where the <<n>> is optional, for example,
.display asis
domains = partial-dbm;/partial/domains
.endd
This causes partial matching logic to be invoked; a description of how this
works is given in section ~~SECTpartiallookup.
.nextp
.index asterisk||in lookup type
Any of the single-key lookup types may be followed by an asterisk. This causes
a default lookup for a key consisting of a single asterisk to be done if the
original lookup fails. This is not a useful feature when using a domain list to
select particular domains (because any domain would match), but it might have
value if the result of the lookup is being used via the \$domain@_data$\
expansion variable.
.nextp
If the pattern starts with the name of a query-style lookup type followed by a
semicolon (for example, `nisplus;' or `ldap;'), the remainder of the pattern
must be an appropriate query for the lookup type, as described in chapter
~~CHAPfdlookup. For example:
.display asis
hold_domains = mysql;select domain from holdlist \
  where domain = '$domain';
.endd
In most cases, the data that is looked up is not used (so for an SQL query, for
example, it doesn't matter what field you select). Exim is interested only in
whether or not the query succeeds. However, when a lookup is used for the
\domains\ option on a router, the data is preserved in the \$domain@_data$\
variable and can be referred to in other options.
.nextp
.index domain list||matching literal domain name
If none of the above cases apply, a caseless textual comparison is made between
the pattern and the domain.
.endp

Here is an example that uses several different kinds of pattern:
.display asis
domainlist funny_domains = \
  @ : \
  lib.unseen.edu : \
  *.foundation.fict.example : \
  \N^[1-2]\d{3}\.fict\.example$\N : \
  partial-dbm;/opt/data/penguin/book : \
  nis;domains.byname : \
  nisplus;[name=$domain,status=local],domains.org_dir
.endd
There are obvious processing trade-offs among the various matching modes. Using
an asterisk is faster than a regular expression, and listing a few names
explicitly probably is too. The use of a file or database lookup is expensive,
but may be the only option if hundreds of names are required. Because the
patterns are tested in order, it makes sense to put the most commonly matched
patterns earlier.


.section Host lists
.rset SECThostlist "~~chapter.~~section"
.index host list||patterns in
.index list||host list
Host lists are used to control what remote hosts are allowed to do. For
example, some hosts may be allowed to use the local host as a relay, and some
may be permitted to use the SMTP \\ETRN\\ command. Hosts can be identified in
two different ways, by name or by IP address. In a host list, some types of
pattern are matched to a host name, and some are matched to an IP address.
You need to be particularly careful with this when single-key lookups are
involved, to ensure that the right value is being used as the key.

.section Special host list patterns
.index empty item in hosts list
.index host list||empty string in
If a host list item is the empty string, it matches only when no remote host is
involved. This is the case when a message is being received from a local
process using SMTP on the standard input, that is, when a TCP/IP connection is
not used.

.index asterisk||in host list
The special pattern `$*$' in a host list matches any host or no host. Neither
the IP address nor the name is actually inspected.


.section Host list patterns that match by IP address
.rset SECThoslispatip "~~chapter.~~section"
.index host list||matching IP addresses
If an IPv4 host calls an IPv6 host and the call is accepted on an IPv6 socket,
the incoming address actually appears in the IPv6 host as
`@:@:$tt{ffff}:<<v4address>>'. When such an address is tested against a host
list, it is converted into a traditional IPv4 address first. (Not all operating
systems accept IPv4 calls on IPv6 sockets, as there have been some security
concerns.)

The following types of pattern in a host list check the remote host by
inspecting its IP address:
.numberpars $.
If the pattern is a plain domain name (not a regular expression, not starting
with $*$, not a lookup of any kind), Exim calls the operating system function
to find the associated IP address(es). Exim uses the newer
\*getipnodebyname()*\ function when available, otherwise \*gethostbyname()*\.
This typically causes a forward DNS lookup of the name. The result is compared
with the IP address of the subject host.

.em
If there is a temporary problem (such as a DNS timeout) with the host name
lookup, a temporary error occurs. For example, if the list is being used in an 
ACL condition, the ACL gives a `defer' response, usually leading to a temporary
SMTP error code. If no IP address can be found for the host name, what happens
is described in section ~~SECTbehipnot below.
.nem

.nextp
.index @@ in a host list
If the pattern is `@@', the primary host name is substituted and used as a
domain name, as just described.
.nextp
If the pattern is an IP address, it is matched against the IP address of the
subject host. IPv4 addresses are given in the normal `dotted-quad' notation.
IPv6 addresses can be given in colon-separated format, but the colons have to
be doubled so as not to be taken as item separators when the default list
separator is used. IPv6 addresses are recognized even when Exim is compiled
without IPv6 support. This means that if they appear in a host list on an
IPv4-only host, Exim will not treat them as host names. They are just addresses
that can never match a client host.
.nextp
.index @@[] in a host list
If the pattern is `@@[]', it matches the IP address of any IP interface on
the local host. For example, if the local host is an IPv4 host with one
interface address 10.45.23.56, these two ACL statements have the same effect:
.display asis
accept hosts = 127.0.0.1 : 10.45.23.56
accept hosts = @[]
.endd
.nextp
If the pattern is an IP address followed by a slash and a mask length (for
example 10.11.42.0/24), it is matched against the IP address of the subject
host under the given mask.
This allows, an entire network of hosts to be included (or excluded) by a
single item.
.index CIDR notation 
The mask uses CIDR notation; it specifies the number of address bits that must
match, starting from the most significant end of the address.

\**Note**\: the mask is \*not*\ a count of addresses, nor is it the high number
of a range of addresses. It is the number of bits in the network portion of the
address. The above example specifies a 24-bit netmask, so it matches all 256
addresses in the 10.11.42.0 network. An item such as
.display asis
192.168.23.236/31
.endd
matches just two addresses, 192.168.23.236 and 192.168.23.237. A mask value of 
32 for an IPv4 address is the same as no mask at all; just a single address 
matches.

Here is another example which shows an IPv4 and an IPv6 network:
.display asis
recipient_unqualified_hosts = 192.168.0.0/16: \
                              3ffe::ffff::836f::::/48
.endd
The doubling of list separator characters applies only when these items
appear inline in a host list. It is not required when indirecting via a file.
For example,
.display asis
recipient_unqualified_hosts = /opt/exim/unqualnets
.endd
could make use of a file containing
.display asis
172.16.0.0/12
3ffe:ffff:836f::/48
.endd
to have exactly the same effect as the previous example. When listing IPv6
addresses inline, it is usually more convenient to use the facility for
changing separator characters. This list contains the same two networks:
.display asis
recipient_unqualified_hosts = <; 172.16.0.0/12; \
                                 3ffe:ffff:836f::/48
.endd
The separator is changed to semicolon by the leading `<;' at the start of the
list.
.endp


.section Host list patterns for single-key lookups by host address
.rset SECThoslispatsikey "~~chapter.~~section"
.index host list||lookup of IP address
When a host is to be identified by a single-key lookup of its complete IP
address, the pattern takes this form:
.display
net-<<single-key-search-type>>;<<search-data>>
.endd
For example:
.display asis
hosts_lookup = net-cdb;/hosts-by-ip.db
.endd
The text form of the IP address of the subject host is used as the lookup key.
IPv6 addresses are converted to an unabbreviated form, using lower case
letters, with dots as separators because colon is the key terminator in
\%lsearch%\ files. [Colons can in fact be used in keys in \%lsearch%\ files by
quoting the keys, but this is a facility that was added later.] The data
returned by the lookup is not used.

.index IP address||masking
.index host list||masked IP address
Single-key lookups can also be performed using masked IP addresses, using
patterns of this form:
.display
net<<number>>-<<single-key-search-type>>;<<search-data>>
.endd
For example:
.display asis
net24-dbm;/networks.db
.endd
The IP address of the subject host is masked using <<number>> as the mask
length. A textual string is constructed from the masked value, followed by the
mask, and this is used as the lookup key. For example, if the host's IP address
is 192.168.34.6, the key that is looked up for the above example is
`192.168.34.0/24'. IPv6 addresses are converted to a text value using lower
case letters and dots as separators instead of the more usual colon, because
colon is the key terminator in \%lsearch%\ files. Full, unabbreviated IPv6
addresses are always used.

\**Warning**\: Specifing \net32@-\ (for an IPv4 address) or \net128@-\ (for an
IPv6 address) is not the same as specifing just \net@-\ without a number. In
the former case the key strings include the mask value, whereas in the latter
case the IP address is used on its own.


.section Host list patterns that match by host name
.rset SECThoslispatnam "~~chapter.~~section"
.index host||lookup failures
.index unknown host name
.index host list||matching host name 
There are several types of pattern that require Exim to know the name of the
remote host. These are either wildcard patterns or lookups by name. (If a
complete hostname is given without any wildcarding, it is used to find an IP
address to match against, as described in the section ~~SECThoslispatip above.)

If the remote host name is not already known when Exim encounters one of these
patterns, it has to be found from the IP address. 
.em
Although many sites on the Internet are conscientious about maintaining reverse
DNS data for their hosts, there are also many that do not do this.
Consequently, a name cannot always be found, and this may lead to unwanted
effects. Take care when configuring host lists with wildcarded name patterns.
Consider what will happen if a name cannot be found.

Because of the problems of determining host names from IP addresses, matching
against host names is not as common as matching against IP addresses.

By default, in order to find a host name, Exim first does a reverse DNS lookup;
if no name is found in the DNS, the system function (\*gethostbyaddr()*\ or
\*getipnodebyaddr()*\ if available) is tried. The order in which these lookups
are done can be changed by setting the \host@_lookup@_order\ option.

There are some options that control what happens if a host name cannot be
found. These are described in section ~~SECTbehipnot below.
.nem


.index host||alias for
.index alias for host
As a result of aliasing, hosts may have more than one name. When processing any
of the following types of pattern, all the host's names are checked:
.numberpars $.
.index asterisk||in host list
If a pattern starts with `$*$' the remainder of the item must match the end of
the host name. For example, \"*.b.c"\ matches all hosts whose names end in
\*.b.c*\. This special simple form is provided because this is a very common
requirement. Other kinds of wildcarding require the use of a regular
expression.
.nextp
.index regular expressions||in host list
.index host list||regular expression in
If the item starts with `@^' it is taken to be a regular expression which is
matched against the host name. For example,
.display asis
^(a|b)\.c\.d$
.endd
is a regular expression that matches either of the two hosts \*a.c.d*\ or
\*b.c.d*\. When a regular expression is used in a host list, you must take care
that backslash and dollar characters are not misinterpreted as part of the
string expansion. The simplest way to do this is to use \"@\N"\ to mark that
part of the string as non-expandable. For example:
.display asis
sender_unqualified_hosts = \N^(a|b)\.c\.d$\N : ....
.endd
.em
\**Warning**\: If you want to match a complete host name, you must include the 
\"@$"\ terminating metacharacter in the regular expression, as in the above 
example. Without it, a match at the start of the host name is all that is 
required.
.nem
.endp


.em
.section Behaviour when an IP address or name cannot be found
.rset SECTbehipnot "~~chapter.~~section"
.index host||lookup failures
While processing a host list, Exim may need to look up an IP address from a 
name (see section ~~SECThoslispatip), or it may need to look up a host name 
from an IP address (see section ~~SECThoslispatnam). In either case, the 
behaviour when it fails to find the information it is seeking is the same.

.index \"+include@_unknown"\
.index \"+ignore@_unknown"\
By default, Exim behaves as if the host does not match the list. This may not
always be what you want to happen. To change Exim's behaviour, the special
items \"+include@_unknown"\ or \"+ignore@_unknown"\ may appear in the list (at
top level -- they are not recognized in an indirected file).
.numberpars $.
If any item that follows \"+include@_unknown"\ requires information that
cannot found, Exim behaves as if the host does match the list. For example,
.display asis
host_reject_connection = +include_unknown:*.enemy.ex
.endd
rejects connections from any host whose name matches \"*.enemy.ex"\, and also
any hosts whose name it cannot find.
.nextp
If any item that follows \"+ignore@_unknown"\ requires information that cannot 
be found, Exim ignores that item and proceeds to the rest of the list. For 
example:
.display asis
accept hosts = +ignore_unknown : friend.example : \
               192.168.4.5
.endd
accepts from any host whose name is \*friend.example*\ and from 192.168.4.5, 
whether or not its host name can be found. Without \"+ignore@_unknown"\, if no 
name can be found for 192.168.4.5, it is rejected.
.endp
Both \"+include@_unknown"\ and \"+ignore@_unknown"\ may appear in the same
list. The effect of each one lasts until the next, or until the end of the 
list.

\**Note**\: This section applies to permanent lookup failures. It does \*not*\
apply to temporary DNS errors. They always cause a defer action.
.nem


.section Host list patterns for single-key lookups by host name
.rset SECThoslispatnamsk "~~chapter.~~section"
.index host||lookup failures
.index unknown host name
.index host list||matching host name
If a pattern is of the form
.display
<<single-key-search-type>>;<<search-data>>
.endd
for example
.display asis
dbm;/host/accept/list
.endd
a single-key lookup is performend, using the host name as its key. If the
lookup succeeds, the host matches the item. The actual data that is looked up
is not used.

\**Reminder**\: With this kind of pattern, you must have host $it{names} as
keys in the file, not IP addresses. If you want to do lookups based on IP
addresses, you must precede the search type with `net-' (see section
~~SECThoslispatsikey). There is, however, no reason why you could not use two
items in the same list, one doing an address lookup and one doing a name
lookup, both using the same file.


.section Host list patterns for query-style lookups
If a pattern is of the form
.display
<<query-style-search-type>>;<<query>>
.endd
the query is obeyed, and if it succeeds, the host matches the item. The actual
data that is looked up is not used. The variables \$sender@_host@_address$\ and
\$sender@_host@_name$\ can be used in the query. For example:
.display asis
hosts_lookup = pgsql;\
  select ip from hostlist where ip='$sender_host_address'
.endd
The value of \$sender@_host@_address$\ for an IPv6 address uses colon
separators. You can use the \sg\ expansion item to change this if you need to.
If you want to use masked IP addresses in database queries, you can use the
\mask\ expansion operator.

If the query contains a reference to \$sender@_host@_name$\, Exim automatically 
looks up the host name if has not already done so. (See section
~~SECThoslispatnam for comments on finding host names.)

Historical note: prior to release 4.30, Exim would always attempt to find a 
host name before running the query, unless the search type was preceded by
\"net-"\. This is no longer the case. For backwards compatibility, \"net-"\ is 
still recognized for query-style lookups, but its presence or absence has no
effect. (Of course, for single-key lookups, \"net-"\ $it{is} important.)


.section Mixing wildcarded host names and addresses in host lists
.rset SECTmixwilhos "~~chapter.~~section"
.index host list||mixing names and addresses in
If you have name lookups or wildcarded host names and IP addresses in the same
host list, you should normally put the IP addresses first. For example, in an
ACL you could have:
.display asis
accept hosts = 10.9.8.7 : *.friend.example
.endd
The reason for this lies in the left-to-right way that Exim processes lists.
It can test IP addresses without doing any DNS lookups, but when it reaches an
item that requires a host name, it fails if it cannot find a host name to
compare with the pattern. If the above list is given in the opposite order, the
\accept\ statement fails for a host whose name cannot be found, even if its
IP address is 10.9.8.7.

If you really do want to do the name check first, and still recognize the IP
address, you can rewrite the ACL like this:
.display asis
accept hosts = *.friend.example
accept hosts = 10.9.8.7
.endd
If the first \accept\ fails, Exim goes on to try the second one. See chapter
~~CHAPACL for details of ACLs.




.section Address lists
.index list||address list
.index address list||empty item
.index address list||patterns
.rset SECTaddresslist "~~chapter.~~section"
Address lists contain patterns that are matched against mail addresses. There
is one special case to be considered: the sender address of a bounce message is
always empty. You can test for this by providing an empty item in an address
list. For example, you can set up a router to process bounce messages by
using this option setting:
.display asis
senders = :
.endd
The presence of the colon creates an empty item. If you do not provide any
data, the list is empty and matches nothing. The empty sender can also be
detected by a regular expression that matches an empty string.

The following kinds of pattern are supported in address lists:
.numberpars $.
.index regular expressions||in address list
.index address list||regular expression in
If (after expansion) a pattern starts with `@^', a regular expression match is
done against the complete address, with the pattern as the regular expression.
You must take care that backslash and dollar characters are not misinterpreted
as part of the string expansion. The simplest way to do this is to use \"@\N"\
to mark that part of the string as non-expandable. For example:
.display asis
deny senders = \N^\d{8}.+@spamhaus.example$\N : ...
.endd
The \"@\N"\ sequences are removed by the expansion, so the item does start
with `@^' by the time it is being interpreted as an address pattern.
.nextp
.index @@@@ with single-key lookup
.index address list||@@@@ lookup type
.index address list||split local part and domain
If a pattern starts with `@@@@' followed by a single-key lookup item 
(for example, \"@@@@lsearch;/some/file"\), the address that is being checked is
split into a local part and a domain. The domain is looked up in the file. If
it is not found, there is no match. If it is found, the data that is looked up
from the file is treated as a colon-separated list of local part patterns, each
of which is matched against the subject local part in turn.

.index asterisk||in address list
The lookup may be a partial one, and/or one involving a search for a default
keyed by `$*$' (see section ~~SECTdefaultvaluelookups). The local part patterns
that are looked up can be regular expressions or begin with `$*$', or even be
further lookups. They may also be independently negated. For example, with
.display asis
deny senders = @@dbm;/etc/reject-by-domain
.endd
the data from which the DBM file is built could contain lines like
.display asis
baddomain.com:  !postmaster : *
.endd
to reject all senders except \postmaster\ from that domain.
.index local part||starting with !
If a local part that actually begins with an exclamation mark is required, it
has to be specified using a regular expression. In \%lsearch%\ files, an entry
may be split over several lines by indenting the second and subsequent lines,
but the separating colon must still be included at line breaks. White space
surrounding the colons is ignored. For example:
.display asis
aol.com:  spammer1 : spammer2 : ^[0-9]+$ :
          spammer3 : spammer4
.endd
As in all colon-separated lists in Exim, a colon can be included in an item by
doubling.

If the last item in the list starts with a right angle-bracket, the remainder
of the item is taken as a new key to look up in order to obtain a continuation
list of local parts. The new key can be any sequence of characters. Thus one
might have entries like
.display asis
aol.com: spammer1 : spammer 2 : >*
xyz.com: spammer3 : >*
*:       ^\d{8}$
.endd
in a file that was searched with \@@@@dbm$*$\, to specify a match for 8-digit
local parts for all domains, in addition to the specific local parts listed for
each domain. Of course, using this feature costs another lookup each time a
chain is followed, but the effort needed to maintain the data is reduced.
.index loop||in lookups
It is possible to construct loops using this facility, and in order to catch
them, the chains may be no more than fifty items long.
.nextp
The @@@@<<lookup>> style of item can also be used with a query-style 
lookup, but in this case, the chaining facility is not available. The lookup 
can only return a single list of local parts.
.nextp
.index address list||lookup for complete address
Complete addresses can be looked up by using a pattern that 
starts with a lookup type terminated by a semicolon, follwed by the data for
the lookup.
For example:
.display asis
deny senders = cdb;/etc/blocked.senders : \
  mysql;select address from blocked where \
  address='${quote_mysql:$sender_address}'
.endd
For a single-key lookup type, Exim uses the complete address as the key.
Partial matching (section ~~SECTpartiallookup) cannot be used, and is ignored
if specified, with an entry being written to the panic log. 

.index @*@@ with single-key lookup
You can configure lookup defaults, as described in section
~~SECTdefaultvaluelookups, but this is useful only for the `$*$@@' type of 
default. For example, with this lookup:
.display asis
accept senders = lsearch*@;/some/file
.endd
the file could contains lines like this:
.display asis
user1@domain1.example
*@domain2.example
.endd
and for the sender address \*nimrod@@jaeger.example*\, the sequence of keys
that are tried is:
.display asis
nimrod@jaeger.example
*@jaeger.example
*
.endd
\**Warning 1**\: Do not include a line keyed by `$*$' in the file, because that 
would mean that every address matches, thus rendering the test useless.

\**Warning 2**\: Do not confuse these two kinds of item:
.display asis
deny recipients = dbm*@;/some/file
deny recipients = *@dbm;/some/file
.endd
The first does a whole address lookup, with defaulting, as just described, 
because it starts with a lookup type. The second matches the local part and
domain independently, as described in the next paragraph.
.nextp
If a pattern contains an @@ character, but is not a regular expression
and does not begin with a lookup type
as described above, the local part of the subject address is compared with the
local part of the pattern, which may start with an asterisk. If the local parts
match, the domain is checked in exactly the same way as for a pattern in a
domain list. For example, the domain can be wildcarded, refer to a named list,
or be a lookup:
.display asis
deny senders = *@*.spamming.site:\
               *@+hostile_domains:\
               bozo@partial-lsearch;/list/of/dodgy/sites:\
.newline
               *@dbm;/bad/domains.db
.endd
.index local part||starting with !
.index address list||local part starting with !
If a local part that begins with an exclamation mark is required, it has to be
specified using a regular expression, because otherwise the exclamation mark is
treated as a sign of negation.
.nextp
If a pattern is not one of the above syntax forms, that is, if a pattern which
is not a regular expression or a lookup does not contain an @@ character, it is
matched against the domain part of the subject address. The only two formats
that are recognized this way are a literal domain, or a domain pattern that
starts with $*$. In both these cases, the effect is the same as if \"*@@"\
preceded the pattern.
.endp

\**Warning**\: there is an important difference between the address list items
in these two examples:
.display asis
senders = +my_list
senders = *@+my_list
.endd
In the first one, \"my@_list"\ is a named address list, whereas in the second
example it is a named domain list.



.section Case of letters in address lists
.rset SECTcasletadd "~~chapter.~~section"
.index case of local parts
.index address list||case forcing
.index case forcing in address lists
Domains in email addresses are always handled caselessly, but for local parts
case may be significant on some systems (see \caseful@_local@_part\ for how
Exim deals with this when routing addresses). However, RFC 2505 ($it{Anti-Spam
Recommendations for SMTP MTAs}) suggests that matching of addresses to blocking
lists should be done in a case-independent manner. Since most address lists in
Exim are used for this kind of control, Exim attempts to do this by default.

The domain portion of an address is always lowercased before matching it to an
address list. The local part is lowercased by default, and any string
comparisons that take place are done caselessly. This means that the data in
the address list itself, in files included as plain file names, and in any file
that is looked up using the `@@@@' mechanism, can be in any case. However, the
keys in files that are looked up by a search type other than \%lsearch%\ (which
works caselessly) must be in lower case, because these lookups are not
case-independent.

.index \"+caseful"\
To allow for the possibility of caseful address list matching, if an item in
an address list is the string `+caseful', the original case of the local
part is restored for any comparisons that follow, and string comparisons are no
longer case-independent. This does not affect the domain, which remains in
lower case. However, although independent matches on the domain alone are still
performed caselessly, regular expressions that match against an entire address
become case-sensitive after `+caseful' has been seen.


.section Local part lists
.rset SECTlocparlis "~~chapter.~~section"
.index list||local part list
.index local part||list
Case-sensitivity in local part lists is handled in the same way as for address
lists, as just described. The `+caseful' item can be used if required. In a
setting of the \local@_parts\ option in a router with \caseful@_local@_part\
set false, the subject is lowercased and the matching is initially
case-insensitive. In this case, `+caseful' will restore case-sensitive matching
in the local part list, but not elsewhere in the router. If
\caseful@_local@_part\ is set true in a router, matching in the \local@_parts\
option is case-sensitive from the start.

If a local part list is indirected to a file (see section ~~SECTfilnamlis),
comments are handled in the same way as address lists -- they are recognized
only if the @# is preceded by white space or the start of the line.
Otherwise, local part lists are matched in the same way as domain lists, except
that the special items that refer to the local host (\"@@"\, \"@@[]"\,
\"@@mx@_any"\, \"@@mx@_primary"\, and \"@@mx@_secondary"\) are not recognized.
Refer to section ~~SECTdomainlist for details of the other available item
types.



.
.
.
.
. ============================================================================
.chapter String expansions
.set runningfoot "string expansions"
.rset CHAPexpand ~~chapter
.index expansion||of strings
Many strings in Exim's run time configuration are expanded before use. Some of
them are expanded every time they are used; others are expanded only once.

When a string is being expanded it is copied verbatim from left to right except
when a dollar or backslash character is encountered. A dollar specifies the
start of a portion of the string which is interpreted and replaced as described
below in section ~~SECTexpansionitems onwards. Backslash is used as an escape 
character, as described in the following section.


.section Literal text in expanded strings
.rset SECTlittext "~~chapter.~~section"
.index expansion||including literal text
An uninterpreted dollar can be included in an expanded string by putting a
backslash in front of it. A backslash can be used to prevent any special
character being treated specially in an expansion, including itself. If the
string appears in quotes in the configuration file, two backslashes are
required because the quotes themselves cause interpretation of backslashes when
the string is read in (see section ~~SECTstrings).

.index expansion||non-expandable substrings
A portion of the string can specified as non-expandable by placing it between
two occurrences of \"@\N"\. This is particularly useful for protecting regular
expressions, which often contain backslashes and dollar signs. For example:
.display asis
deny senders = \N^\d{8}[a-z]@some\.site\.example$\N
.endd
On encountering the first \"@\N"\, the expander copies subsequent characters
without interpretation until it reaches the next \"@\N"\ or the end of the
string.


.section Character escape sequences in expanded strings
.index expansion||escape sequences
A backslash followed by one of the letters `n', `r', or `t' in an expanded
string is recognized as an escape sequence for the character newline, carriage
return, or tab, respectively. A backslash followed by up to three octal digits
is recognized as an octal encoding for a single character, and a backslash
followed by `x' and up to two hexadecimal digits is a hexadecimal encoding.

These escape sequences are also recognized in quoted strings when they are read
in. Their interpretation in expansions as well is useful for unquoted strings,
and for other cases such as looked-up strings that are then expanded.

.section Testing string expansions
.index expansion||testing
.index testing||string expansion
.index \-be-\ option
Many expansions can be tested by calling Exim with the \-be-\ option. This takes
the command arguments, or lines from the standard input if there are no
arguments, runs them through the string expansion code, and writes the results
to the standard output. Variables based on configuration values are set up, but
since no message is being processed, variables such as \$local@_part$\ have no
value. Nevertheless the \-be-\ option can be useful for checking out file and
database lookups, and the use of expansion operators such as \sg\, \substr\ and
\nhash\.

Exim gives up its root privilege when it is called with the \-be-\ option, and
instead runs under the uid and gid it was called with, to prevent users from
using \-be-\ for reading files to which they do not have access.


.section Expansion items
.rset SECTexpansionitems "~~chapter.~~section"
The following items are recognized in expanded strings. White space may be used
between sub-items that are keywords or substrings enclosed in braces inside an
outer set of braces, to improve readability. \**Warning**\: Within braces,
white space is significant.

.startitems

.item "@$<<variable name>>#$rm{or}#@$@{<<variable name>>@}"
.index expansion||variables
Substitute the contents of the named variable, for example
.display asis
$local_part
${domain}
.endd
The second form can be used to separate the name from subsequent alphanumeric
characters. This form (using curly brackets) is available only for variables;
it does $it{not} apply to message headers. The names of the variables are given
in section ~~SECTexpvar below. If the name of a non-existent variable is given,
the expansion fails.

.item "@$@{<<op>>:<<string>>@}"
.index expansion||operators
The string is first itself expanded, and then the operation specified by <<op>>
is applied to it. For example,
.display asis
${lc:$local_part}
.endd
The string starts with the first character after the colon, which may be
leading white space. A list of operators is given in section ~~SECTexpop below.
The operator notation is used for simple expansion items that have just one
argument, because it reduces the number of braces and therefore makes the
string easier to understand.

.item "@$@{extract@{<<key>>@}@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
.index expansion||extracting substrings by key
The key and <<string1>> are first expanded separately. 
Leading and trailing whitespace is removed from the key (but not from any of 
the strings).
The key must not consist entirely of digits. The expanded <<string1>> must be
of the form:
.display
<<key1>> = <<value1>>  <<key2>> = <<value2>> ...
.endd
where the equals signs and spaces (but not both) are optional. If any of the
values contain white space, they must be enclosed in double quotes, and any
values that are enclosed in double quotes are subject to escape processing as
described in section ~~SECTstrings. The expanded <<string1>> is searched for
the value that corresponds to the key. The search is case-insensitive. If the
key is found, <<string2>> is expanded, and replaces the whole item; otherwise
<<string3>> is used. During the expansion of <<string2>> the variable \$value$\
contains the value that has been extracted. Afterwards, it is restored to any
previous value it might have had.

If @{<<string3>>@} is omitted, the item is replaced by an empty string if the
key is not found. If @{<<string2>>@} is also omitted, the value that was
extracted is used. Thus, for example, these two expansions are identical, and
yield `2001':
.display
@$@{extract@{gid@}{uid=1984 gid=2001@}@}
@$@{extract@{gid@}{uid=1984 gid=2001@}@{@$value@}@}
.endd
Instead of @{<<string3>>@} the word `fail' (not in curly brackets) can appear,
for example:
.display
@$@{extract@{Z@}@{A=... B=...@}@{@$value@} fail @}
.endd
@{<<string2>>@} must be present for `fail' to be recognized. When this syntax
is used, if the extraction fails, the entire string expansion fails in a way
that can be detected by the code in Exim which requested the expansion. This is
called `forced expansion failure', and its consequences depend on the
circumstances. In some cases it is no different from any other expansion
failure, but in others a different action may be taken. Such variations are
mentioned in the documentation of the option which is expanded.


.item "@$@{extract@{<<number>>@}@{<<separators>>@}@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
.index expansion||extracting substrings by number
The <<number>> argument must consist entirely of decimal digits,
apart from leading and trailing whitespace, which is ignored. 
This is what distinguishes this form of \extract\ from the previous kind. It
behaves in the same way, except that, instead of extracting a named field, it
extracts from <<string1>> the field whose number is given as the first
argument. You can use \$value$\ in <<string2>> or \"fail"\ instead of
<<string3>> as before.

The fields in the string are separated by any one of the characters in the
separator string. These may include space or tab characters.
The first field is numbered one. If the number is negative, the fields are
counted from the end of the string, with the rightmost one numbered -1. If the
number given is zero, the entire string is returned. If the modulus of the
number is greater than the number of fields in the string, the result is the
expansion of <<string3>>, or the empty string if <<string3>> is not provided.
For example:
.display asis
${extract{2}{:}{x:42:99:& Mailer::/bin/bash}}
.endd
yields `42', and
.display asis
${extract{-4}{:}{x:42:99:& Mailer::/bin/bash}}
.endd
yields `99'. Two successive separators mean that the field between them is
empty (for example, the fifth field above).


.item "@$@{hash@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
.index hash function||textual
.index expansion||textual hash
This is a textual hashing function, and was the first to be implemented in 
early versions of Exim. In current releases, there are other hashing functions 
(numeric, MD5, and SHA-1), which are described below.

The first two strings, after expansion, must be numbers. Call them <<m>> and 
<<n>>. If you are using fixed values for these numbers, that is, if <<string1>> 
and <<string2>> do not change when they are expanded, you can use the
simpler operator notation that avoids some of the braces:
.display
@$@{hash@_<<n>>@_<<m>>:<<string>>@}
.endd
The second number is optional (in both notations).

If <<n>> is greater than or equal to the length of the string, the expansion 
item returns the string. Otherwise it computes a new string of length <<n>> by
applying a hashing function to the string. The new string consists of
characters taken from the first <<m>> characters of the string
.display asis
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQWRSTUVWXYZ0123456789
.endd
If <<m>> is not present the value 26 is used, so that only lower case
letters appear. For example:
.display
@$@{hash@{3@}@{monty@}@}              $rm{yields}  \"jmg"\     
@$@{hash@{5@}@{monty@}@}              $rm{yields}  \"monty"\   
@$@{hash@{4@}@{62@}@{monty python@}@}   $rm{yields}  \"fbWx"\    
.endd


.item "@$header@_<<header name>>:#$rm{or}#@$h@_<<header name>>:"
.item "@$bheader@_<<header name>>:#$rm{or}#@$bh@_<<header name>>:"
.item "@$rheader@_<<header name>>:#$rm{or}#@$rh@_<<header name>>:"
.index expansion||header insertion
.index \$header@_$\
.index \$bheader@_$\
.index \$rheader@_$\
.index header lines||in expansion strings
.index header lines||character sets
.index header lines||decoding
Substitute the contents of the named message header line, for example
.display asis
$header_reply-to:
.endd
The newline that terminates a header line is not included in the expansion, but
internal newlines (caused by splitting the header line over several physical
lines) may be present. 

The difference between \rheader\, \bheader\, and \header\ is in the way the 
data in the header line is interpreted. 
.numberpars $.
\rheader\ gives the original `raw' content of the header line, with no
processing at all, and without the removal of leading and trailing whitespace.
.nextp
.index base64 encoding||in header lines
\bheader\ removes leading and trailing whitespace, and then decodes base64 or
quoted-printable MIME `words' within the header text, but does no character
set translation. If decoding of what looks superficially like a MIME `word'
fails, the raw string is returned. 
.index binary zero||in header line
If decoding produces a binary zero character, it is replaced by a question mark
-- this is what Exim does for binary zeros that are actually received in header
lines.
.nextp
\header\ tries to translate the string as decoded by \bheader\ to a standard
character set. This is an attempt to produce the same string as would be
displayed on a user's MUA. If translation fails, the \bheader\ string is
returned. Translation is attempted only on operating systems that support the
\*iconv()*\ function. This is indicated by the compile-time macro
\\HAVE@_ICONV\\ in a system Makefile or in \(Local/Makefile)\.
.endp

In a filter file, the target character set for \header\ can be specified by a
command of the following form:
.display asis
headers charset "UTF-8"
.endd
This command affects all references to \$h@_$\ (or \$header@_$\) expansions in
subsequently obeyed filter commands. In the absence of this command, the target
character set in a filter is taken from the setting of the \headers@_charset\
option in the runtime configuration. The value of this option defaults to the
value of \\HEADERS@_CHARSET\\ in \(Local/Makefile)\. The ultimate default is
ISO-8859-1.

Header names follow the syntax of RFC 2822, which states that they may contain
any printing characters except space and colon. Consequently, curly brackets
$it{do not} terminate header names, and should not be used to enclose them as
if they were variables. Attempting to do so causes a syntax error.

Only header lines that are common to all copies of a message are visible to
this mechanism. These are the original header lines that are received with the
message, and any that are added by 
an ACL \warn\ statement or by
a system filter. Header lines that are added to a particular copy of a message
by a router or transport are not accessible.

For incoming SMTP messages, no header lines are visible in ACLs that are obeyed
before the \\DATA\\ ACL, because the header structure is not set up until the
message is received. Header lines that are added by \warn\ statements in a
\\RCPT\\ ACL (for example) are saved until the message's incoming header lines
are available, at which point they are added. When a \\DATA\\ ACL is running,
however, header lines added by earlier ACLs are visible.

Upper case and lower case letters are synonymous in header names. If the
following character is white space, the terminating colon may be omitted, but
this is not recommended, because you may then forget it when it is needed. When
white space terminates the header name, it is included in the expanded string.
If the message does not contain the given header, the expansion item is
replaced by an empty string. (See the \def\ condition in section ~~SECTexpcond
for a means of testing for the existence of a header.) 

If there is more than one header with the same name, they are all concatenated
to form the substitution string, up to a maximum length of 64K. A newline
character is inserted between each line.
For the \header\ expansion, for those headers that contain lists of addresses,
a comma is also inserted at the junctions between lines. This does not happen
for the \rheader\ expansion.



.item "@$@{hmac@{<<hashname>>@}@{<<secret>>@}@{<<string>>@}@}"
.index expansion||hmac hashing
This function uses cryptographic hashing (either MD5 or SHA-1) to convert a
shared secret and some text into a message authentication code, as specified in
RFC 2104. 
This differs from \"@$@{md5:secret@_text...@}"\ or
\"@$@{sha1:secret@_text...@}"\ in that the hmac step adds a signature to the 
cryptographic hash, allowing for authentication that is not possible with MD5 
or SHA-1 alone.
The hash name must expand to either \"md5"\ or \"sha1"\ at present. For
example:
.display asis
${hmac{md5}{somesecret}{$primary_hostname $tod_log}}
.endd
For the hostname \*mail.example.com*\ and time 2002-10-17 11:30:59, this
produces:
.display asis
dd97e3ba5d1a61b5006108f8c8252953
.endd
As an example of how this might be used, you might put in the main part of
an Exim configuration:
.display asis
SPAMSCAN_SECRET=cohgheeLei2thahw
.endd
In a router or a transport you could then have:
.display asis
headers_add = \
  X-Spam-Scanned: ${primary_hostname} ${message_id} \
  ${hmac{md5}{SPAMSCAN_SECRET}\
  {${primary_hostname},${message_id},$h_message-id:}}
.endd
Then given a message, you can check where it was scanned by looking at the
::X-Spam-Scanned:: header line. If you know the secret, you can check that this 
header line is authentic by recomputing the authentication code from the host 
name, message ID and the ::Message-id:: header line. This can be done using
Exim's \-be-\ option, or by other means, for example by using the
\*hmac@_md5@_hex()*\ function in Perl.



.item "@${if <<condition>> @{<<string1>>@}@{<<string2>>@}@}"
.index expansion||conditional
If <<condition>> is true, <<string1>> is expanded and replaces the whole item;
otherwise <<string2>> is used. For example,
.display asis
${if eq {$local_part}{postmaster} {yes}{no} }
.endd
The second string need not be present; if it is not and the condition is not
true, the item is replaced with nothing. Alternatively, the word `fail' may be
present instead of the second string (without any curly brackets). In this
case, the expansion is forced to fail if the condition is not true. The
available conditions are described in section ~~SECTexpcond below.


.item "@$@{length@{<<string1>>@}@{<<string2>>@}@}"
.index expansion||string truncation
The \length\ item is used to extract the initial portion of a string. Both 
strings are expanded, and the first one must yield a number, <<n>>, say. If you
are using a fixed value for the number, that is, if <<string1>> does not change
when expanded, you can use the simpler operator notation that avoids some of
the braces:
.display
@$@{length@_<<n>>:<<string>>@}
.endd
The result of this item is either the first <<n>> characters or the whole
of <<string2>>, whichever is the shorter. Do not confuse \length\ with 
\strlen\, which gives the length of a string.


.item "@${lookup@{<<key>>@} <<search type>> @{<<file>>@} @{<<string1>>@} @{<<string2>>@}@}"
.item "@${lookup <<search type>> @{<<query>>@} @{<<string1>>@} @{<<string2>>@}@}"
.index expansion||lookup in
.index file||lookup
.index lookup||in expanded string
These items specify data lookups in files and databases, as discussed in
chapter ~~CHAPfdlookup. The first form is used for single-key lookups, and the
second is used for query-style lookups. The <<key>>, <<file>>, and <<query>>
strings are expanded before use.

If there is any white space in a lookup item which is part of a filter command,
a retry or rewrite rule, a routing rule for the \%manualroute%\ router, or any
other place where white space is significant, the lookup item must be enclosed
in double quotes. The use of data lookups in users' filter files may be locked
out by the system administrator.

.index \$value$\
If the lookup succeeds, <<string1>> is expanded and replaces the entire item.
During its expansion, the variable \$value$\ contains the data returned by the
lookup. Afterwards it reverts to the value it had previously (at the outer
level it is empty). If the lookup fails, <<string2>> is expanded and replaces
the entire item. If @{<<string2>>@} is omitted, the replacement is null on
failure. Alternatively, <<string2>> can itself be a nested lookup, thus
providing a mechanism for looking up a default value when the original lookup
fails.

If a nested lookup is used as part of <<string1>>, \$value$\ contains the data
for the outer lookup while the parameters of the second lookup are expanded,
and also while <<string2>> of the second lookup is expanded, should the second
lookup fail.

Instead of @{<<string2>>@} the word `fail' can appear, and in this case, if the
lookup fails, the entire expansion is forced to fail. If both @{<<string1>>@}
and @{<<string2>>@} are omitted, the result is the looked up value in the case
of a successful lookup, and nothing in the case of failure.

For single-key lookups, the string `partial' is permitted to precede the
search type in order to do partial matching, and $*$ or $*$@@ may follow a
search type to request default lookups if the key does not match (see sections
~~SECTdefaultvaluelookups and ~~SECTpartiallookup for details).

.index numerical variables (\$1$\, \$2$\, etc)||in lookup expansion
If a partial search is used, the variables \$1$\ and \$2$\ contain the wild
and non-wild parts of the key during the expansion of the replacement text.
They return to their previous values at the end of the lookup item.

This example looks up the postmaster alias in the conventional alias file:
.display asis
${lookup {postmaster} lsearch {/etc/aliases} {$value}}
.endd
This example uses NIS+ to look up the full name of the user corresponding to
the local part of an address, forcing the expansion to fail if it is not found:
.display asis
${lookup nisplus {[name=$local_part],passwd.org_dir:gcos} \
  {$value}fail}
.endd


.item "@$@{nhash@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
.index expansion||numeric hash
.index hash function||numeric
The three strings are expanded; the first two must yield numbers. Call them
<<n>> and <<m>>. If you are using fixed values for these numbers, that is, if
<<string1>> and <<string2>> do not change when they are expanded, you can use
the simpler operator notation that avoids some of the braces:
.display
@$@{nhash@_<<n>>@_<<m>>:<<string>>@}
.endd
The second number is optional (in both notations). If there is only one number,
the result is a number in the range 0--<<n>>-1. Otherwise, the string is
processed by a div/mod hash function that returns two numbers, separated by a
slash, in the ranges 0 to <<n>>-1 and 0 to <<m>>-1, respectively. For example,
.display asis
${nhash{8}{64}{supercalifragilisticexpialidocious}}
.endd
returns the string `6/33'.



.item "@$@{perl@{<<subroutine>>@}@{<<arg>>@}@{<<arg>>@}...@}"
.index Perl||use in expanded string
.index expansion||calling Perl from
This item is available only if Exim has been built to include an embedded Perl
interpreter. The subroutine name and the arguments are first separately
expanded, and then the Perl subroutine is called with those arguments. No
additional arguments need be given; the maximum number permitted, including the 
name of the subroutine, is nine.

The return value of the subroutine is inserted into the expanded string, unless
the return value is \undef\. In that case, the expansion fails in the same way
as an explicit `fail' on a lookup item. 
The return value is a scalar. Whatever you return is evaluated in a scalar 
context. For example, if you return the name of a Perl vector, the
return value is the size of the vector, not its contents.

If the subroutine exits by calling Perl's \die\ function, the expansion fails
with the error message that was passed to \die\. More details of the embedded
Perl facility are given in chapter ~~CHAPperl.

The \%redirect%\ router has an option called \forbid@_filter@_perl\ which locks
out the use of this expansion item in filter files.


.item "@$@{readfile@{<<file name>>@}@{<<eol string>>@}@}"
.index expansion||inserting an entire file
.index file||inserting into expansion
The file name and end-of-line string are first expanded separately. The file is
then read, and its contents replace the entire item. All newline characters in
the file are replaced by the end-of-line string if it is present. Otherwise,
newlines are left in the string.
String expansion is not applied to the contents of the file. If you want this, 
you must wrap the item in an \expand\ operator. If the file cannot be read, the 
string expansion fails.

The \%redirect%\ router has an option called \forbid@_filter@_readfile\ which
locks out the use of this expansion item in filter files.



.item "@$@{readsocket@{<<name>>@}@{<<request>>@}@{<<timeout>>@}@{<<eol string>>@}@{<<fail string>>@}@}"
.index expansion||inserting from a socket
.index socket, use of in expansion
This item inserts data that is read from a Unix domain socket into the expanded
string. The minimal way of using it uses just two arguments:
.display asis
${readsocket{/socket/name}{request string}}
.endd
Exim connects to the socket, writes the request string (unless it is an
empty string) and reads from the socket until an end-of-file is read. A timeout
of 5 seconds is applied. Additional, optional arguments extend what can be
done. Firstly, you can vary the timeout. For example:
.display asis
${readsocket{/socket/name}{request-string}{3s}}
.endd
A fourth argument allows you to change any newlines that are in the data
that is read, in the same way as for \readfile\ (see above). This example turns
them into spaces:
.display asis
${readsocket{/socket/name}{request-string}{3s}{ }}
.endd
As with all expansions, the substrings are expanded before the processing
happens. Errors in these sub-expansions cause the expansion to fail. In
addition, the following errors can occur:
.numberpars $.
Failure to create a socket file descriptor;
.nextp
Failure to connect the socket;
.nextp
Failure to write the request-string;
.nextp
Timeout on reading from the socket.
.endp
By default, any of these errors causes the expansion to fail. However, if
you supply a fifth substring, it is expanded and used when any of the above
errors occurs. For example:
.display asis
${readsocket{/socket/name}{request-string}{3s}{\n}\
  {socket failure}}
.endd
You can test for the existence of the socket by wrapping this expansion in
\"@$@{if exists"\, but there is a race condition between that test and the
actual opening of the socket, so it is safer to use the fifth argument if you
want to be absolutely sure of avoiding an expansion error for a non-existent
socket.

The \%redirect%\ router has an option called \forbid@_filter@_readsocket\ which
locks out the use of this expansion item in filter files.

.item "@$rheader@_<<header name>>:#$rm{or}#@$rh@_<<header name>>:"
This item inserts `raw' header lines. It is described with the \header\ 
expansion item above.



.item "@$@{run@{<<command>> <<args>>@}@{<<string1>>@}@{<<string2>>@}@}"
.index expansion||running a command
The command and its arguments are first expanded separately, and then the
command is run in a separate process, but under the same uid and gid. As in
other command executions from Exim, a shell is not used by default. If you want
a shell, you must explicitly code it.
.index return code||from \run\ expansion
If the command succeeds (gives a zero return code) <<string1>> is expanded and
replaces the entire item; during this expansion, the standard output from the
command is in the variable \$value$\. If the command fails, <<string2>>, if
present, is expanded. If it is absent, the result is empty. Alternatively,
<<string2>> can be the word `fail' (not in braces) to force expansion failure
if the command does not succeed. If both strings are omitted, the result is the
standard output on success, and nothing on failure.

The return code from the command is put in the variable \$runrc$\, and this
remains set afterwards, so in a filter file you can do things like this:
.display asis
if "${run{x y z}{}}$runrc" is 1 then ...
  elif $runrc is 2 then ...
  ...
endif
.endd
If execution of the command fails (for example, the command does not exist),
the return code is 127 -- the same code that shells use for non-existent 
commands.

\**Warning**\: In a router or transport, you cannot assume the order in which 
option values are expanded, except for those pre-conditions whose order of 
testing is documented. Therefore, you cannot reliably expect to set \$runrc$\ 
by the expansion of one option, and use it in another.

The \%redirect%\ router has an option called \forbid@_filter@_run\ which locks
out the use of this expansion item in filter files.


.item "@$@{sg@{<<subject>>@}@{<<regex>>@}@{<<replacement>>@}@}"
.index expansion||string substitution
This item works like Perl's substitution operator (s) with the global (/g)
option; hence its name. However, unlike the Perl equivalent, Exim does not
modify the subject string; instead it returns the modified string for insertion
into the overall expansion. The item takes three arguments: the subject string,
a regular expression, and a substitution string. For example
.display asis
${sg{abcdefabcdef}{abc}{xyz}}
.endd
yields `xyzdefxyzdef'. Because all three arguments are expanded before use, if
any @$ or @\ characters are required in the regular expression or in the
substitution string, they have to be escaped. For example
.display asis
${sg{abcdef}{^(...)(...)\$}{\$2\$1}}
.endd
yields `defabc', and
.display asis
${sg{1=A 4=D 3=C}{\N(\d+)=\N}{K\$1=}}
.endd
yields `K1=A K4=D K3=C'.
Note the use of \"@\N"\ to protect the contents of the regular expression from 
string expansion.



.item "@$@{substr@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
.index \substr\
.index substring extraction
.index expansion||substring extraction
The three strings are expanded; the first two must yield numbers. Call them
<<n>> and <<m>>. If you are using fixed values for these numbers, that is, if
<<string1>> and <<string2>> do not change when they are expanded, you can use
the simpler operator notation that avoids some of the braces:
.display
@$@{substr@_<<n>>@_<<m>>:<<string>>@}
.endd
The second number is optional (in both notations).

The \substr\ item can be used to extract more general substrings than \length\.
The first number, <<n>>, is a starting offset, and <<m>> is the length
required. For example
.display asis
${substr{3}{2}{$local_part}}
.endd
If the starting offset is greater than the string length the result is the null
string; if the length plus starting offset is greater than the string length,
the result is the right-hand part of the string, starting from the given
offset. The first character in the string has offset zero.

The \substr\ expansion item can take negative offset values to count
from the right-hand end of its operand. The last character is offset -1, the
second-last is offset -2, and so on. Thus, for example,
.display asis
${substr{-5}{2}{1234567}}
.endd
yields `34'. If the absolute value of a negative offset is greater than the
length of the string, the substring starts at the beginning of the string, and
the length is reduced by the amount of overshoot. Thus, for example,
.display asis
${substr{-5}{2}{12}}
.endd
yields an empty string, but
.display asis
${substr{-3}{2}{12}}
.endd
yields `1'.

If the second number is omitted from \substr\, the remainder of the string is
taken if the offset was positive. If it was negative, all characters in the
string preceding the offset point are taken. For example, an offset of -1 and
no length yields all but the last character of the string.



.item "@$@{tr@{<<subject>>@}@{<<characters>>@}@{<<replacements>>@}@}"
.index expansion||character translation
This item does single-character translation on its subject string. The second
argument is a list of characters to be translated in the subject string. Each
matching character is replaced by the corresponding character from the
replacement list. For example
.display asis
${tr{abcdea}{ac}{13}}
.endd
yields `1b3de1'. If there are duplicates in the second character string, the
last occurrence is used. If the third string is shorter than the second, its
last character is replicated. However, if it is empty, no translation takes
place.

.enditems


.section Expansion operators
.rset SECTexpop "~~chapter.~~section"
.index expansion||operators
For expansion items that perform transformations on a single argument string,
the `operator' notation is used because it is simpler and uses fewer braces.
The substring is first expanded before the operation is applied to it. The
following operations can be performed:

.startitems

.item "@$@{address:<<string>>@}"
.index expansion||RFC 2822 address handling
The string is interpreted as an RFC 2822 address, as it might appear in a
header line, and the effective address is extracted from it. If the string does
not parse successfully, the result is empty.


.item "@$@{base62:<<digits>>@}"
.index base62
.index expansion||conversion to base 62
The string must consist entirely of decimal digits. The number is converted to
base 62 (sic) and output as a string of six characters, including leading
zeros. \**Note**\: Just to be absolutely clear: this is \*not*\ base64
encoding.

.em
.item "@$@{base62d:<<base-62 digits>>@}"
.index base62
.index expansion||conversion to base 62
The string must consist entirely of base-62 digits. The number is converted to
decimal and output as a string.
.nem


.item "@$@{domain:<<string>>@}"
.index domain||extraction
.index expansion||domain extraction
The string is interpreted as an RFC 2822 address and the domain is extracted
from it. If the string does not parse successfully, the result is empty.


.item "@$@{escape:<<string>>@}"
.index expansion||escaping non-printing characters
If the string contains any non-printing characters, they are converted to
escape sequences starting with a backslash. Whether characters with the most
significant bit set (so-called `8-bit characters') count as printing or not is
controlled by the \print@_topbitchars\ option.


.em
.item "@$@{eval:<<string>>@}"
.item "@$@{eval10:<<string>>@}"
.index expansion||expression evaluation
.index expansion||arithmetic expression
These items supports simple arithmetic in expansion strings. The string (after
expansion) must be a conventional arithmetic expression, but it is limited to
the four basic operators (plus, minus, times, divide) and parentheses. All
operations are carried out using integer arithmetic. Plus and minus have a
lower priority than times and divide; operators with the same priority are
evaluated from left to right. 

For \eval\, numbers may be decimal, octal (starting with `0') or hexadecimal
(starting with `0x'). For \eval10\, all numbers are taken as decimal, even if
they start with a leading zero. This can be useful when processing numbers
extracted from dates or times, which often do have leading zeros.
.nem

A number may be followed by `K' or `M' to multiply it by 1024 or 1024$*$1024,
respectively. Negative numbers are supported. The result of the computation is
a decimal representation of the answer (without `K' or `M'). For example:
.display
  @$@{eval:1+1@}       $rm{yields} 2
  @$@{eval:1+2*3@}     $rm{yields} 7
  @$@{eval:(1+2)*3@}   $rm{yields} 9
.endd
As a more realistic example, in an ACL you might have
.display asis
deny   message = Too many bad recipients
       condition =                    \
         ${if and {                   \
           {>{$rcpt_count}{10}}       \
           {                          \
           <                          \
             {$recipients_count}      \
             {${eval:$rcpt_count/2}}  \
           }                          \
         }{yes}{no}}
.endd
The condition is true if there have been more than 10 \\RCPT\\ commands and
fewer than half of them have resulted in a valid recipient.


.item "@$@{expand:<<string>>@}"
.index expansion||re-expansion of substring
The \expand\ operator causes a string to be expanded for a second time. For
example,
.display asis
${expand:${lookup{$domain}dbm{/some/file}{$value}}}
.endd
first looks up a string in a file while expanding the operand for \expand\, and
then re-expands what it has found.


.item "@$@{from@_utf8:<<string>>@}"
.index Unicode
.index UTF-8||conversion from
.index expansion||UTF-8 conversion
The world is slowly moving towards Unicode, although there are no standards for
email yet. However, other applications (including some databases) are starting
to store data in Unicode, using UTF-8 encoding. This operator converts from a
UTF-8 string to an ISO-8859-1 string. UTF-8 code values greater than 255 are
converted to underscores. The input must be a valid UTF-8 string. If it is not,
the result is an undefined sequence of bytes.

Unicode code points with values less than 256 are compatible with ASCII and
ISO-8859-1 (also known as Latin-1).
For example, character 169 is the copyright symbol in both cases, though the 
way it is encoded is different. In UTF-8, more than one byte is needed for
characters with code values greater than 127, whereas ISO-8859-1 is a
single-byte encoding (but thereby limited to 256 characters). This makes 
translation from UTF-8 to ISO-8859-1 straightforward.


.item "@$@{hash@_<<n>>@_<<m>>:<<string>>@}"
.index hash function||textual
.index expansion||textual hash
The \hash\ operator is a simpler interface to the hashing function that can be 
used when the two parameters are fixed numbers (as opposed to strings that 
change when expanded). The effect is the same as
.display
@$@{hash@{<<n>>@}@{<<m>>@}@{<<string>>@}@}
.endd
See the description of the general \hash\ item above for details. The
abbreviation \h\ can be used when \hash\ is used as an operator.



.item "@$@{hex2b64:<<hexstring>>@}"
.index base64 encoding||conversion from hex
.index expansion||hex to base64
This operator converts a hex string into one that is base64 encoded. This can 
be useful for processing the output of the MD5 and SHA-1 hashing functions.


.item "@$@{lc:<<string>>@}"
.index case forcing in strings
.index string||case forcing
.index lower casing
.index expansion||case forcing
This forces the letters in the string into lower-case, for example:
.display asis
${lc:$local_part}
.endd


.item "@$@{length@_<<number>>:<<string>>@}"
.index expansion||string truncation
The \length\ operator is a simpler interface to the \length\ function that can
be used when the parameter is a fixed number (as opposed to a string that
changes when expanded). The effect is the same as
.display
@$@{length@{<<number>>@}@{<<string>>@}@}
.endd
See the description of the general \length\ item above for details. Note that 
\length\ is not the same as \strlen\. The abbreviation \l\ can be used when
\length\ is used as an operator.


.item "@$@{local@_part:<<string>>@}"
.index expansion||local part extraction
The string is interpreted as an RFC 2822 address and the local part is
extracted from it. If the string does not parse successfully, the result is
empty.


.item "@$@{mask:<<IP address>>/<<bit count>>@}"
.index masked IP address
.index IP address||masking
.index CIDR notation
.index expansion||IP address masking
If the form of the string to be operated on is not an IP address followed by a
slash and an integer (that is, a network address in CIDR notation), the
expansion fails. Otherwise, this operator converts the IP address to binary,
masks off the least significant bits according to the bit count, and converts
the result back to text, with mask appended. For example,
.display asis
${mask:10.111.131.206/28}
.endd
returns the string `10.111.131.192/28'. Since this operation is expected to be
mostly used for looking up masked addresses in files, the result for an IPv6
address uses dots to separate components instead of colons, because colon
terminates a key string in lsearch files. So, for example,
.display asis
${mask:3ffe:ffff:836f:0a00:000a:0800:200a:c031/99}
.endd
returns the string
.display asis
3ffe.ffff.836f.0a00.000a.0800.2000.0000/99
.endd
Letters in IPv6 addresses are always output in lower case.


.item "@$@{md5:<<string>>@}"
.index MD5 hash
.index expansion||MD5 hash
The \md5\ operator computes the MD5 hash value of the string, and returns it as
a 32-digit hexadecimal number,
in which any letters are in lower case.


.item "@$@{nhash@_<<n>>@_<<m>>:<<string>>@}"
.index expansion||numeric hash
.index hash function||numeric
The \nhash\ operator is a simpler interface to the numeric hashing function
that can be used when the two parameters are fixed numbers (as opposed to
strings that change when expanded). The effect is the same as
.display
@$@{nhash@{<<n>>@}@{<<m>>@}@{<<string>>@}@}
.endd
See the description of the general \nhash\ item above for details.


.item "@$@{quote:<<string>>@}"
.index quoting||in string expansions
.index expansion||quoting
The \quote\ operator puts its argument into double quotes if it 
is an empty string or
contains anything other than letters, digits, underscores, dots, and hyphens.
Any occurrences of double quotes and backslashes are escaped with a backslash.
Newlines and carriage returns are converted to \"@\n"\ and \"@\r"\,
respectively For example,
.display asis
${quote:ab"*"cd}
.endd
becomes
.display asis
"ab\"*\"cd"
.endd
The place where this is useful is when the argument is a substitution from a
variable or a message header.

.item "@$@{quote@_local@_part:<<string>>@}"
This operator is like \quote\, except that it quotes the string only if 
required to do so by the rules of RFC 2822 for quoting local parts. For 
example, a plus sign would not cause quoting (but it would for \quote\).
If you are creating a new email address from the contents of \$local@_part$\
(or any other unknown data), you should always use this operator.


.item "@$@{quote@_<<lookup-type>>:<<string>>@}"
.index quoting||lookup-specific
This operator applies lookup-specific quoting rules to the string. Each
query-style lookup type has its own quoting rules which are described with
the lookups in chapter ~~CHAPfdlookup. For example,
.display asis
${quote_ldap:two * two}
.endd
returns 
.display asis
two%20%5C2A%20two
.endd
For single-key lookup types, no quoting is ever necessary and this operator
yields an unchanged string.


.item "@$@{rxquote:<<string>>@}"
.index quoting||in regular expressions
.index regular expressions||quoting
The \rxquote\ operator inserts a backslash before any non-alphanumeric
characters in its argument. This is useful when substituting the values of
variables or headers inside regular expressions.


.item "@$@{rfc2047:<<string>>@}"
.index expansion||RFC 2047
This operator encodes text according to the rules of RFC 2047. This is an
encoding that is used in header lines to encode non-ASCII characters. It is
assumed that the input string is in the encoding specified by the
\headers@_charset\ option, which defaults to ISO-8859-1.
If the string contains only characters in the range 33--126, and no instances
of the characters
.display asis
? = ( ) < > @ , ; : \ " . [ ] _ 
.endd
it is not modified. Otherwise, the result is the RFC 2047 encoding, as a single
`coded word'.


.item "@$@{sha1:<<string>>@}"
.index SHA-1 hash
.index expansion||SHA-1 hashing
The \sha1\ operator computes the SHA-1 hash value of the string, and returns it
as a 40-digit hexadecimal number, in which any letters are in upper case.


.item "@$@{stat:<<string>>@}"
.index expansion||statting a file
.index file||extracting characteristics
The string, after expansion, must be a file path. A call to the \*stat()*\
function is made for this path. If \*stat()*\ fails, an error occurs and the
expansion fails. If it succeeds, the data from the stat replaces the item, as a
series of <<name>>=<<value>> pairs, where the values are all numerical, 
except for the value of `smode'. The names are: `mode' (giving the mode as a
4-digit octal number), `smode' (giving the mode in symbolic format as a
10-character string, as for the \*ls*\ command), `inode', `device', `links',
`uid', `gid', `size', `atime', `mtime', and `ctime'. You can extract individual
fields using the \extract\ expansion item. \**Warning**\: The file size may be
incorrect on 32-bit systems for files larger than 2GB.


.item "@$@{strlen:<<string>>@}"
.index expansion||string length
.index string||length in expansion
The item is replace by the length of the expanded string, expressed as a 
decimal number. \**Note**\: Do not confuse \strlen\ with \length\.


.item "@$@{substr@_<<start>>@_<<length>>:<<string>>@}"
.index \substr\
.index substring extraction
.index expansion||substring expansion
The \substr\ operator is a simpler interface to the \substr\ function that can
be used when the two parameters are fixed numbers (as opposed to strings that
change when expanded). The effect is the same as
.display
@$@{substr@{<<start>>@}@{<<length>>@}@{<<string>>@}@}
.endd
See the description of the general \substr\ item above for details. The
abbreviation \s\ can be used when \substr\ is used as an operator.

.em
.item "@$@{time@_interval:<<string>>@}"
.index \time@_interval\
.index time interval||formatting
The argument (after sub-expansion) must be a sequence of decimal digits that
represents an interval of time as a number of seconds. It is converted into a
number of larger units and output in Exim's normal time format, for example,
\"1w3d4h2m6s"\.
.nem

.item "@$@{uc:<<string>>@}"
.index case forcing in strings
.index string||case forcing
.index upper casing
.index expansion||case forcing
This forces the letters in the string into upper-case.

.enditems



.section Expansion conditions
.rset SECTexpcond "~~chapter.~~section"
.index expansion||conditions
The following conditions are available for testing by the \@$@{if\ construct
while expanding strings:

.startitems

.item "!<<condition>>"
.index expansion||negating a condition
Preceding any condition with an exclamation mark negates the result of the
condition.

.item "<<symbolic operator>> @{<<string1>>@}@{<<string2>>@}"
.index numeric comparison
.index expansion||numeric comparison
There are a number of symbolic operators for doing numeric comparisons. They
are:
.display
.tabs 8
=    $t  $rm{equal}
==   $t  $rm{equal}
>    $t  $rm{greater}
>=   $t  $rm{greater or equal}
<    $t  $rm{less}
<=   $t  $rm{less or equal}
.endd
For example,
.display asis
${if >{$message_size}{10M} ...
.endd
Note that the general negation operator provides for inequality testing. The
two strings must take the form of optionally signed decimal integers,
optionally followed by one of the letters `K' or `M' (in either upper or lower
case), signifying multiplication by 1024 or 1024$*$1024, respectively.

.item "crypteq @{<<string1>>@}@{<<string2>>@}"
.index expansion||encrypted comparison
.index encrypted strings, comparing
This condition is included in the Exim binary if it is built to support any
authentication mechanisms (see chapter ~~CHAPSMTPAUTH). Otherwise, it is
necessary to define \\SUPPORT@_CRYPTEQ\\ in \(Local/Makefile)\ to get \crypteq\
included in the binary.

The \crypteq\ condition has two arguments. The first is encrypted and compared
against the second, which is already encrypted. The second string may be in the
LDAP form for storing encrypted strings, which starts with the encryption type
in curly brackets, followed by the data. If the second string does not begin
with `{' it is assumed to be encrypted with \*crypt()*\
or \*crypt16()*\ (see below),
since such strings cannot begin with `{'. Typically this will be a field from a
password file.

An example of an encrypted string in LDAP form is:
.display asis
{md5}CY9rzUYh03PK3k6DJie09g==
.endd
If such a string appears directly in an expansion, the curly brackets have to
be quoted, because they are part of the expansion syntax. For example:
.display asis
${if crypteq {test}{\{md5\}CY9rzUYh03PK3k6DJie09g==}{yes}{no}}
.endd
The following encryption types 
(whose names are matched case-independently)
are supported:
.numberpars $.
.index MD5 hash
.index base64 encoding||in encrypted password
\@{md5@}\ computes the MD5 digest of the first string, and expresses this as
printable characters to compare with the remainder of the second string. If the
length of the comparison string is 24, Exim assumes that it is base64 encoded
(as in the above example). If the length is 32, Exim assumes that it is a
hexadecimal encoding of the MD5 digest. If the length not 24 or 32, the
comparison fails.
.nextp
.index SHA-1 hash
\@{sha1@}\ computes the SHA-1 digest of the first string, and expresses this as 
printable characters to compare with the remainder of the second string. If the 
length of the comparison string is 28, Exim assumes that it is base64 encoded. 
If the length is 40, Exim assumes that it is a hexadecimal encoding of the 
SHA-1 digest. If the length is not 28 or 40, the comparison fails.
.nextp
.index \*crypt()*\
\@{crypt@}\ calls the \*crypt()*\ function, which uses only the first eight 
characters of the password.
.nextp
.index \*crypt16()*\
\@{crypt16@}\ calls the \*crypt16()*\ function (also known as \*bigcrypt()*\),
which uses up to 16 characters of the password.
.endp
Exim has its own version of \*crypt16()*\ (which is just a double call to
\*crypt()*\). For operating systems that have their own version, setting
\\HAVE@_CRYPT16\\ in \(Local/Makefile)\ when building Exim causes it to use the
operating system version instead of its own. This option is set by default in 
the OS-dependent \(Makefile)\ for those operating systems that are known to 
support \*crypt16()*\.

If you do not put any curly bracket encryption type in a \crypteq\ comparison,
the default is either \"@{crypt@}"\ or \"@{crypt16@}"\, as determined by the
setting of \\DEFAULT@_CRYPT\\ in \(Local/Makefile)\. The default default is
\"@{crypt@}"\. Whatever the default, you can always use either function by
specifying it explicitly in curly brackets.

Note that if a password is no longer than 8 characters, the results of
encrypting it with \*crypt()*\ and \*crypt16()*\ are identical. That means that
\*crypt16()*\ is backwards compatible, as long as nobody feeds it a password
longer than 8 characters.


.item "def:<<variable name>>"
.index expansion||checking for empty variable
The \def\ condition must be followed by the name of one of the expansion
variables defined in section ~~SECTexpvar. The condition is true if the named
expansion variable does not contain the empty string, for example
.display asis
${if def:sender_ident {from $sender_ident}}
.endd
Note that the variable name is given without a leading \@$\ character. If the
variable does not exist, the expansion fails.

.item "def:header@_<<header name>>:##or##def:h@_<<header name>>:"
.index expansion||checking header line existence
This condition is true if a message is being processed and the named header
exists in the message. For example,
.display asis
${if def:header_reply-to:{$h_reply-to:}{$h_from:}}
.endd
Note that no \@$\ appears before \header@_\ or \h@_\ in the condition,
and that header names must be terminated by colons if white space does not
follow.

.item "eq @{<<string1>>@}@{<<string2>>@}"
.item "eqi @{<<string1>>@}@{<<string2>>@}"
.index string||comparison
.index expansion||string comparison
The two substrings are first expanded. The condition is true if the two
resulting strings are identical: for \eq\ the comparison includes the case of 
letters, whereas for \eqi\ the comparison is case-independent.

.item "exists @{<<file name>>@}"
.index expansion||file existence test
.index file||existence test
The substring is first expanded and then interpreted as an absolute path. The
condition is true if the named file (or directory) exists. The existence test
is done by calling the \*stat()*\ function. The use of the \exists\ test in
users' filter files may be locked out by the system administrator.

.item "first@_delivery"
.index delivery||first
.index first delivery
.index expansion||first delivery test
This condition, which has no data, is true during a message's first delivery
attempt. It is false during any subsequent delivery attempts.

.em
.item "ge @{<<string1>>@}@{<<string2>>@}"
.item "gei @{<<string1>>@}@{<<string2>>@}"
.index string||comparison
.index expansion||string comparison
The two substrings are first expanded. The condition is true if the first
string is lexically greater than or equal to the second string: for \ge\ the
comparison includes the case of letters, whereas for \gei\ the comparison is
case-independent.

.item "gt @{<<string1>>@}@{<<string2>>@}"
.item "gti @{<<string1>>@}@{<<string2>>@}"
.index string||comparison
.index expansion||string comparison
The two substrings are first expanded. The condition is true if the first
string is lexically greater than the second string: for \gt\ the comparison
includes the case of letters, whereas for \gti\ the comparison is
case-independent.
.nem

.item "isip @{<<string>>@}" 8
.item "isip4 @{<<string>>@}"
.item "isip6 @{<<string>>@}"
.index IP address||testing string format
.index string||testing for IP address
The substring is first expanded, and then tested to see if it has the form of 
an IP address. Both IPv4 and IPv6 addresses are valid for \isip\, whereas 
\isip4\ and \isip6\ test just for IPv4 or IPv6 addresses, respectively. For 
example, you could use
.display asis 
${if isip4{$sender_host_address}...
.endd
to test which version of IP an incoming SMTP connection is using.


.item "ldapauth @{<<ldap query>>@}"
.index LDAP||use for authentication
.index expansion||LDAP authentication test
This condition supports user authentication using LDAP. See section ~~SECTldap
for details of how to use LDAP in lookups and the syntax of queries. For this
use, the query must contain a user name and password. The query itself is not
used, and can be empty. The condition is true if
the password is not empty, and the user name and password are accepted by the
LDAP server. An empty password is rejected without calling LDAP because LDAP 
binds with an empty password are considered anonymous regardless of
the username, and will succeed in most configurations.
See chapter ~~CHAPSMTPAUTH for details of SMTP authentication, and chapter
~~CHAPplaintext for an example of how this can be used.


.em
.item "le @{<<string1>>@}@{<<string2>>@}"
.item "lei @{<<string1>>@}@{<<string2>>@}"
.index string||comparison
.index expansion||string comparison
The two substrings are first expanded. The condition is true if the first
string is lexically less than or equal to the second string: for \le\ the
comparison includes the case of letters, whereas for \lei\ the comparison is
case-independent.

.item "lt @{<<string1>>@}@{<<string2>>@}"
.item "lti @{<<string1>>@}@{<<string2>>@}"
.index string||comparison
.index expansion||string comparison
The two substrings are first expanded. The condition is true if the first
string is lexically less than the second string: for \lt\ the comparison
includes the case of letters, whereas for \lti\ the comparison is
case-independent.
.nem


.item "match @{<<string1>>@}@{<<string2>>@}"
.index expansion||regular expression comparison
.index regular expressions||match in expanded string
The two substrings are first expanded. The second is then treated as a regular
expression and applied to the first. Because of the pre-expansion, if the
regular expression contains dollar, or backslash characters, they must be
escaped. Care must also be taken if the regular expression contains braces
(curly brackets). A closing brace must be escaped so that it is not taken as a
premature termination of <<string2>>. The easiest approach is to use the
\"@\N"\ feature to disable expansion of the regular expression.
For example,
.display asis
${if match {$local_part}{\N^\d{3}\N} ...
.endd
If the whole expansion string is in double quotes, further escaping of
backslashes is also required.

The condition is true if the regular expression match succeeds. 
.em
The regular expression is not required to begin with a circumflex 
metacharacter, but if there is no circumflex, the expression is not anchored,
and it may match anywhere in the subject, not just at the start. If you want 
the pattern to match at the end of the subject, you must include the \"@$"\ 
metacharacter at an appropriate point.
.nem

.index numerical variables (\$1$\, \$2$\, etc)||in \if\ expansion
At the start of an \if\ expansion the values of the numeric variable
substitutions \$1$\ etc. are remembered. Obeying a \match\ condition that
succeeds causes them to be reset to the substrings of that condition and they
will have these values during the expansion of the success string. At the end
of the \if\ expansion, the previous values are restored. After testing a
combination of conditions using \or\, the subsequent values of the numeric
variables are those of the condition that succeeded.

.em
.item "match@_domain @{<<string1>>@}@{<<string2>>@}"
.item "match@_address @{<<string1>>@}@{<<string2>>@}"
.item "match@_local@_part @{<<string1>>@}@{<<string2>>@}"
.index domain list||in expansion condition
.index address list||in expansion condition
.index local part list||in expansion condition
These conditions make it possible to test domain, address, and local
part lists within expansions. Each condition requires two arguments: an item
and a list to match. A trivial example is:
.display asis
${if match_domain{a.b.c}{x.y.z:a.b.c:p.q.r}{yes}{no}}
.endd
In each case, the second argument may contain any of the allowable items for a
list of the appropriate type. Also, because the second argument (after
expansion) is a standard form of list, it is possible to refer to a named list.
Thus, you can use conditions like this:
.display asis
${if match_domain{$domain}{+local_domains}{...
.endd
.index \"+caseful"\
For address lists, the matching starts off caselessly, but the \"+caseful"\
item can be used, as in all address lists, to cause subsequent items to
have their local parts matched casefully. Domains are always matched
caselessly.

\**Note**\: Host lists are \*not*\ supported in this way. This is because
hosts have two identities: a name and an IP address, and it is not clear
how to specify cleanly how such a test would work. At least, I haven't come
up with anything yet.
.nem

.item "pam {<<string1>>:<<string2>>:...@}"
.index PAM authentication
.index \\AUTH\\||with PAM
.index Solaris||PAM support
.index expansion||PAM authentication test
\*Pluggable Authentication Modules*\
(\?http://www.kernel.org/pub/linux/libs/pam/?\)
are a facility which is available in the latest releases of Solaris and in some
GNU/Linux distributions. The Exim support, which is intended for use in
conjunction with the SMTP \\AUTH\\ command, is available only if Exim is
compiled with
.display asis
SUPPORT_PAM=yes
.endd
in \(Local/Makefile)\. You probably need to add \-lpam-\ to \\EXTRALIBS\\, and
in some releases of GNU/Linux \-ldl-\ is also needed.

The argument string is first expanded, and the result must be a colon-separated
list of strings. 
Leading and trailing whitespace is ignored.
The PAM module is initialized with the service name `exim' and the user name
taken from the first item in the colon-separated data string (<<string1>>). The
remaining items in the data string are passed over in response to requests from
the authentication function. In the simple case there will only be one request,
for a password, so the data consists of just two strings.

There can be problems if any of the strings are permitted to contain colon
characters. In the usual way, these have to be doubled to avoid being taken as
separators. If the data is being inserted from a variable, the \sg\ expansion
item can be used to double any existing colons. For example, the configuration
of a LOGIN authenticator might contain this setting:
.display asis
server_condition = ${if pam{$1:${sg{$2}{:}{::}}}{yes}{no}}
.endd
For a PLAIN authenticator you could use:
.display asis
server_condition = ${if pam{$2:${sg{$3}{:}{::}}}{yes}{no}}
.endd
In some operating systems, PAM authentication can be done only from a process
running as root. Since Exim is running as the Exim user when receiving
messages, this means that PAM cannot be used directly in those systems.
A patched version of the \*pam@_unix*\ module that comes with the
Linux PAM package is available from \?http:@/@/www.e-admin.de/pam@_exim/?\.
The patched module allows one special uid/gid combination, in addition to root,
to authenticate. If you build the patched module to allow the Exim user and
group, PAM can then be used from an Exim authenticator.


.item "pwcheck {<<string1>>:<<string2>>@}"
.index \*pwcheck*\ daemon
.index Cyrus
.index expansion||\*pwcheck*\ authentication test
This condition supports user authentication using the Cyrus \*pwcheck*\ daemon.
This is one way of making it possible for passwords to be checked by a process
that is not running as root.
\**Note:**\ The use of \*pwcheck*\ is now deprecated. Its replacement is
\*saslauthd*\ (see below).

The pwcheck support is not included in Exim by default. You need to specify
the location of the pwcheck daemon's socket in \(Local/Makefile)\ before
building Exim. For example:
.display asis
CYRUS_PWCHECK_SOCKET=/var/pwcheck/pwcheck
.endd
You do not need to install the full Cyrus software suite in order to use
the pwcheck daemon. You can compile and install just the daemon alone
from the Cyrus SASL library. Ensure that \*exim*\ is the only user that has
access to the \(/var/pwcheck)\ directory.

The \pwcheck\ condition takes one argument, which must be the user name and
password, separated by a colon. For example, in a LOGIN authenticator
configuration, you might have this:
.display asis
server_condition = ${if pwcheck{$1:$2}{1}{0}}
.endd

.item "queue@_running"
.index queue runner||detecting when delivering from
.index expansion||queue runner test
This condition, which has no data, is true during delivery attempts that are
initiated by queue runner processes, and false otherwise.


.item "radius {<<authentication string>>@}"
.index Radius
.index expansion||Radius authentication
Radius authentication (RFC 2865) is supported in a similar way to PAM. You must
set \\RADIUS@_CONFIG@_FILE\\ in \(Local/Makefile)\ to specify the location of
the Radius client configuration file in order to build Exim with Radius
support. 
You may also have to supply a suitable setting in \\EXTRALIBS\\ so that the
Radius library can be found when Exim is linked.
The string specified by \\RADIUS@_CONFIG@_FILE\\ is expanded and passed to the
Radius client library, which calls the Radius server. The condition is true if
the authentication is successful. For example
.display
server@_condition = @$@{if radius@{<<arguments>>@}@{yes@}@{no@}@}
.endd



.item "saslauthd @{@{<<user>>@}@{<<password>>@}@{<<service>>@}@{<<realm>>@}@}"
.index \*saslauthd*\ daemon
.index Cyrus
.index expansion||\*saslauthd*\ authentication test
This condition supports user authentication using the Cyrus \*saslauthd*\
daemon. This replaces the older \*pwcheck*\ daemon, which is now deprecated.
Using this daemon is one way of making it possible for passwords to be checked
by a process that is not running as root.

The saslauthd support is not included in Exim by default. You need to specify
the location of the saslauthd daemon's socket in \(Local/Makefile)\ before
building Exim. For example:
.display asis
CYRUS_SASLAUTHD_SOCKET=/var/state/saslauthd/mux
.endd
You do not need to install the full Cyrus software suite in order to use
the saslauthd daemon. You can compile and install just the daemon alone
from the Cyrus SASL library.

Up to four arguments can be supplied to the \saslauthd\ condition, but only two
are mandatory. For example:
.display asis
server_condition = ${if saslauthd{{$1}{$2}}{1}{0}}
.endd
The service and the realm are optional (which is why the arguments are enclosed
in their own set of braces). For details of the meaning of the service and
realm, and how to run the daemon, consult the Cyrus documentation.

.enditems



.section Combining expansion conditions
.index expansion||combining conditions
Several conditions can be tested at once by combining them using the \and\ and
\or\ combination conditions. Note that \and\ and \or\ are complete conditions
on their own, and precede their lists of sub-conditions. Each sub-condition
must be enclosed in braces within the overall braces that contain the list. No
repetition of \if\ is used.

.startitems

.item "or @{@{<<cond1>>@}@{<<cond2>>@}...@}"
.index `or' expansion condition
.index expansion||`or' of conditions
The sub-conditions are evaluated from left to right. The condition is true if
any one of the sub-conditions is true.
For example,
.display asis
${if or {{eq{$local_part}{spqr}}{eq{$domain}{testing.com}}}...
.endd
When a true sub-condition is found, the following ones are parsed but not
evaluated. If there are several `match' sub-conditions the values of the
numeric variables afterwards are taken from the first one that succeeds.

.item "and @{@{<<cond1>>@}@{<<cond2>>@}...@}"
.index `and' expansion condition
.index expansion||`and' of conditions
The sub-conditions are evaluated from left to right. The condition is true if
all of the sub-conditions are true. If there are several `match'
sub-conditions, the values of the numeric variables afterwards are taken from
the last one. When a false sub-condition is found, the following ones are
parsed but not evaluated.

.enditems



.section Expansion variables
.rset SECTexpvar "~~chapter.~~section"
.index expansion||variables, list of

The variables that are available for use in expansion strings are:

.push
.indent 2em
.tempindent 0
.index numerical variables (\$1$\, \$2$\, etc)
\$0$\, \$1$\, etc: When a \match\ expansion condition succeeds, these
variables contain the captured substrings identified by the regular expression
during subsequent processing of the success string of the containing \if\
expansion item. They may also be set externally by some other matching process
which precedes the expansion of the string. For example, the commands available
in Exim filter files include an \if\ command with its own regular expression
matching condition.

.tempindent 0
\$acl@_c0$\ -- \$acl@_c9$\: Values can be placed in these variables by the 
\set\ modifier in an ACL. The values persist throughout the lifetime of an SMTP
connection. They can be used to pass information between ACLs and different
invocations of the same ACL. 
When a message is received, the values of these variables are saved with the
message, and can be accessed by filters, routers, and transports during 
subsequent delivery.

.tempindent 0
\$acl@_m0$\ -- \$acl@_m9$\: Values can be placed in these variables by the
\set\ modifier in an ACL. They retain their values while a message is being
received, but are reset afterwards. They are also reset by \\MAIL\\, \\RSET\\,
\\EHLO\\, \\HELO\\, and after starting a TLS session.
When a message is received, the values of these variables are saved with the
message, and can be accessed by filters, routers, and transports during
subsequent delivery.


.tempindent 0
\$acl@_verify@_message$\: During the expansion of the \message\ and 
\log@_message\ modifiers in an ACL statement after an address verification has
failed, this variable contains the original failure message that will be
overridden by the expanded string.

.tempindent 0
\$address@_data$\: This variable is set by means of the \address@_data\
option in routers. The value then remains with the address while it is
processed by subsequent routers and eventually a transport. If the transport is
handling multiple addresses, the value from the first address is used. See
chapter ~~CHAProutergeneric for more details. 
\**Note**\: the contents of \$address@_data$\ are visible in user filter files.

If \$address@_data$\ is set when the routers are called to verify an address
from an ACL, the final value remains available in subsequent conditions in the
ACL statement. If routing the address caused it to be redirected to a single 
address, the child address is also routed as part of the verification, and in 
this case the final value of \$address@_data$\ is from the child's routing.

.tempindent 0
\$address@_file$\: When, as a result of aliasing, forwarding, or filtering, a
message is directed to a specific file, this variable holds the name of the
file when the transport is running. At other times, the variable is empty. For
example, using the default configuration, if user \r2d2\ has a \(.forward)\
file containing
.display asis
/home/r2d2/savemail
.endd
then when the \%address@_file%\ transport is running, \$address@_file$\
contains `/home/r2d2/savemail'.
.index Sieve filter||value of \$address@_file$\
For Sieve filters, the value may be `inbox' or a relative folder name. It is 
then up to the transport configuration to generate an appropriate absolute path 
to the relevant file.


.tempindent 0
\$address@_pipe$\: When, as a result of aliasing or forwarding, a message is
directed to a pipe, this variable holds the pipe command when the transport is
running.

.index authentication||id
.tempindent 0
\$authenticated@_id$\: When a server successfully authenticates a client it may
be configured to preserve some of the authentication information in the
variable \$authenticated@_id$\ (see chapter ~~CHAPSMTPAUTH). For example, a
user/password authenticator configuration might preserve the user name for use
in the routers. When a message is submitted locally (that is, not over a TCP
connection), the value of \$authenticated@_id$\ is the login name of the
calling process.

.index sender||authenticated
.index authentication||sender
.index \\AUTH\\||on \\MAIL\\ command
.tempindent 0
\$authenticated@_sender$\:
.em
When acting as a server, Exim takes note of the \\AUTH=\\ parameter on an
incoming SMTP \\MAIL\\ command
.nem
if it believes the sender is sufficiently trusted, as described in section
~~SECTauthparamail. Unless the data is the string `@<@>', it is set as the
authenticated sender of the message, and the value is available during delivery
in the \$authenticated@_sender$\ variable. If the sender is not trusted, Exim
accepts the syntax of \\AUTH=\\, but ignores the data.

When a message is submitted locally (that is, not over a TCP connection), the
value of \$authenticated@_sender$\ is an address constructed from the login
name of the calling process and \$qualify@_domain$\.


.index authentication||failure
.tempindent 0
\$authentication@_failed$\: 
This variable is set to `1' in an Exim server if a client issues an \\AUTH\\
command that does not succeed. Otherwise it is set to `0'. This makes it
possible to distinguish between `did not try to authenticate'
(\$sender@_host@_authenticated$\ is empty and \$authentication__failed$\ is set
to `0') and `tried to authenticate but failed' (\$sender@_host@_authenticated$\
is empty and \$authentication@_failed$\ is set to `1'). Failure includes any
negative response to an \\AUTH\\ command, including (for example) an attempt to
use an undefined mechanism.


.index message||body, line count
.index body of message||line count
.tempindent 0
\$body@_linecount$\:
When a message is being received or delivered, this variable contains the
number of lines in the message's body.

.index message||body, binary zero count
.index body of message||binary zero count
.index binary zero||in message body
.tempindent 0
.em
\$body@_zerocount$\:
When a message is being received or delivered, this variable contains the
number of binary zero bytes in the message's body.
.nem

.tempindent 0
\$bounce@_recipient$\:
This is set to the recipient address of a bounce message while Exim is creating
it. It is useful if a customized bounce message text file is in use (see
chapter ~~CHAPemsgcust).

.tempindent 0
\$bounce@_return@_size@_limit$\: This contains the value set in the
\bounce@_return@_size@_limit\ option, rounded up to a multiple of 1000. It is
useful when a customized error message text file is in use (see chapter
~~CHAPemsgcust).

.index gid (group id)||caller
.tempindent 0
\$caller@_gid$\: The 
.em
real 
.nem
group id under which the process that called Exim was
running. This is not the same as the group id of the originator of a message
(see \$originator@_gid$\). If Exim re-execs itself, this variable in the new
incarnation normally contains the Exim gid.

.index uid (user id)||caller
.tempindent 0
\$caller@_uid$\: The 
.em
real
.nem
user id under which the process that called Exim was
running. This is not the same as the user id of the originator of a message
(see \$originator@_uid$\). If Exim re-execs itself, this variable in the new
incarnation normally contains the Exim uid.

.tempindent 0
\$compile@_date$\: The date on which the Exim binary was compiled.

.tempindent 0
\$compile@_number$\: The building process for Exim keeps a count of the number
of times it has been compiled. This serves to distinguish different
compilations of the same version of the program.

.index black list (DNS)
.tempindent 0
\$dnslist@_domain$\: When a client host is found to be on a DNS (black) list,
the list's domain name is put into this variable so that it can be included in
the rejection message.

.tempindent 0
\$dnslist@_text$\: When a client host is found to be on a DNS (black) list, the
contents of any associated TXT record are placed in this variable.

.tempindent 0
\$dnslist@_value$\: When a client host is found to be on a DNS (black) list,
the IP address from the resource record is placed in this variable.
If there are multiple records, all the addresses are included, comma-space 
separated.

.tempindent 0
\$domain$\: When an address is being routed, or delivered on its own, this
variable contains the domain. Global address rewriting happens when a message
is received, so the value of \$domain$\ during routing and delivery is the
value after rewriting. \$domain$\ is set during user filtering, but not during
system filtering, because a message may have many recipients and the system
filter is called just once.

When more than one address is being delivered at once (for example, several
\\RCPT\\ commands in one SMTP delivery), \$domain$\ is set only if they all
have the same domain. Transports can be restricted to handling only one domain
at a time if the value of \$domain$\ is required at transport time -- this is
the default for local transports. For further details of the environment in
which local transports are run, see chapter ~~CHAPenvironment.

.index \delay@_warning@_condition\
At the end of a delivery, if all deferred addresses have the same domain, it is
set in \$domain$\ during the expansion of \delay@_warning@_condition\.

The \$domain$\ variable is also used in some other circumstances:
.numberpars $.
When an ACL is running for a \\RCPT\\ command, \$domain$\ contains the domain
of the recipient address.
\**Note:**\ the domain of the sender address is in \$sender@_address@_domain$\ 
at \\MAIL\\ time and at \\RCPT\\ time. \$domain$\ is not set for the \\MAIL\\ 
ACL.
.nextp
When a rewrite item is being processed (see chapter ~~CHAPrewrite), \$domain$\
contains the domain portion of the address that is being rewritten; it can be
used in the expansion of the replacement address, for example, to rewrite
domains by file lookup.
.nextp
With one important exception, whenever a domain list is being scanned,
\$domain$\ contains the subject domain. \**Exception**\: When a domain list in
a \sender@_domains\ condition in an ACL is being processed, the subject domain
is in \$sender@_address@_domain$\ and not in \$domain$\. It works this way so
that, in a \\RCPT\\ ACL, the sender domain list can be dependent on the
recipient domain (which is what is in \$domain$\ at this time).
.nextp
.index \\ETRN\\||value of \$domain$\
.index \smtp@_etrn@_command\
When the \smtp@_etrn@_command\ option is being expanded, \$domain$\ contains
the complete argument of the \\ETRN\\ command (see section ~~SECTETRN).
.endp

.tempindent 0
\$domain@_data$\: When the \domains\ option on a router matches a domain by
means of a lookup, the data read by the lookup is available during the running
of the router as \$domain@_data$\. In addition, if the driver routes the
address to a transport, the value is available in that transport. If the
transport is handling multiple addresses, the value from the first address is
used. 

\$domain@_data$\ is also set when the \domains\ condition in an ACL matches a 
domain by means of a lookup. The data read by the lookup is available during 
the rest of the ACL statement. In all other situations, this variable expands
to nothing.

.em
.tempindent 0
\$exim@_gid$\: This variable contains the numerical value of the Exim group id.

.tempindent 0
\$exim@_path$\: This variable contains the path to the Exim binary.

.tempindent 0
\$exim@_uid$\: This variable contains the numerical value of the Exim user id.
.nem

.tempindent 0
\$header@_<<name>>$\: This is not strictly an expansion variable. It is
expansion syntax for inserting the message header line with the given name.
Note that the name must be terminated by colon or white space, because it may
contain a wide variety of characters.
Note also that braces must \*not*\ be used.

.tempindent 0
\$home$\:
When the \check@_local@_user\ option is set for a router, the user's home
directory is placed in \$home$\ when the check succeeds. In particular, this
means it is set during the running of users' filter files. A router may also
explicitly set a home directory for use by a transport; this can be overridden
by a setting on the transport itself.

When running a filter test via the \-bf-\ option, \$home$\ is set to the value
of the environment variable \\HOME\\.

.tempindent 0
\$host$\:
When the \%smtp%\ transport is expanding its options for encryption using TLS,
\$host$\ contains the name of the host to which it is connected. Likewise, when
used in the client part of an authenticator configuration (see chapter
~~CHAPSMTPAUTH), \$host$\ contains the name of the server to which the client
is connected.
.index transport||filter
.index filter||transport filter
When used in a transport filter (see chapter ~~CHAPtransportgeneric) \$host$\
refers to the host involved in the current connection. When a local transport
is run as a result of a router that sets up a host list, \$host$\ contains the
name of the first host.

.tempindent 0
\$host@_address$\:
This variable is set to the remote host's IP address whenever \$host$\ is set
for a remote connection.

.tempindent 0
\$host@_data$\:
If a \hosts\ condition in an ACL is satisfied by means of a lookup, the result
of the lookup is made available in the \$host@_data$\ variable. This
allows you, for example, to do things like this:
.display asis
deny  hosts = net-lsearch;/some/file
      message = $host_data
.endd

.index host||name lookup, failure of
.tempindent 0
\$host@_lookup@_failed$\:
This variable contains `1' if the message came from a remote host and there was
an attempt to look up the host's name from its IP address, but the attempt
failed. Otherwise the value of the variable is `0'.
.em
Exim checks that a forward lookup of at least one of the names it receives from
a reverse lookup yields the original IP address. If this is not the case, Exim 
does not accept the looked up name(s), and \$host@_lookup@_failed$\ is set to 
`1'. Thus, being able to find a name from an IP address (for example, the 
existence of a PTR record in the DNS) is not sufficient on its own for the 
success of a host name lookup.
.nem

.tempindent 0
\$inode$\:
The only time this variable is set is while expanding the \directory@_file\
option in the \%appendfile%\ transport. The variable contains the inode number
of the temporary file which is about to be renamed. It can be used to construct
a unique name for the file.

.tempindent 0
\$interface@_address$\:
When a message is received over a TCP/IP connection, this variable contains the
address of the local IP interface. See also the \-oMi-\ command line option.
This variable can be used in ACLs and also, for example, to make the file name 
for a TLS certificate depend on which interface is being used.

.tempindent 0
\$interface@_port$\:
When a message is received over a TCP/IP connection, this variable contains the
local port number. See also the \-oMi-\ command line option.
This variable can be used in ACLs and also, for example, to make the file name 
for a TLS certificate depend on which port is being used.

.tempindent 0
\$ldap@_dn$\:
This variable, which is available only when Exim is compiled with LDAP support, 
contains the DN from the last entry in the most recently successful LDAP 
lookup.


.tempindent 0
\$load@_average$\:
This variable contains the system load average, multiplied by 1000 to that it 
is an integer. For example, if the load average is 0.21, the value of the 
variable is 210. The value is recomputed every time the variable is referenced.

.tempindent 0
\$local@_part$\: When an address is being routed, or delivered on its own, this
variable contains the local part. When a number of addresses are being
delivered together (for example, multiple \\RCPT\\ commands in an SMTP
session), \$local@_part$\ is not set.

Global address rewriting happens when a message is received, so the value of
\$local@_part$\ during routing and delivery is the value after rewriting.
\$local@_part$\ is set during user filtering, but not during system filtering,
because a message may have many recipients and the system filter is called just
once.

If a local part prefix or suffix has been recognized, it is not included in the
value of \$local@_part$\ during routing and subsequent delivery. The values of
any prefix or suffix are in \$local@_part@_prefix$\ and
\$local@_part@_suffix$\, respectively.

When a message is being delivered to a file, pipe, or autoreply transport as a
result of aliasing or forwarding, \$local@_part$\ is set to the local part of
the parent address, not to the file name or command (see \$address@_file$\ and
\$address@_pipe$\).

When an ACL is running for a \\RCPT\\ command, \$local@_part$\ contains the
local part of the recipient address.

When a rewrite item is being processed (see chapter ~~CHAPrewrite),
\$local@_part$\ contains the local part of the address that is being rewritten;
it can be used in the expansion of the replacement address, for example.

In all cases, all quoting is removed from the local part. For example, for both
the addresses
.display asis
"abc:xyz"@test.example
abc\:xyz@test.example
.endd
the value of \$local@_part$\ is
.display asis
abc:xyz
.endd
If you use \$local@_part$\ to create another address, you should always wrap it
inside a quoting operator. For example, in a \%redirect%\ router you could have:
.display asis
data = ${quote_local_part:$local_part}@new.domain.example
.endd
.em
\**Note**\: The value of \$local@_part$\ is normally lower cased. If you want 
to process local parts in a case-dependent manner in a router, you can set the 
\caseful@_local@_part\ option (see chapter ~~CHAProutergeneric).
.nem

.tempindent 0
\$local@_part@_data$\:
When the \local@_parts\ option on a router matches a local part by means of a
lookup, the data read by the lookup is available during the running of the
router as \$local@_part@_data$\. In addition, if the driver routes the address
to a transport, the value is available in that transport. If the transport is
handling multiple addresses, the value from the first address is used.

\$local@_part@_data$\ is also set when the \local@_parts\ condition in an ACL
matches a local part by means of a lookup. The data read by the lookup is
available during the rest of the ACL statement. In all other situations, this
variable expands to nothing.

.tempindent 0
\$local@_part@_prefix$\: When an address is being routed or delivered, and a
specific prefix for the local part was recognized, it is available in this
variable, having been removed from \$local@_part$\.

.tempindent 0
\$local@_part@_suffix$\: When an address is being routed or delivered, and a
specific suffix for the local part was recognized, it is available in this
variable, having been removed from \$local@_part$\.

.tempindent 0
\$local@_scan@_data$\: This variable contains the text returned by the
\*local@_scan()*\ function when a message is received. See chapter
~~CHAPlocalscan for more details.

.tempindent 0
\$local@_user@_gid$\: See \$local@_user@_uid$\.

.tempindent 0
\$local@_user@_uid$\: This variable and \$local@_user@_gid$\ are set to
the uid and gid after the \check__local__user\ router precondition succeeds.
This means that their values are available for the remaining preconditions
(\senders\, \require@_files\, and \condition\), for the \address@_data\
expansion, and for any router-specific expansions. At all other times, the
values in these variables are \"(uid@_t)(-1)"\ and \"(gid@_t)(-1)"\,
respectively.


.tempindent 0
\$localhost@_number$\: This contains the expanded value of the
\localhost@_number\ option. The expansion happens after the main options have
been read.

.tempindent 0
\$mailstore@_basename$\: This variable is set only when doing deliveries in 
`mailstore' format in the \%appendfile%\ transport. During the expansion of the 
\mailstore@_prefix\, \mailstore@_suffix\, \message__prefix\, and 
\message@_suffix\ options, it contains the basename of the files that are being
written, that is, the name without the `.tmp', `.env', or `.msg' suffix. At all
other times, this variable is empty.

.index message||age of
.tempindent 0
\$message@_age$\: This variable is set at the start of a delivery attempt to
contain the number of seconds since the message was received. It does not
change during a single delivery attempt.

.index body of message||expansion variable
.index message||body, in expansion
.index binary zero||in message body
.tempindent 0
\$message@_body$\: This variable contains the initial portion of a message's
body while it is being delivered, and is intended mainly for use in filter
files. The maximum number of characters of the body that are put into the
variable is set by the \message@_body@_visible\ configuration option; the
default is 500. Newlines are converted into spaces to make it easier to search
for phrases that might be split over a line break.
Binary zeros are also converted into spaces.

.index body of message||expansion variable
.index message||body, in expansion
.tempindent 0
\$message@_body@_end$\: This variable contains the final portion of a message's
body while it is being delivered. The format and maximum size are as for
\$message@_body$\.

.index body of message||size
.index message||body, size
.tempindent 0
\$message@_body@_size$\: When a message is being processed, this variable
contains the size of the body in bytes. The count starts from the character
after the blank line that separates the body from the header. Newlines are
included in the count. See also \$message@_size$\ and \$body@_linecount$\.

.tempindent 0
\$message@_headers$\:
This variable contains a concatenation of all the header lines when a message
is being processed, except for lines added by routers or transports. The header
lines are separated by newline characters.

.tempindent 0
\$message@_id$\: 
When a message is being received or delivered, this variable contains the
unique message id that is used by Exim to identify the message.
An id is not created for a message until after its header has been 
successfully received.
.em
\**Note**\: This is \*not*\ the contents of the ::Message-ID:: header line; it 
is the local id that Exim assigns to the message, for example: 
\"1BXTIK-0001yO-VA"\.
.nem

.index size||of message
.index message||size
.tempindent 0
\$message@_size$\: 
When a message is being processed, this variable contains its size in bytes. In
most cases, the size includes those headers that were received with the
message, but not those (such as ::Envelope-to::) that are added to individual
deliveries as they are written. However, there is one special case: during the
expansion of the \maildir@_tag\ option in the \%appendfile%\ transport while
doing a delivery in maildir format, the value of \$message@_size$\ is the
precise size of the file that has been written. See also
\$message@_body@_size$\ and \$body@_linecount$\.

.index \\RCPT\\||value of \$message@_size$\
While running an ACL at the time of an SMTP \\RCPT\\ command, \$message@_size$\
contains the size supplied on the \\MAIL\\ command, or 
-1
if no size was given. The value may not, of course, be truthful.

.tempindent 0
\$n0$\ -- \$n9$\: These variables are counters that can be incremented by means
of the \add\ command in filter files.

.tempindent 0
\$original@_domain$\: When a top-level address is being processed for delivery,
this contains the same value as \$domain$\. However, if a `child' address (for
example, generated by an alias, forward, or filter file) is being processed,
this variable contains the domain of the original address. This differs from
\$parent@_domain$\ only when there is more than one level of aliasing or
forwarding. When more than one address is being delivered in a single transport
run, \$original@_domain$\ is not set.

If new an address is created by means of a \deliver\ command in a system
filter, it is set up with an artificial `parent' address. This has the local
part \*system-filter*\ and the default qualify domain.

.tempindent 0
\$original@_local@_part$\: When a top-level address is being processed for
delivery, this contains the same value as \$local@_part$\, unless a prefix or
suffix was removed from the local part, in which case \$original@_local@_part$\
contains the full local part. When a `child' address (for example, generated by
an alias, forward, or filter file) is being processed, this variable contains
the full local part of the original address. If the router that did the
redirection processed the local part case-insensitively, the value in
\$original@_local@_part$\ is in lower case. This variable differs from
\$parent@_local@_part$\ only when there is more than one level of aliasing or
forwarding. When more than one address is being delivered in a single transport
run, \$original@_local@_part$\ is not set.

If new an address is created by means of a \deliver\ command in a system
filter, it is set up with an artificial `parent' address. This has the local
part \*system-filter*\ and the default qualify domain.


.index gid (group id)||of originating user
.index sender||gid
.tempindent 0
\$originator@_gid$\: The value of \$caller@_gid$\ that was set when the message
was received. For messages received via the command line, this is the gid of
the sending user. For messages received by SMTP over TCP/IP, this is normally
the gid of the Exim user.

.index uid (user id)||of originating user
.index sender||uid
.tempindent 0
\$originator@_uid$\: The value of \$caller@_uid$\ that was set when the message
was received. For messages received via the command line, this is the uid of
the sending user. For messages received by SMTP over TCP/IP, this is normally
the uid of the Exim user.

.tempindent 0
\$parent@_domain$\: This variable is similar to \$original@_domain$\ (see
above), except that it refers to the immediately preceding parent address.

.tempindent 0
\$parent@_local@_part$\: This variable is similar to \$original@_local@_part$\
(see above), except that it refers to the immediately preceding parent address.

.index pid (process id)||of current process
.tempindent 0
\$pid$\: This variable contains the current process id.

.index filter||transport filter
.index transport||filter
.tempindent 0
\$pipe@_addresses$\: This is not an expansion variable, but is mentioned here
because the string `@$pipe@_addresses' is handled specially in the command
specification for the \%pipe%\ transport (chapter ~~CHAPpipetransport) and in
transport filters (described under \transport@_filter\ in chapter
~~CHAPtransportgeneric). It cannot be used in general expansion strings, and
provokes an `unknown variable' error if encountered.

.tempindent 0
\$primary@_hostname$\: The value set in the configuration file, or read by the
\*uname()*\ function. If \*uname()*\ returns a single-component name, Exim
calls \*gethostbyname()*\ (or \*getipnodebyname()*\ where available) in an
attempt to acquire a fully qualified host name.
.em
See also \$smtp@_active@_hostname$\.
.nem

.tempindent 0
\$qualify@_domain$\: The value set for this option in the configuration file.

.tempindent 0
\$qualify@_recipient$\: The value set for this option in the configuration file,
or if not set, the value of \$qualify@_domain$\.

.tempindent 0
\$rcpt@_count$\: When a message is being received by SMTP, this variable 
contains the number of \\RCPT\\ commands received for the current message. If
this variable is used in a \\RCPT\\ ACL, its value includes the current
command.

.tempindent 0
\$rcpt@_defer@_count$\: When a message is being received by SMTP, this variable 
contains the number of \\RCPT\\ commands in the current message that have
previously been rejected with a temporary (4\*xx*\) response.

.tempindent 0
\$rcpt@_fail@_count$\: When a message is being received by SMTP, this variable
contains the number of \\RCPT\\ commands in the current message that have
previously been rejected with a permanent (5\*xx*\) response.

.tempindent 0
\$received@_count$\: This variable contains the number of ::Received:: header
lines in the message, including the one added by Exim (so its value is always
greater than zero). It is available in the \\DATA\\ ACL, the non-SMTP ACL, and
while routing and delivering.

.tempindent 0
\$received@_for$\: If there is only a single recipient address in an incoming
message, this variable contains that address when the ::Received:: header line
is being built.
.em
The value is copied after recipient rewriting has happened, but before the
\*local@_scan()*\ function is run.
.nem

.tempindent 0
\$received@_protocol$\: When a message is being processed, this variable
contains the name of the protocol by which it was received. See also the
\-oMr-\ option.

.em
.tempindent 0
\$recipient@_data$\: This variable is set after an indexing lookup success in
an ACL \recipients\ condition. It contains the data from the lookup, and the
value remains set until the next \recipients\ test. Thus, you can do things
like this:
.display
require recipients      = cdb*@@;/some/file
deny    \*some further test involving*\ @$recipient@_data
.endd
\**Warning**\: This variable is set only when a lookup is used as an indexing 
method in the address list, using the semicolon syntax as in the example above.
The variable is not set for a lookup that is used as part of the string
expansion that all such lists undergo before being interpreted.
.nem

.tempindent 0
\$recipients$\: This variable contains a list of envelope recipients for a
message. A comma and a space separate the addresses in the replacement text.
However, the variable is not generally available, to prevent exposure of Bcc
recipients in unprivileged users' filter files. You can use \$recipients$\ only
.numberpars
In a system filter file.
.nextp
In the \\DATA\\ or non-SMTP ACL, that is, in the final ACL for accepting a 
message.
.endp

.tempindent 0
\$recipients@_count$\: When a message is being processed, this variable
contains the number of envelope recipients that came with the message.
Duplicates are not excluded from the count. While a message is being received
over SMTP, the number increases for each accepted recipient. It can be
referenced in an ACL.

.tempindent 0
\$reply@_address$\: When a message is being processed, this variable contains
the contents of the ::Reply-To:: header line if one exists
and it is not empty,
or otherwise the contents of the ::From:: header line.

.tempindent 0
\$return@_path$\: When a message is being delivered, this variable contains the
return path -- the sender field that will be sent as part of the envelope. It
is not enclosed in @<@> characters. 
At the start of routing an address, 
\$return@_path$\ has the same value as \$sender@_address$\, but if, for
example, an incoming message to a mailing list has been expanded by a router
which specifies a different address for bounce messages, \$return@_path$\
subsequently contains the new bounce address, whereas \$sender@_address$\
always contains the original sender address that was received with the message.
In other words, \$sender@_address$\ contains the incoming envelope sender, and 
\$return@_path$\ contains the outgoing envelope sender.

.tempindent 0
\$return@_size@_limit$\: This is an obsolete name for
\$bounce@_return@_size@_limit$\.

.index return code||from \run\ expansion
.tempindent 0
\$runrc$\: This variable contains the return code from a command that is run by
the \@$@{run...@}\ expansion item.
\**Warning**\: In a router or transport, you cannot assume the order in which 
option values are expanded, except for those pre-conditions whose order of 
testing is documented. Therefore, you cannot reliably expect to set \$runrc$\ 
by the expansion of one option, and use it in another.

.tempindent 0
\$self@_hostname$\: When an address is routed to a supposedly remote host that
turns out to be the local host, what happens is controlled by the 
.index \self\ option||value of host name
\self\ generic router option. One of its values causes the address to be passed
to another router. When this happens, \$self@_hostname$\ is set to the name of
the local host that the original router encountered. In other circumstances its
contents are null.

.tempindent 0
\$sender@_address$\: When a message is being processed, this variable contains
the sender's address that was received in the message's envelope. For bounce
messages, the value of this variable is the empty string.
See also \$return@_path$\.

.tempindent 0
\$sender@_address@_domain$\: The domain portion of \$sender@_address$\.

.tempindent 0
\$sender@_address@_local@_part$\: The local part portion of \$sender@_address$\.

.em
.tempindent 0
\$sender@_data$\: This variable is set after a lookup success in an ACL 
\senders\ condition or in a router \senders\ option. It contains the data from
the lookup, and the value remains set until the next \senders\ test. Thus, you
can do things like this:
.display
require senders      = cdb*@@;/some/file
deny    \*some further test involving*\ @$sender@_data
.endd
\**Warning**\: This variable is set only when a lookup is used as an indexing 
method in the address list, using the semicolon syntax as in the example above.
The variable is not set for a lookup that is used as part of the string
expansion that all such lists undergo before being interpreted.
.nem

.tempindent 0
\$sender@_fullhost$\: When a message is received from a remote host, this
variable contains the host name and IP address in a single string. It ends
with the IP address in square brackets, followed by a colon and a port number
if the logging of ports is enabled. The format of the rest of the string
depends on whether the host issued a \\HELO\\ or \\EHLO\\ SMTP command, and
whether the host name was verified by looking up its IP address. (Looking up
the IP address can be forced by the \host@_lookup\ option, independent of
verification.) A plain host name at the start of the string is a verified host
name; if this is not present, verification either failed or was not requested.
A host name in parentheses is the argument of a \\HELO\\ or \\EHLO\\ command.
This is omitted if it is identical to the verified host name or to the host's
IP address in square brackets.

.tempindent 0
\$sender@_helo@_name$\: When a message is received from a remote host that has
issued a \\HELO\\ or \\EHLO\\ command, the argument of that command is placed
in this variable. It is also set if \\HELO\\ or \\EHLO\\ is used when a message
is received using SMTP locally via the \-bs-\ or \-bS-\ options.

.tempindent 0
\$sender@_host@_address$\: When a message is received from a remote host, this
variable contains that host's IP address. For locally submitted messages, it is
empty.

.tempindent 0
\$sender@_host@_authenticated$\: This variable contains the name (not the
public name) of the authenticator driver which successfully authenticated the
client from which the message was received. It is empty if there was no
successful authentication.

.tempindent 0
\$sender@_host@_name$\: When a message is received from a remote host, this
variable contains the host's name as obtained by looking up its IP address. 
For messages received by other means, this variable is empty.

If the host name has not previously been looked up, a reference to
\$sender@_host@_name$\ triggers a lookup (for messages from remote hosts). 
.em
A looked up name is accepted only if it leads back to the original IP address
via a forward lookup. If either the reverse or the forward lookup fails, or if
the forward lookup does not yield the original IP address,
\$sender@_host@_name$\ remains empty, and \$host@_lookup@_failed$\ is set to
`1'.
.nem

Exim does not automatically look up every calling host's name. If you want
maximum efficiency, you should arrange your configuration so that it avoids
these lookups altogether. The lookup happens only if one or more of the
following are true:
.numberpars
A string containing \$sender@_host@_name$\ is expanded.
.nextp
The calling host matches the list in \host@_lookup\. In the default 
configuration, this option is set to $*$, so it must be changed if lookups are
to be avoided. (In the code, the default for \host@_lookup\ is unset.)
.nextp
Exim needs the host name in order to test an item in a host list. The items
that require this are described in sections ~~SECThoslispatnam and
~~SECThoslispatnamsk.
.nextp
The calling host matches \helo@_try@_verify@_hosts\ or \helo@_verify@_hosts\. 
In this case, the host name is required to compare with the name quoted in any 
\\EHLO\\ or \\HELO\\ commands that the client issues.
.nextp
The remote host issues a \\EHLO\\ or \\HELO\\ command that quotes one of the 
domains in \helo@_lookup@_domains\. The default value of this option is 
.display asis
helo_lookup_domains = @ : @[]
.endd
which causes a lookup if a remote host (incorrectly) gives the server's name or 
IP address in an \\EHLO\\ or \\HELO\\ command.
.endp

.tempindent 0
\$sender@_host@_port$\: When a message is received from a remote host, this
variable contains the port number that was used on the remote host.

.tempindent 0
\$sender@_ident$\: When a message is received from a remote host, this variable
contains the identification received in response to an RFC 1413 request. When a
message has been received locally, this variable contains the login name of the
user that called Exim.

.tempindent 0
\$sender@_rcvhost$\: This is provided specifically for use in ::Received::
headers. It starts with either the verified host name (as obtained from a
.index DNS||reverse lookup
.index reverse DNS lookup
reverse DNS lookup) or, if there is no verified host name, the IP address in
square brackets. After that there may be text in parentheses. When the first
item is a verified host name, the first thing in the parentheses is the IP
address in square brackets, followed by a colon and a port number if port
logging is enabled. When the first item is an IP address, the port is recorded
as `port=$it{xxxx}' inside the parentheses.

There may also be items of the form `helo=$it{xxxx}' if \\HELO\\ or \\EHLO\\
was used and its argument was not identical to the real host name or IP
address, and `ident=$it{xxxx}' if an RFC 1413 ident string is available. If all
three items are present in the parentheses, a newline and tab are inserted into
the string, to improve the formatting of the ::Received:: header.

.index \\AUTH\\||argument
.index \\EXPN\\||argument
.index \\ETRN\\||argument
.index \\VRFY\\||argument
.tempindent 0
\$smtp@_command@_argument$\: While an ACL is running to check an \\AUTH\\,
\\EHLO\\, \\EXPN\\, \\ETRN\\, \\HELO\\, or \\VRFY\\ command, this variable
contains the argument for the SMTP command.

.tempindent 0
\$sn0$\ -- \$sn9$\: These variables are copies of the values of the \$n0$\
-- \$n9$\ accumulators that were current at the end of the system filter file.
This allows a system filter file to set values that can be tested in users'
filter files. For example, a system filter could set a value indicating how
likely it is that a message is junk mail.

.tempindent 0
\$spool@_directory$\: The name of Exim's spool directory.

.tempindent 0
\$thisaddress$\: This variable is set only during the processing of the
\foranyaddress\ command in a filter file. Its use is explained in the
description of that command.

.tempindent 0
\$tls@_certificate@_verified$\:
This variable is set to `1' if a TLS certificate was verified when the message
was received, and `0' otherwise.

.tempindent 0
\$tls@_cipher$\: When a message is received from a remote host over an
encrypted SMTP connection, this variable is set to the cipher suite that was
negotiated, for example DES-CBC3-SHA. 
In other circumstances, in particular, for message received over unencrypted 
connections, the variable is empty.
See chapter ~~CHAPTLS for details of TLS support.

.tempindent 0
\$tls@_peerdn$\:  When a message is received from a remote host over an
encrypted SMTP connection, 
and Exim is configured to request a certificate from the client,
the value of the Distinguished Name of the certificate is made available in the
\$tls@_peerdn$\ during subsequent processing.

.tempindent 0
\$tod@_bsdinbox$\: The time of day and date, in the format required for
BSD-style mailbox files, for example: Thu Oct 17 17:14:09 1995.

.tempindent 0
\$tod@_epoch$\: The time and date as a number of seconds since the start of the
Unix epoch.

.tempindent 0
\$tod@_full$\: A full version of the time and date, for example: Wed, 16 Oct
1995 09:51:40 +0100. The timezone is always given as a numerical offset from
UTC, with positive values used for timezones that are ahead (east) of UTC, and 
negative values for those that are behind (west).

.tempindent 0
\$tod@_log$\: The time and date in the format used for writing Exim's log
files, for example: 1995-10-12 15:32:29,
but without a timezone.

.tempindent 0
\$tod@_logfile$\:
This variable contains the date in the format yyyymmdd. This is the format that
is used for datestamping log files when \log@_file@_path\ contains the \"%D"\
flag.

.tempindent 0
\$tod@_zone$\: This variable contains the numerical value of the local
timezone, for example: -0500.

.tempindent 0
\$tod@_zulu$\:
This variable contains the UTC date and time in `Zulu' format, as specified by
ISO 8601, for example: 20030221154023Z.

.index \$value$\
.tempindent 0
\$value$\: This variable contains the result of an expansion lookup, extraction
operation, or external command, as described above.

.tempindent 0
\$version@_number$\: The version number of Exim.

.tempindent 0
\$warn@_message@_delay$\: This variable is set only during the creation of a
message warning about a delivery delay. Details of its use are explained in
section ~~SECTcustwarn.

.tempindent 0
\$warn@_message@_recipients$\: This variable is set only during the creation of
a message warning about a delivery delay. Details of its use are explained in
section ~~SECTcustwarn.
.pop



.
.
. ============================================================================
.chapter Embedded Perl
.set runningfoot "embedded Perl"
.rset CHAPperl "~~chapter"
.index Perl||calling from Exim

Exim can be built to include an embedded Perl interpreter. When this is done,
Perl subroutines can be called as part of the string expansion process. To make
use of the Perl support, you need version 5.004 or later of Perl installed on
your system. To include the embedded interpreter in the Exim binary, include
the line
.display asis
EXIM_PERL = perl.o
.endd
in your \(Local/Makefile)\ and then build Exim in the normal way.

Access to Perl subroutines is via a global configuration option called
.index \perl@_startup\
\perl@_startup\ and an expansion string operator \@$@{perl ...@}\. If there is
no \perl@_startup\ option in the Exim configuration file then no Perl
interpreter is started and there is almost no overhead for Exim (since none of
the Perl library will be paged in unless used). If there is a \perl@_startup\
option then the associated value is taken to be Perl code which is executed in
a newly created Perl interpreter.

The value of \perl@_startup\ is not expanded in the Exim sense, so you do not
need backslashes before any characters to escape special meanings. The option
should usually be something like
.display asis
perl_startup = do '/etc/exim.pl'
.endd
where \(/etc/exim.pl)\ is Perl code which defines any subroutines you want to
use from Exim. Exim can be configured either to start up a Perl interpreter as
soon as it is entered, or to wait until the first time it is needed. Starting
the interpreter at the beginning ensures that it is done while Exim still has
its setuid privilege, but can impose an unnecessary overhead if Perl is not in
fact used in a particular run. Also, note that this does not mean that Exim is
necessarily running as root when Perl is called at a later time. By default,
the interpreter is started only when it is needed, but this can be changed in
two ways:
.numberpars $.
.index \perl@_at@_start\
Setting \perl@_at@_start\ (a boolean option) in the configuration requests
a startup when Exim is entered.
.nextp
The command line option \-ps-\ also requests a startup when Exim is entered,
overriding the setting of \perl@_at@_start\.
.endp
There is also a command line option \-pd-\ (for delay) which suppresses the
initial startup, even if \perl@_at@_start\ is set.

When the configuration file includes a \perl@_startup\ option you can make use
of the string expansion item to call the Perl subroutines that are defined
by the \perl@_startup\ code. The operator is used in any of the following
forms:
.display asis
${perl{foo}}
${perl{foo}{argument}}
${perl{foo}{argument1}{argument2} ... }
.endd
which calls the subroutine \foo\ with the given arguments. A maximum of eight
arguments may be passed. Passing more than this results in an expansion failure
with an error message of the form
.display asis
Too many arguments passed to Perl subroutine "foo" (max is 8)
.endd
The return value of the Perl subroutine is evaluated in a scalar context before
it is passed back to Exim to be inserted into the expanded string. If the
return value is \*undef*\, the expansion fails in the same way as an explicit
`fail' on an \@$@{if ...@}\ or \@$@{lookup...@}\ item.
If the subroutine aborts by obeying Perl's \die\ function, the expansion fails
with the error message that was passed to \die\.

Within any Perl code called from Exim, the function \*Exim@:@:expand@_string*\
is available to call back into Exim's string expansion function. For example,
the Perl code
.display asis
my $lp = Exim::expand_string('$local_part');
.endd
makes the current Exim \$local@_part$\ available in the Perl variable \$lp$\.
Note those are single quotes and not double quotes to protect against
\$local@_part$\ being interpolated as a Perl variable.

If the string expansion is forced to fail by a `fail' item, the result of
\*Exim@:@:expand@_string*\ is \undef\. If there is a syntax error in the
expansion string, the Perl call from the original expansion string fails with
an appropriate error message, in the same way as if \die\ were used.

.index debugging||from embedded Perl
.index log||writing from embedded Perl
Two other Exim functions are available for use from within Perl code.
\*Exim@:@:debug@_write(<<string>>)*\ writes the string to the standard error
stream if Exim's debugging is enabled. If you want a newline at the end, you
must supply it. \*Exim@:@:log@_write(<<string>>)*\ writes the string to Exim's
main log, adding a leading timestamp. In this case, you should not supply a
terminating newline.



.
.
.
.
. ============================================================================
.chapter Starting the daemon and the use of network interfaces
.set runningfoot "starting the daemon"
.rset CHAPinterfaces "~~chapter"
.index daemon||starting
.index interface||listening
.index network interface
.index interface||network
.index IP address||for listening
.index daemon||listening IP addresses
.index TCP/IP||setting listening interfaces
.index TCP/IP||setting listening ports

A host that is connected to a TCP/IP network may have one or more physical
hardware network interfaces. Each of these interfaces may be configured as one
or more `logical' interfaces, which are the entities that a program actually
works with. Each of these logical interfaces is associated with an IP address.
In addition, TCP/IP software supports `loopback' interfaces (127.0.0.1 in IPv4
and @:@:1 in IPv6), which do not use any physical hardware. Exim requires
knowledge about the host's interfaces for use in three different circumstances:
.numberpars
When a listening daemon is started, Exim needs to know which interfaces
and ports to listen on.
.nextp
When Exim is routing an address, it needs to know which IP addresses
are associated with local interfaces. This is required for the correct
processing of MX lists by removing the local host and others with the
same or higher priority values. Also, Exim needs to detect cases
when an address is routed to an IP address that in fact belongs to the
local host. Unless the \self\ router option or the \allow@_localhost\
option of the smtp transport is set (as appropriate), this is treated
as an error situation.
.nextp
When Exim connects to a remote host, it may need to know which interface to use
for the outgoing connection.
.endp

Exim's default behaviour is likely to be appropriate in the vast majority
of cases. If your host has only one interface, and you want all its IP
addresses to be treated in the same way, and you are using only the
standard SMTP port, you should not need to take any special action. The
rest of this chapter does not apply to you.

In a more complicated situation you may want to listen only on certain 
interfaces, or on different ports, and for this reason there are a number of
options that can be used to influence Exim's behaviour. The rest of this
chapter describes how they operate.

When a message is received over TCP/IP, the interface and port that were
actually used are set in \$interface@_address$\ and \$interface@_port$\.


.section Starting a listening daemon
When a listening daemon is started (by means of the \-bd-\ command line
option), the interfaces and ports on which it listens are controlled by the
following options:
.numberpars $.
\daemon@_smtp@_ports\ contains a list of default ports. (For backward
compatibility, this option can also be specified in the singular.)
.nextp
\local@_interfaces\ contains list of interface IP addresses on which to
listen. Each item may optionally also specify a port.
.endp
The default list separator in both cases is a colon, but this can be changed as
described in section ~~SECTlistconstruct. When IPv6 addresses are involved, it
is usually best to change the separator to avoid having to double all the
colons. For example:
.display asis
local_interfaces = <; 127.0.0.1 ; \
                      192.168.23.65 ; \
                      ::1 ; \
                      3ffe:ffff:836f::fe86:a061
.endd              
There are two different formats for specifying a port along with an IP address
in \local@_interfaces\:
.numberpars
The port is added onto the address with a dot separator. For example, to listen 
on port 1234 on two different IP addresses:
.display asis
local_interfaces = <; 192.168.23.65.1234 ; \
                      3ffe:ffff:836f::fe86:a061.1234
.endd                       
.nextp
The IP address is enclosed in square brackets, and the port is added
with a colon separator, for example:
.display asis
local_interfaces = <; [192.168.23.65]:1234 ; \
                      [3ffe:ffff:836f::fe86:a061]:1234
.endd                       
.endp
When a port is not specified, the value of \daemon@_smtp@_ports\ is used. The
default setting contains just one port:
.display asis
daemon_smtp_ports = smtp
.endd
If more than one port is listed, each interface that does not have its own port
specified listens on all of them. Ports that are listed in
\daemon@_smtp@_ports\ can be identified either by name (defined in
\(/etc/services)\) or by number. However, when ports are given with individual
IP addresses in \local@_interfaces\, only numbers (not names) can be used.


.section Special IP listening addresses 
The addresses 0.0.0.0 and @:@:0 are treated specially. They are interpreted
as `all IPv4 interfaces' and `all IPv6 interfaces', respectively. In each
case, Exim tells the TCP/IP stack to `listen on all IPv\*x*\ interfaces'
instead of setting up separate listening sockets for each interface. The
default value of \local@_interfaces\ is
.display asis
local_interfaces = 0.0.0.0
.endd
when Exim is built without IPv6 support; otherwise it is:
.display asis
local_interfaces = <; ::0 ; 0.0.0.0
.endd
Thus, by default, Exim listens on all available interfaces, on the SMTP port.


.section Overriding local@_interfaces and daemon@_smtp@_ports
The \-oX-\ command line option can be used to override the values of
\daemon@_smtp@_ports\ and/or \local@_interfaces\ for a particular daemon
instance. Another way of doing this would be to use macros and the \-D-\
option. However, \-oX-\ can be used by any admin user, whereas modification of
the runtime configuration by \-D-\ is allowed only when the caller is root or
exim.

The value of \-oX-\ is a list of items. The default colon separator can be
changed in the usual way if required. If there are any items that do not
contain dots or colons (that is, are not IP addresses), the value of
\daemon@_smtp@_ports\ is replaced by the list of those items. If there are any
items that do contain dots or colons, the value of \local@_interfaces\ is
replaced by those items. Thus, for example,
.display asis
-oX 1225
.endd
overrides \daemon@_smtp@_ports\, but leaves \local@_interfaces\ unchanged,
whereas
.display asis
-oX 192.168.34.5.1125
.endd
overrides \local@_interfaces\, leaving \daemon@_smtp@_ports\ unchanged.
(However, since \local@_interfaces\ now contains no items without ports, the
value of \daemon@_smtp@_ports\ is no longer relevant in this example.)


.section IPv6 address scopes
IPv6 addresses have `scopes', and a host with multiple hardware interfaces
can, in principle, have the same link-local IPv6 address on different
interfaces. Thus, additional information is needed, over and above the IP
address, to distinguish individual interfaces. A convention of using a
percent sign followed by something (often the interface name) has been
adopted in some cases, leading to addresses like this:
.display asis
3ffe:2101:12:1:a00:20ff:fe86:a061%eth0
.endd
To accommodate this usage, a percent sign followed by an arbitrary string is
allowed at the end of an IPv6 address. By default, Exim calls \*getaddrinfo()*\
to convert a textual IPv6 address for actual use. This function recognizes the
percent convention in operating systems that support it, and it processes the
address appropriately. Unfortunately, some older libraries have problems with
\*getaddrinfo()*\. If
.display asis
IPV6_USE_INET_PTON=yes
.endd
is set in \(Local/Makefile)\ (or an OS-dependent Makefile) when Exim is built,
Exim uses \*inet@_pton()*\ to convert a textual IPv6 address for actual use,
instead of \*getaddrinfo()*\. (Before version 4.14, it always used this
function.) Of course, this means that the additional functionality of
\*getaddrinfo()*\ -- recognizing scoped addresses -- is lost.


.section Examples of starting a listening daemon
The default case in an IPv6 environment is
.display asis
daemon_smtp_port = smtp
local_interfaces = <; ::0 ; 0.0.0.0
.endd
This specifies listening on the smtp port on all IPv6 and IPv4 interfaces.
Either one or two sockets may be used, depending on the characteristics of
the TCP/IP stack. (This is complicated and messy; for more information,
read the comments in the \(daemon.c)\ source file.)

To specify listening on ports 25 and 26 on all interfaces:
.display asis
daemon_smtp_ports = 25 : 26
.endd
(leaving \local@_interfaces\ at the default setting) or, more explicitly:
.display asis
local_interfaces = <; ::0.25     ; ::0.26 \
                      0.0.0.0.25 ; 0.0.0.0.26
.endd
To listen on the default port on all IPv4 interfaces, and on port 26 on the
IPv4 loopback address only:
.display asis
local_interfaces = 0.0.0.0 : 127.0.0.1.26
.endd
To specify listening on the default port on specific interfaces only:
.display asis
local_interfaces = 192.168.34.67 : 192.168.34.67
.endd
\**Note**\: such a setting excludes listening on the loopback interfaces.


.section Recognising the local host
.rset SECTreclocipadd "~~chapter.~~section"
The \local@_interfaces\ option is also used when Exim needs to determine
whether or not an IP address refers to the local host. That is, the IP
addresses of all the interfaces on which a daemon is listening are always
treated as local.

For this usage, port numbers in \local@_interfaces\ are ignored. If either of
the items 0.0.0.0 or @:@:0 are encountered, Exim gets a complete list of
available interfaces from the operating system, and extracts the relevant
(that is, IPv4 or IPv6) addresses to use for checking.

Some systems set up large numbers of virtual interfaces in order to provide
many virtual web servers. In this situation, you may want to listen for
email on only a few of the available interfaces, but nevertheless treat all
interfaces as local when routing. You can do this by setting
\extra@_local@_interfaces\ to a list of IP addresses, possibly including the
`all' wildcard values. These addresses are recognized as local, but are not
used for listening. Consider this example:
.display asis
local_interfaces = <; 127.0.0.1 ; ::1 ; \
                      192.168.53.235 ; \
                      3ffe:2101:12:1:a00:20ff:fe86:a061

extra_local_interfaces = <; ::0 ; 0.0.0.0
.endd
The daemon listens on the loopback interfaces and just one IPv4 and one IPv6
address, but all available interface addresses are treated as local when
Exim is routing.

In some environments the local host name may be in an MX list, but with an IP 
address that is not assigned to any local interface. In other cases it may be 
desirable to treat other host names as if they referred to the local host. Both
these cases can be handled by setting the \hosts@_treat@_as@_local\ option.
This contains host names rather than IP addresses. When a host is referenced
during routing, either via an MX record or directly, it is treated as the local
host if its name matches \hosts@_treat@_as@_local\, or if any of its IP
addresses match \local@_interfaces\ or \extra@_local@_interfaces\.


.section Delivering to a remote host
Delivery to a remote host is handled by the smtp transport. By default, it
allows the system's TCP/IP functions to choose which interface to use (if
there is more than one) when connecting to a remote host. However, the
\interface\ option can be set to specify which interface is used. See the
description of the smtp transport in chapter ~~CHAPsmtptrans for more details.





.
.
.
.
. ============================================================================
.chapter Main configuration
.set runningfoot "main configuration"
.rset CHAPmainconfig "~~chapter"
.index configuration file||main section
.index main configuration
The first part of the run time configuration file contains three types of item:
.numberpars $.
Macro definitions: These lines start with an upper case letter. See section
~~SECTmacrodefs for details of macro processing.
.nextp
Named list definitions: These lines start with one of the words `domainlist',
`hostlist', `addresslist', or `localpartlist'. Their use is described in
section ~~SECTnamedlists.
.nextp
Main configuration settings: Each setting occupies one line of the file
(with possible continuations). If any setting is preceded by the word
`hide', the \-bP-\ command line option displays its value to admin users only.
See section ~~SECTcos for a description of the syntax of these option settings.
.endp
This chapter specifies all the main configuration options, along with their
types and default values. For ease of finding a particular option, they appear
in alphabetical order in section ~~SECTalomo below. However, because there are
now so many options, they are first listed briefly in functional groups, as an
aid to finding the name of the option you are looking for.
Some options are listed in more than one group.

.set savedisplayflowcheck ~~displayflowcheck
.set displayflowcheck 0

.section Miscellaneous
.display flow rm
.tabs 31
\bi@_command\                           $t$rm{to run for \-bi-\ command line option}
\keep@_malformed\                       $t$rm{for broken files -- should not happen}
\localhost@_number\                     $t$rm{for unique message ids in clusters}
\message@_body@_visible\                $t$rm{how much to show in \$message@_body$\}
\print@_topbitchars\                    $t$rm{top-bit characters are printing}
\timezone\                              $t$rm{force time zone}
.endd

.section Exim parameters
.display flow rm
.tabs 31
\exim@_group\                           $t$rm{override compiled-in value}
\exim@_path\                            $t$rm{override compiled-in value}
\exim@_user\                            $t$rm{override compiled-in value}
\primary@_hostname\                     $t$rm{default from \*uname()*\}
\split@_spool@_directory\               $t$rm{use multiple directories}
\spool@_directory\                      $t$rm{override compiled-in value}
.endd

.section Privilege controls
.display flow rm
.tabs 31
\admin@_groups\                         $t$rm{groups that are Exim admin users}
\deliver@_drop@_privilege\              $t$rm{drop root for delivery processes}
\local@_from@_check\                    $t$rm{insert ::Sender:: if necessary}
\local@_from@_prefix\                   $t$rm{for testing ::From:: for local sender}
\local@_from@_suffix\                   $t$rm{for testing ::From:: for local sender}
\local@_sender@_retain\                 $t$rm{keep ::Sender:: from untrusted user}
\never@_users\                          $t$rm{do not run deliveries as these}
\prod@_requires@_admin\                 $t$rm{forced delivery requires admin user}
\queue@_list@_requires@_admin\          $t$rm{queue listing requires admin user}
\trusted@_groups\                       $t$rm{groups that are trusted}
\trusted@_users\                        $t$rm{users that are trusted}
.endd

.section Logging
.display flow rm
.tabs 31
\log@_file@_path\                       $t$rm{override compiled-in value}
\log@_selector\                         $t$rm{set/unset optional logging}
\log@_timezone\                         $t$rm{add timezone to log lines}
\message@_logs\                         $t$rm{create per-message logs}
\preserve@_message@_logs\               $t$rm{in another directory after message completion}
\process@_log@_path\                    $t$rm{for SIGUSR1 and \*exiwhat*\}
\syslog@_duplication\                   $t$rm{controls duplicate log lines on syslog }
\syslog@_facility\                      $t$rm{set syslog `facility' field}
\syslog@_processname\                   $t$rm{set syslog `ident' field}
\syslog@_timestamp\                     $t$rm{timestamp syslog lines}
.newline
.em
\write@_rejectlog\                      $t$rm{control use of message log}
.newline
.nem
.endd

.section Frozen messages
.display flow rm
.tabs 31
\auto@_thaw\                            $t$rm{sets time for retrying frozen messages}
\freeze@_tell\                          $t$rm{send message when freezing}
\move@_frozen@_messages\                $t$rm{to another directory}
\timeout@_frozen@_after\                $t$rm{keep frozen messages only so long}
.endd

.section Data lookups
.display flow rm
.tabs 31
\ldap@_default@_servers\                $t$rm{used if no server in query}
\ldap@_version\                         $t$rm{set protocol version}
\lookup@_open@_max\                     $t$rm{lookup files held open}
\mysql@_servers\                        $t$rm{as it says}
\oracle@_servers\                       $t$rm{as it says}
\pgsql@_servers\                        $t$rm{as it says}
.endd

.section Message ids
.display flow rm
.tabs 31
\message@_id@_header@_domain\           $t$rm{used to build ::Message-ID:: header}
\message@_id@_header@_text\             $t$rm{ditto}
.endd

.section Embedded Perl Startup
.display flow rm
.tabs 31
\perl@_at@_start\                       $t$rm{always start the interpreter}
\perl@_startup\                         $t$rm{code to obey when starting Perl}
.endd

.section Daemon
.display flow rm
.tabs 31
\daemon@_smtp@_ports\                   $t$rm{default ports}
\extra@_local@_interfaces\              $t$rm{not necessarily listened on}
\local@_interfaces\                     $t$rm{on which to listen, with optional ports}
\pid@_file@_path\                       $t$rm{override compiled-in value}
\queue@_run@_max\                       $t$rm{maximum number of simultaneous queue runners}
.endd

.section Resource control
.display flow rm
.tabs 31
\check@_log@_inodes\                    $t$rm{before accepting a message}
\check@_log@_space\                     $t$rm{before accepting a message}
\check@_spool@_inodes\                  $t$rm{before accepting a message}
\check@_spool@_space\                   $t$rm{before accepting a message}
\deliver@_queue@_load@_max\             $t$rm{no queue deliveries if load high}
\queue@_only@_load\                     $t$rm{queue incoming if load high}
\queue@_run@_max\                       $t$rm{maximum number of simultaneous queue runners}
\remote@_max@_parallel\                 $t$rm{parallel SMTP delivery per message}
\smtp@_accept@_max\                     $t$rm{simultaneous incoming connections}
\smtp@_accept@_max@_nommail\            $t$rm{non-mail commands}
\smtp@_accept@_max@_nonmail@_hosts\     $t$rm{hosts to which the limit applies}
\smtp@_accept@_max@_per@_connection\    $t$rm{messages per connection}
\smtp@_accept@_max@_per@_host\          $t$rm{connections from one host}
\smtp@_accept@_queue\                   $t$rm{queue mail if more connections}
\smtp@_accept@_queue@_per@_connection\  $t$rm{queue if more messages per connection}
\smtp@_accept@_reserve\                 $t$rm{only reserve hosts if more connections}
\smtp@_check@_spool@_space\             $t$rm{from \\SIZE\\ on \\MAIL\\ command}
\smtp@_connect@_backlog\                $t$rm{passed to TCP/IP stack}
\smtp@_load@_reserve\                   $t$rm{SMTP from reserved hosts if load high}
\smtp@_reserve@_hosts\                  $t$rm{these are the reserve hosts}
.endd

.section Policy controls
.display flow rm
.tabs 31
\acl@_not@_smtp\                        $t$rm{set ACL for non-SMTP messages}
\acl@_smtp@_auth\                       $t$rm{set ACL for \\AUTH\\}
\acl@_smtp@_connect\                    $t$rm{set ACL for connection}
\acl@_smtp@_data\                       $t$rm{set ACL for \\DATA\\}
\acl@_smtp@_etrn\                       $t$rm{set ACL for \\ETRN\\}
\acl@_smtp@_expn\                       $t$rm{set ACL for \\EXPN\\}
\acl@_smtp@_helo\                       $t$rm{set ACL for \\EHLO\\ or \\HELO\\}
\acl@_smtp@_mail\                       $t$rm{set ACL for \\MAIL\\}
\acl@_smtp@_mailauth\                   $t$rm{set ACL for \\AUTH\\ on \\MAIL\\ command}
\acl@_smtp@_rcpt\                       $t$rm{set ACL for \\RCPT\\}
\acl@_smtp@_starttls\                   $t$rm{set ACL for \\STARTTLS\\}
\acl@_smtp@_vrfy\                       $t$rm{set ACL for \\VRFY\\}
\header@_maxsize\                       $t$rm{total size of message header}
\header@_line@_maxsize\                 $t$rm{individual header line limit}
\helo@_accept@_junk@_hosts\             $t$rm{allow syntactic junk from these hosts}
\helo@_allow@_chars\                    $t$rm{allow illegal chars in \\HELO\\ names}
\helo@_lookup@_domains\                 $t$rm{lookup hostname for these \\HELO\\ names}
\helo@_try@_verify@_hosts\              $t$rm{\\HELO\\ soft-checked for these hosts}
\helo@_verify@_hosts\                   $t$rm{\\HELO\\ hard-checked for these hosts}
\host@_lookup\                          $t$rm{host name looked up for these hosts}
\host@_lookup@_order\                   $t$rm{order of DNS and local name lookups}
\host@_reject@_connection\              $t$rm{reject connection from these hosts}
\hosts@_treat@_as@_local\               $t$rm{useful in some cluster configurations}
\local@_scan@_timeout\                  $t$rm{timeout for \*local@_scan()*\}
\message@_size@_limit\                  $t$rm{for all messages}
\percent@_hack@_domains\                $t$rm{recognize %-hack for these domains}
.endd

.section Callout cache
.display flow rm
.tabs 31
\callout@_domain@_negative@_expire\     $t$rm{timeout for negative domain cache item}
\callout@_domain@_positive@_expire\     $t$rm{timeout for positive domain cache item}
\callout@_negative@_expire\             $t$rm{timeout for negative address cache item}
\callout@_positive@_expire\             $t$rm{timeout for positive address cache item}
\callout@_random@_local@_part\          $t$rm{string to use for `random' testing}
.endd

.section TLS
.display flow rm
.tabs 31
\tls@_advertise@_hosts\                 $t$rm{advertise TLS to these hosts}
\tls@_certificate\                      $t$rm{location of server certificate}
.newline
.em
\tls@_crl\                              $t$rm{certificate revocation list}
.newline
.nem
\tls@_dhparam\                          $t$rm{DH parameters for server}
\tls@_privatekey\                       $t$rm{location of server private key}
\tls@_remember@_esmtp\                  $t$rm{don't reset after starting TLS}
.newline
.em
\tls@_require@_ciphers\                 $t$rm{specify acceptable cipers}
.newline
.nem
\tls@_try@_verify@_hosts\               $t$rm{try to verify client certificate}
\tls@_verify@_certificates\             $t$rm{expected client certificates}
\tls@_verify@_hosts\                    $t$rm{insist on client certificate verify}
.endd

.section Local user handling 
.display flow rm
.tabs 31
\finduser@_retries\                     $t$rm{useful in NIS environments}
\gecos@_name\                           $t$rm{used when creating ::Sender::}
\gecos@_pattern\                        $t$rm{ditto}
\max@_username@_length\                 $t$rm{for systems that truncate}
\unknown@_login\                        $t$rm{used when no login name found}
\unknown@_username\                     $t$rm{ditto}
\uucp@_from@_pattern\                   $t$rm{for recognizing `From ' lines}
\uucp@_from@_sender\                    $t$rm{ditto}
.endd

.section All incoming messages (SMTP and non-SMTP)
.display flow rm
.tabs 31
\header@_maxsize\                       $t$rm{total size of message header}
\header@_line@_maxsize\                 $t$rm{individual header line limit}
\message@_size@_limit\                  $t$rm{applies to all messages}
\percent@_hack@_domains\                $t$rm{recognize %-hack for these domains}
\received@_header@_text\                $t$rm{expanded to make ::Received::}
\received@_headers@_max\                $t$rm{for mail loop detection}
\recipients@_max\                       $t$rm{limit per message}
\recipients@_max@_reject\               $t$rm{permanently reject excess}
.endd


.section Non-SMTP incoming messages
.display rm
.tabs 31
\receive@_timeout\                      $t$rm{for non-SMTP messages}
.endd



.section Incoming SMTP messages
See also the \*Policy controls*\ section above.
.display flow rm
.tabs 31
\host@_lookup\                          $t$rm{host name looked up for these hosts}
\host@_lookup@_order\                   $t$rm{order of DNS and local name lookups}
\recipient@_unqualified@_hosts\         $t$rm{may send unqualified recipients}
\rfc1413@_hosts\                        $t$rm{make ident calls to these hosts}
\rfc1413@_query@_timeout\               $t$rm{zero disables ident calls}
\sender@_unqualified@_hosts\            $t$rm{may send unqualified senders}
\smtp@_accept@_keepalive\               $t$rm{some TCP/IP magic}
\smtp@_accept@_max\                     $t$rm{simultaneous incoming connections}
\smtp@_accept@_max@_nommail\            $t$rm{non-mail commands}
\smtp@_accept@_max@_nonmail@_hosts\     $t$rm{hosts to which the limit applies}
\smtp@_accept@_max@_per@_connection\    $t$rm{messages per connection}
\smtp@_accept@_max@_per@_host\          $t$rm{connections from one host}
\smtp@_accept@_queue\                   $t$rm{queue mail if more connections}
\smtp@_accept@_queue@_per@_connection\  $t$rm{queue if more messages per connection}
\smtp@_accept@_reserve\                 $t$rm{only reserve hosts if more connections}
.newline
.em
\smtp@_active@_hostname\                $t$rm{host name to use in messages}
.newline
.nem
\smtp@_banner\                          $t$rm{text for welcome banner}
\smtp@_check@_spool@_space\             $t$rm{from \\SIZE\\ on \\MAIL\\ command}
\smtp@_connect@_backlog\                $t$rm{passed to TCP/IP stack}
\smtp@_enforce@_sync\                   $t$rm{of SMTP command/responses}
\smtp@_etrn@_command\                   $t$rm{what to run for \\ETRN\\}
\smtp@_etrn@_serialize\                 $t$rm{only one at once}
\smtp@_load@_reserve\                   $t$rm{only reserve hosts if this load}
\smtp@_max@_unknown@_commands\          $t$rm{before dropping connection}
\smtp@_ratelimit@_hosts\                $t$rm{apply ratelimiting to these hosts}
\smtp@_ratelimit@_mail\                 $t$rm{ratelimit for \\MAIL\\ commands}
\smtp@_ratelimit@_rcpt\                 $t$rm{ratelimit for \\RCPT\\ commands}
\smtp@_receive@_timeout\                $t$rm{per command or data line}
\smtp@_reserve@_hosts\                  $t$rm{these are the reserve hosts}
\smtp@_return@_error@_details\          $t$rm{give detail on rejections}
.endd

.section SMTP extensions
.display flow rm
.tabs 31
\accept@_8bitmime\                      $t$rm{advertise \\8BITMIME\\}
\auth@_advertise@_hosts\                $t$rm{advertise \\AUTH\\ to these hosts}
\ignore@_fromline@_hosts\               $t$rm{allow `From ' from these hosts}
\ignore@_fromline@_local\               $t$rm{allow `From ' from local SMTP}
\pipelining@_advertise@_hosts\          $t$rm{advertise pipelining to these hosts}
\tls@_advertise@_hosts\                 $t$rm{advertise TLS to these hosts}
.endd

.section Processing messages
.display flow rm
.tabs 31
\allow@_domain@_literals\               $t$rm{recognize domain literal syntax}
\allow@_mx@_to@_ip\                     $t$rm{allow MX to point to IP address}
\allow@_utf8@_domains\                  $t$rm{in addresses}
\delivery@_date@_remove\                $t$rm{from incoming messages}
\envelope@_to@_remote\                  $t$rm{from incoming messages}
\extract@_addresses@_remove@_arguments\ $t$rm{affects \-t-\ processing}
\headers@_charset\                      $t$rm{default for translations}
\qualify@_domain\                       $t$rm{default for senders}
\qualify@_recipient\                    $t$rm{default for recipients}
\return@_path@_remove\                  $t$rm{from incoming messages}
\strip@_excess@_angle@_brackets\        $t$rm{in addresses}
\strip@_trailing@_dot\                  $t$rm{at end of addresses}
\untrusted@_set@_sender\                $t$rm{untrusted can set envelope sender}
.endd

.section System filter
.display flow rm
.tabs 31
\system@_filter\                        $t$rm{locate system filter}
\system@_filter@_directory@_transport\  $t$rm{transport for delivery to a directory}
\system@_filter@_file@_transport\       $t$rm{transport for delivery to a file}
\system@_filter@_group\                 $t$rm{group for filter running}
\system@_filter@_pipe@_transport\       $t$rm{transport for delivery to a pipe}
\system@_filter@_reply@_transport\      $t$rm{transport for autoreply delivery}
\system@_filter@_user\                  $t$rm{user for filter running}
.endd

.section Routing and delivery
.display flow rm
.tabs 31
\dns@_again@_means@_nonexist\           $t$rm{for broken domains}
\dns@_check@_names@_pattern\            $t$rm{pre-DNS syntax check}
\dns@_ipv4@_lookup\                     $t$rm{only v4 lookup for these domains}
\dns@_retrans\                          $t$rm{parameter for resolver}
\dns@_retry\                            $t$rm{parameter for resolver}
\hold@_domains\                         $t$rm{hold delivery for these domains}
\local@_interfaces\                     $t$rm{for routing checks}
\queue@_domains\                        $t$rm{no immediate delivery for these}
\queue@_only\                           $t$rm{no immediate delivery at all}
\queue@_only@_file\                     $t$rm{no immediate deliveryif file exists}
\queue@_only@_load\                     $t$rm{no immediate delivery if load is high}
\queue@_only@_override\                 $t$rm{allow command line to override}
\queue@_run@_in@_order\                 $t$rm{order of arrival}
\queue@_run@_max\                       $t$rm{of simultaneous queue runners}
\queue@_smtp@_domains\                  $t$rm{no immediate SMTP delivery for these}
\remote@_max@_parallel\                 $t$rm{parallel SMTP delivery (per message, not overall)}
\remote@_sort@_domains\                 $t$rm{order of remote deliveries}
\retry@_data@_expire\                   $t$rm{timeout for retry data}
\retry@_interval@_max\                  $t$rm{safety net for retry rules}
.endd

.section Bounce and warning messages
.display flow rm
.tabs 31
\bounce@_message@_file\                 $t$rm{content of bounce}
\bounce@_message@_text\                 $t$rm{content of bounce}
\bounce@_return@_body\                  $t$rm{include body if returning message}
\bounce@_return@_message\               $t$rm{include original message in bounce}
\bounce@_return@_size@_limit\           $t$rm{limit on returned message}
\bounce@_sender@_authentication\        $t$rm{send authenticated sender with bounce}
\errors@_copy\                          $t$rm{copy bounce messages}
\errors@_reply@_to\                     $t$rm{::Reply-to:: in bounces}
\delay@_warning\                        $t$rm{time schedule}
\delay@_warning@_condition\             $t$rm{condition for warning messages}
\ignore@_bounce@_errors@_after\         $t$rm{discard undeliverable bounces}
\warn@_message@_file\                   $t$rm{content of warning message}
.endd

.set displayflowcheck ~~savedisplayflowcheck

.section Alphabetical list of main options
.rset SECTalomo "~~chapter.~~section"
.if ~~sgcal
Those options that undergo string expansion before use are marked with $**$.
.fi

.startconf

.index \\8BITMIME\\
.index 8-bit characters
.conf accept@_8bitmime boolean false
This option causes Exim to send \\8BITMIME\\ in its response to an SMTP
\\EHLO\\ command, and to accept the \\BODY=\\ parameter on \\MAIL\\ commands.
However, though Exim is 8-bit clean, it is not a protocol converter, and it
takes no steps to do anything special with messages received by this route.
Consequently, this option is turned off by default.

.index ~~ACL||for non-SMTP messages
.index non-SMTP messages, ACL for
.conf acl@_not@_smtp string$**$ unset
This option defines the ACL that is run when a non-SMTP message is on the point 
of being accepted. See chapter ~~CHAPACL for further details.

.index ~~ACL||on SMTP connection 
.conf acl@_smtp@_connect string$**$ unset
This option defines the ACL that is run when an SMTP connection is received.
See chapter ~~CHAPACL for further details.

.index ~~ACL||setting up for SMTP commands
.index \\AUTH\\||ACL for
.conf acl@_smtp@_auth string$**$ unset
This option defines the ACL that is run when an SMTP \\AUTH\\ command is
received. See chapter ~~CHAPACL for further details.

.index \\DATA\\, ACL for
.conf acl@_smtp@_data string$**$ unset
This option defines the ACL that is run after an SMTP \\DATA\\ command has been
processed and the message itself has been received, but before the final
acknowledgement is sent. See chapter ~~CHAPACL for further details.

.index \\ETRN\\||ACL for
.conf acl@_smtp@_etrn string$**$ unset
This option defines the ACL that is run when an SMTP \\ETRN\\ command is
received. See chapter ~~CHAPACL for further details.

.index \\EXPN\\||ACL for
.conf acl@_smtp@_expn string$**$ unset
This option defines the ACL that is run when an SMTP \\EXPN\\ command is
received. See chapter ~~CHAPACL for further details.

.index \\EHLO\\||ACL for
.index \\HELO\\||ACL for
.conf acl@_smtp@_helo string$**$ unset
This option defines the ACL that is run when an SMTP \\EHLO\\ or \\HELO\\
command is received. See chapter ~~CHAPACL for further details.

.index \\MAIL\\||ACL for
.conf acl@_smtp@_mail string$**$ unset
This option defines the ACL that is run when an SMTP \\MAIL\\ command is
received. See chapter ~~CHAPACL for further details.

.index \\AUTH\\||on \\MAIL\\ command
.conf acl@_smtp@_mailauth string$**$ unset
This option defines the ACL that is run when there is an \\AUTH\\ parameter on 
a \\MAIL\\ command. See chapter ~~CHAPACL for details of ACLs, and chapter
~~CHAPSMTPAUTH for details of authentication.

.index \\RCPT\\||ACL for
.conf acl@_smtp@_rcpt string$**$ unset
This option defines the ACL that is run when an SMTP \\RCPT\\ command is
received. See chapter ~~CHAPACL for further details.

.index \\STARTTLS\\, ACL for
.conf acl@_smtp@_starttls string$**$ unset
This option defines the ACL that is run when an SMTP \\STARTTLS\\ command is
received. See chapter ~~CHAPACL for further details.

.index \\VRFY\\||ACL for
.conf acl@_smtp@_vrfy string$**$ unset
This option defines the ACL that is run when an SMTP \\VRFY\\ command is
received. See chapter ~~CHAPACL for further details.

.conf admin@_groups "string list" unset
.index admin user
If the current group or any of the supplementary groups of the caller is in
this colon-separated list, the caller has admin privileges. If all your system
programmers are in a specific group, for example, you can give them all Exim
admin privileges by putting that group in \admin@_groups\. However, this does
not permit them to read Exim's spool files (whose group owner is the Exim gid).
To permit this, you have to add individuals to the Exim group.

.conf allow@_domain@_literals boolean false
.index domain literal
If this option is set, the RFC 2822 domain literal format is permitted in
email addresses. The option is not set by default, because the domain literal
format is not normally required these days, and few people know about it. It
has, however, been exploited by mail abusers.

Unfortunately, it seems that some DNS black list maintainers are using this 
format to report black listing to postmasters. If you want to accept messages 
addressed to your hosts by IP address, you need to set 
\allow@_domain@_literals\ true, and also to add \"@@[]"\ to the list of local 
domains (defined in the named domain list \local@_domains\ in the default 
configuration). This `magic string' matches the domain literal form of all the 
local host's IP addresses.

.conf allow@_mx@_to@_ip boolean false
.index MX record||pointing to IP address
It appears that more and more DNS zone administrators are breaking the rules
and putting domain names that look like IP addresses on the right hand side of
MX records. Exim follows the rules and rejects this, giving an error message
that explains the mis-configuration. However, some other MTAs support this
practice, so to avoid `Why can't Exim do this?' complaints, \allow@_mx@_to@_ip\
exists, in order to enable this heinous activity. It is not recommended, except
when you have no other choice.

.index domain||UTF-8 characters in
.index UTF-8||in domain name
.conf allow@_utf8@_domains boolean false
Lots of discussion is going on about internationalized domain names. One
camp is strongly in favour of just using UTF-8 characters, and it seems
that at least two other MTAs permit this. This option allows Exim users to 
experiment if they wish.

If it is set true, Exim's domain parsing function allows valid
UTF-8 multicharacters to appear in domain name components, in addition to
letters, digits, and hyphens. However, just setting this option is not
enough; if you want to look up these domain names in the DNS, you must also
adjust the value of \dns@_check@_names@_pattern\ to match the extended form. A
suitable setting is:
.display asis
dns_check_names_pattern = (?i)^(?>(?(1)\.|())[a-z0-9\xc0-\xff]\
  (?>[-a-z0-9\x80-\xff]*[a-z0-9\x80-\xbf])?)+$
.endd
Alternatively, you can just disable this feature by setting
.display asis
dns_check_names_pattern =
.endd
That is, set the option to an empty string so that no check is done.

.conf auth@_advertise@_hosts "host list$**$" $*$
.index authentication||advertising
.index \\AUTH\\||advertising
If any server authentication mechanisms are configured, Exim advertises them in
response to an \\EHLO\\ command only if the calling host matches this list.
Otherwise, Exim does not advertise \\AUTH\\.
Exim does not accept \\AUTH\\ commands from clients to which it has not 
advertised the availability of \\AUTH\\. The advertising of individual 
authentication mechanisms can be controlled by the use of the
\server@_advertise@_condition\ generic authenticator option on the individual 
authenticators. See chapter ~~CHAPSMTPAUTH for further details.

Certain mail clients (for example, Netscape) require the user to provide a name
and password for authentication if \\AUTH\\ is advertised, even though it may
not be needed (the host may accept messages from hosts on its local LAN without
authentication, for example). The \auth@_advertise@_hosts\ option can be used
to make these clients more friendly by excluding them from the set of hosts to
which Exim advertises \\AUTH\\.

.index \\AUTH\\||advertising when encrypted
If you want to advertise the availability of \\AUTH\\ only when the connection
is encrypted using TLS, you can make use of the fact that the value of this
option is expanded, with a setting like this:
.display asis
auth_advertise_hosts = ${if eq{$tls_cipher}{}{}{*}}
.endd
If \$tls@_cipher$\ is empty, the session is not encrypted, and the result of 
the expansion is empty, thus matching no hosts. Otherwise, the result of the 
expansion is $*$, which matches all hosts.

.conf auto@_thaw time 0s
.index thawing messages
.index unfreezing messages
If this option is set to a time greater than zero, a queue runner will try a
new delivery attempt on any frozen message if this much time has passed since
it was frozen. This may result in the message being re-frozen if nothing has
changed since the last attempt. It is a way of saying `keep on trying, even
though there are big problems'. See also \timeout@_frozen@_after\ and
\ignore@_bounce@_errors@_after\.

.conf bi@_command string unset
.index \-bi-\ option
This option supplies the name of a command that is run when Exim is called with
the \-bi-\ option (see chapter ~~CHAPcommandline). The string value is just the
command name, it is not a complete command line. If an argument is required, it
must come from the \-oA-\ command line option.

.conf bounce@_message@_file string unset
.index bounce message||customizing
.index customizing||bounce message
This option defines a template file containing paragraphs of text to be used
for constructing bounce messages.  Details of the file's contents are given in
chapter ~~CHAPemsgcust. See also \warn@_message@_file\.

.conf bounce@_message@_text string unset
When this option is set, its contents are included in the default bounce
message immediately after `This message was created automatically by mail
delivery software.' It is not used if \bounce@_message@_file\ is set.

.index bounce message||including body
.conf bounce@_return@_body boolean true
This option controls whether the body of an incoming message is included in a 
bounce message when \bounce@_return@_message\ is true. If it is not set, only 
the message header is included.

.index bounce message||including original
.conf bounce@_return@_message boolean true
If this option is set false, the original message is not included in bounce
messages generated by Exim. See also \bounce@_return@_size@_limit\.

.conf bounce@_return@_size@_limit integer 100K
.index size||of bounce, limit
.index bounce message||size limit
.index limit||bounce message size
This option sets a limit in bytes on the size of messages that are returned to
senders as part of bounce messages when \bounce@_return@_message\ is true. The
limit should be less than the value of the global \message@_size@_limit\ and of
any \message@_size@_limit\ settings on transports, to allow for the bounce text
that Exim generates. If this option is set to zero there is no limit.

When the body of any message that is to be included in a bounce message is
greater than the limit, it is truncated, and a comment pointing this out is
added at the top. The actual cutoff may be greater than the value given, owing
to the use of buffering for transferring the message in chunks (typically 8K in
size). The idea is to save bandwidth on those undeliverable 15-megabyte
messages.

.index bounce message||sender authentication
.index authentication||bounce message
.index \\AUTH\\||on bounce message
.conf bounce@_sender@_authentication string unset
This option provides an authenticated sender address that is sent with any
bounce messages generated by Exim that are sent over an authenticated SMTP
connection. A typical setting might be:
.display asis
bounce_sender_authentication = mailer-daemon@my.domain.example
.endd
which would cause bounce messages to be sent using the SMTP command:
.display asis
MAIL FROM:<> AUTH=mailer-daemon@my.domain.example
.endd
The value of \bounce@_sender@_authentication\ must always be a complete email
address.

.index caching||callout, timeouts
.index callout||caching timeouts
.conf callout@_domain@_negative@_expire time 3h
This option specifies the expiry time for negative callout cache data for a
domain. See section ~~SECTcallver for details of callout verification, and
section ~~SECTcallvercache for details of the caching.

.conf callout@_domain@_positive@_expire time 7d
This option specifies the expiry time for positive callout cache data for a
domain. See section ~~SECTcallver for details of callout verification, and
section ~~SECTcallvercache for details of the caching.

.conf callout@_negative@_expire time 2h
This option specifies the expiry time for negative callout cache data for an
address. See section ~~SECTcallver for details of callout verification, and
section ~~SECTcallvercache for details of the caching.

.conf callout@_positive@_expire time 24h
This option specifies the expiry time for positive callout cache data for an
address. See section ~~SECTcallver for details of callout verification, and
section ~~SECTcallvercache for details of the caching.

.conf callout@_random@_local@_part string$**$ "see below"
This option defines the `random' local part that can be used as part of callout 
verification. The default value is
.display asis
$primary_host_name-$tod_epoch-testing
.endd
See section ~~CALLaddparcall for details of how this value is used.

.conf check@_log@_inodes integer 0
See \check@_spool@_space\ below.

.conf check@_log@_space integer 0
See \check@_spool@_space\ below.

.conf check@_spool@_inodes integer 0
See \check@_spool@_space\ below.

.conf check@_spool@_space integer 0
.index checking disk space
.index disk space, checking
.index spool directory||checking space
The four \check@_...\ options allow for checking of disk resources before a
message is accepted. \check@_spool@_space\ and \check@_spool@_inodes\ check the
spool partition if either value is greater than zero, for example:
.display asis
check_spool_space = 10M
check_spool_inodes = 100
.endd
The spool partition is the one which contains the directory defined by
\\SPOOL@_DIRECTORY\\ in \(Local/Makefile)\. It is used for holding messages in
transit.

\check@_log@_space\ and \check@_log@_inodes\  check the partition in which log
files are written if either is greater than zero. These should be set only if
\log@_file@_path\ and \spool@_directory\ refer to different partitions.

If there is less space or fewer inodes than requested, Exim refuses to accept
incoming mail. In the case of SMTP input this is done by giving a 452 temporary
error response to the \\MAIL\\ command. If ESMTP is in use and there was a
\\SIZE\\ parameter on the \\MAIL\\ command, its value is added to the
\check@_spool@_space\ value, and the check is performed even if
\check@_spool@_space\ is zero, unless \no@_smtp@_check@_spool@_space\ is set.

The values for \check@_spool@_space\ and \check@_log@_space\ are held as a
number of kilobytes. If a non-multiple of 1024 is specified, it is rounded up.

For non-SMTP input and for batched SMTP input, the test is done at start-up; on
failure a message is written to stderr and Exim exits with a non-zero code, as
it obviously cannot send an error message of any kind.

.index port||for daemon
.index TCP/IP||setting listening ports
.conf daemon@_smtp@_ports string "$tt{smtp}"
This option specifies one or more default SMTP ports on which the Exim daemon
listens. See chapter ~~CHAPinterfaces for details of how it is used. For 
backward compatibility, \daemon@_smtp@_port\ (singular) is a synonym.

.conf delay@_warning "time list" 24h
.index warning of delay
.index delay warning, specifying
When a message is delayed, Exim sends a warning message to the sender at
intervals specified by this option. If it is set to a zero, no warnings are
sent. The data is a colon-separated list of times after which to send warning
messages. Up to 10 times may be given. If a message has been on the queue for
longer than the last time, the last interval between the times is used to
compute subsequent warning times. For example, with
.display asis
delay_warning = 4h:8h:24h
.endd
the first message is sent after 4 hours, the second after 8 hours, and
the third one after 24 hours. After that, messages are sent every 16 hours, 
because that is the interval between the last two times on the list. If you set 
just one time, it specifies the repeat interval. For example, with:
.display asis
delay_warning = 6h
.endd
messages are repeated every six hours. To stop warnings after a given time, set
a very large time at the end of the list. For example:
.display asis
delay_warning = 2h:12h:99d
.endd

.conf delay@_warning@_condition string$**$ "see below"
The string is expanded at the time a warning message might be sent. If all the
deferred addresses have the same domain, it is set in \$domain$\ during the
expansion. Otherwise \$domain$\ is empty. If the result of the expansion is a
forced failure, an empty string, or a string matching any of `0', `no' or
`false' (the comparison being done caselessly) then the warning message is not
sent. The default is
.display asis
delay_warning_condition = \
  ${if match{$h_precedence:}{(?i)bulk|list|junk}{no}{yes}}
.endd
which suppresses the sending of warnings about messages that have `bulk',
`list' or `junk' in a ::Precedence:: header.

.index unprivileged delivery
.index delivery||unprivileged
.conf deliver@_drop@_privilege boolean false
If this option is set true, Exim drops its root privilege at the start of a
delivery process, and runs as the Exim user throughout. This severely restricts
the kinds of local delivery that are possible, but is viable in certain types
of configuration. There is a discussion about the use of root privilege in
chapter ~~CHAPsecurity.

.index load average
.index queue runner||abandoning
.conf deliver@_queue@_load@_max fixed-point unset
When this option is set, a queue run is abandoned if the system load average
becomes greater than the value of the option. The option has no effect on
ancient operating systems on which Exim cannot determine the load average.
See also \queue@_only@_load\ and \smtp@_load@_reserve\.

.conf delivery@_date@_remove boolean true
.index ::Delivery-date:: header line
Exim's transports have an option for adding a ::Delivery-date:: header to a
message when it is delivered -- in exactly the same way as ::Return-path:: is
handled. ::Delivery-date:: records the actual time of delivery. Such headers
should not be present in incoming messages, and this option causes them to be
removed at the time the message is received, to avoid any problems that might
occur when a delivered message is subsequently sent on to some other recipient.

.index DNS||`try again' response, overriding
.conf dns@_again@_means@_nonexist "domain list$**$" unset
DNS lookups give a `try again' response for the DNS errors `non-authoritative
host not found' and `\\SERVERFAIL\\'. This can cause Exim to keep trying to
deliver a message, or to give repeated temporary errors to incoming mail.
Sometimes the effect is caused by a badly set up name server and may persist
for a long time. If a domain which exhibits this problem matches anything in
\dns__again__means__nonexist\, it is treated as if it did not exist. This
option should be used with care.
.em
You can make it apply to reverse lookups by a setting such as this:
.display asis
dns_again_means_nonexist = *.in-addr.arpa
.endd
.nem

.index DNS||pre-check of name syntax
.conf dns@_check@_names@_pattern string "see below"
When this option is set to a non-empty string, it causes Exim to check domain
names for illegal characters before handing them to the DNS resolver, because
some resolvers give temporary errors for malformed names. If a domain name
contains any illegal characters, a `not found' result is forced, and the
resolver is not called. The check is done by matching the domain name against a
regular expression, which is the value of this option. The default pattern is
.display asis
dns_check_names_pattern = \
  (?i)^(?>(?(1)\.|())[^\W_](?>[a-z0-9-]*[^\W_])?)+$
.endd
which permits only letters, digits, and hyphens in components, but they may not
start or end with a hyphen.
If you set \allow@_utf8@_domains\, you must modify this pattern, or set the 
option to an empty string.

.conf dns@_ipv4@_lookup "domain list$**$" unset
.index IPv6||DNS lookup for AAAA records
.index DNS||IPv6 lookup for AAAA records
When Exim is compiled with IPv6 support, it looks for IPv6 address records
(AAAA and, if configured, A6) as well as IPv4 address records when trying to
find IP addresses for hosts, unless the host's domain matches this list.

This is a fudge to help with name servers that give big delays or otherwise do
not work for the new IPv6 record types. If Exim is handed an IPv6 address
record as a result of an MX lookup, it always recognizes it, and may as a
result make an outgoing IPv6 connection. All this option does is to make Exim
look only for IPv4-style A records when it needs to find an IP address for a
host name. In due course, when the world's name servers have all been upgraded,
there should be no need for this option.

.conf dns@_retrans time 0s
.index DNS||resolver options
The options \dns@_retrans\ and \dns@_retry\ can be used to set the
retransmission and retry parameters for DNS lookups. Values of zero (the
defaults) leave the system default settings unchanged. The first value is the
time between retries, and the second is the number of retries. It isn't
totally clear exactly how these settings affect the total time a DNS lookup may
take. I haven't found any documentation about timeouts on DNS lookups; these
parameter values are available in the external resolver interface structure,
but nowhere does it seem to describe how they are used or what you might want
to set in them.

.conf dns@_retry integer 0
See \dns@_retrans\ above.

.conf drop@_cr boolean false
This is an obsolete option that is now a no-op. It used to affect the way Exim 
handled CR and LF characters in incoming messages. What happens now is 
described in section ~~SECTlineendings.

.conf envelope@_to@_remove boolean true
.index ::Envelope-to:: header line
Exim's transports have an option for adding an ::Envelope-to:: header to a
message when it is delivered -- in exactly the same way as ::Return-path:: is
handled. ::Envelope-to:: records the original recipient address from the
messages's envelope that caused the delivery to happen. Such headers should not
be present in incoming messages, and this option causes them to be removed at
the time the message is received, to avoid any problems that might occur when a
delivered message is subsequently sent on to some other recipient.

.conf errors@_copy "string list$**$" unset
.index bounce message||copy to other address
.index copy of bounce message
Setting this option causes Exim to send bcc copies of bounce messages that it
generates to other addresses. \**Note**\: this does not apply to bounce messages
coming from elsewhere. The value of the option is a colon-separated list of
items. Each item consists of a pattern, terminated by white space, followed by
a comma-separated list of email addresses. If a pattern contains spaces, it
must be enclosed in double quotes.

Each pattern is processed in the same way as a single item in an address list
(see section ~~SECTaddresslist). When a pattern matches the recipient of the
bounce message, the message is copied to the addresses on the list. The items
are scanned in order, and once a matching one is found, no further items are
examined. For example:
.display asis
errors_copy = spqr@mydomain   postmaster@mydomain.example :\
              rqps@mydomain   hostmaster@mydomain.example,\
                              postmaster@mydomain.example
.endd
The address list is expanded before use. The expansion variables
\$local@_part$\ and \$domain$\ are set from the original recipient of the error
message, and if there was any wildcard matching in the pattern, the expansion
.index numerical variables (\$1$\, \$2$\, etc)||in \errors@_copy\        
variables \$0$\, \$1$\, etc. are set in the normal way.

.conf errors@_reply@_to string unset
.index bounce message||::Reply-to:: in
Exim's bounce and delivery warning messages contain the header line
.display
From: Mail Delivery System @<Mailer-Daemon@@<<qualify-domain>>@>
.endd
where <<qualify-domain>> is the value of the \qualify@_domain\ option. 
Experience shows that people reply to bounce messages. If the
\errors@_reply@_to\ option is set, a ::Reply-To:: header is added to bounce and
warning messages. For example:
.display asis
errors_reply_to = postmaster@my.domain.example
.endd
The value of the option is not expanded. It must specify a valid RFC 2822
address.

.conf exim@_group string "compile-time configured"
.index gid (group id)||Exim's own
.index Exim group
This option changes the gid under which Exim runs when it gives up root
privilege. The default value is compiled into the binary. The value of this
option is used only when \exim@_user\ is also set. Unless it consists entirely
of digits, the string is looked up using \*getgrnam()*\, and failure causes a
configuration error. See chapter ~~CHAPsecurity for a discussion of security
issues.

.conf exim@_path string "see below"
.index Exim binary, path name
This option specifies the path name of the Exim binary, which is used when Exim
needs to re-exec itself. The default is set up to point to the file \*exim*\ in
the directory configured at compile time by the \\BIN@_DIRECTORY\\ setting. It
is necessary to change \exim@_path\ if, exceptionally, Exim is run from some
other place.
\**Warning**\: Do not use a macro to define the value of this option, because 
you will break those Exim utilities that scan the configuration file to find 
where the binary is. (They then use the \-bP-\ option to extract option 
settings such as the value of \spool@_directory\.)

.conf exim@_user string "compile-time configured"
.index uid (user id)||Exim's own
.index Exim user
This option changes the uid under which Exim runs when it gives up root
privilege. The default value is compiled into the binary. Ownership of the run
time configuration file and the use of the \-C-\ and \-D-\ command line options
is checked against the values in the binary, not what is set here.

Unless it consists entirely of digits, the string is looked up using
\*getpwnam()*\, and failure causes a configuration error. If \exim@_group\ is
not also supplied, the gid is taken from the result of \*getpwnam()*\ if it is
used. See chapter ~~CHAPsecurity for a discussion of security issues.

.conf extra@_local@_interfaces "string list" unset
.index 
This option defines network interfaces that are to be considered local when 
routing, but which are not used for listening by the daemon. See section 
~~SECTreclocipadd for details.

.conf extract@_addresses@_remove@_arguments boolean true
.index \-t-\ option
.index command line||addresses with \-t-\
.index Sendmail compatibility||\-t-\ option
According to some Sendmail documentation (Sun, IRIX, HP-UX), if any addresses
are present on the command line when the \-t-\ option is used to build an
envelope from a message's ::To::, ::Cc:: and ::Bcc:: headers, the command line
addresses are removed from the recipients list. This is also how Smail behaves.
However, other Sendmail documentation (the O'Reilly book) states that command
line addresses are added to those obtained from the header lines. When
\extract@_addresses@_remove@_arguments\ is true (the default), Exim subtracts
argument headers. If it is set false, Exim adds rather than removes argument
addresses.

.conf finduser@_retries integer 0
.index NIS, looking up users, retrying
On systems running NIS or other schemes in which user and group information is
distributed from a remote system, there can be times when \*getpwnam()*\ and
related functions fail, even when given valid data, because things time out.
Unfortunately these failures cannot be distinguished from genuine `not found'
errors. If \finduser@_retries\ is set greater than zero, Exim will try that
many extra times to find a user or a group, waiting for one second between
retries.

.conf freeze@_tell "string list, comma separated" unset
.index freezing messages||sending a message when freezing
On encountering certain errors, or when configured to do so in a system filter,
or in an ACL,
Exim freezes a message. This means that no further delivery attempts take place
until an administrator (or the \auto@_thaw\ feature) thaws the message. If
\freeze@_tell\ is set, Exim generates a warning message whenever it freezes
something, unless the message it is freezing is a 
locally-generated
bounce message. (Without this exception there is the possibility of looping.)
The warning message is sent to the addresses supplied as the comma-separated
value of this option. If several of the message's addresses cause freezing,
only a single message is sent. 
If the freezing was automatic, the reason(s) for freezing can be found in the
message log. If you configure freezing in a filter or ACL, you must arrange for 
any logging that you require.

.conf gecos@_name string$**$ unset
.index HP-UX
.index `gecos' field, parsing
Some operating systems, notably HP-UX, use the `gecos' field in the system
password file to hold other information in addition to users' real names. Exim
looks up this field for use when it is creating ::Sender:: or ::From:: headers.
If either \gecos@_pattern\ or \gecos@_name\ are unset, the contents of the
field are used unchanged, except that, if an ampersand is encountered, it is
replaced by the user's login name with the first character forced to
upper case, since this is a convention that is observed on many systems.

When these options are set, \gecos@_pattern\ is treated as a regular expression
that is to be applied to the field (again with & replaced by the login name),
and if it matches, \gecos@_name\ is expanded and used as the user's name.
.index numerical variables (\$1$\, \$2$\, etc)||in \gecos@_name\  
Numeric variables such as \$1$\, \$2$\, etc. can be used in the expansion to
pick up sub-fields that were matched by the pattern. In HP-UX, where the user's
name terminates at the first comma, the following can be used:
.display asis
gecos_pattern = ([^,]*)
gecos_name = $1
.endd

.conf gecos@_pattern string unset
See \gecos@_name\ above.

.conf headers@_charset string "see below"
This option sets a default character set for translating from encoded MIME
`words' in header lines, when referenced by an \$h@_xxx$\ expansion item. The
default is the value of \\HEADERS@_CHARSET\\ in \(Local/Makefile)\. The
ultimate default is ISO-8859-1. For more details see the description of header
insertions in section ~~SECTexpansionitems.


.conf header@_maxsize integer "see below"
.index header section||maximum size of
.index limit||size of message header section
This option controls the overall maximum size of a message's header
section. The default is the value of \\HEADER@_MAXSIZE\\ in
\(Local/Makefile)\; the default for that is 1M. Messages with larger header 
sections are rejected.

.conf header@_line@_maxsize integer 0
.index header lines||maximum size of 
.index limit||size of one header line
This option limits the length of any individual header line in a message, after
all the continuations have been joined together. Messages with individual
header lines that are longer than the limit are rejected. The default value of
zero means `no limit'.



.conf helo@_accept@_junk@_hosts "host list$**$" unset
.index \\HELO\\||accepting junk data
.index \\EHLO\\||accepting junk data
Exim checks the syntax of \\HELO\\ and \\EHLO\\ commands for incoming SMTP
mail, and gives an error response for invalid data. Unfortunately, there are
some SMTP clients that send syntactic junk. They can be accommodated by setting
this option. Note that this is a syntax check only. See \helo@_verify@_hosts\
if you want to do semantic checking.
See also \helo@_allow@_chars\ for a way of extending the permitted character 
set.

.conf helo@_allow@_chars string unset
.index \\HELO\\||underscores in
.index \\EHLO\\||underscores in
.index underscore in \\EHLO\\/\\HELO\\
This option can be set to a string of rogue characters that are permitted in
all \\EHLO\\ and \\HELO\\ names in addition to the standard letters, digits,
hyphens, and dots. If you really must allow underscores, you can set
.display asis
helo_allow_chars = _
.endd
Note that the value is one string, not a list.

.conf helo@_lookup@_domains "domain list$**$" "$tt{@@:@@[]}"
.index \\HELO\\||forcing reverse lookup
.index \\EHLO\\||forcing reverse lookup
If the domain given by a client in a \\HELO\\ or \\EHLO\\ command matches this
list, a reverse lookup is done in order to establish the host's true name. The
default forces a lookup if the client host gives the server's name or any of
its IP addresses (in brackets), something that broken clients have been seen to
do.

.conf helo@_try@_verify@_hosts "host list$**$" unset
.index \\HELO\\||verifying, optional
.index \\EHLO\\||verifying, optional
The RFCs mandate that a server must not reject a message because it doesn't
like the \\HELO\\ or \\EHLO\\ command. By default, Exim just checks the syntax
of these commands (see \helo__accept__junk__hosts\ and \helo@_allow@_chars\
above). However, some sites like to be stricter. If the calling host matches
\helo@_try@_verify@_hosts\, Exim checks that the host name given in the \\HELO\\
or \\EHLO\\ command either:
.numberpars $.
is an IP literal matching the calling address of the host (the RFCs
specifically allow this), or
.nextp
.index DNS||reverse lookup
.index reverse DNS lookup
matches the host name that Exim obtains by doing a reverse lookup of the
calling host address, or
.nextp
when looked up using \*gethostbyname()*\ (or \*getipnodebyname()*\ when
available) yields the calling host address.
.endp
However, the \\EHLO\\ or \\HELO\\ command is not rejected if any of the checks 
fail. Processing continues, but the result of the check is remembered, and can
be detected later in an ACL by the \"verify = helo"\ condition. If you want
verification failure to cause rejection of \\EHLO\\ or \\HELO\\, use
\helo@_verify@_hosts\ instead.


.conf helo@_verify@_hosts "host list$**$" unset
.index \\HELO\\||verifying, mandatory
.index \\EHLO\\||verifying, mandatory
For hosts that match this option, Exim checks the host name given in the
\\HELO\\ or \\EHLO\\ in the same way as for \helo@_try@_verify@_hosts\. If the
check fails, the \\HELO\\ or \\EHLO\\ command is rejected with a 550 error, and
entries are written to the main and reject logs. If a \\MAIL\\ command is
received before \\EHLO\\ or \\HELO\\, it is rejected with a 
503 
error.

.conf hold@_domains "domain list$**$" unset
.index domain||delaying delivery
.index delivery||delaying certain domains
This option allows mail for particular domains to be held on the queue
manually. The option is overridden if a message delivery is forced with the
\-M-\, \-qf-\, \-Rf-\ or \-Sf-\ options, and also while testing or verifying
addresses using \-bt-\ or \-bv-\. Otherwise, if a domain matches an item in
\hold@_domains\, no routing or delivery for that address is done, and it is
deferred every time the message is looked at.

This option is intended as a temporary operational measure for delaying the
delivery of mail while some problem is being sorted out, or some new
configuration tested. If you just want to delay the processing of some
domains until a queue run occurs, you should use \queue@_domains\ or
\queue@_smtp@_domains\, not \hold@_domains\.

A setting of \hold@_domains\ does not override Exim's code for removing
messages from the queue if they have been there longer than the longest retry
time in any retry rule. If you want to hold messages for longer than the normal
retry times, insert a dummy retry rule with a long retry time.

.conf host@_lookup "host list$**$" unset
.index host||name lookup, forcing
Exim does not look up the name of a calling host from its IP address unless it
is required to compare against some host list, or the host matches
\helo@_try@_verify@_hosts\ or \helo@_verify@_hosts\, or the host matches this
option (which normally contains IP addresses rather than host names). The
default configuration file contains
.display asis
host_lookup = *
.endd
which causes a lookup to happen for all hosts. If the expense of these lookups
is felt to be too great, the setting can be changed or removed.

After a successful reverse lookup, Exim does a forward lookup on the name it
has obtained, to verify that it yields the IP address that it started with. If
this check fails, Exim behaves as if the name lookup failed.

After any kind of failure, the host name (in \$sender@_host@_name$\) remains
unset, and \$host@_lookup@_failed$\ is set to the string `1'. See also
\dns@_again@_means@_nonexist\, \helo__lookup__domains\, and \"verify =
reverse@_host@_lookup"\ in ACLs.

.conf host@_lookup@_order "string list" $tt{bydns:byaddr}
This option specifies the order of different lookup methods when Exim is trying
to find a host name from an IP address. The default is to do a DNS lookup 
first, and then to try a local lookup (using \*gethostbyaddr()*\ or equivalent)
if that fails. You can change the order of these lookups, or omit one entirely,
if you want.

\**Warning**\: the `byaddr' method does not always yield aliases when there are
multiple PTR records in the DNS and the IP address is not listed in 
\(/etc/hosts)\. Different operating systems give different results in this
case. That is why the default tries a DNS lookup first.


.conf host@_reject@_connection "host list$**$" unset
.index host||rejecting connections from
If this option is set, incoming SMTP calls from the hosts listed are rejected
as soon as the connection is made. 
This option is obsolete, and retained only for backward compatibility, because
nowadays the ACL specified by \acl@_smtp@_connect\ can also reject incoming
connections immediately.

The ability to give an immediate rejection (either by this option or using an
ACL) is provided for use in unusual cases. Many hosts will just try again,
sometimes without much delay. Normally, it is better to use an ACL to reject
incoming messages at a later stage, such as after \\RCPT\\ commands. See
chapter ~~CHAPACL.

.conf hosts@_treat@_as@_local "domain list$**$" unset
.index local host||domains treated as
.index host||treated as local
If this option is set, any host names that match the domain list are treated as
if they were the local host when Exim is scanning host lists obtained from MX
records
or other sources. Note that the value of this option is a domain list, not a
host list, because it is always used to check host names, not IP addresses.

This option also applies when Exim is matching the special items
\"@@mx@_any"\, \"@@mx@_primary"\, and \"@@mx@_secondary"\ in a domain list (see
section ~~SECTdomainlist), and when checking the \hosts\ option in the \%smtp%\
transport for the local host (see the \allow@_localhost\ option in that
transport).
See also \local@_interfaces\, \extra@_local@_interfaces\, and chapter 
~~CHAPinterfaces, which contains a discussion about local network interfaces 
and recognising the local host.

.conf ignore@_bounce@_errors@_after time 10w
.index bounce message||discarding
.index discarding bounce message
This option affects the processing of bounce messages that cannot be delivered, 
that is, those that suffer a permanent delivery failure. (Bounce messages that 
suffer temporary delivery failures are of course retried in the usual way.)

After a permanent delivery failure, bounce messages are frozen,
because there is no sender to whom they can be returned. When a frozen bounce
message has been on the queue for more than the given time, it is unfrozen at
the next queue run, and a further delivery is attempted. If delivery fails
again, the bounce message is discarded. This makes it possible to keep failed
bounce messages around for a shorter time than the normal maximum retry time
for frozen messages. For example,
.display asis
ignore_bounce_errors_after = 12h
.endd
retries failed bounce message deliveries after 12 hours, discarding any further
failures. If the value of this option is set to a zero time period, bounce
failures are discarded immediately. Setting a very long time (as in the default
value) has the effect of disabling this option. For ways of automatically
dealing with other kinds of frozen message, see \auto@_thaw\ and
\timeout@_frozen@_after\.

.conf ignore@_fromline@_hosts "host list$**$" unset
.index `From' line
.index UUCP||`From' line
Some broken SMTP clients insist on sending a UUCP-like `From' line before the
headers of a message. By default this is treated as the start of the message's
body, which means that any following headers are not recognized as such. Exim
can be made to ignore it by setting \ignore@_fromline@_hosts\ to match those
hosts that insist on sending it. If the sender is actually a local process
rather than a remote host, and is using \-bs-\ to inject the messages,
\ignore__fromline__local\ must be set to achieve this effect.

.conf ignore@_fromline@_local boolean false
See \ignore@_fromline@_hosts\ above.

.conf keep@_malformed time 4d
This option specifies the length of time to keep messages whose spool files
have been corrupted in some way. This should, of course, never happen. At the
next attempt to deliver such a message, it gets removed. The incident is
logged.

.conf ldap@_default@_servers "string list" unset
.index LDAP||default servers
This option provides a list of LDAP servers which are tried in turn when an
LDAP query does not contain a server. See section ~~SECTforldaque for details
of LDAP queries. This option is available only when Exim has been built with
LDAP support.

.conf ldap@_version integer unset
.index LDAP||protocol version, forcing
This option can be used to force Exim to set a specific protocol version for
LDAP. If it option is unset, it is shown by the \-bP-\ command line option as
-1. When this is the case, the default is 3 if \\LDAP@_VERSION3\\ is defined in
the LDAP headers; otherwise it is 2. This option is available only when Exim
has been built with LDAP support.


.conf local@_from@_check boolean true
.index ::Sender:: header line||disabling addition of
.index ::From:: header line||disabling checking of
When a message is submitted locally (that is, not over a TCP/IP connection) by
an untrusted user, Exim removes any existing ::Sender:: header line, and checks
that the ::From:: header line matches the login of the calling user. You can
use \local@_from@_prefix\ and \local@_from@_suffix\ to permit affixes on the
local part. If the ::From:: header line does not match, Exim adds a ::Sender::
header with an address constructed from the calling user's login and the
default qualify domain.

If \local@_from@_check\ is set false, the ::From:: header check is disabled,
and no ::Sender:: header is ever added. If, in addition, you want to retain
::Sender:: header lines supplied by untrusted users, you must also set
\local@_sender@_retain\ to be true.

.index envelope sender
These options affect only the header lines in the message. The envelope sender
is still forced to be the login id at the qualify domain unless
\untrusted@_set@_sender\ permits the user to supply an envelope sender.
Section ~~SECTthesenhea has more details about ::Sender:: processing.


.conf local@_from@_prefix string unset
When Exim checks the ::From:: header line of locally submitted messages for
matching the login id (see \local@_from@_check\ above), it can be configured to
ignore certain prefixes and suffixes in the local part of the address. This is
done by setting \local@_from@_prefix\ and/or \local@_from@_suffix\ to
appropriate lists, in the same form as the \local@_part@_prefix\ and
\local@_part@_suffix\ router options (see chapter ~~CHAProutergeneric). For
example, if
.display asis
local_from_prefix = *-
.endd
is set, a ::From:: line containing
.display asis
From: anything-user@your.domain.example
.endd
will not cause a ::Sender:: header to be added if \*user@@your.domain.example*\
matches the actual sender address that is constructed from the login name and
qualify domain.

.conf local@_from@_suffix string unset
See \local@_from@_prefix\ above.

.conf local@_interfaces "string list" "see below"
This option controls which network interfaces are used by the daemon for 
listening; they are also used to identify the local host when routing. Chapter 
~~CHAPinterfaces contains a full description of this option and the related 
options \extra@_local@_interfaces\ and \hosts@_treat@_as@_local\. The default 
value for \local@_interfaces\ is
.display asis
local_interfaces = 0.0.0.0
.endd
when Exim is built without IPv6 support; otherwise it is
.display asis
local_interfaces = <; ::0 ; 0.0.0.0
.endd

.conf local@_scan@_timeout time 5m
.index timeout||for \*local@_scan()*\ function
.index \*local@_scan()*\ function||timeout
This timeout applies to the \*local@_scan()*\ function (see chapter
~~CHAPlocalscan). Zero means `no timeout'. If the timeout is exceeded, the
incoming message is rejected with a temporary error if it is an SMTP message.
For a non-SMTP message, the message is dropped and Exim ends with a non-zero
code. The incident is logged on the main and reject logs.


.conf local@_sender@_retain boolean false
.index ::Sender:: header line||retaining from local submission
When a message is submitted locally (that is, not over a TCP/IP connection) by
an untrusted user, Exim removes any existing ::Sender:: header line. If you
do not want this to happen, you must set \local@_sender@_retain\, and you must
also set \local@_from@_check\ to be false (Exim will complain if you do not).
Section ~~SECTthesenhea has more details about ::Sender:: processing.



.conf localhost@_number string$**$ unset
.index host||locally unique number for
.index message||ids, with multiple hosts
Exim's message ids are normally unique only within the local host. If
uniqueness among a set of hosts is required, each host must set a different
value for the \localhost@_number\ option. The string is expanded immediately
after reading the configuration file (so that a number can be computed from the
host name, for example) and the result of the expansion must be a number in the
range 0--16 (or 0--10 on operating systems with case-insensitive file systems).
This is available in subsequent string expansions via the variable
\$localhost@_number$\. When \localhost@_number is set\, the final two
characters of the message id, instead of just being a fractional part of the
time, are computed from the time and the local host number as described in
section ~~SECTmessiden.


.conf log@_file@_path "string list$**$" "set at compile time"
.index log||file path for
This option sets the path which is used to determine the names of Exim's log
files, or indicates that logging is to be to syslog, or both. It is expanded
when Exim is entered, so it can, for example, contain a reference to the host
name. If no specific path is set for the log files at compile or run time, they
are written in a sub-directory called \(log)\ in Exim's spool directory.
Chapter ~~CHAPlog contains further details about Exim's logging, and section
~~SECTwhelogwri describes how the contents of \log@_file@_path\ are used. If
this string is fixed at your installation (contains no expansion variables) it
is recommended that you do not set this option in the configuration file, but
instead supply the path using \\LOG@_FILE@_PATH\\ in \(Local/Makefile)\ so that
it is available to Exim for logging errors detected early on -- in particular,
failure to read the configuration file.

.conf log@_selector string unset
.index log||selectors
This option can be used to reduce or increase the number of things that Exim
writes to its log files. Its argument is made up of names preceded by plus or
minus characters. For example:
.display asis
log_selector = +arguments -retry_defer
.endd
A list of possible names and what they control is given in the chapter on
logging, in section ~~SECTlogselector.

.conf log@_timezone boolean false
.index log||timezone for entries
By default, the timestamps on log lines are in local time without the
timezone. This means that if your timezone changes twice a year, the timestamps
in log lines are ambiguous for an hour when the clocks go back. One way of
avoiding this problem is to set the timezone to UTC. An alternative is to set
\log@_timezone\ true. This turns on the addition of the timezone offset to
timestamps in log lines. Turning on this option can add quite a lot to the size
of log files because each line is extended by 6 characters. Note that the
\$tod@_log$\ variable contains the log timestamp without the zone, but there is
another variable called \$tod@_zone$\ that contains just the timezone offset.

.conf lookup@_open@_max integer 25
.index too many open files
.index open files, too many
.index file||too many open
.index lookup||maximum open files
.index limit||open files for lookups
This option limits the number of simultaneously open files for single-key
lookups that use regular files (that is, \%lsearch%\, \%dbm%\, and \%cdb%\). Exim
normally keeps these files open during routing, because often the same file is
required several times. If the limit is reached, Exim closes the least recently
used file. Note that if you are using the \*ndbm*\ library, it actually opens
two files for each logical DBM database, though it still counts as one for the
purposes of \lookup@_open@_max\. If you are getting `too many open files'
errors with NDBM, you need to reduce the value of \lookup@_open@_max\.

.conf max@_username@_length integer 0
.index length of login name
.index user name||maximum length
.index limit||user name length
Some operating systems are broken in that they truncate long arguments to
\*getpwnam()*\ to eight characters, instead of returning `no such user'. If
this option is set greater than zero, any attempt to call \*getpwnam()*\ with
an argument that is longer behaves as if \*getpwnam()*\ failed.


.conf message@_body@_visible integer 500
.index body of message||visible size
.index message||body, visible size
This option specifies how much of a message's body is to be included in the
\$message@_body$\ and \$message@_body@_end$\ expansion variables.

.conf message@_id@_header@_domain string$**$ unset
.index ::Message-ID:: header line
If this option is set, the string is expanded and used as the right hand side
(domain) of the ::Message-ID:: header that Exim creates if a
locally-originated incoming message does not have one. `Locally-originated'
means `not received over TCP/IP.'
Otherwise, the primary host name is used.
Only letters, digits, dot and hyphen are accepted; any other characters are
replaced by hyphens. If the expansion is forced to fail, or if the result is an
empty string, the option is ignored.

.conf message@_id@_header@_text string$**$ unset
If this variable is set, the string is expanded and used to augment the text of
the ::Message-id:: header that Exim creates if a
locally-originated
incoming message does not have one. The text of this header is required by RFC
2822 to take the form of an address. By default, Exim uses its internal message
id as the local part, and the primary host name as the domain. If this option
is set, it is expanded, and provided the expansion is not forced to fail, and
does not yield an empty string, the result is inserted into the header
immediately before the @@, separated from the internal message id by a dot. Any
characters that are illegal in an address are automatically converted into
hyphens. This means that variables such as \$tod@_log$\ can be used, because
the spaces and colons will become hyphens.

.conf message@_logs boolean true
.index message||log, disabling
.index log||message log, disabling
If this option is turned off, per-message log files are not created in the
\(msglog)\ spool sub-directory. This reduces the amount of disk I/O required by
Exim, by reducing the number of files involved in handling a message from a
minimum of four (header spool file, body spool file, delivery journal, and
per-message log) to three. The other major I/O activity is Exim's main log,
which is not affected by this option.

.conf message@_size@_limit string$**$ 50M
.index message||size limit
.index limit||message size
.index size||of message, limit
This option limits the maximum size of message that Exim will process. The
value is expanded for each incoming 
connection so, for example, it can be made to depend on the IP address of the
remote host for messages arriving via TCP/IP. \**Note**\: This limit cannot be
made to depend on a message's sender or any other properties of an individual
message, because it has to be advertised in the server's response to \\EHLO\\.
String expansion failure causes a temporary error. A value of zero means no
limit, but its use is not recommended. See also \bounce@_return@_size@_limit\.

Incoming SMTP messages are failed with a 552 error if the limit is
exceeded; locally-generated messages either get a stderr message or a delivery
failure message to the sender, depending on the \-oe-\ setting. Rejection of an
oversized message is logged in both the main and the reject logs. See also the
generic transport option \message@_size@_limit\, which limits the size of
message that an individual transport can process.

.conf move@_frozen@_messages boolean false
.index frozen messages||moving
This option, which is available only if Exim has been built with the setting
.display asis
SUPPORT_MOVE_FROZEN_MESSAGES=yes
.endd
in \(Local/Makefile)\, causes frozen messages and their message logs to be
moved from the \(input)\ and \(msglog)\ directories on the spool to \(Finput)\
and \(Fmsglog)\, respectively. There is currently no support in Exim or the
standard utilities for handling such moved messages, and they do not show up in
lists generated by \-bp-\ or by the Exim monitor.

.conf mysql@_servers "string list" unset
.index MySQL||server list
This option provides a list of MySQL servers and associated connection data, to
be used in conjunction with \%mysql%\ lookups (see section ~~SECTsql). The
option is available only if Exim has been built with MySQL support.

.conf never@_users "string list" unset
Local message deliveries are normally run in processes that are setuid to the
recipient, and remote deliveries are normally run under Exim's own uid and gid.
It is usually desirable to prevent any deliveries from running as root, as a
safety precaution.
 
When Exim is built, an option called \\FIXED@_NEVER@_USERS\\ can be set to a 
list of users that must not be used for local deliveries. This list is fixed in 
the binary and cannot be overridden by the configuration file. By default, it 
contains just the single user name `root'. The \never@_users\ runtime option 
can be used to add more users to the fixed list.

If a message is to be delivered as one of the users on the fixed list or the
\never@_users\ list, an error occurs, and delivery is deferred. A common
example is
.display
never@_users = root:daemon:bin
.endd
Including root is redundant if it is also on the fixed list, but it does no
harm.
This option overrides the \pipe@_as@_creator\ option of the \%pipe%\ transport
driver.

.conf oracle@_servers "string list" unset
.index Oracle||server list
This option provides a list of Oracle servers and associated connection data,
to be used in conjunction with \%oracle%\ lookups (see section ~~SECTsql). The
option is available only if Exim has been built with Oracle support.

.conf percent@_hack@_domains "domain list$**$" unset
.index `percent hack'
.index source routing||in email address
.index address||source-routed
The `percent hack' is the convention whereby a local part containing a percent
sign is re-interpreted as a new email address, with the percent replaced by @@.
This is sometimes called `source routing', though that term is also applied to
RFC 2822 addresses that begin with an @@ character. If this option is set, Exim
implements the percent facility for those domains listed, but no others. This
happens before an incoming SMTP address is tested against an ACL.

\**Warning**\: The `percent hack' has often been abused by people who are
trying to get round relaying restrictions. For this reason, it is best avoided
if at all possible. Unfortunately, a number of less security-conscious MTAs
implement it unconditionally. If you are running Exim on a gateway host, and
routing mail through to internal MTAs without processing the local parts, it is
a good idea to reject recipient addresses with percent characters in their
local parts. Exim's default configuration does this.

.conf perl@_at@_start boolean false
This option is available only when Exim is built with an embedded Perl
interpreter. See chapter ~~CHAPperl for details of its use.

.conf perl@_startup string unset
This option is available only when Exim is built with an embedded Perl
interpreter. See chapter ~~CHAPperl for details of its use.

.conf pgsql@_servers "string list" unset
.index PostgreSQL lookup type||server list
This option provides a list of PostgreSQL servers and associated connection
data, to be used in conjunction with \%pgsql%\ lookups (see section ~~SECTsql).
The option is available only if Exim has been built with PostgreSQL support.

.conf pid@_file@_path string$**$ "set at compile time"
.index daemon||pid file path
.index pid file, path for
This option sets the name of the file to which the Exim daemon writes its
process id. The string is expanded, so it can contain, for example, references
to the host name:
.display asis
pid_file_path = /var/log/$primary_hostname/exim.pid
.endd
If no path is set, the pid is written to the file \(exim-daemon.pid)\ in Exim's
spool directory.
The value set by the option can be overridden by the \-oP-\ command line 
option. A pid file is not written if a `non-standard' daemon is run by means of 
the \-oX-\ option, unless a path is explicitly supplied by \-oP-\.

.conf pipelining@_advertise@_hosts "host list$**$" $*$
.index \\PIPELINING\\||advertising, suppressing
This option can be used to suppress the advertisement of the SMTP
\\PIPELINING\\ extension to specific hosts. When \\PIPELINING\\ is not
advertised and \smtp@_enforce@_sync\ is true, an Exim server enforces strict
synchronization for each SMTP command and response.
.em
When \\PIPELINING\\ is advertised, Exim assumes that clients will use it; `out
of order' commands that are `expected' do not count as protocol errors (see 
\smtp@_max@_synprot@_errors\).
.nem

.conf preserve@_message@_logs boolean false
.index message logs, preserving
If this option is set, message log files are not deleted when messages are
completed. Instead, they are moved to a sub-directory of the spool directory
called \(msglog.OLD)\, where they remain available for statistical or debugging
purposes. This is a dangerous option to set on systems with any appreciable
volume of mail. Use with care!

.conf primary@_hostname string "see below"
.index name||of local host
.index host||name of local
.index local host||name of
.em
This specifies the name of the current host. It is used in the default \\EHLO\\
or \\HELO\\ command for outgoing SMTP messages (changeable via the \helo@_data\
option in the \%smtp%\ transport),
.nem
and as the default for \qualify@_domain\. If it is not set, Exim calls
\*uname()*\ to find it. If this fails, Exim panics and dies. If the name
returned by \*uname()*\ contains only one component, Exim passes it to
\*gethostbyname()*\ (or \*getipnodebyname()*\ when available) in order to
obtain the fully qualified version.

.em
The value of \$primary@_hostname$\ is also used by default in some SMTP
response messages from an Exim server. This can be changed dynamically by
setting \smtp@_active@_hostname\.
.nem

.conf print@_topbitchars boolean false
.index printing characters
.index 8-bit characters
By default, Exim considers only those characters whose codes lie in the range
32--126 to be printing characters. In a number of circumstances (for example,
when writing log entries) non-printing characters are converted into escape
sequences, primarily to avoid messing up the layout. If \print@_topbitchars\ is
set, code values of 128 and above are also considered to be printing
characters.

.conf process@_log@_path string unset
.index process log path
.index log||process log 
.index \*exiwhat*\
This option sets the name of the file to which an Exim process writes its
`process log' when sent a USR1 signal. This is used by the \*exiwhat*\ utility
script. If this option is unset, the file called \(exim-process.info)\ in
Exim's spool directory is used. The ability to specify the name explicitly can
be useful in environments where two different Exims are running, using
different spool directories.

.conf prod@_requires@_admin boolean true
.index \-M-\ option
.index \-R-\ option
.index \-q-\ option
The \-M-\, \-R-\, and \-q-\ command-line options require the caller to be an
admin user unless \prod@_requires@_admin\ is set false. See also
\queue@_list@_requires@_admin\.

.conf qualify@_domain string "see below"
.index domain||for qualifying addresses
.index address||qualification
This option specifies the domain name that is added to any sender addresses
that do not have a domain qualification. It also applies to recipient addresses
if \qualify@_recipient\ is not set. Such addresses are accepted by default only
for locally-generated messages. Messages from external sources must always
contain fully qualified addresses, unless the sending host matches
\sender@_unqualified@_hosts\ or \recipient@_unqualified@_hosts\ (as
appropriate), in which case incoming addresses are qualified with
\qualify@_domain\ or \qualify@_recipient\ as necessary. Internally, Exim always
works with fully qualified addresses.
If \qualify@_domain\ is not set, it defaults to the \primary@_hostname\ value.

.conf qualify@_recipient string "see below"
This specifies the domain name that is added to any recipient addresses that do
not have a domain qualification. Such addresses are accepted by default only
for locally-generated messages. Messages from external sources must always
contain fully qualified recipient addresses, unless the sending host matches
\recipient@_unqualified@_hosts\,
in which case incoming recipient addresses are qualified with
\qualify@_recipient\.
If \qualify@_recipient\ is not set, it defaults to the \qualify@_domain\ value.

.conf queue@_domains "domain list$**$" unset
.index domain||specifying non-immediate delivery
.index queueing incoming messages
.index message||queueing certain domains
This option lists domains for which immediate delivery is not required.
A delivery process is started whenever a message is received, but only those
domains that do not match are processed. All other deliveries wait until the
next queue run. See also \hold@_domains\ and \queue@_smtp@_domains\.

.conf queue@_list@_requires@_admin boolean true
.index \-bp-\ option
The \-bp-\ command-line option, which lists the messages that are on the queue,
requires the caller to be an admin user unless \queue__list__requires__admin\
is set false. See also \prod@_requires@_admin\.

.conf queue@_only boolean false
.index queueing incoming messages
.index message||queueing unconditionally
If \queue@_only\ is set, a delivery process is not automatically started
whenever a message is received. Instead, the message waits on the queue for the
next queue run. Even if \queue@_only\ is false, incoming messages may not get
delivered immediately when certain conditions (such as heavy load) occur.

The \-odq-\ command line has the same effect as \queue@_only\. The \-odb-\ and
\-odi-\ command line options override \queue@_only\ unless
\queue@_only@_override\ is set false. See also \queue@_only@_file\,
\queue@_only@_load\, and \smtp@_accept@_queue\.

.conf queue@_only@_file string unset
.index queueing incoming messages
.index message||queueing by file existence
This option can be set to a colon-separated list of absolute path names, each
one optionally preceded by `smtp'. When Exim is receiving a message,
it tests for the existence of each listed path using a call to \*stat()*\. For
each path that exists, the corresponding queuing option is set.
For paths with no prefix, \queue@_only\ is set; for paths prefixed by `smtp',
\queue@_smtp@_domains\ is set to match all domains. So, for example,
.display asis
queue_only_file = smtp/some/file
.endd
causes Exim to behave as if \queue@_smtp@_domains\ were set to `$*$' whenever
\(/some/file)\ exists.

.conf queue@_only@_load fixed-point unset
.index load average
.index queueing incoming messages
.index message||queueing by load
If the system load average is higher than this value, incoming messages from
all sources are queued, and no automatic deliveries are started. If this
happens during local or remote SMTP input, all subsequent messages on the same
connection are queued. Deliveries will subsequently be performed by queue
runner processes. This option has no effect on ancient operating systems on
which Exim cannot determine the load average. See also
\deliver@_queue@_load@_max\ and \smtp@_load@_reserve\.

.conf queue@_only@_override boolean true
.index queueing incoming messages
When this option is true, the \-od\*x*\-\ command line options override the
setting of \queue@_only\ or \queue@_only@_file\ in the configuration file. If
\queue@_only@_override\ is set false, the \-od\*x*\-\ options cannot be used to
override; they are accepted, but ignored.

.conf queue@_run@_in@_order boolean false
.index queue runner||processing messages in order
If this option is set, queue runs happen in order of message arrival instead of
in an arbitrary order. For this to happen, a complete list of the entire queue
must be set up before the deliveries start. When the queue is all in a single
directory (the default), this happens anyway, but if \split@_spool@_directory\
is set it does not -- for delivery in random order, the sub-directories are
processed one at a time (in random order), to avoid setting up one huge list.
Thus, setting \queue@_run@_in@_order\ with \split@_spool@_directory\ may
degrade performance when the queue is large. In most situations,
\queue@_run@_in@_order\ should not be set.

.conf queue@_run@_max integer 5
.index queue runner||maximum number of
This controls the maximum number of queue runner processes that an Exim daemon
can run simultaneously. This does not mean that it starts them all at once,
but rather that if the maximum number are still running when the time comes to
start another one, it refrains from starting another one. This can happen with
very large queues and/or very sluggish deliveries. This option does not,
however, interlock with other processes, so additional queue runners can be
started by other means, or by killing and restarting the daemon.

.conf queue@_smtp@_domains "domain list$**$" unset
.index queueing incoming messages
.index message||queueing remote deliveries
When this option is set, a delivery process is started whenever a message is
received, routing is performed, and local deliveries take place.
However, if any SMTP deliveries are required for domains that match
\queue@_smtp@_domains\, they are not immediately delivered, but instead the
message waits on the queue for the next queue run. Since routing of the message
has taken place, Exim knows to which remote hosts it must be delivered, and so
when the queue run happens, multiple messages for the same host are delivered
over a single SMTP connection. The \-odqs-\ command line option causes all SMTP
deliveries to be queued in this way, and is equivalent to setting
\queue@_smtp@_domains\ to `$*$'. See also \hold@_domains\ and \queue@_domains\.

.conf receive@_timeout time 0s
.index timeout||for non-SMTP input
This option sets the timeout for accepting a non-SMTP message, that is, the
maximum time that Exim waits when reading a message on the standard input. If
the value is zero, it will wait for ever. This setting is overridden by the
\-or-\ command line option. The timeout for incoming SMTP messages is
controlled by \smtp@_receive@_timeout\.

.index customizing|| ::Received:: header
.index ::Received:: header line||customizing
.conf received@_header@_text string$**$ "see below"
This string defines the contents of the ::Received:: message header that is
added to each message, except for the timestamp, which is automatically added
on at the end (preceded by a semicolon). The string is expanded each time it is
used. If the expansion yields an empty string, no ::Received:: header line is
added to the message. Otherwise, the string should start with the text
`Received:' and conform to the RFC 2822 specification for ::Received:: header
lines. The default setting is:
.display asis
received_header_text = Received: \
    ${if def:sender_rcvhost {from $sender_rcvhost\n\t}\
    {${if def:sender_ident {from $sender_ident }}\
    ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
    by $primary_hostname \
    ${if def:received_protocol {with $received_protocol}} \
    ${if def:tls_cipher {($tls_cipher)\n\t}}\
    (Exim $version_number)\n\t\
    id $message_id\
    ${if def:received_for {\n\tfor $received_for}}
.endd
Note the use of quotes, to allow the sequences \"@\n"\ and \"@\t"\ to be used
for newlines and tabs, respectively. The reference to the TLS cipher is omitted
when Exim is built without TLS support. The use of conditional expansions
ensures that this works for both locally generated messages and messages
received from remote hosts, giving header lines such as the following:
.display asis
Received: from scrooge.carol.example ([192.168.12.25] ident=root)
        by marley.carol.example with esmtp (Exim 4.00)
        id 16IOWa-00019l-00
        for chas@dickens.example; Tue, 25 Dec 2001 14:43:44 +0000
Received: by scrooge.carol.example with local (Exim 4.00)
        id 16IOWW-000083-00; Tue, 25 Dec 2001 14:43:41 +0000
.endd
.em
Until the body of the message has been received, the timestamp is the time when 
the message started to be received. Once the body has arrived, and all policy 
checks have taken place, the timestamp is updated to the time at which the 
message was accepted.
.nem

.conf received@_headers@_max integer 30
.index loop||prevention
.index mail loop prevention
.index ::Received:: header line||counting
When a message is to be delivered, the number of ::Received:: headers is
counted, and if it is greater than this parameter, a mail loop is assumed to
have occurred, the delivery is abandoned, and an error message is generated.
This applies to both local and remote deliveries.

.conf recipient@_unqualified@_hosts "host list$**$" unset
.index unqualified addresses
.index host||unqualified addresses from
This option lists those hosts from which Exim is prepared to accept unqualified
recipient addresses in message envelopes. The addresses are made fully
qualified by the addition of the \qualify@_recipient\ value. This option also
affects message header lines. Exim does not reject unqualified recipient
addresses in headers, but it qualifies them only if the message came from a
host that matches \recipient@_unqualified@_hosts\,
.em
or if the message was submitted locally (not using TCP/IP), and the \-bnq-\
option was not set.
.nem

.conf recipients@_max integer 0
.index limit||number of recipients
.index recipient||maximum number 
If this option is set greater than zero, it specifies the maximum number of
original recipients for any message. Additional recipients that are generated
by aliasing or forwarding do not count. SMTP messages get a 452 response for
all recipients over the limit; earlier recipients are delivered as normal.
Non-SMTP messages with too many recipients are failed, and no deliveries are
done.
.index \\RCPT\\||maximum number of incoming
Note that the RFCs specify that an SMTP server should accept at least 100
\\RCPT\\ commands in a single message.

.conf recipients@_max@_reject boolean false
If this option is set true, Exim rejects SMTP messages containing too many
recipients by giving 552 errors to the surplus \\RCPT\\ commands, and a 554
error to the eventual \\DATA\\ command. Otherwise (the default) it gives a 452
error to the surplus \\RCPT\\ commands and accepts the message on behalf of the
initial set of recipients. The remote server should then re-send the message
for the remaining recipients at a later time.

.conf remote@_max@_parallel integer 2
.index delivery||parallelism for remote
This option controls parallel delivery of one message to a number of remote
hosts. If the value is less than 2, parallel delivery is disabled, and Exim
does all the remote deliveries for a message one by one. Otherwise, if a single
message has to be delivered to more than one remote host, or if several copies
have to be sent to the same remote host, up to \remote@_max@_parallel\
deliveries are done simultaneously. If more than \remote@_max@_parallel\
deliveries are required, the maximum number of processes are started, and as
each one finishes, another is begun. The order of starting processes is the
same as if sequential delivery were being done, and can be controlled by the
\remote@_sort@_domains\ option. If parallel delivery takes place while running
with debugging turned on, the debugging output from each delivery process is
tagged with its process id.

This option controls only the maximum number of parallel deliveries for one
message in one Exim delivery process. Because Exim has no central queue
manager, there is no way of controlling the total number of simultaneous
deliveries if the configuration allows a delivery attempt as soon as a message
is received.
.index number of deliveries
.index delivery||maximum number of
If you want to control the total number of deliveries on the system, you
need to set the \queue@_only\ option. This ensures that all incoming messages
are added to the queue without starting a delivery process. Then set up an Exim
daemon to start queue runner processes at appropriate intervals (probably
fairly often, for example, every minute), and limit the total number of queue
runners by setting the \queue__run__max\ parameter. Because each queue runner
delivers only one message at a time, the maximum number of deliveries that can
then take place at once is \queue@_run@_max\ multiplied by
\remote@_max@_parallel\.

If it is purely remote deliveries you want to control, use \queue@_smtp\
instead of \queue@_only\. This has the added benefit of doing the SMTP routing
before queuing, so that several messages for the same host will eventually get
delivered down the same connection.

.conf remote@_sort@_domains "domain list$**$" unset
.index sorting remote deliveries
.index delivery||sorting remote
When there are a number of remote deliveries for a message, they are sorted by
domain into the order given by this list. For example,
.display asis
remote_sort_domains = *.cam.ac.uk:*.uk
.endd
would attempt to deliver to all addresses in the \*cam.ac.uk*\ domain first, then
to those in the \uk\ domain, then to any others.

.conf retry@_data@_expire time 7d
.index hints database||data expiry
This option sets a `use before' time on retry information in Exim's hints
database. Any older retry data is ignored. This means that, for example, once a
host has not been tried for 7 days, Exim behaves as if it has no knowledge of
past failures.

.conf retry@_interval@_max time 24h
.index retry||limit on interval
.index limit||on retry interval
Chapter ~~CHAPretry describes Exim's mechanisms for controlling the intervals
between delivery attempts for messages that cannot be delivered straight away.
This option sets an overall limit to the length of time between retries.

.conf return@_path@_remove boolean true
.index ::Return-path:: header line||removing
RFC 2821, section 4.4, states that an SMTP server must insert a ::Return-path::
header line into a message when it makes a `final delivery'. The ::Return-path::
header preserves the sender address as received in the \\MAIL\\ command. This
description implies that this header should not be present in an incoming
message. If \return@_path@_remove\ is true, any existing ::Return-path::
headers are removed from messages at the time they are received. Exim's
transports have options for adding ::Return-path:: headers at the time of
delivery. They are normally used only for final local deliveries.

.conf return@_size@_limit integer 100K
This option is an obsolete synonym for \bounce@_return@_size@_limit\.

.conf rfc1413@_hosts "host list$**$" $*$
.index RFC 1413
.index host||for RFC 1413 calls
RFC 1413 identification calls are made to any client host which matches an item
in the list.

.conf rfc1413@_query@_timeout time 30s
.index RFC 1413||query timeout
.index timeout||for RFC 1413 call
This sets the timeout on RFC 1413 identification calls. If it is set to zero,
no RFC 1413 calls are ever made.

.conf sender@_unqualified@_hosts "host list$**$" unset
.index unqualified addresses
.index host||unqualified addresses from
This option lists those hosts from which Exim is prepared to accept unqualified
sender addresses. The addresses are made fully qualified by the addition of
\qualify@_domain\. This option also affects message header lines. Exim does not
reject unqualified addresses in headers that contain sender addresses, but it
qualifies them only if the message came from a host that matches
\sender@_unqualified@_hosts\,
.em
or if the message was submitted locally (not using TCP/IP), and the \-bnq-\
option was not set.
.nem

.conf smtp@_accept@_keepalive boolean true
.index keepalive||on incoming connection
This option controls the setting of the \\SO@_KEEPALIVE\\ option on incoming
TCP/IP socket connections. When set, it causes the kernel to probe idle
connections periodically, by sending packets with `old' sequence numbers. The
other end of the connection should send an acknowledgement if the connection is
still okay or a reset if the connection has been aborted. The reason for doing
this is that it has the beneficial effect of freeing up certain types of
connection that can get stuck when the remote host is disconnected without
tidying up the TCP/IP call properly. The keepalive mechanism takes several
hours to detect unreachable hosts.


.conf smtp@_accept@_max integer 20
.index limit||incoming SMTP connections
.index SMTP||incoming connection count
.index inetd
This option specifies the maximum number of simultaneous incoming SMTP calls
that Exim will accept. It applies only to the listening daemon; there is no
control (in Exim) when incoming SMTP is being handled by \*inetd*\. If the value
is set to zero, no limit is applied. However, it is required to be non-zero if
either \smtp@_accept@_max@_per@_host\ or \smtp@_accept@_queue\ is set. See also
\smtp@_accept@_reserve\.


.conf smtp@_accept@_max@_nonmail integer 10
.index limit||non-mail SMTP commands
.index SMTP||limiting non-mail commands
Exim counts the number of `non-mail' commands in an SMTP session, and drops the
connection if there are too many. This option defines `too many'. The check
catches some denial-of-service attacks, repeated failing \\AUTH\\s, or a mad
client looping sending \\EHLO\\, for example. The check is applied only if the 
client host matches \smtp@_accept@_max@_nonmail@_hosts\.

When a new message is expected, one occurrence of \\RSET\\ is not counted. This
allows a client to send one \\RSET\\ between messages (this is not necessary,
but some clients do it). Exim also allows one uncounted occurence of \\HELO\\
or \\EHLO\\, and one occurrence of \\STARTTLS\\ between messages. After
starting up a TLS session, another \\EHLO\\ is expected, and so it too is not
counted. The first occurrence of \\AUTH\\ in a connection, or immediately
following \\STARTTLS\\ is not counted. Otherwise, all commands other than
\\MAIL\\, \\RCPT\\, \\DATA\\, and \\QUIT\\ are counted.

.conf smtp@_accept@_max@_nonmail@_hosts "host list$**$" $*$
You can control which hosts are subject to the \smtp@_accept@_max@_nonmail\
check by setting this option. The default value makes it apply to all hosts. By
changing the value, you can exclude any badly-behaved hosts that you have to
live with.


.conf smtp@_accept@_max@_per@_connection integer 1000
.index SMTP||incoming message count, limiting
.index limit||messages per SMTP connection
The value of this option limits the number of \\MAIL\\ commands that Exim is
prepared to accept over a single SMTP connection, whether or not each command
results in the transfer of a message. After the limit is reached, a 421
response is given to subsequent \\MAIL\\ commands. This limit is a safety
precaution against a client that goes mad (incidents of this type have been
seen).

.conf smtp@_accept@_max@_per@_host string$**$ unset
.index limit||SMTP connections from one host
.index host||limiting SMTP connections from
This option restricts the number of simultaneous IP connections from a single
host (strictly, from a single IP address) to the Exim daemon. The option is
expanded, to enable different limits to be applied to different hosts by
reference to \$sender@_host@_address$\. Once the limit is reached, additional
connection attempts from the same host are rejected with error code 421. The
default value of zero imposes no limit. If this option is set, it is required
that \smtp@_accept@_max\ be non-zero.

\**Warning**\: When setting this option you should not use any expansion
constructions that take an appreciable amount of time. The expansion and test
happen in the main daemon loop, in order to reject additional connections
without forking additional processes (otherwise a denial-of-service attack
could cause a vast number or processes to be created). While the daemon is
doing this processing, it cannot accept any other incoming connections.


.conf smtp@_accept@_queue integer 0
.index SMTP||incoming connection count
.index queueing incoming messages
.index message||queueing by SMTP connection count
If the number of simultaneous incoming SMTP calls handled via the listening
daemon exceeds this value, messages received by SMTP are just placed on the
queue; no delivery processes are started automatically. A value of zero implies
no limit, and clearly any non-zero value is useful only if it is less than the
\smtp@_accept@_max\ value (unless that is zero). See also \queue@_only\,
\queue@_only@_load\, \queue@_smtp@_domains\, and the various \-od-\ command
line options.

.conf smtp@_accept@_queue@_per@_connection integer 10
.index queueing incoming messages
.index message||queueing by message count
This option limits the number of delivery processes that Exim starts
automatically when receiving messages via SMTP, whether via the daemon or by
the use of \-bs-\ or \-bS-\. If the value of the option is greater than zero,
and the number of messages received in a single SMTP session exceeds this
number, subsequent messages are placed on the queue, but no delivery processes
are started. This helps to limit the number of Exim processes when a server
restarts after downtime and there is a lot of mail waiting for it on other
systems. On large systems, the default should probably be increased, and on
dial-in client systems it should probably be set to zero (that is, disabled).

.conf smtp@_accept@_reserve integer 0
.index SMTP||incoming call count
.index host||reserved
When \smtp@_accept@_max\ is set greater than zero, this option specifies a
number of SMTP connections that are reserved for connections from the hosts
that are specified in \smtp@_reserve@_hosts\. The value set in
\smtp@_accept@_max\ includes this reserve pool. The specified hosts are not
restricted to this number of connections; the option specifies a minimum number
of connection slots for them, not a maximum. It is a guarantee that that group
of hosts can always get at least \smtp@_accept@_reserve\ connections.

For example, if \smtp@_accept@_max\ is set to 50 and \smtp@_accept@_reserve\ is
set to 5, once there are 45 active connections (from any hosts), new
connections are accepted only from hosts listed in \smtp@_reserve@_hosts\.
See also \smtp@_accept@_max@_per@_host\.

.em
.conf smtp@_active@_hostname string$**$ unset
.index host||name in SMTP responses
.index SMTP||host name in responses
This option is provided for multi-homed servers that want to masquerade as
several different hosts. At the start of an SMTP connection, its value is
expanded and used instead of the value of \$primary@_hostname$\ in SMTP
responses. For example, it is used as domain name in the response to an
incoming \\HELO\\ or \\EHLO\\ command. If this option is unset, or if its
expansion is forced to fail, or if the expansion results in an empty string,
the value of \$primary@_hostname$\ is used. Other expansion failures cause a
message to be written to the main and panic logs, and the SMTP command receives
a temporary error. Typically, the value of \smtp@_active@_hostname\ depends on
the incoming interface address. For example:
.display asis
smtp_active_hostname = ${if eq{$interface_address}{10.0.0.1}\
  {cox.mydomain}{box.mydomain}}
.endd
If you set \smtp@_active@_hostname\, you probably also want to set
\smtp@_banner\, since its default value references \$primary@_hostname$\.
.nem

.conf smtp@_banner string$**$ "see below"
.index SMTP||welcome banner
.index banner for SMTP
.index welcome banner for SMTP
.index customizing||SMTP banner
This string, which is expanded every time it is used, is output as the initial
positive response to an SMTP connection. The default setting is:
.display asis
smtp_banner = $primary_hostname ESMTP Exim $version_number \
  $tod_full
.endd
Failure to expand the string causes a panic error. If you want to create a
multiline response to the initial SMTP connection, use `@\n' in the string at
appropriate points, but not at the end. Note that the 220 code is not included
in this string. Exim adds it automatically (several times in the case of a
multiline response).

.conf smtp@_check@_spool@_space boolean true
.index checking disk space
.index disk space, checking
.index spool directory||checking space
When this option is set, if an incoming SMTP session encounters the \\SIZE\\
option on a \\MAIL\\ command, it checks that there is enough space in the
spool directory's partition to accept a message of that size, while still
leaving free the amount specified by \check@_spool@_space\ (even if that value
is zero). If there isn't enough space, a temporary error code is returned.

.conf smtp@_connect@_backlog integer 20
.index connection backlog
.index SMTP||connection backlog
.index backlog of connections
This option specifies a maximum number of waiting SMTP connections. Exim passes
this value to the TCP/IP system when it sets up its listener. Once this number
of connections are waiting for the daemon's attention, subsequent connection
attempts are refused at the TCP/IP level. At least, that is what the manuals
say; in some circumstances such connection attempts have been observed to time
out instead. For large systems it is probably a good idea to increase the
value (to 50, say). It also gives some protection against denial-of-service
attacks by SYN flooding.

.conf smtp@_enforce@_sync boolean true
.index SMTP||synchronization checking
.index synchronization checking in SMTP
The SMTP protocol specification requires the client to wait for a response from
the server at certain points in the dialogue. Without \\PIPELINING\\ these
synchronization points are after every command; with \\PIPELINING\\ they are
fewer, but they still exist. Some spamming sites send out a complete set of
SMTP commands without waiting for any response. Exim protects against this by
rejecting a message if the client has sent further input when it should not
have. The error response `554 SMTP synchronization error' is sent, and the
connection is dropped. Testing for this error cannot be perfect because of
transmission delays (unexpected input may be on its way but not yet received
when Exim checks). However, it does detect many instances. The check can be
disabled by setting \smtp@_enforce@_sync\ false.
.em
See also \pipelining@_advertise@_hosts\.
.nem

.conf smtp@_etrn@_command string$**$ unset
.index \\ETRN\\||command to be run
If this option is set, the given command is run whenever an SMTP \\ETRN\\
command is received from a host that is permitted to issue such commands (see
chapter ~~CHAPACL). The string is split up into separate arguments which are
independently expanded. The expansion variable \$domain$\ is set to the
argument of the \\ETRN\\ command, and no syntax checking is done on it. For
example:
.display asis
smtp_etrn_command = /etc/etrn_command $domain $sender_host_address
.endd
A new process is created to run the command, but Exim does not wait for it to
complete. Consequently, its status cannot be checked. If the command cannot be
run, a line is written to the panic log, but the \\ETRN\\ caller still receives
a 250 success response. Exim is normally running under its own uid when
receiving SMTP, so it is not possible for it to change the uid before running
the command.

.conf smtp@_etrn@_serialize boolean true
.index \\ETRN\\||serializing
When this option is set, it prevents the simultaneous execution of more than
one identical command as a result of \\ETRN\\ in an SMTP connection. See
section ~~SECTETRN for details.

.conf smtp@_load@_reserve fixed-point unset
.index load average
If the system load average ever gets higher than this, incoming SMTP calls are
accepted only from those hosts that match an entry in \smtp@_reserve@_hosts\.
If \smtp@_reserve@_hosts\ is not set, no incoming SMTP calls are accepted when
the load is over the limit. The option has no effect on ancient operating
systems on which Exim cannot determine the load average. See also
\deliver@_queue@_load@_max\ and \queue@_only@_load\.


.conf smtp@_max@_synprot@_errors integer 3
.index SMTP||limiting syntax and protocol errors
.index limit||SMTP syntax and protocol errors
Exim rejects SMTP commands that contain syntax or protocol errors. In 
particular, a syntactically invalid email address, as in this command:
.display asis
RCPT TO:<abc xyz@a.b.c>
.endd
causes immediate rejection of the command, before any other tests are done.
(The ACL cannot be run if there is no valid address to set up for it.) An
example of a protocol error is receiving \\RCPT\\ before \\MAIL\\. If there are
too many syntax or protocol errors in one SMTP session, the connection is
dropped. The limit is set by this option.

.em
.index \\PIPELINING\\||expected errors
When the \\PIPELINING\\ extension to SMTP is in use, some protocol errors are 
`expected', for instance, a \\RCPT\\ command after a rejected \\MAIL\\ command. 
Exim assumes that \\PIPELINING\\ will be used if it advertises it (see 
\pipelining@_advertise@_hosts\), and in this situation, `expected' errors do 
not count towards the limit.
.nem


.conf smtp@_max@_unknown@_commands integer 3
.index SMTP||limiting unknown commands
.index limit||unknown SMTP commands
If there are too many unrecognized commands in an incoming SMTP session, an 
Exim server drops the connection. This is a defence against some kinds of abuse 
that subvert web 
.em
clients 
.nem
into making connections to SMTP ports; in these circumstances, a number of
non-SMTP command lines are sent first.


.conf smtp@_ratelimit@_hosts "host list$**$" unset
.index SMTP||rate limiting
.index limit||rate of message arrival
.index \\RCPT\\||rate limiting
Some sites find it helpful to be able to limit the rate at which certain hosts
can send them messages, and the rate at which an individual message can specify
recipients. When a host matches \smtp@_ratelimit@_hosts\, the values of
\smtp@_ratelimit@_mail\ and \smtp@_ratelimit@_rcpt\ are used to control the
rate of acceptance of \\MAIL\\ and \\RCPT\\ commands in a single SMTP session,
respectively. Each option, if set, must contain a set of four comma-separated
values:
.numberpars $.
A threshold, before which there is no rate limiting.
.nextp
An initial time delay. Unlike other times in Exim, numbers with decimal
fractional parts are allowed here.
.nextp
A factor by which to increase the delay each time.
.nextp
A maximum value for the delay. This should normally be less than 5 minutes,
because after that time, the client is liable to timeout the SMTP command.
.endp
For example, these settings have been used successfully at the site which
first suggested this feature, for controlling mail from their customers:
.display asis
smtp_ratelimit_mail = 2,0.5s,1.05,4m
smtp_ratelimit_rcpt = 4,0.25s,1.015,4m
.endd
The first setting specifies delays that are applied to \\MAIL\\ commands after
two have been received over a single connection. The initial delay is 0.5
seconds, increasing by a factor of 1.05 each time. The second setting applies
delays to \\RCPT\\ commands when more than four occur in a single message.

It is also possible to configure delays explicitly in ACLs. See section 
~~SECTACLmodi for details.


.conf smtp@_ratelimit@_mail string unset
See \smtp@_ratelimit@_hosts\ above.

.conf smtp@_ratelimit@_rcpt string unset
See \smtp@_ratelimit@_hosts\ above.

.conf smtp@_receive@_timeout time 5m
.index timeout||for SMTP input
.index SMTP||timeout, input
This sets a timeout value for SMTP reception. It applies to all forms of SMTP
input, including batch SMTP. If a line of input (either an SMTP command or a
data line) is not received within this time, the SMTP connection is dropped and
the message is abandoned. 
A line is written to the log containing one of the following messages:
.display asis
SMTP command timeout on connection from...
SMTP data timeout on connection from...
.endd
The former means that Exim was expecting to read an SMTP command; the latter 
means that it was in the \\DATA\\ phase, reading the contents of a message.


.index \-os-\ option
The value set by this option can be overridden by the
\-os-\ command-line option. A setting of zero time disables the timeout, but
this should never be used for SMTP over TCP/IP. (It can be useful in some cases
of local input using \-bs-\ or \-bS-\.) For non-SMTP input, the reception
timeout is controlled by \receive@_timeout\ and \-or-\.

.conf smtp@_reserve@_hosts "host list$**$" unset
This option defines hosts for which SMTP connections are reserved; see
\smtp@_accept@_reserve\ and \smtp@_load@_reserve\ above.

.conf smtp@_return@_error@_details boolean false
.index SMTP||details policy failures
.index policy control||rejection, returning details
In the default state, Exim uses bland messages such as
`Administrative prohibition' when it rejects SMTP commands for policy
reasons. Many sysadmins like this because it gives away little information
to spammers. However, some other syadmins who are applying strict checking
policies want to give out much fuller information about failures. Setting
\smtp@_return@_error@_details\ true causes Exim to be more forthcoming. For
example, instead of `Administrative prohibition', it might give:
.display asis
550-Rejected after DATA: '>' missing at end of address:
550 failing address in "From" header is: <user@dom.ain
.endd

.conf split@_spool@_directory boolean false
.index multiple spool directories
.index spool directory||split
.index directories, multiple
If this option is set, it causes Exim to split its input directory into 62
subdirectories, each with a single alphanumeric character as its name. The
sixth character of the message id is used to allocate messages to
subdirectories; this is the least significant base-62 digit of the time of
arrival of the message.

Splitting up the spool in this way may provide better performance on systems
where there are long mail queues, by reducing the number of files in any one
directory. The msglog directory is also split up in a similar way to the input
directory; however, if \preserve@_message@_logs\ is set, all old msglog files
are still placed in the single directory \(msglog.OLD)\.

It is not necessary to take any special action for existing messages when
changing \split@_spool@_directory\. Exim notices messages that are in the
`wrong' place, and continues to process them. If the option is turned off after
a period of being on, the subdirectories will eventually empty and be
automatically deleted.

When \split@_spool@_directory\ is set, the behaviour of queue runner processes
changes. Instead of creating a list of all messages in the queue, and then
trying to deliver each one in turn, it constructs a list of those in one
sub-directory and tries to deliver them, before moving on to the next
sub-directory. The sub-directories are processed in a random order. This
spreads out the scanning of the input directories, and uses less memory. It is
particularly beneficial when there are lots of messages on the queue. However,
if \queue@_run@_in@_order\ is set, none of this new processing happens. The
entire queue has to be scanned and sorted before any deliveries can start.

.conf spool@_directory string$**$ "set at compile time"
.index spool directory||path to
This defines the directory in which Exim keeps its spool, that is, the messages
it is waiting to deliver. The default value is taken from the compile-time
configuration setting, if there is one. If not, this option must be set. The
string is expanded, so it can contain, for example, a reference to
\$primary@_hostname$\.

If the spool directory name is fixed on your installation, it is recommended
that you set it at build time rather than from this option, particularly if the
log files are being written to the spool directory (see \log@_file@_path\).
Otherwise log files cannot be used for errors that are detected early on, such
as failures in the configuration file.

By using this option to override the compiled-in path, it is possible to run
tests of Exim without using the standard spool.

.conf strip@_excess@_angle@_brackets boolean false
.index angle brackets, excess
If this option is set, redundant pairs of angle brackets round `route-addr'
items in addresses are stripped. For example, \*@<@<xxx@@a.b.c.d@>@>*\ is treated
as \*@<xxx@@a.b.c.d@>*\. If this is in the envelope and the message is passed on
to another MTA, the excess angle brackets are not passed on. If this option is
not set, multiple pairs of angle brackets cause a syntax error.

.conf strip@_trailing@_dot boolean false
.index trailing dot on domain
.index dot||trailing on domain
If this option is set, a trailing dot at the end of a domain in an address is
ignored. If this is in the envelope and the message is passed on to another
MTA, the dot is not passed on. If this option is not set, a dot at the end of a
domain causes a syntax error.
.em
However, addresses in header lines are checked only when an ACL requests header 
syntax checking.
.nem

.conf syslog@_duplication boolean true
.index syslog||duplicate log lines, suppressing
When Exim is logging to syslog, it writes the log lines for its three
separate logs at different syslog priorities so that they can in principle
be separated on the logging hosts. Some installations do not require this
separation, and in those cases, the duplication of certain log lines is a
nuisance. If \syslog@_duplication\ is set false, only one copy of any
particular log line is written to syslog. For lines that normally go to
both the main log and the reject log, the reject log version (possibly
containing message header lines) is written, at \\LOG@_NOTICE\\ priority.
Lines that normally go to both the main and the panic log are written at
the \\LOG@_ALERT\\ priority.

.conf syslog@_facility string unset
.index syslog||facility, setting
This option sets the syslog `facility' name, used when Exim is logging to 
syslog. The value must be one of the strings `mail', `user', `news', `uucp',
`daemon', or `local\*x*\' where \*x*\ is a digit between 0 and 7. If this 
option is unset, `mail' is used. See chapter ~~CHAPlog for details of Exim's
logging.


.conf syslog@_processname string "$tt{exim}"
.index syslog||process name, setting
This option sets the syslog `ident' name, used when Exim is logging to syslog.
The value must be no longer than 32 characters. See chapter ~~CHAPlog for
details of Exim's logging.


.conf syslog@_timestamp boolean true
.index syslog||timestamps
If \syslog@_timestamp\ is set false, the timestamps on Exim's log lines are
omitted when these lines are sent to syslog. See chapter ~~CHAPlog for
details of Exim's logging.

.conf system@_filter string$**$ unset
.index filter||system filter
.index system filter||specifying
.index Sieve filter||not available for system filter
This option specifies an Exim filter file that is applied to all messages at
the start of each delivery attempt, before any routing is done. System filters
must be Exim filters; they cannot be Sieve filters. If the system filter
generates any deliveries to files or pipes, or any new mail messages, the
appropriate \system@_filter@_...@_transport\ option(s) must be set, to define
which transports are to be used. Details of this facility are given in chapter
~~CHAPsystemfilter.

.conf system@_filter@_directory@_transport string$**$ unset
This sets the name of the transport driver that is to be used when the
\save\ command in a system message filter specifies a path ending in `/',
implying delivery of each message into a separate file in some directory.
During the delivery, the variable \$address@_file$\ contains the path name.

.conf system@_filter@_file@_transport string$**$ unset
.index file||transport for system filter
This sets the name of the transport driver that is to be used when the \save\
command in a system message filter specifies a path not ending in `/'. During
the delivery, the variable \$address@_file$\ contains the path name.

.index gid (group id)||system filter
.conf system@_filter@_group string unset
This option is used only when \system@_filter@_user\ is also set. It sets the
gid under which the system filter is run, overriding any gid that is associated
with the user. The value may be numerical or symbolic.

.conf system@_filter@_pipe@_transport string$**$ unset 7
.index \%pipe%\ transport||for system filter
This specifies the transport driver that is to be used when a \pipe\ command is
used in a system filter. During the delivery, the variable \$address@_pipe$\
contains the pipe command.

.conf system@_filter@_reply@_transport string$**$ unset
.index \%autoreply%\ transport||for system filter
This specifies the transport driver that is to be used when a \mail\ command is
used in a system filter.

.index uid (user id)||system filter
.conf system@_filter@_user string unset
If this option is not set, the system filter is run in the main Exim delivery
process, as root. When the option is set, the system filter runs in a separate
process, as the given user. Unless the string consists entirely of digits, it
is looked up in the password data. Failure to find the named user causes a
configuration error. The gid is either taken from the password data, or
specified by \system@_filter@_group\. When the uid is specified numerically,
\system@_filter@_group\ is required to be set.

If the system filter generates any pipe, file, or reply deliveries, the uid
under which the filter is run is used when transporting them, unless a
transport option overrides.
Normally you should set \system@_filter@_user\ if your system filter generates
these kinds of delivery.

.conf tcp@_nodelay boolean true
.index daemon||\\TCP@_NODELAY\\ on sockets
.index Nagle algorithm
.index \\TCP@_NODELAY\\ on listening sockets
If this option is set false, it stops the Exim daemon setting the
\\TCP@_NODELAY\\ option on its listening sockets. Setting \\TCP@_NODELAY\\
turns off the `Nagle algorithm', which is a way of improving network
performance in interactive (character-by-character) situations. Turning it off
should improve Exim's performance a bit, so that is what happens by default.
However, it appears that some broken clients cannot cope, and time out. Hence
this option. It affects only those sockets that are set up for listening by the
daemon. Sockets created by the smtp transport for delivering mail always set
\\TCP@_NODELAY\\.

.conf timeout@_frozen@_after time 0s
.index frozen messages||timing out
.index timeout||frozen messages
If \timeout@_frozen@_after\ is set to a time greater than zero, a frozen
message of any kind that has been on the queue for longer than the given
time is automatically cancelled at the next queue run. If it is a bounce
message, it is just discarded; otherwise, a bounce is sent to the sender, in a
similar manner to cancellation by the \-Mg-\ command line option. If you want
to timeout frozen bounce messages earlier than other kinds of frozen message,
see \ignore@_bounce@_errors@_after\.

.conf timezone string unset
.index timezone, setting
The value of \timezone\ is used to set the environment variable \\TZ\\ while
running Exim (if it is different on entry). This ensures that all timestamps
created by Exim are in the required timezone. If you want all your timestamps
to be in UTC (aka GMT) you should set
.display asis
timezone = UTC
.endd
The default value is taken from \\TIMEZONE@_DEFAULT\\ in \(Local/Makefile)\,
or, if that is not set, from the value of the TZ environment variable when Exim
is built. If \timezone\ is set to the empty string, either at build or run
time, any existing \\TZ\\ variable is removed from the environment when Exim
runs. This is appropriate behaviour for obtaining wall-clock time on some, but
unfortunately not all, operating systems.

.conf tls@_advertise@_hosts "host list$**$" unset
.index TLS||advertising
.index encryption||on SMTP connection
.index SMTP||encrypted connection
When Exim is built with support for TLS encrypted connections, the availability
of the \\STARTTLS\\ command to set up an encrypted session is advertised in
response to \\EHLO\\ only to those client hosts that match this option. See
chapter ~~CHAPTLS for details of Exim's support for TLS.

.conf tls@_certificate string$**$ unset
.index TLS||server certificate, location of
.index certificate||for server, location of
The value of this option is expanded, and must then be the absolute path to a
file which contains the server's certificates. The server's private key is also
assumed to be in this file if \tls@_privatekey\ is unset. See chapter ~~CHAPTLS
for further details.

\**Note**\: The certificates defined by this option are used only when Exim is 
receiving incoming messages as a server. If you want to supply certificates for
use when sending messages as a client, you must set the \tls@_certificate\
option in the relevant \%smtp%\ transport.

.em
.conf tls@_crl string$**$ unset
.index TLS||server certificate revocation list
.index certificate||revocation list for server
This option specifies a certificate revocation list. The expanded value must
be the name of a file that contains a CRL in PEM format.
.nem

.conf tls@_dhparam string$**$ unset
.index TLS||D-H parameters for server
The value of this option is expanded, and must then be the absolute path to
a file which contains the server's DH parameter values.
This is used only for OpenSSL. When Exim is linked with GnuTLS, this option is 
ignored. See section ~~SECTopenvsgnu for further details.

.conf tls@_privatekey string$**$ unset
.index TLS||server private key, location of
The value of this option is expanded, and must then be the absolute path to
a file which contains the server's private key.
If this option is unset, the private key is assumed to be in the same file as 
the server's certificates. See chapter ~~CHAPTLS for further details.

.conf tls@_remember@_esmtp boolean false
.index TLS||esmtp state, remembering
.index TLS||broken clients
If this option is set true, Exim violates the RFCs by remembering that it is in
`esmtp' state after successfully negotiating a TLS session. This provides
support for broken clients that fail to send a new \\EHLO\\ after starting a
TLS session.

.em
.conf tls@_require@_ciphers string$**$ unset
.index TLS||requiring specific ciphers
.index cipher||requiring specific
This option controls which ciphers can be used for incoming TLS connections.
(The \%smtp%\ transport has an option of the same name for controlling outgoing 
connections.) This option is expanded for each connection, so can be varied for
different clients if required. The value of this option must be a list of
permitted cipher suites. The OpenSSL and GnuTLS libraries handle cipher control
in somewhat different ways. Details are given in section ~~SECTreqciphsslgnu.
.nem

.conf tls@_try@_verify@_hosts "host list$**$" unset
.index TLS||client certificate verification
.index certificate||verification of client
See \tls@_verify@_hosts\ below.

.conf tls@_verify@_certificates string$**$ unset
.index TLS||client certificate verification
.index certificate||verification of client
The value of this option is expanded, and must then be the absolute path to
a file containing permitted certificates for clients that
match \tls@_verify@_hosts\ or \tls@_try@_verify@_hosts\. Alternatively, if you
are using OpenSSL, you can set \tls@_verify@_certificates\ to the name of a
directory containing certificate files. This does not work with GnuTLS; the
option must be set to the name of a single file if you are using GnuTLS.

.conf tls@_verify@_hosts "host list$**$" unset
.index TLS||client certificate verification
.index certificate||verification of client
This option, along with \tls@_try@_verify@_hosts\, controls the checking of
certificates from clients. 
The expected certificates are defined by \tls@_verify@_certificates\, which 
must be set. A configuration error occurs if either \tls@_verify@_hosts\ or 
\tls@_try@_verify@_hosts\ is set and \tls@_verify@_certificates\ is not set.

Any client that matches \tls@_verify@_hosts\ is constrained by
\tls@_verify@_certificates\. The client must present one of the listed
certificates. If it does not, the connection is aborted.

A weaker form of checking is provided by \tls@_try@_verify@_hosts\. If a client
matches this option (but not \tls@_verify@_hosts\), Exim requests a
certificate and checks it against \tls@_verify@_certificates\, but does not
abort the connection if there is no certificate or if it does not match. This
state can be detected in an ACL, which makes it possible to implement policies
such as `accept for relay only if a verified certificate has been received, but
accept for local delivery if encrypted, even without a verified certificate'.

Client hosts that match neither of these lists are not asked to present
certificates.

.conf trusted@_groups "string list" unset
.index trusted group
.index group||trusted
If this option is set, any process that is running in one of the listed groups,
or which has one of them as a supplementary group, is trusted. 
The groups can be specified numerically or by name.
See section ~~SECTtrustedadmin for details of what trusted callers are
permitted to do. If neither \trusted@_groups\ nor \trusted@_users\ is set, only
root and the Exim user are trusted.

.conf trusted@_users "string list" unset
.index trusted user
.index user||trusted
If this option is set, any process that is running as one of the listed users
is trusted. 
The users can be specified numerically or by name.
See section ~~SECTtrustedadmin for details of what trusted callers are
permitted to do. If neither \trusted@_groups\ nor \trusted@_users\ is set, only
root and the Exim user are trusted.

.index uid (user id)||unknown caller
.conf unknown@_login string$**$ unset
This is a specialized feature for use in unusual configurations. By default, if
the uid of the caller of Exim cannot be looked up using \*getpwuid()*\, Exim
gives up. The \unknown@_login\ option can be used to set a login name to be
used in this circumstance. It is expanded, so values like \user@$caller@_uid\
can be set. When \unknown@_login\ is used, the value of \unknown@_username\ is
used for the user's real name (gecos field), unless this has been set by the
\-F-\ option.

.conf unknown@_username string unset
See \unknown@_login\.

.conf untrusted@_set@_sender "address list$**$" unset
.index trusted user
.index sender||setting by untrusted user
.index untrusted user, setting sender
.index user||untrusted setting sender
.index envelope sender
When an untrusted user submits a message to Exim using the standard input, Exim
normally creates an envelope sender address from the user's login and the
default qualification domain. Data from the \-f-\ option (for setting envelope
senders on non-SMTP messages) or the SMTP \\MAIL\\ command (if \-bs-\ or \-bS-\
is used) is ignored.

However, untrusted users are permitted to set an empty envelope sender address,
to declare that a message should never generate any bounces. For example:
.display asis
exim -f '<>' user@domain.example
.endd
The \untrusted@_set@_sender\ option allows you to permit untrusted users to set
other envelope sender addresses in a controlled way. When it is set, untrusted
users are allowed to set envelope sender addresses that match any of the
patterns in the list. Like all address lists, the string is expanded. The
identity of the user is in \$sender@_ident$\, so you can, for example, restrict
users to setting senders that start with their login ids 
followed by a hyphen
by a setting like this:
.display asis
untrusted_set_sender = ^$sender_ident-
.endd
If you want to allow untrusted users to set envelope sender addresses without
restriction, you can use
.display asis
untrusted_set_sender = *
.endd
The \untrusted@_set@_sender\ option applies to all forms of local input, but
only to the setting of the envelope sender. It does not permit untrusted users
to use the other options which trusted user can use to override message
parameters. Furthermore, it does not stop Exim from removing an existing
::Sender:: header in the message, or from adding a ::Sender:: header if
necessary. See \local__sender__retain\ and \local@_from@_check\ for ways of
overriding these actions. The handling of the ::Sender:: header is also
described in section ~~SECTthesenhea.

The log line for a message's arrival shows the envelope sender following `<='.
For local messages, the user's login always follows, after `U='. In \-bp-\
displays, and in the Exim monitor, if an untrusted user sets an envelope sender
address, the user's login is shown in parentheses after the sender address.

.conf uucp@_from@_pattern string "see below"
.index `From' line
.index UUCP||`From' line
Some applications that pass messages to an MTA via a command line interface use
an initial line starting with `From' to pass the envelope sender. In
particular, this is used by UUCP software. Exim recognizes such a line by means
of a regular expression that is set in \uucp@_from@_pattern\. When the pattern
matches, the sender address is constructed by expanding the contents of
\uucp@_from@_sender\, provided that the caller of Exim is a trusted user. The
default pattern recognizes lines in the following two forms:
.display asis
   From ph10 Fri Jan  5 12:35 GMT 1996
   From ph10 Fri, 7 Jan 97 14:00:00 GMT
.endd
The pattern can be seen by running
.display asis
exim -bP uucp_from_pattern
.endd
It checks only up to the hours and minutes, and allows for a 2-digit or 4-digit
year in the second case. The first word after `From' is matched in the regular
expression by a parenthesized subpattern. The default value for
\uucp@_from@_sender\ is `$1', which therefore just uses this first word (`ph10'
in the example above) as the message's sender. See also
\ignore@_fromline@_hosts\.

.conf uucp@_from@_sender string$**$ "$tt{@$1}"
See \uucp@_from@_pattern\ above.

.conf warn@_message@_file string unset
.index warning of delay||customizing the message
.index customizing||warning message
This option defines a template file containing paragraphs of text to be used
for constructing the warning message which is sent by Exim when a message has
been on the queue for a specified amount of time, as specified by
\delay@_warning\. Details of the file's contents are given in chapter
~~CHAPemsgcust. See also \bounce@_message@_file\.

.em
.conf write@_rejectlog boolean true
.index reject log||disabling
If this option is set false, Exim no longer writes anything to the reject log.
See chapter ~~CHAPlog for details of what Exim writes to its logs.
.nem

.endconf



.
.
.
.
. ============================================================================
.chapter Generic options for routers
.rset CHAProutergeneric "~~chapter"
.set runningfoot "generic router options"
.index options||generic, for routers
.index generic options||router

This chapter describes the generic options that apply to all routers, 
identifying those that are preconditions. For a general description of how a
router operates, see sections ~~SECTrunindrou and ~~SECTrouprecon. The second
of these sections specifies the order in which the preconditions are tested.
The order of expansion of the options that provide data for a transport is: 
\errors@_to\, \headers@_add\, \headers@_remove\, \transport\.

.startconf

.conf address@_data string$**$ unset
.index router||data attached to address
The string is expanded just before the router is run, that is, after all the
precondition tests have succeeded. If the expansion is forced to fail, the
router declines. Other expansion failures cause delivery of the address to be
deferred.

When the expansion succeeds, the value is retained with the address, and can be
accessed using the variable \$address@_data$\ in the current router, subsequent
routers, and the eventual transport. 

\**Warning**\: if the current or any subsequent router is a \%redirect%\ router 
that runs a user's filter file, the contents of \$address@_data$\ are
accessible in the filter. This is not normally a problem, because such data is
usually either not confidential or it `belongs' to the current user, but if you 
do put confidential data into \$address@_data$\ you need to remember this 
point.

Even if the router declines or passes, the value of \$address@_data$\ remains
with the address, though it can be changed by another \address@_data\ setting
on a subsequent router. If a router generates child addresses, the value of
\$address@_data$\ propagates to them. This also applies to the special kind of
`child' that is generated by a router with the \unseen\ option.

The idea of \address@_data\ is that you can use it to look up a lot of data for
the address once, and then pick out parts of the data later. For example, you
could use a single LDAP lookup to return a string of the form
.display asis
uid=1234 gid=5678 mailbox=/mail/xyz forward=/home/xyz/.forward
.endd
In the transport you could pick out the mailbox by a setting such as
.display asis
file = ${extract{mailbox}{$address_data}}
.endd
This makes the configuration file less messy, and also reduces the number of
lookups. (Exim does cache the most recent lookup, but there may be several
addresses in a message which cause lookups to occur.)

The \address@_data\ facility is also useful as a means of passing information 
from one router to another,
and from a router to a transport. In addition, if \address@_data\ is set by a 
router when verifying an address from an ACL, its value is available for use in 
the rest of the ACL statement.


.conf address@_test "boolean (precondition)" true
.index \-bt-\ option
.index router||skipping when address testing
If this option is set false, the router is skipped when routing is being tested
by means of the \-bt-\ command line option. This can be a convenience when your
first router sends messages to an external scanner, because it saves you 
having to set the `already scanned' indicator when testing real address 
routing.


.conf cannot@_route@_message string$**$ unset
.index router||customizing `cannot route' message
.index customizing||`cannot route' message
This option specifies a text message that is used when an address cannot be
routed because Exim has run out of routers. The default message is `Unrouteable
address'. This option is useful only on routers that have \more\ set false, or
on the very last router in a configuration, because the value that is used is
taken from the last router that inspects an address. For example, using the
default configuration, you could put:
.display asis
cannot_route_message = Remote domain not found in DNS
.endd
on the first (\%dnslookup%\) router, and
.display asis
cannot_route_message = Unknown local user
.endd
on the final router that checks for local users. If string expansion fails, the 
default message is used.
Unless the expansion failure was explicitly forced, a message about the failure
is written to the main and panic logs, in addition to the normal message about
the routing failure.

.conf caseful@_local@_part boolean false
.index case of local parts
.index router||case of local parts
By default, routers handle the local parts of addresses in a case-insensitive
manner, though the actual case is preserved for transmission with the message.
If you want the case of letters to be significant in a router, you must set
this option true. For individual router options that contain address or local
part lists (for example, \local@_parts\), case-sensitive matching can be turned
on by `+caseful' as a list item. See section ~~SECTcasletadd for more details.


.conf check@_local@_user "boolean (precondition)" false
.index local user, checking in router
.index router||checking for local user
When this option is true, Exim checks that the local part of the recipient
address (with affixes removed if relevant) is the name of an account on the
local system. The check is done by calling the \*getpwnam()*\ function rather
than trying to read \(/etc/passwd)\ directly. This means that other methods of
holding password data (such as NIS) are supported. If the local part is a local
user, \$home$\ is set from the password data, and can be tested in other
preconditions that are evaluated after this one 
(the order of evaluation is given in section ~~SECTrouprecon). However, the
value of \$home$\ can be overridden by \router@_home@_directory\.
If the local part is not a local user, the router is skipped.

If you want to check that the local part is either the name of a local user
or matches something else, you cannot combine \check@_local@_user\ with a 
setting of \local@_parts\, because that specifies the logical \*and*\ of the 
two conditions. However, you can use a \%passwd%\ lookup in a \local@_parts\ 
setting to achieve this. For example:
.display asis
local_parts = passwd;$local_part : lsearch;/etc/other/users
.endd
Note, however, that the side effects of \check@_local@_user\ (such as setting
up a home directory) do not occur when a \%passwd%\ lookup is used in a
\local@_parts\ (or any other) precondition.

.conf condition "string$**$ (precondition)"  unset
.index router||customized precondition
This option specifies a general precondition test that has to succeed for the
router to be called. The string is expanded, and if the result is a forced
failure or an empty string or one of the strings `0' or `no' or `false'
(checked without regard to the case of the letters), the router is skipped, and
the address is offered to the next one. This provides a means of applying
special-purpose conditions to the running of routers.

If the expansion fails (other than forced failure) delivery is deferred. Some
of the other options below are common special cases that could in fact be
specified using \condition\.
Note that \condition\ is the last precondition to be evaluated (see
section ~~SECTrouprecon). 


.conf debug@_print string$**$ unset
.index testing||variables in drivers
If this option is set and debugging is enabled (see the \-d-\ command line
option), the string is expanded and included in the debugging output. 
If expansion of the string fails, the error message is written to the debugging 
output, and Exim carries on processing.
This option is provided to help with checking out the values of variables and
so on when debugging router configurations. For example, if a \condition\
option appears not to be working, \debug@_print\ can be used to output the
variables it references. The output happens after checks for \domains\,
\local@_parts\, and \check@_local@_user\ but before any other preconditions are
tested. A newline is added to the text if it does not end with one.


.conf disable@_logging boolean false
If this option is set true, nothing is logged for any routing errors
.em
or for any deliveries caused by this router. You should not set this option
unless you really, really know what you are doing. See also the generic
transport option of the same name.
.nem

.conf domains "domain list$**$ (precondition)" unset
.index router||restricting to specific domains
If this option is set, the router is skipped unless the current domain matches
the list. If the match is achieved by means of a file lookup, the data that the
lookup returned for the domain is placed in \$domain@_data$\ for use in string
expansions of the driver's private options.
See section ~~SECTrouprecon for a list of the order in which preconditions 
are evaluated.


.conf driver string unset
This option must always be set. It specifies which of the available routers is
to be used.


.conf errors@_to string$**$ unset
.index envelope sender
.index router||changing address for errors
If a router successfully handles an address, it may queue the address for
delivery or it may generate child addresses. In both cases, if there is a
delivery problem during later processing, the resulting bounce message is sent
to the address that results from expanding this string, provided that the
address verifies successfully. 
\errors@_to\ is expanded before \headers@_add\, \headers@_remove\, and 
\transport\.

If the option is unset, or the expansion is forced to fail, or the result of
the expansion fails to verify, the errors address associated with the incoming
address is used. At top level, this is the envelope sender. A non-forced
expansion failure causes delivery to be deferred.

If an address for which \errors@_to\ has been set ends up being delivered over
SMTP, the envelope sender for that delivery is the \errors@_to\ value, so that
any bounces that are generated by other MTAs on the delivery route are also
sent there. The most common use of \errors@_to\ is probably to direct mailing
list bounces to the manager of the list, as described in section
~~SECTmailinglists.

The \errors@_to\ setting associated with an address can be overridden if it
subsequently passes through other routers that have their own \errors@_to\
settings,
or if it is delivered by a transport with a \return@_path\ setting.

You can set \errors@_to\ to the empty string by either of these settings:
.display asis
errors_to =
errors_to = ""
.endd
An expansion item that yields an empty string has the same effect. If you do
this, a locally detected delivery error for addresses processed by this router
no longer gives rise to a bounce message; the error is discarded. If the
address is delivered to a remote host, the return path is set to \"<>"\, unless
overridden by the \return@_path\ option on the transport.

If for some reason you want to discard local errors, but use a non-empty
\\MAIL\\ command for remote delivery, you can preserve the original return
path in \$address@_data$\ in the router, and reinstate it in the transport by
setting \return@_path\.


.conf expn "boolean (precondition)" true
.index address||testing
.index testing||addresses
.index \\EXPN\\||router skipping
.index router||skipping for \\EXPN\\
If this option is turned off, the router is skipped when testing an address
as a result of processing an SMTP \\EXPN\\ command. You might, for example,
want to turn it off on a router for users' \(.forward)\ files, while leaving it
on for the system alias file. 
See section ~~SECTrouprecon for a list of the order in which preconditions 
are evaluated.

The use of the SMTP \\EXPN\\ command is controlled by an ACL (see chapter
~~CHAPACL). When Exim is running an \\EXPN\\ command, it is similar to testing
an address with \-bt-\. Compare \\VRFY\\, whose counterpart is \-bv-\.


.conf fail@_verify boolean false
.index router||forcing verification failure
Setting this option has the effect of setting both \fail@_verify@_sender\ and
\fail@_verify@_recipient\ to the same value.


.conf fail@_verify@_recipient boolean false
If this option is true and an address is accepted by this router when
verifying a recipient, verification fails.


.conf fail@_verify@_sender boolean false
If this option is true and an address is accepted by this router when
verifying a sender, verification fails.


.conf fallback@_hosts "string list" unset
.index router||fallback hosts
.index fallback||hosts specified on router
String expansion is not applied to this option. The argument must be a
colon-separated list of host names or IP addresses. If a router queues an
address for a remote transport, this host list is associated with the address,
and used instead of the transport's fallback host list. If \hosts@_randomize\
is set on the transport, the order of the list is randomized for each use. See
the \fallback@_hosts\ option of the \%smtp%\ transport for further details.

.conf group string$**$ "see below"
.index gid (group id)||local delivery
.index local transports||uid and gid
.index transport||local
.index router||setting group
When a router queues an address for a transport, and the transport does not
specify a group, the group given here is used when running the delivery
process. 
The group may be specified numerically or by name. If expansion fails, the 
error is logged and delivery is deferred.
The default is unset, unless \check@_local@_user\ is set, when the default
is taken from the password information. See also \initgroups\ and \user\ and
the discussion in chapter ~~CHAPenvironment.


.conf headers@_add string$**$ unset
.index header lines||adding
.index router||adding header lines
This option specifies a string of text that is expanded at routing time, and
associated with any addresses that are processed by the router
when delivering a message. This option has no effect when an address is just
being verified.

The \headers@_add\ option is expanded after \errors@_to\, but before
\headers@_remove\ and \transport\.
If the expanded string is empty, or if the expansion is forced to fail, the
option has no effect. Other expansion failures are treated as configuration
errors. The expanded string must be in the form of one or more RFC 2822 header
lines, separated by newlines (coded as `@\n'). For example:
.display asis
headers_add = X-added-header: added by $primary_hostname\n\
              X-added-second: another added header line
.endd
Exim does not check the syntax of these added header lines. If an address
passes through several routers as a result of aliasing or forwarding
operations, any \headers@_add\ or \headers@_remove\ specifications are
cumulative. This does not apply for multiple routers that result from the use
of `unseen'.

At transport time, all the original headers listed in \headers__remove\ are
removed. If there are multiple instances of any listed header, they are all
removed.
Then the new headers specified by \headers@_add\ are added, in the order in
which they were attached to the address. Finally, any additional headers
specified by the transport are added. It is not possible to remove headers
added to an address by \headers@_add\.

Because the addition does not happen until transport time, header lines that
are added by \headers@_add\ are not accessible by means of the \$header@_xxx$\
expansion syntax. Conversely, header lines that are removed by
\headers@_remove\ remain visible.

Addresses with different \headers@_add\ or \headers@_remove\ settings cannot be
delivered together in a batch. The \headers@_add\ option cannot be used for a
\%redirect%\ router that has the \one@_time\ option set.


.conf headers@_remove string$**$ unset
.index header lines||removing
.index router||removing header lines
The string is expanded at routing time and is then associated with any
addresses that are processed by the router when delivering a message. This
option has no effect when an address is being verified. The \headers@_remove\
option is expanded after \errors@_to\ and \headers@_add\, but before
\transport\. If the expansion is forced to fail, the option has no effect.
Other expansion failures are treated as configuration errors. 

.em
After expansion, the string must consist of a colon-separated list of header
names. This is confusing, because header names themselves are often terminated
by colons. In this case, the colons are the list separators, not part of the
names.
.nem
For example:
.display asis
headers_remove = return-receipt-to:acknowledge-to
.endd
The list is used at transport time as described under \headers@_add\ above. The
\headers@_remove\ option cannot be used for a \%redirect%\ router that has the
\one@_time\ option set.

.conf ignore@_target@_hosts "host list$**$" unset
.index IP address||discarding
.index router||discarding IP addresses
Although this option is a host list, it should normally contain IP address
entries rather than names. If any host that is looked up by the router has an
IP address that matches an item in this list, Exim behaves as if that IP
address did not exist. This option allows you to cope with rogue DNS entries
like
.display asis
remote.domain.example.  A  127.0.0.1
.endd
by setting
.display asis
ignore_target_hosts = 127.0.0.1
.endd
on the relevant router. 
.em
If all the hosts found by a \%dnslookup%\ router are discarded in this way, the
router declines. In a conventional configuration, an attempt to mail to such a
domain would then normally provoke the `unrouteable domain' error, and an
attempt to verify an address in the domain would fail.

Similarly, if \ignore@_target@_hosts\ is set on an \%ipliteral%\ router, the
router declines if presented with one of the listed addresses.
.nem

This option may also be useful for ignoring link-local and site-local IPv6
addresses. Because, like all host lists, the value of \ignore@_target@_hosts\
is expanded before use as a list, it is possible to make it dependent on the
domain that is being routed.



.index additional groups
.index groups, additional
.index local transports||uid and gid
.index transport||local
.conf initgroups boolean false
If the router queues an address for a transport, and this option is true, and
the uid supplied by the router is not overridden by the transport, the
\*initgroups()*\ function is called when running the transport to ensure that
any additional groups associated with the uid are set up. See also \group\ and
\user\ and the discussion in chapter ~~CHAPenvironment.


.conf local@_part@_prefix "string list (precondition)" unset
.index router||prefix for local part
.index prefix||for local part, used in router
If this option is set, the router is skipped unless the local part
starts with one of the given strings, or \local@_part@_prefix@_optional\ is
true.
See section ~~SECTrouprecon for a list of the order in which preconditions
are evaluated.

The list is scanned from left to right, and the first prefix that matches is
used. A limited form of wildcard is available; if the prefix begins with an
asterisk, it matches the longest possible sequence of arbitrary characters at
the start of the local part. An asterisk should therefore always be followed by
some character that does not occur in normal local parts.
.index multiple mailboxes
.index mailbox||multiple
Wildcarding can be used to set up multiple user mailboxes, as described in
section ~~SECTmulbox.

During the testing of the \local@_parts\ option, and while the router is
running, the prefix is removed from the local part, and is available in the
expansion variable \$local@_part@_prefix$\. If the router accepts the address,
this remains true during subsequent delivery.
In particular, the local part that is transmitted in the \\RCPT\\ command 
for LMTP, SMTP, and BSMTP deliveries has the prefix removed by default. This 
behaviour can be overridden by setting \rcpt@_include@_affixes\ true on the 
relevant transport.

The prefix facility is commonly used to handle local parts of the form
\owner-something\. Another common use is to support local parts of the form
\real-username\ to bypass a user's \(.forward)\ file -- helpful when trying to
tell a user their forwarding is broken -- by placing a router like this one
immediately before the router that handles \(.forward)\ files:
.display asis
real_localuser:
  driver = accept
  local_part_prefix = real-
  check_local_user
  transport = local_delivery
.endd
If both \local@_part@_prefix\ and \local@_part@_suffix\ are set for a router,
both conditions must be met if not optional. Care must be taken if wildcards
are used in both a prefix and a suffix on the same router. Different
separator characters must be used to avoid ambiguity.

.conf local@_part@_prefix@_optional boolean false
See \local@_part@_prefix\ above.


.conf local@_part@_suffix "string list (precondition)" unset
.index router||suffix for local part
.index suffix for local part, used in router
This option operates in the same way as \local@_part@_prefix\, except that the
local part must end (rather than start) with the given string, the
\local@_part@_suffix@_optional\ option determines whether the suffix is
mandatory, and the wildcard $*$ character, if present, must be the last
character of the suffix. This option facility is commonly used to handle local
parts of the form \something-request\ and multiple user mailboxes of the form
\username-foo\.

.conf local@_part@_suffix@_optional boolean false
See \local@_part@_suffix\ above.


.conf local@_parts "local part list$**$ (precondition)" unset
.index router||restricting to specific local parts
.index local part||checking in router
The router is run only if the local part of the address matches the list.
See section ~~SECTrouprecon for a list of the order in which preconditions 
are evaluated, and
section ~~SECTlocparlis for a discussion of local part lists. Because the
string is expanded, it is possible to make it depend on the domain, for
example:
.display asis
local_parts = dbm;/usr/local/specials/$domain
.endd
If the match is achieved by a lookup, the data that the lookup returned
for the local part is placed in the variable \$local@_part@_data$\ for use in
expansions of the router's private options. You might use this option, for
example, if you have a large number of local virtual domains, and you want to
send all postmaster mail to the same place without having to set up an alias in
each virtual domain:
.display asis
postmaster:
  driver = redirect
  local_parts = postmaster
  data = postmaster@real.domain.example
.endd


.conf log@_as@_local boolean "see below"
.index log||delivery line
.index delivery||log line format
Exim has two logging styles for delivery, the idea being to make local
deliveries stand out more visibly from remote ones. In the `local' style, the
recipient address is given just as the local part, without a domain. The use of
this style is controlled by this option. It defaults to true for the \%accept%\
router, and false for all the others.


.conf more boolean$**$ true
The result of string expansion for this option must be a valid boolean value,
that is, one of the strings `yes', `no', `true', or `false'. Any other result
causes an error, and delivery is deferred. If the expansion is forced to fail,
the default value for the option (true) is used. Other failures cause delivery
to be deferred.

If this option is set false, and the router is run, but declines to handle the
address, no further routers are tried, routing fails, and the address is
bounced.
.index \self\ option
However, if the router explicitly passes an address to the following router by
means of the setting
.display asis
self = pass
.endd
or otherwise, the setting of \more\ is ignored. Also, the setting of \more\
does not affect the behaviour if one of the precondition tests fails. In that
case, the address is always passed to the next router.


.conf pass@_on@_timeout boolean false
.index timeout||of router
.index router||timeout
If a router times out during a host lookup, it normally causes deferral of the
address. If \pass@_on@_timeout\ is set, the address is passed on to the next
router, overriding \no@_more\. This may be helpful for systems that are
intermittently connected to the Internet, or those that want to pass to a smart
host any messages that cannot immediately be delivered.

There are occasional other temporary errors that can occur while doing DNS
lookups. They are treated in the same way as a timeout, and this option
applies to all of them.


.conf pass@_router string unset
.index router||go to after `pass'
When a router returns `pass', the address is normally handed on to the next
router in sequence. This can be changed by setting \pass@_router\ to the name
of another router. However (unlike \redirect@_router\) the named router must be
below the current router, to avoid loops. Note that this option applies only to
the special case of `pass'. It does not apply when a router returns `decline'.


.conf redirect@_router string unset
.index router||start at after redirection
Sometimes an administrator knows that it is pointless to reprocess addresses
generated from alias or forward files with the same router again. For
example, if an alias file translates real names into login ids there is no
point searching the alias file a second time, especially if it is a large file.

The \redirect@_router\ option can be set to the name of any router instance. It
causes the routing of any generated addresses to start at the named router
instead of at the first router. This option has no effect if the router in
which it is set does not generate new addresses.


.conf require@_files "string list$**$ (precondition)" unset
.index file||requiring for router
.index router||requiring file existence
This option provides a general mechanism for predicating the running of a
router on the existence or non-existence of certain files or directories.
Before running a router, as one of its precondition tests, Exim works its way
through the \require@_files\ list, expanding each item separately. 

Because the list is split before expansion, any colons in expansion items must
be doubled, or the facility for using a different list separator must be used.
If any expansion is forced to fail, the item is ignored. Other expansion 
failures cause routing of the address to be deferred.

If any expanded string is empty, it is ignored. Otherwise, except as described
below, each string must be a fully qualified file path, optionally preceded by
`!'. The paths are passed to the \*stat()*\ function to test for the existence
of the files or directories. The router is skipped if any paths not preceded by
`!' do not exist, or if any paths preceded by `!' do exist.

.index NFS
If \*stat()*\ cannot determine whether a file exists or not, delivery of
the message is deferred. This can happen when NFS-mounted filesystems are
unavailable.

This option is checked after the \domains\, \local@_parts\, and \senders\
options, so you cannot use it to check for the existence of a file in which to
look up a domain, local part, or sender. (See section ~~SECTrouprecon for a
full list of the order in which preconditions are evaluated.) However, as
these options are all expanded, you can use the \exists\ expansion condition to
make such tests. The \require@_files\ option is intended for checking files
that the router may be going to use internally, or which are needed by a
transport (for example \(.procmailrc)\).

During delivery, the \*stat()*\ function is run as root, but there is a
facility for some checking of the accessibility of a file by another user. 
This is not a proper permissions check, but just a `rough' check that
operates as follows:

If an item in a \require@_files\ list does not contain any forward slash
characters, it is taken to be the user (and optional group, separated by a
comma) to be checked for subsequent files in the list. If no group is specified
but the user is specified symbolically, the gid associated with the uid is
used. For example:
.display asis
require_files = mail:/some/file
require_files = $local_part:$home/.procmailrc
.endd
If a user or group name in a \require@_files\ list does not exist, the
\require@_files\ condition fails.

Exim performs the check by scanning along the components of the file path, and
checking the access for the given uid and gid. It checks for `x' access on
directories, and `r' access on the final file. Note that this means that file
access control lists, if the operating system has them, are ignored.

\**Warning 1**\: When the router is being run to verify addresses for an
incoming SMTP message, Exim is not running as root, but under its own uid. This
may affect the result of a \require@_files\ check. In particular, \*stat()*\
may yield the error \\EACCES\\ (`Permission denied'). This means that the Exim
user is not permitted to read one of the directories on the file's path.

\**Warning 2**\: Even when Exim is running as root while delivering a message, 
\*stat()*\ can yield \\EACCES\\ for a file on an NFS directory that is mounted 
without root access.

In both cases, 
the default action is to consider this a configuration error, and routing is
deferred because the existence or non-existence of the file cannot be
determined. However, in some circumstances it may be desirable to treat this
condition as if the file did not exist. If the file name (or the exclamation
mark that precedes the file name for non-existence) is preceded by a plus sign,
the \\EACCES\\ error is treated as if the file did not exist. For example:
.display asis
require_files = +/some/file
.endd
If the router is not an essential part of verification (for example, it
handles users' \(.forward)\ files), another solution is to set the \verify\ 
option false so that the router is skipped when verifying.


.conf retry@_use@_local@_part boolean "see below"
.index hints database||retry keys
.index local part||in retry keys
When a delivery suffers a temporary routing failure, a retry record is created
in Exim's hints database. For addresses whose routing depends only on the
domain, the key for the retry record should not involve the local part, but for
other addresses, both the domain and the local part should be included.
Usually, remote routing is of the former kind, and local routing is of the
latter kind.

This option controls whether the local part is used to form the key for retry
hints for addresses that suffer temporary errors while being handled by this
router. The default value is true for any router that has \check@_local@_user\
set, and false otherwise. Note that this option does not apply to hints keys
for transport delays; they are controlled by a generic transport option of the
same name.

.em
The setting of \retry@_use@_local@_part\ applies only to the router on which it 
appears. If the router generates child addresses, they are routed 
independently; this setting does not become attached to them.
.nem


.conf router@_home@_directory string$**$ unset
.index router||home directory for
.index home directory||for router
This option sets a home directory for use while the router is running. (Compare
\transport__home@_directory\, which sets a home directory for later
transporting.) In particular, if used on a \%redirect%\ router, this option
sets a value for \$home$\ while a filter is running. The value is expanded;
forced expansion failure causes the option to be ignored -- other failures
cause the router to defer.

Expansion of \router@_home@_directory\ happens immediately after the
\check@_local@_user\ test (if configured), before any further expansions take
place. 
(See section ~~SECTrouprecon for a list of the order in which preconditions
are evaluated.)
While the router is running, \router__home@_directory\ overrides the value of
\$home$\ that came from \check@_local@_user\.

When a router accepts an address and routes it to a transport (including the
cases when a redirect router generates a pipe, file, or autoreply delivery),
the home directory setting for the transport is taken from the first of these
values that is set:
.numberpars $.
The \home@_directory\ option on the transport;
.nextp
The \transport@_home@_directory\ option on the router;
.nextp
The password data if \check@_local@_user\ is set on the router;
.nextp
The \router@_home@_directory\ option on the router.
.endp
In other words, \router@_home@_directory\ overrides the password data for the
router, but not for the transport.


.conf self string "freeze"
.index MX record||pointing to local host
.index local host||MX pointing to
This option applies to those routers that use a recipient address to find a
list of remote hosts. Currently, these are the \%dnslookup%\, \%ipliteral%\,
and \%manualroute%\ routers. 
Certain configurations of the \%queryprogram%\ router can also specify a list
of remote hosts.
Usually such routers are configured to send the message to a remote host via an
\%smtp%\ transport. The \self\ option specifies what happens when the first
host on the list turns out to be the local host.
The way in which Exim checks for the local host is described in section
~~SECTreclocipadd.

Normally this situation indicates either an error in Exim's configuration (for
example, the router should be configured not to process this domain), or an
error in the DNS (for example, the MX should not point to this host). For this
reason, the default action is to log the incident, defer the address, and
freeze the message. The following alternatives are provided for use in special
cases:
.numberpars $.
\defer\
.newline
Delivery of the message is tried again later, but the message is not frozen.
.nextp
\reroute: <<domain>>\
.newline
The domain is changed to the given domain, and the address is passed back to
be reprocessed by the routers. No rewriting of headers takes place. This
behaviour is essentially a redirection.
.nextp
\reroute: rewrite: <<domain>>\
.newline
The domain is changed to the given domain, and the address is passed back to be
reprocessed by the routers. Any headers that contain the original domain are
rewritten.
.nextp
\pass\
.newline
The router passes the address to the next router, or to the router named in the
\pass@_router\ option if it is set.
.index \more\ option
This overrides \no@_more\.

During subsequent routing and delivery, the variable
\$self@_hostname$\ contains the name of the local host that the router
encountered. This can be used to distinguish between different cases for hosts
with multiple names. The combination
.display asis
self = pass
no_more
.endd
ensures that only those addresses that routed to the local host are passed on.
Without \no@_more\, addresses that were declined for other reasons would also
be passed to the next router.
.nextp
\fail\
.newline
Delivery fails and an error report is generated.
.nextp
\send\
.newline
.index local host||sending to
The anomaly is ignored and the address is queued for the transport. This
setting should be used with extreme caution. For an \%smtp%\ transport, it makes
sense only in cases where the program that is listening on the SMTP port is not
this version of Exim. That is, it must be some other MTA, or Exim with a
different configuration file that handles the domain in another way.
.endp

.conf senders "address list$**$ (precondition)" unset
.index router||checking senders
If this option is set, the router is skipped unless the message's sender
address matches something on the list. 
See section ~~SECTrouprecon for a list of the order in which preconditions 
are evaluated.

There are issues concerning verification when the running of routers is
dependent on the sender. When Exim is verifying the address in an \errors@_to\
setting, it sets the sender to the null string. When using the \-bt-\ option to
check a configuration file, it is necessary also to use the \-f-\ option to set
an appropriate sender. For incoming mail, the sender is unset when verifying
the sender, but is available when verifying any recipients. If the SMTP
\\VRFY\\ command is enabled, it must be used after \\MAIL\\ if the sender
address matters.

.conf translate@_ip@_address string$**$ unset
.index IP address||translating
.index packet radio
.index router||IP address translation
There exist some rare networking situations (for example, packet radio) where
it is helpful to be able to translate IP addresses generated by normal routing
mechanisms into other IP addresses, thus performing a kind of manual IP
routing. This should be done only if the normal IP routing of the TCP/IP stack
is inadequate or broken. Because this is an extremely uncommon requirement, the
code to support this option is not included in the Exim binary unless
\\SUPPORT__TRANSLATE__IP__ADDRESS\\=yes is set in \(Local/Makefile)\.

The \translate@_ip@_address\ string is expanded for every IP address generated
by the router, with the generated address set in \$host@_address$\. If the
expansion is forced to fail, no action is taken. 
For any other expansion error, delivery of the message is deferred.
If the result of the expansion is an IP address, that replaces the original
address; otherwise the result is assumed to be a host name -- this is looked up
using \*gethostbyname()*\ (or \*getipnodebyname()*\ when available) to produce
one or more replacement IP addresses. For example, to subvert all IP addresses
in some specific networks, this could be added to a router:
.display
$smc{translate@_ip@_address = @\
  @$@{lookup@{@$@{mask:@$host@_address/26@}@}lsearch@{/some/file@}@{@$value@}fail@}}
.endd
The file would contain lines like
.display asis
10.2.3.128/26    some.host
10.8.4.34/26     10.44.8.15
.endd
You should not make use of this facility unless you really understand what you
are doing.


.conf transport string$**$ unset
This option specifies the transport to be used when a router accepts an address
and sets it up for delivery. A transport is never needed if a router is used
only for verification. The value of the option is expanded at routing time, 
after the expansion of \errors@_to\, 
\headers@_add\, and \headers@_remove\,
and result must be the name of one of the configured transports. If it is
not, delivery is deferred.

The \transport\ option is not used by the \%redirect%\ router, but it does have
some private options that set up transports for pipe and file deliveries (see
chapter ~~CHAPredirect).


.conf transport@_current@_directory string$**$ unset
.index current directory for local transport
This option associates a current directory with any address that is routed
to a local transport. This can happen either because a transport is
explicitly configured for the router, or because it generates a delivery to a
file or a pipe. During the delivery process (that is, at transport time), this
option string is expanded and is set as the current directory, unless
overridden by a setting on the transport.
If the expansion fails for any reason, including forced failure, an error is
logged, and delivery is deferred.
See chapter ~~CHAPenvironment for details of the local delivery environment.



.conf transport@_home@_directory string$**$ "see below"
.index home directory||for local transport
This option associates a home directory with any address that is routed to a
local transport. This can happen either because a transport is explicitly
configured for the router, or because it generates a delivery to a file or a
pipe. During the delivery process (that is, at transport time), the option
string is expanded and is set as the home directory, unless overridden by a
setting of \home@_directory\ on the transport.
If the expansion fails for any reason, including forced failure, an error is
logged, and delivery is deferred.

If the transport does not specify a home directory, and
\transport@_home@_directory\ is not set for the router, the home directory for
the tranport is taken from the password data if \check@_local@_user\ is set for
the router. Otherwise it is taken from \router@_home@_directory\ if that option
is set; if not, no home directory is set for the transport. 

See chapter ~~CHAPenvironment for further details of the local delivery
environment.



.conf unseen boolean$**$ false
.index router||carrying on after success
The result of string expansion for this option must be a valid boolean value,
that is, one of the strings `yes', `no', `true', or `false'. Any other result
causes an error, and delivery is deferred. If the expansion is forced to fail,
the default value for the option (false) is used. Other failures cause delivery
to be deferred.

When this option is set true, routing does not cease if the router accepts the
address. Instead, a copy of the incoming address is passed to the next router,
overriding a false setting of \more\. There is little point in setting \more\ 
false if \unseen\ is always true, but it may be useful in cases when the value 
of \unseen\ contains expansion items (and therefore, presumably, is sometimes
true and sometimes false).

The \unseen\ option can be used to cause
.index copy of message (\unseen\ option)
copies of messages to be delivered to some other destination, while also
carrying out a normal delivery. In effect, the current address is made into a 
`parent' that has two children -- one that is delivered as specified by this 
router, and a clone that goes on to be routed further.

Header lines added to the address (or specified for removal) by this router or
by previous routers affect the `unseen' copy of the message only. The clone
that continues to be processed by further routers starts with no added headers 
and none specified for removal.

However, any data that was set by the \address@_data\ option in the current or
previous routers is passed on. Setting this option has a similar effect to the
\unseen\ command qualifier in filter files.


.conf user string$**$ "see below"
.index uid (user id)||local delivery
.index local transports||uid and gid
.index transport||local
.index router||user for filter processing
.index filter||user for processing
When a router queues an address for a transport, and the transport does not
specify a user, the user given here is used when running the delivery process.
The user may be specified numerically or by name. If expansion fails, the 
error is logged and delivery is deferred.
This user is also used by the \%redirect%\ router when running a filter file.
The default is unset, except when \check@_local@_user\ is set. In this case,
the default is taken from the password information. If the user is specified as
a name, and \group\ is not set, the group associated with the user is used. See
also \initgroups\ and \group\ and the discussion in chapter ~~CHAPenvironment.


.conf verify "boolean (precondition)" true
Setting this option has the effect of setting \verify@_sender\ and
\verify@_recipient\ to the same value.

.conf verify@_only "boolean (precondition)" false
.index \\EXPN\\||with \verify@_only\
.index \-bv-\ option
.index router||used only when verifying
If this option is set, the router is used only when verifying an address or
testing with the \-bv-\ option, not when actually doing a delivery, testing
with the \-bt-\ option, or running the SMTP \\EXPN\\ command. It can be further
restricted to verifying only senders or recipients by means of \verify@_sender\
and \verify@_recipient\.

\**Warning**\: When the router is being run to verify addresses for an incoming
SMTP message, Exim is not running as root, but under its own uid. If the router 
accesses any files, you need to make sure that they are accessible to the Exim 
user or group.

.conf verify@_recipient "boolean (precondition)" true
If this option is false, the router is skipped when verifying recipient
addresses
or testing recipient verification using \-bv-\.
See section ~~SECTrouprecon for a list of the order in which preconditions 
are evaluated.

.conf verify@_sender "boolean (precondition)" true
If this option is false, the router is skipped when verifying sender addresses
or testing sender verification using \-bvs-\.
See section ~~SECTrouprecon for a list of the order in which preconditions 
are evaluated.

.endconf





.
.
.
.
. ============================================================================
.chapter The accept router
.set runningfoot "accept router"
.index \%accept%\ router
.index routers||\%accept%\
The \%accept%\ router has no private options of its own. Unless it is being used
purely for verification (see \verify@_only\) a transport is required to be
defined by the generic \transport\ option. If the preconditions that are
specified by generic options are met, the router accepts the address and queues
it for the given transport. The most common use of this router is for setting
up deliveries to local mailboxes. For example:
.display asis
localusers:
  driver = accept
  domains = mydomain.example
  check_local_user
  transport = local_delivery
.endd
The \domains\ condition in this example checks the domain of the address, and
\check@_local@_user\ checks that the local part is the login of a local user.
When both preconditions are met, the \%accept%\ router runs, and queues the
address for the \%local@_delivery%\ transport.






.
.
.
.
. ============================================================================
.chapter The dnslookup router
.rset CHAPdnslookup "~~chapter"
.set runningfoot "dnslookup router"
.index \%dnslookup%\ router
.index routers||\%dnslookup%\
The \%dnslookup%\ router looks up the hosts that handle mail for the given
domain in the DNS. A transport must always be set for this router, unless
\verify@_only\ is set.

.em
If SRV support is configured (see \check@_srv\ below), Exim first searches for 
SRV records. If none are found, or if SRV support is not configured,
MX records are looked up. If no MX records exist, address records are sought.
However, \mx@_domains\ can be set to disable the direct use of address records.

MX records of equal priority are sorted by Exim into a random order. Exim then
looks for address records for the host names obtained from MX or SRV records.
When a host has more than one IP address, they are sorted into a random order,
except that IPv6 addresses are always sorted before IPv4 addresses. If all the
IP addresses found are discarded by a setting of the \ignore@_target@_hosts\
generic option, the router declines.

Unless they have the highest priority (lowest MX value), MX records that point
to the local host, or to any host name that matches \hosts__treat__as__local\,
are discarded, together with any other MX records of equal or lower priority.
.nem

.index MX record||pointing to local host
.index local host||MX pointing to
.index \self\ option||in \%dnslookup%\ router
If the host pointed to by the highest priority MX record, or looked up as an
address record, is the local host, or matches \hosts__treat__as__local\, what
happens is controlled by the generic \self\ option.

There are a number of private options that can be used to vary the way the DNS
lookup is handled.


.startconf
.index options||\%dnslookup%\ router
.conf check@_secondary@_mx boolean false
.index MX record||checking for secondary
If this option is set, the router declines unless the local host is found in
(and removed from) the list of hosts obtained by MX lookup. This can be used to
process domains for which the local host is a secondary mail exchanger
differently to other domains. The way in which Exim decides whether a host is
the local host is described in section ~~SECTreclocipadd.

.em
.conf check@_srv string$**$ unset
.index SRV record||enabling use of
The dnslookup router supports the use of SRV records (see RFC 2782) in
addition to MX and address records. The support is disabled by default. To
enable SRV support, set the \check@_srv\ option to the name of the service
required. For example,
.display asis
check_srv = smtp
.endd
looks for SRV records that refer to the normal smtp service. The option is
expanded, so the service name can vary from message to message or address
to address. This might be helpful if SRV records are being used for a
submission service. If the expansion is forced to fail, the \check@_srv\
option is ignored, and the router proceeds to look for MX records in the
normal way.

When the expansion succeeds, the router searches first for SRV records for
the given service (it assumes TCP protocol). A single SRV record with the
host name \"."\ indicates `no such service for this domain'; if this is
encountered, the router declines. If other kinds of SRV record are found,
they are used to construct a host list for delivery according to the rules
of RFC 2782. MX records are not sought in this case.

However, when no SRV records are found, MX records (and address records)
are sought in the traditional way. In other words, SRV records take
precedence over MX records, just as MX records take precedence over address
records. Note that this behaviour is not sanctioned by RFC 2782, though a
previous draft RFC defined it. It is apparently believed that MX records
are sufficient for email and that SRV records should not be used for this
purpose. However, SRV records have an additional `weight' feature which
some people might find useful when trying to split an SMTP load between
hosts of different power.
.nem

.conf mx@_domains "domain list$**$" unset
.index MX record||required to exist
.index SRV record||required to exist
.em
A domain that matches \mx@_domains\ is required to have either an MX or an SRV
record in order to be recognised. (The name of this option could be improved.)
.nem
For example, if all the mail hosts in \*fict.example*\ are known to have MX
records, except for those in \*discworld.fict.example*\, you could use this
setting:
.display asis
mx_domains = ! *.discworld.fict.example : *.fict.example
.endd
This specifies that messages addressed to a domain that matches the list but
has no MX record should be bounced immediately instead of being routed using
the address record.

.conf qualify@_single boolean true
.index DNS||resolver options
.index DNS||qualifying single-component names
When this option is true, the resolver option \\RES@_DEFNAMES\\ is set for DNS
lookups. Typically, but not standardly, this causes the resolver to qualify
single-component names with the default domain. For example, on a machine
called \*dictionary.ref.example*\, the domain \*thesaurus*\ would be changed to
\*thesaurus.ref.example*\ inside the resolver. For details of what your resolver
actually does, consult your man pages for \*resolver*\ and \*resolv.conf*\.


.conf rewrite@_headers boolean true
.index rewriting||header lines
.index header lines||rewriting
If the domain name in the address that is being processed is not fully
qualified, it may be expanded to its full form by a DNS lookup. For example, if
an address is specified as \*dormouse@@teaparty*\, the domain might be
expanded to \*teaparty.wonderland.fict.example*\. Domain expansion can also
occur as a result of setting the \widen@_domains\ option. If \rewrite@_headers\
is true, all occurrences of the abbreviated domain name in any ::Bcc::, ::Cc::,
::From::, ::Reply-to::, ::Sender::, and ::To:: header lines of the message are
rewritten with the full domain name.

This option should be turned off only when it is known that no message is
ever going to be sent outside an environment where the abbreviation makes
sense.

When an MX record is looked up in the DNS and matches a wildcard record, name
servers normally return a record containing the name that has been looked up,
making it impossible to detect whether a wildcard was present or not. However,
some name servers have recently been seen to return the wildcard entry. If the
name returned by a DNS lookup begins with an asterisk, it is not used for
header rewriting.

.conf same@_domain@_copy@_routing boolean false
.index address||copying routing
Addresses with the same domain are normally routed by the \%dnslookup%\ router
to the same list of hosts. However, this cannot be presumed, because the router
options and preconditions may refer to the local part of the address. By
default, therefore, Exim routes each address in a message independently. DNS
servers run caches, so repeated DNS lookups are not normally expensive, and in
any case, personal messages rarely have more than a few recipients.

If you are running mailing lists with large numbers of subscribers at the same
domain, and you are using a \%dnslookup%\ router which is independent of the
local part, you can set \same__domain__copy@_routing\ to bypass repeated DNS
lookups for identical domains in one message. In this case, when \%dnslookup%\
routes an address to a remote transport, any other unrouted addresses in the
message that have the same domain are automatically given the same routing
without processing them independently,
provided the following conditions are met:
.numberpars $.
No router that processed the address specified \headers@_add\ or 
\headers@_remove\.
.nextp
The router did not change the address in any way, for example, by `widening' 
the domain.
.endp


.conf search@_parents boolean false
.index DNS||resolver options
When this option is true, the resolver option \\RES@_DNSRCH\\ is set for DNS
lookups. This is different from the \qualify@_single\ option in that it applies
to domains containing dots. Typically, but not standardly, it causes the
resolver to search for the name in the current domain and in parent domains.
For example, on a machine in the \*fict.example*\ domain, if looking up
\*teaparty.wonderland*\ failed, the resolver would try
\*teaparty.wonderland.fict.example*\. For details of what your resolver
actually does, consult your man pages for \*resolver*\ and \*resolv.conf*\.

Setting this option true can cause problems in domains that have a wildcard MX
record, because any domain that does not have its own MX record matches the
local wildcard.

.conf widen@_domains "string list" unset
.index domain||partial, widening
If a DNS lookup fails and this option is set, each of its strings in turn is
added onto the end of the domain, and the lookup is tried again. For example,
if
.display asis
widen_domains = fict.example:ref.example
.endd
is set and a lookup of \*klingon.dictionary*\ fails,
\*klingon.dictionary.fict.example*\ is looked up, and if this fails,
\*klingon.dictionary.ref.example*\ is tried. Note that the \qualify@_single\
and \search@_parents\ options can cause some widening to be undertaken inside
the DNS resolver.

.endconf

.em
.section Effect of qualify@_single and search@_parents
When a domain from an envelope recipient is changed by the resolver as a result 
of the \qualify@_single\ or \search@_parents\ options, Exim rewrites the
corresponding address in the message's header lines unless \rewrite@_headers\
is set false. Exim then re-routes the address, using the full domain.

These two options affect only the DNS lookup that takes place inside the router
for the domain of the address that is being routed. They do not affect lookups
such as that implied by
.display asis
domains = @mx_any
.endd
that may happen while processing a router precondition before the router is
entered. No widening ever takes place for these lookups.
.nem









.
.
.
.
. ============================================================================
.chapter The ipliteral router
.set runningfoot "ipliteral router"
.index \%ipliteral%\ router
.index domain literal||routing 
.index routers||\%ipliteral%\
This router has no private options. Unless it is being used purely for
verification (see \verify@_only\) a transport is required to be defined by the
generic \transport\ option. The router accepts the address if its domain part
takes the form of an RFC 2822 domain literal, that is, an IP address enclosed
in square brackets. For example, this router handles the address
.display asis
root@[192.168.1.1]
.endd
by setting up delivery to the host with that IP address. 

.em
If the IP address matches something in \ignore@_target@_hosts\, the router 
declines.
.nem
.index \self\ option||in \%ipliteral%\ router
If an IP literal turns out to refer to the local host, the generic \self\
option determines what happens. 

The RFCs require support for domain literals; however, their use is
controversial in today's Internet. If you want to use this router, you must
also set the main configuration option \allow@_domain@_literals\. Otherwise,
Exim will not recognize the domain literal syntax in addresses.



.
.
.
.
. ============================================================================
.chapter The iplookup router
.set runningfoot "iplookup router"
.index \%iplookup%\ router
.index routers||\%iplookup%\
The \%iplookup%\ router was written to fulfil a specific requirement in
Cambridge University. For this reason, it is not included in the binary of Exim
by default. If you want to include it, you must set
.display asis
ROUTER_IPLOOKUP=yes
.endd
in your \(Local/Makefile)\ configuration file.

The \%iplookup%\ router routes an address by sending it over a TCP or UDP
connection to one or more specific hosts. The host can then return the same or
a different address -- in effect rewriting the recipient address in the
message's envelope. The new address is then passed on to subsequent routers.


If this process fails, the address can be passed on to
other routers, or delivery can be deferred.

Background, for those that are interested: We have an Oracle database of all
Cambridge users, and one of the items of data it maintains for each user is
where to send mail addressed to \*user@@cam.ac.uk*\. The MX records for
\*cam.ac.uk*\ point to a central machine that has a large alias list that is
abstracted from the database. Mail from outside is switched by this system, and
originally internal mail was also done this way. However, this resulted in a
fair number of messages travelling from some of our larger systems to the
switch and back again. The Oracle machine now runs a UDP service that can be
called by the \%iplookup%\ router in Exim to find out where \*user@@cam.ac.uk*\
addresses really have to go; this saves passing through the central switch, and
in many cases saves doing any remote delivery at all.

Since \%iplookup%\ is just a rewriting router, a transport must not be
specified for it.

.startconf
.index options||\%iplookup%\ router

.conf hosts string unset
This option must be supplied. Its value is a colon-separated list of host
names. The hosts are looked up using \*gethostbyname()*\ 
(or \*getipnodebyname()*\ when available)
and are tried in order until one responds to the query. If none respond, what
happens is controlled by \optional\.

.conf optional boolean false
If \optional\ is true, if no response is obtained from any host, the address is
passed to the next router, overriding \no@_more\. If \optional\ is false,
delivery to the address is deferred.

.conf port integer 0
.index port||\%iplookup%\ router
This option must be supplied. It specifies the port number for the TCP or UDP
call.

.conf protocol string "udp"
This option can be set to `udp' or `tcp' to specify which of the two protocols
is to be used.

.conf query string$**$ "$tt{@$local@_part@@@$domain @$local@_part@@@$domain}"
This defines the content of the query that is sent to the remote hosts. The
repetition serves as a way of checking that a response is to the correct query
in the default case (see \response@_pattern\ below).

.conf reroute string$**$ unset
If this option is not set, the rerouted address is precisely the byte string
returned by the remote host, up to the first white space, if any. If set, the
string is expanded to form the rerouted address. It can include parts matched
in the response by \response@_pattern\ by means of numeric variables such as
\$1$\, \$2$\, etc. The variable \$0$\ refers to the entire input string,
whether or not a pattern is in use. In all cases, the rerouted address must end
up in the form \*local@_part@@domain*\.

.conf response@_pattern string unset
This option can be set to a regular expression that is applied to the string
returned from the remote host. If the pattern does not match the response, the
router declines. If \response@_pattern\ is not set, no checking of the response
is done, unless the query was defaulted, in which case there is a check that
the text returned after the first white space is the original address. This
checks that the answer that has been received is in response to the correct
question. For example, if the response is just a new domain, the following
could be used:
.display asis
response_pattern = ^([^@]+)$
reroute = $local_part@$1
.endd

.conf timeout time 5s
This specifies the amount of time to wait for a response from the remote
machine. The same timeout is used for the \*connect()*\ function for a TCP
call. It does not apply to UDP.

.endconf




.
.
.
.
. ============================================================================
.chapter The manualroute router
.set runningfoot "manualroute router"
.index \%manualroute%\ router
.index routers||\%manualroute%\
.index domain||manually routing
The \%manualroute%\ router is so-called because it provides a way of manually
routing an address according to its domain. It is mainly used when you want to
route addresses to remote hosts according to your own rules, bypassing the
normal DNS routing that looks up MX records. However, \%manualroute%\ can also
route to local transports, a facility that may be useful if you want to save
messages for dial-in hosts in local files.

The \%manualroute%\ router compares a list of domain patterns with the domain it
is trying to route. If there is no match, the router declines. Each pattern has
associated with it a list of hosts and some other optional data, which may
include a transport. The combination of a pattern and its data is called a
`routing rule'. For patterns that do not have an associated transport, the
generic \transport\ option must specify a transport, unless the router is being
used purely for verification (see \verify@_only\).

In the case of verification, matching the domain pattern is sufficient for the
router to accept the address. When actually routing an address for delivery,
an address that matches a domain pattern is queued for the associated
transport. If the transport is not a local one, a host list must be associated
with the pattern; IP addresses are looked up for the hosts, and these are
passed to the transport along with the mail address. For local transports, a
host list is optional. If it is present, it is passed in \$host$\ as a single
text string.

The list of routing rules can be provided as an inline string in \route@_list\,
or the data can be obtained by looking up the domain in a file or database by
setting \route@_data\. Only one of these settings may appear in any one
instance of \%manualroute%\. The format of routing rules is described below,
following the list of private options.

.section Private options for manualroute
.rset SECTprioptman "~~chapter.~~section"

The private options for the \%manualroute%\ router are as follows:

.startconf
.index options||\%manualroute%\ router

.conf host@_find@_failed string "freeze"
This option controls what happens when \%manualroute%\ tries to find an IP
address for a host, and the host does not exist. The option can be set to one
of
.display asis
decline
defer
fail
freeze
pass
.endd
The default assumes that this state is a serious configuration error. The
difference between `pass' and `decline' is that the former forces the address
to be passed to the next router (or the router defined by \pass@_router\),
.index \more\ option
overriding \no@_more\, whereas the latter passes the address to the next router
only if \more\ is true.

This option applies only to a definite `does not exist' state; if a host lookup
gets a temporary error, delivery is deferred unless the generic
\pass@_on@_timeout\ option is set.

.conf hosts@_randomize boolean false
.index randomized host list
.index host||list of, randomized
If this option is set, the order of the items in a host list in a routing rule
is randomized each time the list is used, unless an option in the routing rule
overrides (see below). Randomizing the order of a host list can be used to do
crude load sharing. However, if more than one mail address is routed by the
same router to the same host list, the host lists are considered to be the same
(even though they may be randomized into different orders) for the purpose of
deciding whether to batch the deliveries into a single SMTP transaction.

When \hosts@_randomize\ is true, a host list may be split
into groups whose order is separately randomized. This makes it possible to
set up MX-like behaviour. The boundaries between groups are indicated by an
item that is just \"+"\ in the host list. For example:
.display asis
route_list = * host1:host2:host3:+:host4:host5
.endd
The order of the first three hosts and the order of the last two hosts is
randomized for each use, but the first three always end up before the last two.
If \hosts@_randomize\ is not set, a \"+"\ item in the list is ignored. If a
randomized host list is passed to an \%smtp%\ transport that also has
\hosts@_randomize set\, the list is not re-randomized.

.conf route@_data string$**$ unset
If this option is set, it must expand to yield the data part of a routing rule.
Typically, the expansion string includes a lookup based on the domain. For
example:
.display asis
route_data = ${lookup{$domain}dbm{/etc/routes}}
.endd
If the expansion is forced to fail, or the result is an empty string, the
router declines. Other kinds of expansion failure cause delivery to be
deferred.

.conf route@_list "string list, semicolon-separated" unset
This string is a list of routing rules, in the form defined below. Note that,
unlike most string lists, the items are separated by semicolons. This is so
that they may contain colon-separated host lists.

.conf same@_domain@_copy@_routing boolean false
.index address||copying routing
Addresses with the same domain are normally routed by the \%manualroute%\ router
to the same list of hosts. However, this cannot be presumed, because the router
options and preconditions may refer to the local part of the address. By
default, therefore, Exim routes each address in a message independently. DNS
servers run caches, so repeated DNS lookups are not normally expensive, and in
any case, personal messages rarely have more than a few recipients.

If you are running mailing lists with large numbers of subscribers at the same
domain, and you are using a \%manualroute%\ router which is independent of the
local part, you can set \same@_domain@_copy@_routing\ to bypass repeated DNS
lookups for identical domains in one message. In this case, when \%manualroute%\
routes an address to a remote transport, any other unrouted addresses in the
message that have the same domain are automatically given the same routing
without processing them independently. However, this is only done if
\headers@_add\ and \headers@_remove\ are unset.

.endconf


.section Routing rules in route@_list
The value of \route@_list\ is a string consisting of a sequence of routing
rules, separated by semicolons. If a semicolon is needed in a rule, it can be
entered as two semicolons. Empty rules are ignored. The format of each rule is
.display
<<domain pattern>>  <<list of hosts>>  <<options>>
.endd
The following example contains two rules, each with a simple domain pattern and
no options:
.display asis
route_list = \
  dict.ref.example  mail-1.ref.example:mail-2.ref.example ; \
  thes.ref.example  mail-3.ref.example:mail-4.ref.example
.endd
The three parts of a rule are separated by white space. The pattern and the 
list of hosts can be enclosed in quotes if necessary, and if they are, the
usual quoting rules apply. Each rule in a \route@_list\ must start with a
single domain pattern, which is the only mandatory item in the rule. The
pattern is in the same format as one item in a domain list (see section
~~SECTdomainlist), 
except that it may not be the name of an interpolated file.
That is, it may be wildcarded, or a regular expression, or a file or database
lookup (with semicolons doubled, because of the use of semicolon as a separator
in a \route@_list\).

The rules in \route@_list\ are searched in order until one of the patterns
matches the domain that is being routed. The list of hosts and then options are
then used as described below. If there is no match, the router declines. When
\route@_list\ is set, \route@_data\ must not be set.


.section Routing rules in route@_data
The use of \route@_list\ is convenient when there are only a small number of
routing rules. For larger numbers, it is easier to use a file or database to
hold the routing information, and use the \route@_data\ option instead.
The value of \route@_data\ is a list of hosts, followed by (optional) options.
Most commonly, \route@_data\ is set as a string that contains an
expansion lookup. For example, suppose we place two routing rules in a file
like this:
.display asis
dict.ref.example:  mail-1.ref.example:mail-2.ref.example
thes.ref.example:  mail-3.ref.example:mail-4.ref.example
.endd
This data can be accessed by setting
.display asis
route_data = ${lookup{$domain}lsearch{/the/file/name}}
.endd
Failure of the lookup results in an empty string, causing the router to
decline. However, you do not have to use a lookup in \route@_data\. The only
requirement is that the result of expanding the string is a list of hosts,
possibly followed by options, separated by white space. The list of hosts must
be enclosed in quotes if it contains white space.



.section Format of the list of hosts
A list of hosts, whether obtained via \route@_data\ or \route@_list\, is always
separately expanded before use. If the expansion fails, the router declines.
The result of the expansion must be a colon-separated list of names and/or
IP addresses. IP addresses are not enclosed in brackets.

If the list of hosts was obtained from a \route@_list\ item, the following
variables are set during its expansion:
.index numerical variables (\$1$\, \$2$\, etc)||in \%manualroute%\ router
.numberpars $.
If the domain was matched against a regular expression, the numeric variables
\$1$\, \$2$\, etc. may be set.
.nextp
\$0$\ is always set to the entire domain.
.nextp
\$1$\ is also set when partial matching is done in a file lookup.
.nextp
.index \$value$\
If the pattern that matched the domain was a lookup item, the data that was
looked up is available in the expansion variable \$value$\.
.endp


.em
.section How the list of hosts is used
When an address is routed to an \%smtp%\ transport by \%manualroute%\, each of 
the hosts is tried, in the order specified, when carrying out the SMTP
delivery. However, the order can be changed by setting the \hosts@_randomize\
option, either on the router (see section ~~SECTprioptman above), or on the
transport.

Hosts may be listed by name or by IP address. An unadorned name in the list of
hosts is interpreted as a host name. A name that is followed by \"/MX"\ is
interpreted as an indirection to a sublist of hosts obtained by looking up MX
records in the DNS. For example:
.display asis
route_list = *  x.y.z:p.q.r/MX:e.f.g
.endd
If the \hosts@_randomize\ option is set, the order of the items in the list is
randomized before any lookups are done. Exim then scans the list; for any name 
that is not followed by \"/MX"\ it looks up an IP address. If this turns out to 
be an interface on the local host and the item is not the first in the list,
Exim discards it and any subsequent items. If it is the first item, what
happens is controlled by the 
.index \self\ option||in \%manualroute%\ router
\self\ option of the router.

A name on the list that is followed by \"/MX"\ is replaced with the list of
hosts obtained by looking up MX records for the name. This is always a DNS
lookup; the \bydns\ and \byname\ options (see section ~~SECThowoptused below)
are not relevant here. The order of these hosts is determined by the preference
values in the MX records, according to the usual rules. Because randomizing
happens before the MX lookup, it does not affect the order that is defined by
MX preferences.
.nem

If the local host is present in the sublist obtained from MX records, but is
not the most preferred host in that list, it and any equally or less
preferred hosts are removed before the sublist is inserted into the main list.

If the local host is the most preferred host in the MX list, what happens
depends on where in the original list of hosts the \"/MX"\ item appears. If it
is not the first item (that is, there are previous hosts in the main list),
Exim discards this name and any subsequent items in the main list.

If the MX item is first in the list of hosts, and the local host is the
most preferred host, what happens is controlled by the \self\ option of the
router.

DNS failures when lookup up the MX records are treated in the same way as DNS
failures when looking up IP addresses: \pass@_on@_timeout\ and
\host@_find@_failed\ are used when relevant.

.em
The generic \ignore@_target@_hosts\ option applies to all hosts in the list,
whether obtained from an MX lookup or not.
.nem


.section How the options are used
.rset SECThowoptused "~~chapter.~~section"
The options are a sequence of words; in practice no more than three are ever
present. One of the words can be the name of a transport; this overrides the
\transport\ option on the router for this particular routing rule only. The
other words (if present) control randomization of the list of hosts on a
per-rule basis, and how the IP addresses of the hosts are to be found when
routing to a remote transport. These options are as follows:
.numberpars $.
\randomize\: randomize the order of the hosts in this list, overriding the 
setting of \hosts@_randomize\ for this routing rule only.
.nextp
\no@_randomize\: do not randomize the order of the hosts in this list,
overriding the setting of \hosts@_randomize\ for this routing rule only.
.nextp
\byname\: use \*getipnodebyname()*\ (\*gethostbyname()*\ on older systems) to
find IP addresses. This function may ultimately cause a DNS lookup, but it may
also look in \(/etc/hosts)\ or other sources of information.
.nextp
\bydns\: look up address records for the hosts directly in the DNS; fail if
no address records are found. If there is a temporary DNS error (such as a 
timeout), delivery is deferred. 
.endp
For example:
.display asis
route_list = domain1  host1:host2:host3  randomize bydns;\
             domain2  host4:host5
.endd
If neither \byname\ nor \bydns\ is given, Exim behaves as follows: First, a DNS
lookup is done. If this yields anything other than \\HOST@_NOT@_FOUND\\, that
result is used. Otherwise, Exim goes on to try a call to \*getipnodebyname()*\
or \*gethostbyname()*\, and the result of the lookup is the result of that
call.

\**Warning**\: It has been discovered that on some systems, if a DNS lookup
called via \*getipnodebyname()*\ times out, \\HOST@_NOT@_FOUND\\ is returned
instead of \\TRY@_AGAIN\\. That is why the default action is to try a DNS
lookup first. Only if that gives a definite `no such host' is the local
function called.



If no IP address for a host can be found, what happens is controlled by the
\host@_find@_failed\ option.

When an address is routed to a local transport, IP addresses are not looked up.
The host list is passed to the transport in the \$host$\ variable.


.section Manualroute examples
In some of the examples that follow, the presence of the \remote@_smtp\
transport, as defined in the default configuration file, is assumed:

.numberpars $.
.index smart host||example router
The \%manualroute%\ router can be used to forward all external mail to a
\*smart host*\. If you have set up, in the main part of the configuration, a
named domain list that contains your local domains, for example,
.display asis
domainlist local_domains = my.domain.example
.endd
you can arrange for all other domains to be routed to a smart host by making
your first router something like this:
.display asis
smart_route:
  driver = manualroute
  domains = !+local_domains
  transport = remote_smtp
  route_list = * smarthost.ref.example
.endd
This causes all non-local addresses to be sent to the single host
\*smarthost.ref.example*\. If a colon-separated list of smart hosts is given,
they are tried in order
(but you can use \hosts@_randomize\ to vary the order each time).
Another way of configuring the same thing is this:
.display asis
smart_route:
  driver = manualroute
  transport = remote_smtp
  route_list = !+local_domains  smarthost.ref.example
.endd
There is no difference in behaviour between these two routers as they stand.
However, they behave differently if \no@_more\ is added to them. In the first
example, the router is skipped if the domain does not match the \domains\
precondition; the following router is always tried. If the router runs, it
always matches the domain and so can never decline. Therefore, \no@_more\ would
have no effect. In the second case, the router is never skipped; it always
runs. However, if it doesn't match the domain, it declines. In this case
\no@_more\ would prevent subsequent routers from running.

.nextp
.index mail hub example
A \*mail hub*\ is a host which receives mail for a number of domains via MX
records in the DNS and delivers it via its own private routing mechanism. Often
the final destinations are behind a firewall, with the mail hub being the one
machine that can connect to machines both inside and outside the firewall. The
\%manualroute%\ router is usually used on a mail hub to route incoming messages
to the correct hosts. For a small number of domains, the routing can be inline,
using the \route@_list\ option, but for a larger number a file or database
lookup is easier to manage.

If the domain names are in fact the names of the machines to which the mail is
to be sent by the mail hub, the configuration can be quite simple. For
example,
.display asis
hub_route:
  driver = manualroute
  transport = remote_smtp
  route_list = *.rhodes.tvs.example  $domain
.endd
This configuration routes domains that match \"*.rhodes.tvs.example"\ to hosts
whose names are the same as the mail domains. A similar approach can be taken
if the host name can be obtained from the domain name by a string manipulation
that the expansion facilities can handle. Otherwise, a lookup based on the
domain can be used to find the host:
.display asis
through_firewall:
  driver = manualroute
  transport = remote_smtp
  route_data = ${lookup {$domain} cdb {/internal/host/routes}}
.endd
The result of the lookup must be the name or IP address of the host (or
hosts) to which the address is to be routed. If the lookup fails, the route
data is empty, causing the router to decline. The address then passes to the
next router.

.nextp
.index batched SMTP output example
.index SMTP||batched outgoing, example
You can use \%manualroute%\ to deliver messages to pipes or files in batched
SMTP format for onward transportation by some other means. This is one way of
storing mail for a dial-up host when it is not connected. The route list entry
can be as simple as a single domain name in a configuration like this:
.display asis
save_in_file:
  driver = manualroute
  transport = batchsmtp_appendfile
  route_list = saved.domain.example
.endd
though often a pattern is used to pick up more than one domain. If there are
several domains or groups of domains with different transport requirements,
different transports can be listed in the routing information:
.display asis
save_in_file:
  driver = manualroute
  route_list = \
    *.saved.domain1.example  $domain  batch_appendfile; \
    *.saved.domain2.example  \
      ${lookup{$domain}dbm{/domain2/hosts}{$value}fail} \
      batch_pipe
.endd
The first of these just passes the domain in the \$host$\ variable, which
doesn't achieve much (since it is also in \$domain$\), but the second does a
file lookup to find a value to pass, causing the router to decline to handle
the address if the lookup fails.
.nextp
.index UUCP||example of router for
Routing mail directly to UUCP software is a specific case of the use of
\%manualroute%\ in a gateway to another mail environment. This is an example of
one way it can be done:
.display asis
# Transport
uucp:
  driver = pipe
  user = nobody
  command = /usr/local/bin/uux -r - \
    ${substr_-5:$host}!rmail ${local_part}
  return_fail_output = true
.endd
.display asis
# Router
uucphost:
  transport = uucp
  driver = manualroute
  route_data = \
    ${lookup{$domain}lsearch{/usr/local/exim/uucphosts}}
.endd
The file \(/usr/local/exim/uucphosts)\ contains entries like
.display asis
darksite.ethereal.example:           darksite.UUCP
.endd
It can be set up more simply without adding and removing `.UUCP' but this way
makes clear the distinction between the domain name
\*darksite.ethereal.example*\ and the UUCP host name \*darksite*\.
.endp






.
.
.
.
. ============================================================================
.chapter The queryprogram router
.set runningfoot "queryprogram router"
.rset CHAPdriverlast "~~chapter"
.index \%queryprogram%\ router
.index routers||\%queryprogram%\
.index routing||by external program
The \%queryprogram%\ router routes an address by running an external command and
acting on its output. This is an expensive way to route, and is intended mainly
for use in lightly-loaded systems, or for performing experiments. However, if
it is possible to use the precondition options (\domains\, \local@_parts\,
etc) to skip this router for most addresses, it could sensibly be used in
special cases, even on a busy host. There are the following private options:

.startconf
.index options||\%queryprogram%\ router
.conf command string$**$ unset
This option must be set. It specifies the command that is to be run. The
command is split up into a command name and arguments, and then each is
expanded separately (exactly as for a \%pipe%\ transport, described in chapter
~~CHAPpipetransport).

.conf command@_group string unset
.index gid (group id)||in \%queryprogram%\ router
This option specifies a gid to be set when running the command. It must be set
if \command@_user\ specifies a numerical uid. If it begins with a digit, it is
interpreted as the numerical value of the gid. Otherwise it is looked up using
\*getgrnam()*\.

.conf command@_user string unset
.index uid (user id)||for \%queryprogram%\
This option must be set. It specifies the uid which is set when running the
command. If it begins with a digit it is interpreted as the numerical value of
the uid. Otherwise, it is looked up using \*getpwnam()*\ to obtain a value for
the uid and, if \command@_group\ is not set, a value for the gid also.

.conf current@_directory string /
This option specifies an absolute path which is made the current directory
before running the command.

.conf timeout time 1h
If the command does not complete within the timeout period, its process group
is killed and the message is frozen. A value of zero time specifies no
timeout.

.endconf

The standard output of the command is connected to a pipe, which is read when
the command terminates. It should consist of a single line of output,
containing up to five fields, separated by white space. The first field is one
of the following words (case-insensitive):
.numberpars $.
\*Accept*\: routing succeeded; the remaining fields specify what to do (see
below).
.nextp
\*Decline*\: the router declines; pass the address to the next router, unless
\no@_more\ is set.
.nextp
\*Fail*\: routing failed; do not pass the address to any more routers. Any
subsequent text on the line is an error message. If the router is run as part
of address verification during an incoming SMTP message, the message is
included in the SMTP response.
.nextp
\*Defer*\: routing could not be completed at this time; try again later. Any
subsequent text on the line is an error message which is logged. It is not
included in any SMTP response.
.nextp
\*Freeze*\: the same as \*defer*\, except that the message is frozen.
.nextp
\*Pass*\: pass the address to the next router (or the router specified by
\pass@_router\), overriding \no@_more\.
.nextp
\*Redirect*\: the message is redirected. The remainder of the line is a list of
new addresses, which are routed independently, starting with the first router,
or the router specified by \redirect@_router\, if set.
.endp
When the first word is \*accept*\, the remainder of the line consists of a
number of keyed data values, as follows (split into two lines here, to fit on
the page):
.display
ACCEPT TRANSPORT=<<transport>> HOSTS=<<list of hosts>>
       LOOKUP=byname|bydns DATA=<<text>>
.endd
The data items can be given in any order, and all are optional. If no transport
is included, the transport specified by the generic \transport\ option is used.
The list of hosts and the lookup type are needed only if the transport is an
\%smtp%\ transport that does not itself supply a list of hosts.

The format of the list of hosts is the same as for the \%manualroute%\ router. 
As well as host names and IP addresses, it may contain names followed by
\"/MX"\ to specify sublists of hosts that are obtained by looking up MX
records.

If the lookup type is not specified, Exim behaves as follows when trying to 
find an IP address for each host: First, a DNS lookup is done. If this yields
anything other than \\HOST@_NOT@_FOUND\\, that result is used. Otherwise, Exim
goes on to try a call to \*getipnodebyname()*\ or \*gethostbyname()*\, and the
result of the lookup is the result of that call.

If the DATA field is set, its value is placed in the \$address@_data$\
variable. For example, this return line
.display asis
accept hosts=x1.y.example:x2.y.example data="rule1"
.endd
routes the address to the default transport, with a host list containing two
hosts. When the transport runs, the string `rule1' is in \$address@_data$\.



.
.
.
.
. ============================================================================
.chapter The redirect router
.set runningfoot "redirect router"
.rset CHAPredirect "~~chapter"
.index \%redirect%\ router
.index routers||\%redirect%\
.index alias file||in a \%redirect%\ router
.index address redirection||\%redirect%\ router
The \%redirect%\ router handles several kinds of address redirection. Its most
common uses are for resolving local part aliases from a central alias file
(usually called \(/etc/aliases)\) and for handling users' personal \(.forward)\
files, but it has many other potential uses. The incoming address can be
redirected in several different ways:
.numberpars $.
It can be replaced by one or more new addresses which are themselves routed
independently.
.nextp
It can be routed to be delivered to a given file or directory.
.nextp
It can be routed to be delivered to a specified pipe command.
.nextp
It can cause an automatic reply to be generated.
.nextp
It can be forced to fail, with a custom error message.
.nextp
It can be temporarily deferred.
.nextp
It can be discarded.
.endp
The generic \transport\ option must not be set for \%redirect%\ routers.
However, there are some private options which define transports for delivery to
files and pipes, and for generating autoreplies. See the \file@_transport\,
\pipe@_transport\ and \reply@_transport\ descriptions below.


.section Redirection data
The router operates by interpreting a text string which it obtains either by
expanding the contents of the \data\ option, or by reading the entire contents
of a file whose name is given in the \file\ option. These two options are
mutually exclusive. The first is commonly used for handling system aliases, in
a configuration like this:
.display asis
system_aliases:
  driver = redirect
  data = ${lookup{$local_part}lsearch{/etc/aliases}}
.endd
.em
If the lookup fails, the expanded string in this example is empty. When the 
expansion of \data\ results in an empty string, the router declines. A forced
expansion failure also causes the router to decline; other expansion failures
cause delivery to be deferred.
.nem

A configuration using \file\ is commonly used for handling users' \(.forward)\
files, like this:
.display asis
userforward:
  driver = redirect
  check_local_user
  file = $home/.forward
  no_verify
.endd
If the file does not exist, or causes no action to be taken (for example, it is
empty or consists only of comments), the router declines. \**Warning**\: This
is not the case when the file contains syntactically valid items that happen to
yield empty addresses, for example, items containing only RFC 2822 address
comments.


.section Forward files and address verification
.index address redirection||while verifying
It is usual to set \no@_verify\ on \%redirect%\ routers which handle users'
\(.forward)\ files, as in the example above. There are two reasons for this:
.numberpars $.
When Exim is receiving an incoming SMTP message from a remote host, it is
running under the Exim uid, not as root. 
No additional groups are set up, even if the Exim uid is a member of other 
groups (that is, the \*initgroups()*\ function is not run).
Exim is unable to change uid to read the file as the user, and it may not be
able to read it as the Exim user. So in practice the router may not be able to
operate.
.nextp
However, even when the router can operate, the existence of a \(.forward)\ file
is unimportant when verifying an address. What should be checked is whether the
local part is a valid user name or not. Cutting out the redirection processing
saves some resources.
.endp




.section Interpreting redirection data
.index Sieve filter||specifying in redirection data
.index filter||specifying in redirection data
The contents of the data string, whether obtained from \data\ or \file\, can be
interpreted in two different ways:
.numberpars $.
If the \allow@_filter\ option is set true, and the data begins with the text
`@#Exim filter' or `@#Sieve filter', it is interpreted as a list of
\*filtering*\ instructions in the form of an Exim or Sieve filter file,
respectively. Details of the syntax and semantics of filter files are described
in a separate document entitled \*Exim's interfaces to mail filtering*\; this
document is intended for use by end users.
.nextp
Otherwise, the data must be a comma-separated list of redirection items, as
described in the next section.
.endp
When a message is redirected to a file (a `mail folder'), the file name given 
in a non-filter redirection list must always be an absolute path. A filter may 
generate a relative path -- how this is handled depends on the transport's 
configuration. See section ~~SECTfildiropt for a discussion of this issue for 
the \%appendfile%\ transport.


.section Items in a non-filter redirection list
.rset SECTitenonfilred "~~chapter.~~section"
.index address redirection||non-filter list items
When the redirection data is not an Exim or Sieve filter, for example, if it
comes from a conventional alias or forward file, it consists of a list of
addresses, file names, pipe commands, or certain special items (see section
~~SECTspecitredli below). The special items can be individually enabled or
disabled by means of options whose names begin with \allow@_\ or \forbid@_\,
depending on their default values. The items in the list are separated by
commas or newlines.
If a comma is required in an item, the entire item must be enclosed in double
quotes.

Lines starting with a @# character are comments, and are ignored, and @# may
also appear following a comma, in which case everything between the @# and the
next newline character is ignored.

If an item is entirely enclosed in double quotes, these are removed. Otherwise
double quotes are retained because some forms of mail address require their use
(but never to enclose the entire address). In the following description, `item'
refers to what remains after any surrounding double quotes have been removed.

\**Warning**\: If you use an Exim expansion to construct a redirection address, 
and the expansion contains a reference to \$local@_part$\, you should make use 
of the \quote\ expansion operator, in case the local part contains special 
characters. For example, to redirect all mail for the domain 
\*obsolete.example*\, retaining the existing local part, you could use this 
setting:
.display asis
data = ${quote:$local_part}@newdomain.example
.endd


.section Redirecting to a local mailbox
.rset SECTredlocmai "~~chapter.~~section"
.index routing||loops in
.index loop||while routing, avoidance of
.index address redirection||to local mailbox
A redirection item may safely be the same as the address currently under
consideration. This does not cause a routing loop, because a router is
automatically skipped if any ancestor of the address that is being processed
.em
is the same as the current address and was processed by the current router. 
.nem
Such an address is therefore passed to the following routers, so it is handled
as if there were no redirection. When making this loop-avoidance test, the
complete local part, including any prefix or suffix, is used.

.index address redirection||local part without domain
Specifying the same local part without a domain is a common usage in personal
filter files when the user wants to have messages delivered to the local
mailbox and also forwarded elsewhere. For example, the user whose login is
\*cleo*\ might have a \(.forward)\ file containing this:
.display asis
cleo, cleopatra@egypt.example
.endd
.index backslash in alias file
.index alias file||backslash in
For compatibility with other MTAs, such unqualified local parts may be
preceeded by `@\', but this is not a requirement for loop prevention. However,
it does make a difference if more than one domain is being handled
synonymously.

If an item begins with `@\' and the rest of the item parses as a valid RFC 2822
address that does not include a domain, the item is qualified using the domain
of the incoming address. In the absence of a leading `@\', unqualified
addresses are qualified using the value in \qualify@_recipient\, but you can
force the incoming domain to be used by setting \qualify__preserve@_domain\.

Care must be taken if there are alias names for local users. 
.em
Consider an MTA handling a single local domain where the system alias file
contains:
.display asis
Sam.Reman: spqr
.endd
Now suppose that Sam (whose login id is \*spqr*\) wants to save copies of
messages in the local mailbox, and also forward copies elsewhere. He creates 
this forward file:
.display asis
Sam.Reman, spqr@reme.elsewhere.example
.endd
With these settings, an incoming message addressed to \*Sam.Reman*\ fails. The
\%redirect%\ router for system aliases does not process \*Sam.Reman*\ the
second time round, because it has previously routed it, 
.nem
and the following routers presumably cannot handle the alias. The forward file
should really contain
.display asis
spqr, spqr@reme.elsewhere.example
.endd
but because this is such a common error, the \check@_ancestor\ option (see
below) exists to provide a way to get round it. This is normally set on a
\%redirect%\ router that is handling users' \(.forward)\ files.


.section Special items in redirection lists
.rset SECTspecitredli "~~chapter.~~section"
In addition to addresses, the following types of item may appear in redirection
lists (that is, in non-filter redirection data):

.numberpars $.
.index pipe||in redirection list
.index address redirection||to pipe
An item is treated as a pipe command if it begins with `|' and does not parse
as a valid RFC 2822 address that includes a domain. A transport for running the
command must be specified by the \pipe@_transport\ option. 
.em
Normally, either the router or the transport specifies a user and a group under
which to run the delivery. The default is to use the Exim user and group.
.nem

Single or double quotes can be used for enclosing the individual arguments of
the pipe command; no interpretation of escapes is done for single quotes. If
the command contains a comma character, it is necessary to put the whole item
in double quotes, for example:
.display asis
"|/some/command ready,steady,go"
.endd
since items in redirection lists are terminated by commas. Do not, however,
quote just the command. An item such as
.display asis
|"/some/command ready,steady,go"
.endd
is interpreted as a pipe with a rather strange command name, and no arguments.
.nextp
.index file||in redirection list
.index address redirection||to file
An item is interpreted as a path name if it begins with `/' and does not parse
as a valid RFC 2822 address that includes a domain. For example,
.display asis
/home/world/minbari
.endd
is treated as a file name, but
.display asis
/s=molari/o=babylon/@x400gate.way
.endd
is treated as an address. For a file name, a transport must be specified using
the \file@_transport\ option. However, if the generated path name ends with a
forward slash character, it is interpreted as a directory name rather than a
file name, and \directory@_transport\ is used instead.

.em
Normally, either the router or the transport specifies a user and a group under
which to run the delivery. The default is to use the Exim user and group.
.index \(/dev/null)\
However, if a redirection item is the path \(/dev/null)\, delivery to it is
bypassed at a high level, and the log entry shows `$*$$*$bypassed$*$$*$'
instead of a transport name. In this case the user and group are not used.
.nem
.nextp
.index included address list
.index address redirection||included external list
If an item is of the form
.display
:include:<<path name>>
.endd
a list of further items is taken from the given file and included at that
point. 
\**Note**\: such a file can not be a filter file; it is just an out-of-line 
addition to the list.
The items in the included list are separated by commas or newlines and are not
subject to expansion. If this is the first item in an alias list in an
\%lsearch%\ file, a colon must be used to terminate the alias name. This
example is incorrect:
.display asis
list1    :include:/opt/lists/list1
.endd
It must be given as
.display asis
list1:   :include:/opt/lists/list1
.endd
.nextp
.index address redirection||to black hole
Sometimes you want to throw away mail to a particular local part. Making the
\data\ option expand to an empty string does not work, because that causes the
router to decline. Instead, the alias item
.index black hole
.index abandoning mail
.display
:blackhole:
.endd
can be used. It does what its name implies. No delivery is done, and no error
message is generated. This has the same effect as specifing \(/dev/null)\, but
can be independently disabled.

\**Warning**\: If \":blackhole:"\ appears anywhere in a redirection list, no 
delivery is done for the original local part, even if other redirection items 
are present. If you are generating a multi-item list (for example, by reading a 
database) and need the ability to provide a no-op item, you must use 
\(/dev/null)\.

.nextp
.index delivery||forcing failure
.index delivery||forcing deferral
.index failing delivery||forcing
.index deferred delivery, forcing
.index customizing||failure message
An attempt to deliver a particular address can be deferred or forced to fail by
redirection items of the form
.display
:defer:
$rm{or}
:fail:
.endd
respectively. When a redirection list contains such an item, it applies to the
entire redirection; any other items in the list are ignored (:::blackhole:: is
different). Any text following :::fail:: or :::defer:: is placed in the error
text associated with the failure. For example, an alias file might contain:
.display asis
X.Employee:  :fail: Gone away, no forwarding address
.endd
In the case of an address that is being verified from an ACL or as the subject
of a \\VRFY\\ command, the text is included in the SMTP error response by 
default. In an ACL, an explicitly provided message overrides the default, but
the default message is available in the variable \$acl@_verify@_message$\ and
can therefore be included in a custom message if this is desired. Exim sends a
451 SMTP code for a :::defer::, and 550 for :::fail::. In non-SMTP cases the
text is included in the error message that Exim generates.



Normally the error text is the rest of the redirection list -- a comma does not
terminate it -- but a newline does act as a terminator. Newlines are not
normally present in alias expansions. In \%lsearch%\ lookups they are removed as
part of the continuation process, but they may exist in other kinds of lookup
and in :::include:: files.

During routing for message delivery (as opposed to verification), a redirection
containing :::fail:: causes an immediate failure of the incoming address,
whereas :::defer:: causes the message to remain on the queue so that a
subsequent delivery attempt can happen at a later time. If an address is
deferred for too long, it will ultimately fail, because the normal retry
rules still apply.
.nextp
.index alias file||exception to default
Sometimes it is useful to use a single-key search type with a default (see
chapter ~~CHAPfdlookup) to look up aliases. However, there may be a need for
exceptions to the default. These can be handled by aliasing them to
.display asis
:unknown:
.endd
This differs from :::fail:: in that it causes the \%redirect%\ router to decline,
whereas :::fail:: forces routing to fail. A lookup which results in an empty
redirection list has the same effect.
.endp

.section Duplicate addresses
.index duplicate addresses
.index address||duplicate, discarding
.index pipe||duplicated
Exim removes duplicate addresses from the list to which it is delivering, so as
to deliver just one copy to each address. This does not apply to deliveries
routed to pipes by different immediate parent addresses, but an indirect
aliasing scheme of the type
.display asis
pipe:       |/some/command $local_part
localpart1: pipe
localpart2: pipe
.endd
does not work with a message that is addressed to both local parts, because
when the second is aliased to the intermediate local part `pipe' it gets
discarded as being the same as a previously handled address. However, a scheme
such as
.display asis
localpart1: |/some/command $local_part
localpart2: |/some/command $local_part
.endd
does result in two different pipe deliveries, because the immediate parents of
the pipes are distinct.


.section Repeated redirection expansion
.index repeated redirection expansion
.index address redirection||repeated for each delivery attempt
When a message cannot be delivered to all of its recipients immediately,
leading to two or more delivery attempts, redirection expansion is carried out
afresh each time for those addresses whose children were not all previously
delivered. If redirection is being used as a mailing list, this can lead to new
members of the list receiving copies of old messages. The \one@_time\ option
can be used to avoid this.

.section Errors in redirection lists
.index address redirection||errors
If \skip@_syntax@_errors\ is set, a malformed address that causes a parsing
error is skipped, and an entry is written to the main log. This may be useful
for mailing lists that are automatically managed. Otherwise, if an error is
detected while generating the list of new addresses, the original address is
deferred. See also \syntax@_errors@_to\.


.section Private options for the redirect router

The private options for the \%redirect%\ router are as follows:

.startconf
.index options||\%redirect%\ router

.conf allow@_defer boolean false
Setting this option allows the use of :::defer:: in non-filter redirection
data,
or the \defer\ command in an Exim filter file.

.conf allow@_fail boolean false
.index failing delivery||from filter
If this option is true, the :::fail:: item can be used in a redirection list,
and the \fail\ command may be used in a filter file.

.conf allow@_filter boolean false
.index filter||enabling use of
.index Sieve filter||enabling use of
Setting this option allows Exim to interpret redirection data that starts with
`@#Exim filter' or `@#Sieve filter' as a set of filtering instructions. There
are some features of Exim filter files that some administrators may wish to
lock out; see the \forbid@_filter@_xxx\ options below. The filter is run using
the uid and gid set by the generic \user\ and \group\ options. These take their
defaults from the password data if \check@_local@_user\ is set, so in the
normal case of users' personal filter files, the filter is run as the relevant
user. When \allow@_filter\ is set true, Exim insists that either
\check@_local@_user\ or \user\ is set.


.conf allow@_freeze boolean false
.index freezing messages||allowing in filter
Setting this option allows the use of the \freeze\ command in an Exim filter.
This command is more normally encountered in system filters, and is disabled by
default for redirection filters because it isn't something you usually want to
let ordinary users do.


.conf check@_ancestor boolean false
This option is concerned with handling generated addresses that are the same
as some address in the list of redirection ancestors of the current address.
Although it is turned off by default in the code, it is set in the default
configuration file for handling users' \(.forward)\ files. It is recommended
for this use of the \%redirect%\ router.

.em
When \check@_ancestor\ is set, if a generated address (including the domain) is
the same as any ancestor of the current address, it is replaced by a copy of
the current address. This helps in the case where local part A is aliased to B,
and B has a \(.forward)\ file pointing back to A. For example, within a single 
domain, the local part `Joe.Bloggs' is aliased to `jb' and \(@~jb/.forward)\
contains:
.nem
.display
@\Joe.Bloggs, <<other item(s)>>
.endd
Without the \check@_ancestor\ setting, either local part (`jb' or `joe.bloggs')
gets processed once by each router and so ends up as it was originally. If `jb'
is the real mailbox name, mail to `jb' gets delivered (having been turned into
`joe.bloggs' by the \(.forward)\ file and back to `jb' by the alias), but mail
to `joe.bloggs' fails. Setting \check@_ancestor\ on the \%redirect%\ router that
handles the \(.forward)\ file prevents it from turning `jb' back into
`joe.bloggs' when that was the original address. See also the \repeat@_use\
option below.

.conf check@_group boolean "see below"
When the \file\ option is used, the group owner of the file is checked only
when this option is set. The permitted groups are those listed in the
\owngroups\ option, together with the user's default group if
\check@_local@_user\ is set. If the file has the wrong group, routing is
deferred. The default setting for this option is true if \check@_local@_user\
is set and the \modemask\ option permits the group write bit, or if the
\owngroups\ option is set. Otherwise it is false, and no group check occurs.


.conf check@_owner boolean "see below"
When the \file\ option is used, the owner of the file is checked only when this
option is set. If \check@_local@_user\ is set, the local user is permitted;
otherwise the owner must be one of those listed in the \owners\ option. The
default value for this option is true if \check@_local@_user\ or \owners\ is
set. Otherwise the default is false, and no owner check occurs.

.conf data string$**$ unset
This option is mutually exclusive with \file\. One or other of them must be
set, but not both. The contents of \data\ are expanded, and then used as the
list of forwarding items, or as a set of filtering instructions. If the
expansion is forced to fail, or the result is an empty string or a string that
has no effect (consists entirely of comments), the router declines.

When filtering instructions are used, the string must begin with `@#Exim
filter', and all comments in the string, including this initial one, must be
terminated with newline characters. For example:
.display asis
data = #Exim filter\n\
       if $h_to: contains Exim then save $home/mail/exim endif
.endd
If you are reading the data from a database where newlines cannot be included,
you can use the \$@{sg@}$\ expansion item to turn the escape string of your
choice into a newline.

.conf directory@_transport string$**$ unset
A \%redirect%\ router sets up a direct delivery to a directory when a path name
ending with a slash is specified as a new `address'. The transport used is
specified by this option, which, after expansion, must be the name of a
configured transport. This should normally be an \%appendfile%\ transport.

.conf file string$**$ unset
This option specifies the name of a file that contains the redirection data. It
is mutually exclusive with the \data\ option. The string is expanded before
use; if the expansion is forced to fail, the router declines. Other expansion
failures cause delivery to be deferred. The result of a successful expansion
must be an absolute path. The entire file is read and used as the redirection
data. If the data is an empty string or a string that has no effect (consists
entirely of comments), the router declines.

.index NFS||checking for file existence
If the attempt to open the file fails with a `does not exist' error, Exim
runs a check on the containing directory,
unless \ignore@_enotdir\ is true (see below).
If the directory does not appear to exist, delivery is deferred. This can
happen when users' \(.forward)\ files are in NFS-mounted directories, and there
is a mount problem. If the containing directory does exist, but the file does
not, the router declines.

.conf file@_transport string$**$ unset
A \%redirect%\ router sets up a direct delivery to a file when a path name not
ending in a slash is specified as a new `address'. The transport used is
specified by this option, which, after expansion, must be the name of a
configured transport. 
This should normally be an \%appendfile%\ transport.
When it is running, the file name is in \$address@_file$\.

.conf forbid@_blackhole boolean false
If this option is true, the :::blackhole:: item may not appear in a redirection
list.

.conf forbid@_file boolean false
.index delivery||to file, forbidding
.index Sieve filter||forbidding delivery to a file
.index Sieve filter||`keep' facility, disabling
If this option is true, this router may not generate a new address that
specifies delivery to a local file or directory, either from a filter or from a
conventional forward file. This option is forced to be true if \one@_time\ is
set. It applies to Sieve filters as well as to Exim filters, but if true, it
locks out the Sieve's `keep' facility.

.conf forbid@_filter@_existstest boolean false
.index filter||locking out certain features
If this option is true, string expansions in Exim filters are not allowed to
make use of the \exists\ condition.

.conf forbid@_filter@_logwrite boolean false
If this option is true, use of the logging facility in Exim filters is not
permitted. Logging is in any case available only if the filter is being run
under some unprivileged uid (which is normally the case for ordinary users'
\(.forward)\ files).

.conf forbid@_filter@_lookup boolean false
If this option is true, string expansions in Exim filter files are not allowed
to make use of \lookup\ items.

.conf forbid@_filter@_perl boolean false
This option is available only if Exim is built with embedded Perl support. If
it is true, string expansions in Exim filter files are not allowed to make use
of the embedded Perl support.

.conf forbid@_filter@_readfile boolean false
If this option is true, string expansions in Exim filter files are not allowed
to make use of \readfile\ items.

.conf forbid@_filter@_readsocket boolean false
If this option is true, string expansions in Exim filter files are not allowed
to make use of \readsocket\ items.

.conf forbid@_filter@_reply boolean false
If this option is true, this router may not generate an automatic reply
message. Automatic replies can be generated only from Exim filter files, not
from traditional forward files or Sieve filters. This option is forced to be
true if \one@_time\ is set.

.conf forbid@_filter@_run boolean false
If this option is true, string expansions in Exim filter files are not allowed
to make use of \run\ items.

.conf forbid@_include boolean false
If this option is true, items of the form
.display
:include:<<path name>>
.endd
are not permitted in non-filter redirection lists.

.conf forbid@_pipe boolean false
.index delivery||to pipe, forbidding
If this option is true, this router may not generate a new address which
specifies delivery to a pipe, either from an Exim filter or from a conventional
forward file. This option is forced to be true if \one@_time\ is set.

.conf hide@_child@_in@_errmsg boolean false
.index bounce message||redirection details, suppressing
If this option is true, it prevents Exim from quoting a child address if it
generates a bounce or delay message for it. Instead it says `an address
generated from <<the top level address>>'. Of course, this applies only to
bounces generated locally. If a message is forwarded to another host, $it{its}
bounce may well quote the generated address.

.conf ignore@_eacces boolean false
.index \\EACCES\\
If this option is set and an attempt to open a redirection file yields the
\\EACCES\\ error (permission denied), the \%redirect%\ router behaves as if the
file did not exist.

.conf ignore@_enotdir boolean false
.index \\ENOTDIR\\
If this option is set and an attempt to open a redirection file yields the
\\ENOTDIR\\ error (something on the path is not a directory), the \%redirect%\
router behaves as if the file did not exist.

Setting \ignore@_enotdir\ has another effect as well: When a \%redirect%\
router that has the \file\ option set discovers that the file does not exist
(the \\ENOENT\\ error), it tries to \*stat()*\ the parent directory, as a check
against unmounted NFS directories. If the parent can not be statted, delivery
is deferred. However, it seems wrong to do this check when \ignore@_enotdir\ is
set, because that option tells Exim to ignore `something on the path is not a
directory' (the \\ENOTDIR\\ error). This is a confusing area, because it seems
that some operating systems give \\ENOENT\\ where others give \\ENOTDIR\\.


.conf include@_directory string unset
If this option is set, the path names of any :::include:: items in a redirection
list must start with this directory.

.conf modemask "octal integer" 022
This specifies mode bits which must not be set for a file specified by the
\file\ option. If any of the forbidden bits are set, delivery is deferred.

.conf one@_time boolean false
.index one-time aliasing/forwarding expansion
.index alias file||one-time expansion
.index forward file||one-time expansion
.index mailing lists||one-time expansion
.index address redirection||one-time expansion
Sometimes the fact that Exim re-evaluates aliases and reprocesses redirection
files each time it tries to deliver a message causes a problem
when one or more of the generated addresses fails be delivered at the first 
attempt. The problem is not one of duplicate delivery -- Exim is clever enough 
to handle that -- but of what happens when the redirection list changes during
the time that the message is on Exim's queue. This is particularly true in the
case of mailing lists, where new subscribers might receive copies of messages
that were posted before they subscribed.

If \one@_time\ is set and any addresses generated by the router fail to
deliver at the first attempt, the failing addresses are added to the message as
`top level' addresses, and the parent address that generated them is marked
`delivered'. Thus, redirection does not happen again at the next
delivery attempt.

\**Warning 1**\: This means that any header line addition or removal that is
specified by this router would be lost if delivery did not succeed at the
first attempt. For this reason, the \headers@_add\ and \headers@_remove\
generic options are not permitted when \one@_time\ is set.

\**Warning 2**\: To ensure that the router generates only addresses (as opposed
to pipe or file deliveries or auto-replies) \forbid@_file\, \forbid@_pipe\,
and \forbid@_filter@_reply\ are forced to be true when \one@_time\ is set.

The original top-level address is remembered with each of the generated
addresses, and is output in any log messages. However, any intermediate parent
addresses are not recorded. This makes a difference to the log only if
\all__parents\ log selector is set. It is expected that \one@_time\ will
typically be used for mailing lists, where there is normally just one level of
expansion.

.conf owners "string list" unset
.index ownership||alias file
.index ownership||forward file
.index alias file||ownership
.index forward file||ownership
This specifies a list of permitted owners for the file specified by \file\.
This list is in addition to the local user when \check@_local@_user\ is set.
See \check@_owner\ above.

.conf owngroups "string list" unset
This specifies a list of permitted groups for the file specified by \file\. The
list is in addition to the local user's primary group when \check@_local@_user\
is set. See \check@_group\ above.

.em
.conf qualify@_domain string$**$ unset
If this option is set and an unqualified address (one without a domain) is
generated, it is qualified with the domain specified by expanding this string,
instead of the global setting in \qualify@_recipient\. If the expansion fails,
the router declines. If you want to revert to the default, you can have the
expansion generate \$qualify@_recipient$\.
.nem

.conf pipe@_transport string$**$ unset
A \%redirect%\ router sets up a direct delivery to a pipe when a string starting
with a vertical bar character is specified as a new `address'. The transport
used is specified by this option, which, after expansion, must be the name of a
configured transport. 
This should normally be a \%pipe%\ transport.
When the transport is run, the pipe command is in \$address@_pipe$\.

.conf qualify@_preserve@_domain boolean false
.index domain||in redirection, preserving
.index preserving domain in redirection
.index address redirection||domain, preserving
If this is set and an unqualified address (one without a domain) is generated,
it is qualified with the domain of the 
.em
parent address (the immediately preceding ancestor) instead of the local
\qualify@_domain\ or global \qualify@_recipient\ value.
.nem

.conf repeat@_use boolean true
If this option is set false, the router is skipped for a child address that has
any ancestor that was routed by this router. This test happens before any of
the other preconditions are tested. Exim's default anti-looping rules skip
only when the ancestor is the same as the current address. See also
\check@_ancestor\ above and the generic \redirect@_router\ option.

.conf reply@_transport string$**$ unset
A \%redirect%\ router sets up an automatic reply when a \mail\ or \vacation\
command is used in a filter file. The transport used is specified by this
option, which, after expansion, must be the name of a configured transport.
This should normally be an \%autoreply%\ transport. Other transports are 
unlikely to do anything sensible or useful.

.conf rewrite boolean true
.index address redirection||disabling rewriting
If this option is set false, addresses generated by the router are not
subject to address rewriting. Otherwise, they are treated like new addresses
and are rewritten according to the global rewriting rules.

.conf skip@_syntax@_errors boolean false
.index forward file||broken
.index address redirection||broken files
.index alias file||broken
.index broken alias or forward files
.index ignoring faulty addresses
.index skipping faulty addresses
.index error||skipping bad syntax
If \skip@_syntax@_errors\ is set, syntactically malformed addresses in
non-filter redirection data are skipped, and each failing address is logged. If
\syntax@_errors@_to\ is set, a message is sent to the address it defines,
giving details of the failures. If \syntax@_errors@_text\ is set, its contents
are expanded and placed at the head of the error message generated by
\syntax@_errors@_to\. Usually it is appropriate to set \syntax@_errors@_to\ to
be the same address as the generic \errors@_to\ option. The
\skip@_syntax@_errors\ option is often used when handling mailing lists.

If all the addresses in a redirection list are skipped because of syntax
errors, the router declines to handle the original address, and it is passed to
the following routers.

If \skip@_syntax@_errors\ is set when an Exim filter is interpreted, any syntax
error in the filter causes filtering to be abandoned without any action being
taken. The incident is logged, and the router declines to handle the address,
so it is passed to the following routers.

.index Sieve filter||syntax errors in
Currently, any syntax errors in a Sieve filter file cause the `keep' action to 
occur. The values of \skip@_syntax@_errors\, \syntax@_errors@_to\, and 
\syntax@_errors@_text\ are not used.

\skip@_syntax@_errors\ can be used to specify that errors in users' forward
lists or filter files should not prevent delivery. The \syntax@_errors@_to\
option, used with an address that does not get redirected, can be used to
notify users of these errors, by means of a router like this:
.display flow asis
userforward:
  driver = redirect
  allow_filter
  check_local_user
  file = $home/.forward
  file_transport = address_file
  pipe_transport = address_pipe
  reply_transport = address_reply
  no_verify
  skip_syntax_errors
  syntax_errors_to = real-$local_part@$domain
  syntax_errors_text = \
    This is an automatically generated message. An error has\n\
    been found in your .forward file. Details of the error are\n\
    reported below. While this error persists, you will receive\n\
    a copy of this message for every message that is addressed\n\
    to you. If your .forward file is a filter file, or if it is\n\
    a non-filter file containing no valid forwarding addresses,\n\
    a copy of each incoming message will be put in your normal\n\
    mailbox. If a non-filter file contains at least one valid\n\
    forwarding address, forwarding to the valid addresses will\n\
    happen, and those will be the only deliveries that occur.
.endd
You also need a router to ensure that local addresses that are prefixed by
\"real-"\ are recognized, but not forwarded or filtered. For example, you could
put this immediately before the \%userforward%\ router:
.display asis
real_localuser:
  driver = accept
  check_local_user
  local_part_prefix = real-
  transport = local_delivery
.endd

.conf syntax@_errors@_text string$**$ unset
See \skip@_syntax@_errors\ above.

.conf syntax@_errors@_to string unset
See \skip@_syntax@_errors\ above.

.endconf





.
.
.
. ============================================================================
.chapter Environment for running local transports
.rset CHAPenvironment "~~chapter"
.set runningfoot "local transport environment"
.index local transports||environment for
.index environment for local transports
.index transport||local, environment for
Local transports handle deliveries to files and pipes. (The \%autoreply%\
transport can be thought of as similar to a pipe.) Exim always runs transports
in subprocesses, under specified uids and gids. Typical deliveries to local
mailboxes run under the uid and gid of the local user.

Exim also sets a specific current directory while running the transport; for
some transports a home directory setting is also relevant. The \%pipe%\
transport is the only one which sets up environment variables; see section
~~SECTpipeenv for details.

The values used for the uid, gid, and the directories may come from several
different places. In many cases, the router that handles the address associates
settings with that address as a result of its \check@_local@_user\, \group\, or
\user\ options. However, values may also be given in the transport's own
configuration, and these override anything that comes from the router.

.section Uids and gids
.rset SECTenvuidgid "~~chapter.~~section"
.index local transports||uid and gid
.index transport||local, uid and gid
All transports have the options \group\ and \user\. If \group\ is set, it
overrides any group that the router set in the address, even if \user\ is not
set for the transport. This makes it possible, for example, to run local mail
delivery under the uid of the recipient (set by the router), but in a special
group (set by the transport). For example:
.display asis
# Routers ...
# User/group are set by check_local_user in this router
local_users:
  driver = accept
  check_local_user
  transport = group_delivery  

# Transports ...
# This transport overrides the group
group_delivery:
  driver = appendfile
  file = /var/spool/mail/$local_part
  group = mail
.endd
If \user\ is set for a transport, its value overrides what is set in the
address. If \user\ is non-numeric and \group\ is not set, the gid associated
with the user is used. If \user\ is numeric, \group\ must be set.

.index \initgroups\ option
When the uid is taken from the transport's configuration, the \*initgroups()*\
function is called for the groups associated with that uid if the \initgroups\
option is set for the transport. When the uid is not specified by the
transport, but is associated with the address by a router, the option for
calling \*initgroups()*\ is taken from the router configuration.

.index \%pipe%\ transport||uid for
The \%pipe%\ transport contains the special option \pipe@_as@_creator\. If this
is set and \user\ is not set, the uid of the process that called Exim to
receive the message is used, and if \group\ is not set, the corresponding
original gid is also used.


.section Current and home directories
.index current directory for local transport
.index home directory||for local transport
.index transport||local, home directory for
.index transport||local, current directory for
Routers may set current and home directories for local transports by means of
the \transport__current@_directory\ and \transport@_home@_directory\ options.
However, if the transport's \current__directory\ or \home@_directory\ options
are set, they override the router's values. In detail, the home directory
for a local transport is taken from the first of these values that is set:
.numberpars $.
The \home@_directory\ option on the transport;
.nextp
The \transport@_home@_directory\ option on the router;
.nextp
The password data if \check@_local@_user\ is set on the router;
.nextp
The \router@_home@_directory\ option on the router.
.endp
The current directory is taken from the first of these values that is set:
.numberpars $.
The \current@_directory\ option on the transport;
.nextp
The \transport@_current@_directory\ option on the router.
.endp

If neither the router nor the transport sets a current directory, Exim uses the
value of the home directory, if it is set. Otherwise it sets the current
directory to \(/)\ before running a local transport.


.section Expansion variables derived from the address
Normally a local delivery is handling a single address, and in that case the
variables such as \$domain$\ and \$local@_part$\ are set during local
deliveries. However, in some circumstances more than one address may be handled
at once (for example, while writing batch SMTP for onward transmission by some
other means). In this case, the variables associated with the local part are
never set, \$domain$\ is set only if all the addresses have the same
domain, and \$original@_domain$\ is never set.







.
.
.
. ============================================================================
.chapter Generic options for transports
.rset CHAPtransportgeneric "~~chapter"
.set runningfoot "generic transport options"

.index generic options||transport
.index options||generic, for transports
.index transport||generic options for
The following generic options apply to all transports:

.startconf
.conf body@_only boolean false
.index transport||body only
.index message||transporting body only
.index body of message||transporting
If this option is set, the message's headers are not transported. It is
mutually exclusive with \headers@_only\. If it is used with the \%appendfile%\ or
\%pipe%\ transports, the settings of \message@_prefix\ and \message@_suffix\
should be checked, because this option does not automatically suppress them.

.conf current@_directory string$**$ unset
.index transport||current directory for
This specifies the current directory that is to be set while running the
transport, overriding any value that may have been set by the router.
If the expansion fails for any reason, including forced failure, an error is
logged, and delivery is deferred.

.conf disable@_logging boolean false
If this option is set true, nothing is logged for any 
.em
deliveries by the transport or for any 
.nem
transport errors. You should not set this option unless you really, really know
what you are doing.

.conf debug@_print string$**$ unset
.index testing||variables in drivers
If this option is set and debugging is enabled (see the \-d-\ command line
option), the string is expanded and included in the debugging output when the
transport is run. 
If expansion of the string fails, the error message is written to the debugging 
output, and Exim carries on processing.
This facility is provided to help with checking out the values of variables and
so on when debugging driver configurations. For example, if a \headers@_add\
option is not working properly, \debug@_print\ could be used to output the
variables it references. A newline is added to the text if it does not end with
one.

.conf delivery@_date@_add boolean false
.index ::Delivery-date:: header line
If this option is true, a ::Delivery-date:: header is added to the message. This
gives the actual time the delivery was made. As this is not a standard header,
Exim has a configuration option (\delivery@_date@_remove\) which requests its
removal from incoming messages, so that delivered messages can safely be resent
to other recipients.

.conf driver string unset
This specifies which of the available transport drivers is to be used.
There is no default, and this option must be set for every transport.

.conf envelope@_to@_add boolean false
.index ::Envelope-to:: header line
If this option is true, an ::Envelope-to:: header is added to the message. This
gives the original address(es) in the incoming envelope that caused this
delivery to happen. More than one address may be present if the transport is
configured to handle several addresses at once, or if more than one original
address was redirected to the same final address. As this is not a standard
header, Exim has a configuration option (\envelope@_to@_remove\) which requests
its removal from incoming messages, so that delivered messages can safely be
resent to other recipients.

.conf group string$**$ "Exim group"
.index transport||group, specifying
This option specifies a gid for running the transport process, overriding any
value that the router supplies, and also overriding any value associated with
\user\ (see below).

.conf headers@_add string$**$ unset
.index header lines||adding in transport
.index transport||header lines, adding
This option specifies a string of text which is expanded and added to the
header portion of a message as it is transported. If the result of the
expansion is an empty string, or if the expansion is forced to fail, no action
is taken. Other expansion failures are treated as errors and cause the delivery
to be deferred. The expanded string should be in the form of one or more RFC
2822 header lines, separated by newlines (coded as `@\n'), for example:
.display asis
headers_add = X-added: this is a header added at $tod_log\n\
              X-added: this is another
.endd
Exim does not check the syntax of these added header lines. They are added at
the end of the existing header lines. If you include a blank line within the
string, you can subvert this facility into adding text at the start of the
message's body. This is not recommended. Additional header lines can also be
specified by routers. See chapter ~~CHAProutergeneric and section
~~SECTheadersaddrem.

.conf headers@_only boolean false
.index transport||header lines only
.index message||transporting headers only
.index header lines||transporting
If this option is set, the message's body is not transported. It is mutually
exclusive with \body@_only\. If it is used with the \%appendfile%\ or \%pipe%\
transports, the settings of \message@_prefix\ and \message__suffix\ should be
checked, since this option does not automatically suppress them.

.conf headers@_remove string$**$ unset
.index header lines||removing
.index transport||header lines, removing
This option is expanded; the result must consist of a colon-separated list of
header names, not including the terminating colon, for example:
.display asis
headers_remove = return-receipt-to:acknowledge-to
.endd
Any existing headers matching those names are not included in any message that
is transmitted by the transport. 
If the result of the expansion is an empty string, or if the expansion is
forced to fail, no action is taken. Other expansion failures are treated as
errors and cause the delivery to be deferred.

If there are multiple instances of a header, they are all removed. However,
added headers may have these names. Thus it is possible to replace a header by
specifying it in \headers@_remove\ and supplying the replacement in
\headers@_add\. Headers to be removed can also be specified by routers. See
chapter ~~CHAProutergeneric and section ~~SECTheadersaddrem.

.conf headers@_rewrite string unset
.index transport||header lines, rewriting
.index rewriting||at transport time
This option allows addresses in header lines to be rewritten at transport time,
that is, as the message is being copied to its destination. The contents of the
option are a colon-separated list of rewriting rules. Each rule is in exactly
the same form as one of the general rewriting rules that are applied when a
message is received. These are described in chapter ~~CHAPrewrite. For example,
.display asis
headers_rewrite = a@b c@d f : \
                  x@y w@z
.endd
changes \a@@b\ into \c@@d\ in ::From:: header lines, and \x@@y\ into \w@@z\ in
all address-bearing header lines. The rules are applied to the header lines
just before they are written out at transport time, so they affect only those
copies of the message that pass through the transport. However, only the
message's original header lines, and any that were added by a system filter,
are rewritten. If a router or transport adds header lines, they are
not affected by this option. These rewriting rules are $it{not} applied to the
envelope. You can change the return path using \return@_path\, but you cannot
change envelope recipients at this time.

.conf home@_directory string$**$ unset
.index transport||home directory for
This option specifies a home directory setting for the transport, overriding
any value that may be set by the router. The home directory is placed in
\$home$\ while expanding the transport's private options. It is also used as
the current directory if no current directory is set by the
\current__directory\ option on the transport or the
\transport__current__directory\ option on the router.
If the expansion fails for any reason, including forced failure, an error is
logged, and delivery is deferred.


.index additional groups
.index groups, additional
.index transport||group, additional
.conf initgroups boolean false
If this option is true and the uid for the delivery process is provided by the
transport, the \*initgroups()*\ function is called when running the transport
to ensure that any additional groups associated with the uid are set up.

.conf message@_size@_limit string$**$ 0
.index limit||message size per transport
.index size||of message, limit
.index transport||message size, limiting
This option controls the size of messages passed through the transport. It is
expanded before use; the result of the expansion must be a sequence of digits,
optionally followed by K or M.
If the expansion fails for any reason, including forced failure, or if the 
result is not of the required form, delivery is deferred.
If the value is greater than zero and the size of a message exceeds this
limit, the address is failed. If there is any chance that the resulting bounce
message could be routed to the same transport, you should ensure that
\return@_size@_limit\ is less than the transport's \message@_size@_limit\, as
otherwise the bounce message will fail to get delivered.


.conf rcpt@_include@_affixes boolean false
.index prefix||for local part, including in envelope
.index suffix||for local part, including in envelope
.index local part||prefix
.index local part||suffix
When this option is false (the default), and an address that has had any
affixes (prefixes or suffixes) removed from the local part is delivered by any
form of SMTP or LMTP, the affixes are not included. For example, if a router
that contains
.display asis
local_part_prefix = *-
.endd
routes the address \*abc-xyz@@some.domain*\ to an SMTP transport, the envelope
is delivered with
.display asis
RCPT TO:<xyz@some.domain>
.endd
If \rcpt@_include@_affixes\ is set true, the whole local part is included in
the \\RCPT\\ command. This option applies to BSMTP deliveries by the
\%appendfile%\ and \%pipe%\ transports as well as to the \%lmtp%\ and \%smtp%\
transports.

.conf retry@_use@_local@_part boolean "see below"
.index hints database||retry keys
When a delivery suffers a temporary failure, a retry record is created
in Exim's hints database. For remote deliveries, the key for the retry record
is based on the name and/or IP address of the failing remote host. For local
deliveries, the key is normally the entire address, including both the local
part and the domain. This is suitable for most common cases of local delivery
temporary failure -- for example, exceeding a mailbox quota should delay only
deliveries to that mailbox, not to the whole domain.

However, in some special cases you may want to treat a temporary local delivery
as a failure associated with the domain, and not with a particular local part.
(For example, if you are storing all mail for some domain in files.) You can do
this by setting \retry@_use@_local@_part\ false.

For all the local transports, its default value is true. For remote transports,
the default value is false for tidiness, but changing the value has no effect
on a remote transport in the current implementation.

.conf return@_path string$**$ unset
.index envelope sender
.index transport||return path, changing
.index return path||changing in transport
If this option is set, the string is expanded at transport time and replaces
the existing return path (envelope sender) value in the copy of the message
that is being delivered. An empty return path is permitted. This feature is
designed for remote deliveries, where the value of this option is used in the
SMTP \\MAIL\\ command. If you set \return@_path\ for a local transport, the
only effect is to change the address that is placed in the ::Return-path::
header line, if one is added to the message (see the next option).

The expansion can refer to the existing value via \$return@_path$\. This is
either the message's envelope sender, or an address set by the
\errors@_to\ option on a router. If the expansion is forced to fail, no
replacement occurs; if it fails for another reason, delivery is deferred. This
option can be used to support VERP (Variable Envelope Return Paths) -- see
chapter ~~CHAPSMTP.

\**Note**\: If a delivery error is detected locally, 
.em
including the case when a remote server rejects a message at SMTP time,
the bounce message is not sent to the value of this option, but to the
previously set errors address (which defaults to the incoming sender address).
.nem


.conf return@_path@_add boolean false
.index ::Return-path:: header line
If this option is true, a ::Return-path:: header is added to the message.
Although the return path is normally available in the prefix line of BSD
mailboxes, this is commonly not displayed by MUAs, and so the user does not
have easy access to it.

RFC 2821 states that the ::Return-path:: header is added to a message `when the
delivery SMTP server makes the final delivery'. This implies that this header
should not be present in incoming messages. Exim has a configuration option,
\return@_path@_remove\, which requests removal of this header from incoming
messages, so that delivered messages can safely be resent to other recipients.

.conf shadow@_condition string$**$ unset
See \shadow@_transport\ below.

.conf shadow@_transport string unset
.index shadow transport
.index transport||shadow
A local transport may set the \shadow@_transport\ option to the name of another
local transport. Shadow remote transports are not supported.

Whenever a delivery to the main transport succeeds, and either
\shadow@_condition\ is unset, or its expansion does not result in the empty
string or one of the strings `0' or `no' or `false', the message is also passed
to the shadow transport, with the same delivery address or addresses.
If expansion fails, no action is taken except that non-forced expansion 
failures cause a log line to be written.

The result of the shadow transport is discarded and does not affect the
subsequent processing of the message. Only a single level of shadowing is
provided; the \shadow@_transport\ option is ignored on any transport when it is
running as a shadow. Options concerned with output from pipes are also ignored.

The log line for the successful delivery has an item added on the end, of the
form
.display
ST=<<shadow transport name>>
.endd
If the shadow transport did not succeed, the error message is put in
parentheses afterwards.

Shadow transports can be used for a number of different purposes, including
keeping more detailed log information than Exim normally provides, and
implementing automatic acknowledgement policies based on message headers that
some sites insist on.

.conf transport@_filter string$**$ unset
.index transport||filter
.index filter||transport filter
This option sets up a filtering (in the Unix shell sense) process for messages
at transport time. It should not be confused with mail filtering as set up by
individual users or via a system filter.

When the message is about to be written out, the command specified by
\transport@_filter\ is started up in a separate process, and the entire
message, including the header lines, is passed to it on its standard input
(this in fact is done from a third process, to avoid deadlock).
The command must be specified as an absolute path.

The message is passed to the filter before any SMTP-specific processing, such
as turning `@\n' into `@\r@\n' and escaping lines beginning with a dot, and
also before any processing implied by the settings of \check@_string\ and
\escape@_string\ in the \%appendfile%\ or \%pipe%\ transports.

The filter's standard output is read and written to the message's destination.
The filter can perform any transformations it likes, but of course should take
care not to break RFC 2822 syntax. A demonstration Perl script is provided in
\(util/transport-filter.pl)\; this makes a few arbitrary modifications just to
show the possibilities. Exim does not check the result, except to test for a
final newline when SMTP is in use. All messages transmitted over SMTP must end
with a newline, so Exim supplies one if it is missing.

.index SMTP||\\SIZE\\
A problem might arise if the filter increases the size of a message that is
being sent down an SMTP connection. If the receiving SMTP server has indicated
support for the \\SIZE\\ parameter, Exim will have sent the size of the message
at the start of the SMTP session. If what is actually sent is substantially
more, the server might reject the message. This can be worked round by setting
the \size@_addition\ option on the \%smtp%\ transport, either to allow for
additions to the message, or to disable the use of \\SIZE\\ altogether.

The value of the option is the command string for starting up the filter, which
is run directly from Exim, not under a shell. The string is parsed by Exim in
the same way as a command string for the \%pipe%\ transport: Exim breaks it up
into arguments and then expands each argument separately. The special argument
\$pipe@_addresses$\ is replaced by a number of arguments, one for each address
that applies to this delivery. (This isn't an ideal name for this feature here,
but as it was already implemented for the \%pipe%\ transport, it seemed sensible
not to change it.)

.index \$host$\
.index \$host@_address$\
The expansion variables \$host$\ and \$host@_address$\ are available when the
transport is a remote one. They contain the name and IP address of the host to
which the message is being sent. For example:
.display asis
transport_filter = /some/directory/transport-filter.pl \
  $host $host_address $sender_address $pipe_addresses
.endd
The filter process is run under the same uid and gid as the normal delivery.
For remote deliveries this is the Exim uid/gid by default.

If a transport filter is set on an autoreply transport, the original message is
passed through the filter as it is being copied into the newly generated
message, which happens if the \return@_message\ option is set.

.conf transport@_filter@_timeout time 5m
.index transport||filter, timeout
When Exim is reading the output of a transport filter, it a applies a timeout 
that can be set by this option. Exceeding the timeout is treated as a 
temporary delivery failure.


.conf user string$**$ "Exim user"
.index uid (user id)||local delivery
.index transport||user, specifying
This option specifies the user under whose uid the delivery process is to be
run, overriding any uid that may have been set by the router. If the user is
given as a name, the uid is looked up from the password data, and the
associated group is taken as the value of the gid to be used if the \group\
option is not set.

.em
For deliveries that use local transports, a user and group are normally
specified explicitly or implicitly (for example, as a result of
\check@_local@_user\) by the router or transport.
.nem

.index hints database||access by remote transport
For remote transports, you should leave this option unset unless you really are
sure you know what you are doing. When a remote transport is running, it needs
to be able to access Exim's hints databases, because each host may have its own
retry data.

.endconf





.
.
.
. ============================================================================
.chapter Address batching in local transports
.set runningfoot "address batching"
.rset CHAPbatching ~~chapter
.index transport||local, address batching in
The only remote transport (\%smtp%\) is normally configured to handle more than
one address at a time, so that when several addresses are routed to the same
remote host, just one copy of the message is sent. Local transports, however,
normally handle one address at a time. That is, a separate instance of the
transport is run for each address that is routed to the transport. A separate
copy of the message is delivered each time.

.index batched local delivery
.index \batch@_max\
.index \batch@_id\
In special cases, it may be desirable to handle several addresses at once in a
local transport, for example:
.numberpars $.
In an \%appendfile%\ transport, when storing messages in files for later
delivery by some other means, a single copy of the message with multiple
recipients saves space.
.nextp
In an \%lmtp%\ transport, when delivering over `local SMTP' to some process,
a single copy saves time, and is the normal way LMTP is expected to work.
.nextp
In a \%pipe%\ transport, when passing the message 
to a scanner program or 
to some other delivery mechanism such as UUCP, multiple recipients may be
acceptable.
.endp
The three local transports (\%appendfile%\, \%lmtp%\, and \%pipe%\) all have
the same options for controlling multiple (`batched') deliveries, namely
\batch@_max\ and \batch@_id\. To save repeating the information for each
transport, these options are described here.

The \batch@_max\ option specifies the maximum number of addresses that can be
delivered together in a single run of the transport. Its default value is one.
When more than one address is routed to a transport that has a \batch@_max\
value greater than one, the addresses are delivered in a batch (that is, in a
single run of the transport), subject to certain conditions:
.numberpars $.
If any of the transport's options contain a reference to \$local@_part$\, no
batching is possible.
.nextp
If any of the transport's options contain a reference to \$domain$\, only
addresses with the same domain are batched.
.nextp
.index customizing||batching condition
If \batch@_id\ is set, it is expanded for each address, and only those
addresses with the same expanded value are batched. This allows you to specify
customized batching conditions.
Failure of the expansion for any reason, including forced failure, disables 
batching, but it does not stop the delivery from taking place. 
.nextp
Batched addresses must also have the same errors address (where to send
delivery errors), the same header additions and removals, the same user and
group for the transport, and if a host list is present, the first host must
be the same.
.endp
.index ::Envelope-to:: header line
If the generic \envelope@_to@_add\ option is set for the transport, the
::Envelope-to:: header that is added to the message contains all the addresses
that are batched together.

The \%appendfile%\ and \%pipe%\ transports have an option called \use@_bsmtp\,
which causes them to deliver the message in `batched SMTP' format, with the
envelope represented as SMTP commands. The \check@_string\ and \escape@_string\
options are forced to the values
.display asis
check_string = "."
escape_string = ".."
.endd
when batched SMTP is in use. A full description of the batch SMTP mechanism is
given in section ~~SECTbatchSMTP. The \%lmtp%\ transport does not have a
\use@_bsmtp\ option, because it always delivers using the SMTP protocol.

.index \%pipe%\ transport||with multiple addresses
If you are not using BSMTP, but are using a \%pipe%\ transport, you can include 
\$pipe@_addresses$\ as part of the command. This is not a true variable; it is 
a bit of magic that causes each of the recipient addresses to be inserted into 
the command as a separate argument. This provides a way of accessing all the 
addresses that are being delivered in the batch.

If you are using a batching \%appendfile%\ transport without \use@_bsmtp\, the
only way to preserve the recipient addresses is to set the \envelope@_to@_add\
option. This causes an ::Envelope-to:: header line to be added to the message, 
containing all the recipients.



.
.
.
. ============================================================================
.chapter The appendfile transport
.set runningfoot "appendfile transport"
.rset CHAPappendfile ~~chapter
.index \%appendfile%\ transport
.index transports||\%appendfile%\
.index directory creation
.index creating directories
The \%appendfile%\ transport delivers a message by appending it to an existing
file, or by creating an entirely new file in a specified directory. Single
files to which messages are appended can be in the traditional Unix mailbox
format, or optionally in the MBX format supported by the Pine MUA and
University of Washington IMAP daemon, $it{inter alia}. When each message is
being delivered as a separate file, `maildir' format can optionally be used to
give added protection against failures that happen part-way through the
delivery. A third form of separate-file delivery known as `mailstore' is also
supported. For all file formats, Exim attempts to create as many levels of
directory as necessary, provided that \create@_directory\ is set.

The code for the optional formats is not included in the Exim binary by
default. It is necessary to set \\SUPPORT@_MBX\\, \\SUPPORT@_MAILDIR\\ and/or
\\SUPPORT@_MAILSTORE\\ in \(Local/Makefile)\ to have the appropriate code
included.

.index quota||system
Exim recognises system quota errors, and generates an appropriate message. Exim
also supports its own quota control within the transport, for use when the
system facility is unavailable or cannot be used for some reason.

If there is an error while appending to a file (for example, quota exceeded or
partition filled), Exim attempts to reset the file's length and last
modification time back to what they were before. If there is an error while
creating an entirely new file, the new file is removed.

Before appending to a file, a number of security checks are made, and the
file is locked. A detailed description is given below, after the list of
private options.

\%appendfile%\ is most commonly used for local deliveries to users' mailboxes.
However, it can also be used as a pseudo-remote transport for putting messages
into files for remote delivery by some means other than Exim. `Batch SMTP'
format is often used in this case (see the \use@_bsmtp\ option). 


.section The file and directory options
.rset SECTfildiropt "~~chapter.~~section"
The \file\ option specifies a single file, to which the message is appended; 
the \directory\ option specifies a directory, in which a new file containing 
the message is created. Only one of these two options can be set, and for
normal deliveries to mailboxes, one of them \*must*\ be set.

However, \%appendfile%\ is also used for delivering messages to files or
directories whose names (or parts of names) are obtained from alias,
forwarding, or filtering operations (for example, a \save\ command in a user's
Exim filter). When such a transport is running, \$local@_part$\ contains the
local part that was aliased or forwarded, and \$address@_file$\ contains the
name (or partial name) of the file or directory generated by the redirection
operation. There are two cases:
.numberpars $.
If neither \file\ nor \directory\ is set, the redirection operation
must specify an absolute path (one that begins with \"/"\). This is the most 
common case when users with local accounts use filtering to sort mail into 
different folders. See for example, the \%address@_file%\ transport in the
default configuration. If the path ends with a slash, it is assumed to be the
name of a directory. A delivery to a directory can also be forced by setting 
\maildir@_format\ or \mailstore@_format\.
.nextp
If \file\ or \directory\ is set for a delivery from a redirection, it is used
to determine the file or directory name for the delivery. Normally, the
contents of \$address@_file$\ are used in some way in the string expansion. 
.endp

.index Sieve filter||configuring \%appendfile%\
.index Sieve filter||relative mailbox path handling
As an example of the second case, consider an environment where users do not
have home directories. They may be permitted to use Exim filter commands of the
form:
.display asis
save folder23
.endd
or Sieve filter commands of the form:
.display asis
require "fileinto"; 
fileinto "folder23";
.endd
In this situation, the expansion of \file\ or \directory\ in the transport must
transform the relative path into an appropriate absolute file name. In the case 
of Sieve filters, the name \*inbox*\ must be handled. It is the name that is 
used as a result of a `keep' action in the filter. This example shows one way 
of handling this requirement:
.display asis
file = ${if eq{$address_file}{inbox} \
            {/var/mail/$local_part} \
            {${if eq{${substr_0_1:$address_file}}{/} \
                  {$address_file} \
                  {$home/mail/$address_file} \
            }} \
       }
.endd
With this setting of \file\, \*inbox*\ refers to the standard mailbox location, 
absolute paths are used without change, and other folders are in the \(mail)\
directory within the home directory.

\**Note 1**\: While processing an Exim filter, a relative path such as
\(folder23)\ is turned into an absolute path if a home directory is known to
the router. In particular, this is the case if \check@_local@_user\ is set. If
you want to prevent this happening at routing time, you can set
\router@_home@_directory\ empty. This forces the router to pass the relative
path to the transport.

\**Note 2**\: An absolute path in \$address@_file$\ is not treated specially;
the \file\ or \directory\ option is still used if it is set.



.section Private options for appendfile
.index options||\%appendfile%\ transport

.startconf

.conf allow@_fifo boolean false
.index fifo (named pipe)
.index named pipe (fifo)
.index pipe||named (fifo)
Setting this option permits delivery to named pipes (FIFOs) as well as to
regular files. If no process is reading the named pipe at delivery time, the
delivery is deferred.

.conf allow@_symlink boolean false
.index symbolic link||to mailbox
.index mailbox||symbolic link
By default, \%appendfile%\ will not deliver if the path name for the file is
that of a symbolic link. Setting this option relaxes that constraint, but there
are security issues involved in the use of symbolic links. Be sure you know
what you are doing if you set this. Details of exactly what this option affects
are included in the discussion which follows this list of options.

.conf batch@_id string$**$ unset
See the description of local delivery batching in chapter ~~CHAPbatching.
However, batching is automatically disabled for \%appendfile%\ deliveries that 
happen as a result of forwarding or aliasing or other redirection directly to a 
file.

.conf batch@_max integer 1
See the description of local delivery batching in chapter ~~CHAPbatching.

.conf check@_group boolean false
When this option is set, the group owner of the file defined by the \file\
option is checked to see that it is the same as the group under which the
delivery process is running. The default setting is false because the default
file mode is 0600, which means that the group is irrelevant.

.conf check@_owner boolean true
When this option is set, the owner of the file defined by the \file\ option is
checked to ensure that it is the same as the user under which the delivery
process is running.

.conf check@_string string "see below"
.index `From' line
As \%appendfile%\ writes the message, the start of each line is tested for
matching \check@_string\, and if it does, the initial matching characters are
replaced by the contents of \escape@_string\. The value of \check@_string\ is a
literal string, not a regular expression, and the case of any letters it
contains is significant.

If \use@_bsmtp\ is set the values of \check@_string\ and \escape@_string\ are
forced to `.' and `..' respectively, and any settings in the configuration are
ignored. Otherwise, they default to `From ' and `>From ' when the \file\ option
is set, and unset when 
any of the \directory\, \maildir\, or \mailstore\ options are set.

The default settings, along with \message@_prefix\ and \message@_suffix\, are
suitable for traditional `BSD' mailboxes, where a line beginning with `From '
indicates the start of a new message. All four options need changing if another
format is used. For example, to deliver to mailboxes in MMDF format:
.index MMDF format mailbox
.index mailbox||MMDF format
.display asis
check_string = "\1\1\1\1\n"
escape_string = "\1\1\1\1 \n"
message_prefix = "\1\1\1\1\n"
message_suffix = "\1\1\1\1\n"
.endd

.index directory creation
.conf create@_directory boolean true
When this option is true, Exim attempts to create any missing superior
directories for the file that it is about to write. A created directory's mode
is given by the \directory@_mode\ option.

.conf create@_file string "anywhere"
This option constrains the location of files and directories that are created
by this transport. It applies to files defined by the \file\ option and
directories defined by the \directory\ option. In the case of maildir delivery,
it applies to the top level directory, not the maildir directories beneath.

The option must be set to one of the words `anywhere', `inhome', or
`belowhome'. In the second and third cases, a home directory must have been set
for the transport. This option is not useful when an explicit file name is
given for normal mailbox deliveries. It is intended for the case when file
names are generated from users' \(.forward)\ files. These are usually handled
by an \%appendfile%\ transport called \address@_file\. See also
\file@_must@_exist\.

.conf directory string$**$ unset
This option is mutually exclusive with the \file\ option, but one of \file\ or
\directory\ must be set, unless the delivery is the direct result of a
redirection (see section ~~SECTfildiropt).

When \directory\ is set, the string is expanded, and the message is delivered
into a new file or files in or below the given directory, instead of being
appended to a single mailbox file. A number of different formats are provided
(see \maildir@_format\ and \mailstore@_format\), and see section ~~SECTopdir
for further details of this form of delivery.

.conf directory@_file string$**$ "$tt{q@$@{base62:@$tod@_epoch@}-@$inode}"
.index base62
When \directory\ is set, but neither \maildir@_format\ nor \mailstore@_format\
is set, \%appendfile%\ delivers each message into a file whose name is obtained
by expanding this string. The default value generates a unique name from the
current time, in base 62 form, and the inode of the file. The variable
\$inode$\ is available only when expanding this option.

.conf directory@_mode "octal integer" 0700
If \%appendfile%\ creates any directories as a result of the \create@_directory\
option, their mode is specified by this option.

.conf escape@_string string "see description"
See \check@_string\ above.

.conf file string$**$ unset
This option is mutually exclusive with the \directory\ option, but one of
\file\ or \directory\ must be set, unless the delivery is the direct result of
a redirection (see section ~~SECTfildiropt). The \file\ option specifies a
single file, to which the message is appended. One or more of
\use@_fcntl@_lock\, \use@_flock@_lock\, or \use@_lockfile\ must be set with
\file\.
.index NFS||lock file
.index locking files
.index lock files
If you are using more than one host to deliver over NFS into the same
mailboxes, you should always use lock files.

The string value is expanded for each delivery, and must yield an absolute
path. The most common settings of this option are variations on one of these
examples:
.display asis
file = /var/spool/mail/$local_part
file = /home/$local_part/inbox
file = $home/inbox
.endd
.index `sticky' bit
In the first example, all deliveries are done into the same directory. If Exim
is configured to use lock files (see \use@_lockfile\ below) it must be able to
create a file in the directory, so the `sticky' bit must be turned on for
deliveries to be possible, or alternatively the \group\ option can be used to
run the delivery under a group id which has write access to the directory.


.conf file@_format string unset
.index file||mailbox, checking existing format
This option requests the transport to check the format of an existing file
before adding to it. The check consists of matching a specific string at the
start of the file. The value of the option consists of an even number of
colon-separated strings. The first of each pair is the test string, and the
second is the name of a transport. If the transport associated with a matched
string is not the current transport, control is passed over to the other
transport. For example, suppose the standard \%local@_delivery%\ transport has
this added to it:
.display asis
file_format = "From       : local_delivery :\
               \1\1\1\1\n : local_mmdf_delivery"
.endd
Mailboxes that begin with `From' are still handled by this transport, but if a
mailbox begins with four binary ones followed by a newline, control is passed
to a transport called \local__mmdf__delivery\, which presumably is configured
to do the delivery in MMDF format. If a mailbox does not exist or is empty, it
is assumed to match the current transport. If the start of a mailbox doesn't
match any string, or if the transport named for a given string is not defined,
delivery is deferred.

.conf file@_must@_exist boolean false
If this option is true, the file specified by the \file\ option must exist, and
an error occurs if it does not. Otherwise, it is created if it does not exist.

.conf lock@_fcntl@_timeout time 0s
.index timeout||mailbox locking
.index mailbox locking||blocking and non-blocking
.index locking files
By default, the \%appendfile%\ transport uses non-blocking calls to \*fcntl()*\
when locking an open mailbox file. If the call fails, the delivery process
sleeps for \lock@_interval\ and tries again, up to \lock@_retries\ times.
Non-blocking calls are used so that the file is not kept open during the wait
for the lock; the reason for this is to make it as safe as possible for
deliveries over NFS in the case when processes might be accessing an NFS
mailbox without using a lock file. This should not be done, but
misunderstandings and hence misconfigurations are not unknown.

On a busy system, however, the performance of a non-blocking lock approach is
not as good as using a blocking lock with a timeout. In this case, the waiting
is done inside the system call, and Exim's delivery process acquires the lock
and can proceed as soon as the previous lock holder releases it.

If \lock@_fcntl@_timeout\ is set to a non-zero time, blocking locks, with that
timeout, are used. There may still be some retrying: the maximum number of
retries is
.display asis
(lock_retries * lock_interval) / lock_fcntl_timeout
.endd
rounded up to the next whole number. In other words, the total time during
which \%appendfile%\ is trying to get a lock is roughly the same, unless
\lock@_fcntl@_timeout\ is set very large.

You should consider setting this option if you are getting a lot of delayed
local deliveries because of errors of the form
.display asis
failed to lock mailbox /some/file (fcntl)
.endd

.conf lock@_flock@_timeout time 0s
This timeout applies to file locking when using \*flock()*\ (see \use@_flock\);
the timeout operates in a similar manner to \lock@_fcntl@_timeout\.

.conf lock@_interval time 3s
This specifies the time to wait between attempts to lock the file. See below
for details of locking.

.conf lock@_retries integer 10
This specifies the maximum number of attempts to lock the file. A value of zero
is treated as 1. See below for details of locking.

.conf lockfile@_mode "octal integer" 0600
This specifies the mode of the created lock file, when a lock file is being
used (see \use@_lockfile\).

.conf lockfile@_timeout time 30m
.index timeout||mailbox locking
When a lock file is being used (see \use@_lockfile\), if a lock file already
exists and is older than this value, it is assumed to have been left behind by
accident, and Exim attempts to remove it.

.conf maildir@_format boolean false
.index maildir format||specifying
If this option is set with the \directory\ option, the delivery is into a new
file, in the `maildir' format that is used by other mail software. When the
transport is activated directly from a \%redirect%\ router (for example, the
\%address@_file%\ transport in the default configuration), setting
\maildir@_format\ causes the path received from the router to be treated as a
directory, whether or not it ends with \"/"\. This option is available only if
\\SUPPORT@_MAILDIR\\ is present in \(Local/Makefile)\. See section
~~SECTmaildirdelivery below for further details.

.em
.conf maildir@_quota@_directory@_regex string "See below"
.index maildir format||quota, directories included in
.index quota||maildir, directories included in
This option is relevant only when \maildir@_use@_size@_file\ is set. It defines
a regular expression for specifying directories that should be included in the
quota calculation. The default value is
.display asis
maildir_quota_directory_regex = ^(?:cur|new|\..*)$
.endd
which includes the \(cur)\ and \(new)\ directories, and any maildir++ folders
(directories whose names begin with a dot). If you want to exclude the 
\(Trash)\
folder from the count (as some sites do), you need to change this setting to
.display asis
maildir_quota_directory_regex = ^(?:cur|new|\.(?!Trash).*)$
.endd
This uses a negative lookahead in the regular expression to exclude the
directory whose name is \(.Trash)\.
.nem

.conf maildir@_retries integer 10
This option specifies the number of times to retry when writing a file in
`maildir' format. See section ~~SECTmaildirdelivery below.

.conf maildir@_tag string$**$ unset
This option applies only to deliveries in maildir format, and is described in
section ~~SECTmaildirdelivery below.

.conf maildir@_use@_size@_file boolean false
.index maildir format||\(maildirsize)\ file
Setting this option true enables support for \(maildirsize)\ files. Exim
creates a \(maildirsize)\ file in a maildir if one does not exist, taking the
quota from the \quota\ option of the transport. If \quota\ is unset, the value
is zero. See section ~~SECTmaildirdelivery below for further details.

.conf mailstore@_format boolean false
.index mailstore format||specifying
If this option is set with the \directory\ option, the delivery is into two new
files in  `mailstore' format. The option is available only if
\\SUPPORT@_MAILSTORE\\ is present in \(Local/Makefile)\. See section
~~SECTopdir below for further details.

.conf mailstore@_prefix string$**$ unset
This option applies only to deliveries in mailstore format, and is described in
section ~~SECTopdir below.

.conf mailstore@_suffix string$**$ unset
This option applies only to deliveries in mailstore format, and is described in
section ~~SECTopdir below.

.conf mbx@_format boolean false
.index locking files
.index file||locking
.index file||MBX format
.index MBX format, specifying
This option is available only if Exim has been compiled with \\SUPPORT@_MBX\\
set in \(Local/Makefile)\. If \mbx@_format\ is set with the \file\ option,
the message is appended to the mailbox file in MBX format instead of
traditional Unix format. This format is supported by Pine4 and its associated
IMAP and POP daemons, by means of the \*c-client*\ library that they all use.

\**Note**\: The \message@_prefix\ and \message@_suffix\ options are not
automatically changed by the use of \mbx@_format\. They should normally be set
empty when using MBX format, so this option almost always appears in this 
combination:
.display asis
mbx_format = true
message_prefix =
message_suffix =
.endd

If none of the locking options are mentioned in the configuration,
\use@_mbx@_lock\ is assumed and the other locking options default to false. It
is possible to specify the other kinds of locking with \mbx@_format\, but
\use@_fcntl@_lock\ and \use@_mbx@_lock\ are mutually exclusive. MBX locking
interworks with \*c-client*\, providing for shared access to the mailbox. It
should not be used if any program that does not use this form of locking is
going to access the mailbox, nor should it be used if the mailbox file is NFS
mounted, because it works only when the mailbox is accessed from a single host.

If you set \use@_fcntl@_lock\ with an MBX-format mailbox, you cannot use
the standard version of \*c-client*\, because as long as it has a mailbox open
(this means for the whole of a Pine or IMAP session), Exim will not be able to
append messages to it.

.conf message@_prefix string$**$ "see below"
.index `From' line
The string specified here is expanded and output at the start of every message.
The default is unset unless \file\ is specified and \use@_bsmtp\ is not set, in
which case it is:
.display asis
message_prefix = "From ${if def:return_path{$return_path}\
  {MAILER-DAEMON}} $tod_bsdinbox\n"
.endd

.conf message@_suffix string$**$ "see below"
The string specified here is expanded and output at the end of every message.
The default is unset unless \file\ is specified and \use@_bsmtp\ is not set, in
which case it is a single newline character. The suffix can be suppressed by
setting
.display asis
message_suffix =
.endd

.conf mode "octal integer" 0600
If the output file is created, it is given this mode. If it already exists and
has wider permissions, they are reduced to this mode. If it has narrower
permissions, an error occurs unless \mode__fail__narrower\ is false. However,
if the delivery is the result of a \save\ command in a filter file specifing a
particular mode, the mode of the output file is always forced to take that
value, and this option is ignored.

.conf mode@_fail@_narrower boolean true
This option applies in the case when an existing mailbox file has a narrower
mode than that specified by the \mode\ option. If \mode@_fail@_narrower\ is
true, the delivery is deferred (`mailbox has the wrong mode'); otherwise Exim
continues with the delivery attempt, using the existing mode of the file.

.conf notify@_comsat boolean false
If this option is true, the \*comsat*\ daemon is notified after every successful
delivery to a user mailbox. This is the daemon that notifies logged on users
about incoming mail.

.conf quota string$**$ unset
.index quota||imposed by Exim
This option imposes a limit on the size of the file to which Exim is appending,
or to the total space used in the directory tree when the \directory\ option is
set. In the latter case, computation of the space used is expensive, because
all the files in the directory (and any sub-directories) have to be
individually inspected and their sizes summed. 
.em
(See \quota@_size@_regex\ and \maildir@_use@_size@_file\ for ways to avoid this
in environments where users have no shell access to their mailboxes).

As there is no interlock against two simultaneous deliveries into a
multi-file mailbox, it is possible for the quota to be overrun in this case.
For single-file mailboxes, of course, an interlock is a necessity.
.nem

A file's size is taken as its \*used*\ value. Because of blocking effects, this
may be a lot less than the actual amount of disk space allocated to the file.
If the sizes of a number of files are being added up, the rounding effect can
become quite noticeable, especially on systems that have large block sizes.
Nevertheless, it seems best to stick to the \*used*\ figure, because this is
the obvious value which users understand most easily.

The value of the option is expanded, and must then be a numerical value
(decimal point allowed), optionally followed by one of the letters K or M. The
expansion happens while Exim is running as root, before it changes uid for the
delivery. This means that files which are inaccessible to the end user can be
used to hold quota values that are looked up in the expansion. When delivery
fails because this quota is exceeded, the handling of the error is as for
system quota failures.

.em
\**Note**\: A value of zero is interpreted as `no quota'. 
.nem

By default, Exim's quota checking mimics system quotas, and restricts the
mailbox to the specified maximum size, though the value is not accurate to the
last byte, owing to separator lines and additional headers that may get added
during message delivery. When a mailbox is nearly full, large messages may get
refused even though small ones are accepted, because the size of the current
message is added to the quota when the check is made. This behaviour can be
changed by setting \quota@_is@_inclusive\ false. When this is done, the check
for exceeding the quota does not include the current message. Thus, deliveries
continue until the quota has been exceeded; thereafter, no further messages are
delivered. See also \quota@_warn@_threshold\.

.conf quota@_directory string$**$ unset
This option defines the directory to check for quota purposes when delivering
into individual files. The default is the delivery directory, or, if a file
called \(maildirfolder)\ exists in a maildir directory, the parent of the
delivery directory.

.conf quota@_filecount string$**$ 0
This option applies when the \directory\ option is set. It limits the total
number of files in the directory (compare the inode limit in system quotas). It
can only be used if \quota\ is also set. The value is expanded; an expansion
failure causes delivery to be deferred.

.conf quota@_is@_inclusive boolean true
See \quota\ above.

.conf quota@_size@_regex string unset
This option applies when one of the delivery modes that writes a separate file
for each message is being used. When Exim wants to find the size of one of
these files in order to test the quota, it first checks \quota@_size@_regex\.
If this is set to a regular expression that matches the file name, and it
captures one string, that string is interpreted as a representation of the
file's size. The value of \quota@_size@_regex\ is not expanded.

This feature is useful only when users have no shell access to their mailboxes
-- otherwise they could defeat the quota simply by renaming the files. This
facility can be used with maildir deliveries, by setting \maildir@_tag\ to add
the file length to the file name. For example:
.display asis
maildir_tag = ,S=$message_size
quota_size_regex = ,S=(\d+)
.endd
The regular expression should not assume that the length is at the end of the 
file name (even though \maildir@_tag\ puts it there) because maildir MUAs 
sometimes add other information onto the ends of message file names.

.conf quota@_warn@_message string$**$ "see below"
See below for the use of this option. If it is not set when
\quota@_warn@_threshold\ is set, it defaults to
.display asis
quota_warn_message = "\
  To: $local_part@$domain\n\
  Subject: Your mailbox\n\n\
  This message is automatically created \
  by mail delivery software.\n\n\
  The size of your mailbox has exceeded \
  a warning threshold that is\n\
  set by the system administrator.\n"
.endd

.conf quota@_warn@_threshold string$**$ 0
.index quota||warning threshold
.index mailbox||size warning
.index size||of mailbox
This option is expanded in the same way as \quota\ (see above). If the
resulting value is greater than zero, and delivery of the message causes the
size of the file or total space in the directory tree to cross the given
threshold, a warning message is sent. If \quota\ is also set, the threshold may
be specified as a percentage of it by following the value with a percent sign.
For example:
.display asis
quota = 10M
quota_warn_threshold = 75%
.endd
If \quota\ is not set, a setting of \quota@_warn@_threshold\ that ends with a
percent sign is ignored.

The warning message itself is specified by the \quota@_warn@_message\ option,
and it must start with a ::To:: header line containing the recipient(s). A
::Subject:: line should also normally be supplied. The \quota\ option does not
have to be set in order to use this option; they are independent of one
another except when the threshold is specified as a percentage.

.conf use@_bsmtp boolean false
.index envelope sender
If this option is set true, \%appendfile%\ writes messages in `batch SMTP'
format, with the envelope sender and recipient(s) included as SMTP commands. If
you want to include a leading \\HELO\\ command with such messages, you can do
so by setting the \message@_prefix\ option. See section ~~SECTbatchSMTP for
details of batch SMTP.

.conf use@_crlf boolean false
.index carriage return
.index linefeed
This option causes lines to be terminated with the two-character CRLF sequence
(carriage return, linefeed) instead of just a linefeed character. In the case
of batched SMTP, the byte sequence written to the file is then an exact image
of what would be sent down a real SMTP connection.

The contents of the \message@_prefix\ and \message@_suffix\ options are written
verbatim, so must contain their own carriage return characters if these are
needed. In cases where these options have non-empty defaults, the values end
with a single linefeed, so they 
must
be changed to end with \"@\r@\n"\ if \use@_crlf\ is set.

.conf use@_fcntl@_lock boolean "see below"
This option controls the use of the \*fcntl()*\ function to lock a file for
exclusive use when a message is being appended. It is set by default unless
\use@_flock@_lock\ is set. Otherwise, it should be turned off only if you know
that all your MUAs use lock file locking. When both \use@_fcntl@_lock\ and
\use@_flock@_lock\ are unset, \use@_lockfile\ must be set.

.conf use@_flock@_lock boolean false
This option is provided to support the use of \*flock()*\ for file locking, for
the few situations where it is needed. Most modern operating systems support
\*fcntl()*\ and \*lockf()*\ locking, and these two functions interwork with
each other. Exim uses \*fcntl()*\ locking by default.

This option is required only if you are using an operating system where
\*flock()*\ is used by programs that access mailboxes (typically MUAs), and
where \*flock()*\ does not correctly interwork with \*fcntl()*\. You can use
both \*fcntl()*\ and \*flock()*\ locking simultaneously if you want.

.index Solaris||\*flock()*\ support
Not all operating systems provide \*flock()*\. Some versions of Solaris do not
have it (and some, I think, provide a not quite right version built on top of
\*lockf()*\). If the OS does not have \*flock()*\, Exim will be built without
the ability to use it, and any attempt to do so will cause a configuration
error.

\**Warning**\: \*flock()*\ locks do not work on NFS files (unless \*flock()*\
is just being mapped onto \*fcntl()*\ by the OS).

.conf use@_lockfile boolean "see below"
If this option is turned off, Exim does not attempt to create a lock file when
appending to a mailbox file. In this situation, the only locking is by
\*fcntl()*\. You should only turn \use@_lockfile\ off if you are absolutely
sure that every MUA that is ever going to look at your users' mailboxes uses
\*fcntl()*\ rather than a lock file, and even then only when you are not
delivering over NFS from more than one host.

.index NFS||lock file
In order to append to an NFS file safely from more than one host, it is
necessary to take out a lock $it{before} opening the file, and the lock file
achieves this. Otherwise, even with \*fcntl()*\ locking, there is a risk of
file corruption.

The \use@_lockfile\ option is set by default unless \use@_mbx@_lock\ is set. It
is not possible to turn both \use@_lockfile\ and \use@_fcntl@_lock\ off, except
when \mbx@_format\ is set.

.conf use@_mbx@_lock boolean "see below"
This option is available only if Exim has been compiled with \\SUPPORT@_MBX\\
set in \(Local/Makefile)\. Setting the option specifies that special MBX
locking rules be used. It is set by default if \mbx@_format\ is set and none of
the locking options are mentioned in the configuration. The locking rules are
the same as are used by the \*c-client*\ library that underlies Pine and the
IMAP4 and POP daemons that come with it (see the discussion below). The rules
allow for shared access to the mailbox. However, this kind of locking does not
work when the mailbox is NFS mounted.

You can set \use@_mbx@_lock\ with either (or both) of \use@_fcntl@_lock\ and
\use@_flock@_lock\ to control what kind of locking is used in implementing the
MBX locking rules. The default is to use \*fcntl()*\ if \use@_mbx@_lock\ is set
without \use@_fcntl@_lock\ or \use@_flock@_lock\.
.endconf


.section Operational details for appending
.rset SECTopappend "~~chapter.~~section"
.index appending to a file
.index file||appending
Before appending to a file, the following preparations are made:
.numberpars $.
If the name of the file is \(/dev/null)\, no action is taken, and a success
return is given.
.nextp
.index directory creation
If any directories on the file's path are missing, Exim creates them if the
\create@_directory\ option is set. A created directory's mode is given by the
\directory@_mode\ option.
.nextp
If \file@_format\ is set, the format of an existing file is checked. If this
indicates that a different transport should be used, control is passed to that
transport.
.nextp
.index file||locking
.index locking files
.index NFS||lock file
If \use@_lockfile\ is set, a lock file is built in a way that will work
reliably over NFS, as follows:
.numberpars $.
Create a `hitching post' file whose name is that of the lock file with the
current time, primary host name, and process id added, by opening for writing
as a new file. If this fails with an access error, delivery is deferred.
.nextp
Close the hitching post file, and hard link it to the lock file name.
.nextp
If the call to \*link()*\ succeeds, creation of the lock file has succeeded.
Unlink the hitching post name.
.nextp
Otherwise, use \*stat()*\ to get information about the hitching post file, and
then unlink hitching post name. If the number of links is exactly two, creation
of the lock file succeeded but something (for example, an NFS server crash and
restart) caused this fact not to be communicated to the \*link()*\ call.
.nextp
If creation of the lock file failed, wait for \lock@_interval\ and try again,
up to \lock@_retries\ times. However, since any program that writes to a
mailbox should complete its task very quickly, it is reasonable to time out old
lock files that are normally the result of user agent and system crashes. If an
existing lock file is older than \lockfile@_timeout\ Exim attempts to unlink it
before trying again.
.endp
.nextp
A call is made to \*lstat()*\ to discover whether the main file exists, and if
so, what its characteristics are. If \*lstat()*\ fails for any reason other
than non-existence, delivery is deferred.
.nextp
.index symbolic link||to mailbox
.index mailbox||symbolic link
If the file does exist and is a symbolic link, delivery is deferred, unless the
\allow@_symlink\ option is set, in which case the ownership of the link is
checked, and then \*stat()*\ is called to find out about the real file, which
is then subjected to the checks below. The check on the top-level link
ownership prevents one user creating a link for another's mailbox in a sticky
directory, though allowing symbolic links in this case is definitely not a good
idea. If there is a chain of symbolic links, the intermediate ones are not
checked.
.nextp
If the file already exists but is not a regular file, or if the file's owner
and group (if the group is being checked -- see \check@_group\ above) are
different from the user and group under which the delivery is running,
delivery is deferred.
.nextp
If the file's permissions are more generous than specified, they are reduced.
If they are insufficient, delivery is deferred, unless \mode@_fail@_narrower\
is set false, in which case the delivery is tried using the existing
permissions.
.nextp
The file's inode number is saved, and the file is then opened for appending. If
this fails because the file has vanished, \%appendfile%\ behaves as if it hadn't
existed (see below). For any other failures, delivery is deferred.
.nextp
If the file is opened successfully, check that the inode number hasn't
changed, that it is still a regular file, and that the owner and permissions
have not changed. If anything is wrong, defer delivery and freeze the message.
.nextp
If the file did not exist originally, defer delivery if the \file@_must@_exist\
option is set. Otherwise, check that the file is being created in a permitted
directory if the \create@_file\ option is set (deferring on failure), and then
open for writing as a new file, with the \\O@_EXCL\\ and \\O@_CREAT\\ options,
except when dealing with a symbolic link (the \allow@_symlink\ option must be
set). In this case, which can happen if the link points to a non-existent file,
the file is opened for writing using \\O@_CREAT\\ but not \\O@_EXCL\\, because
that prevents link following.
.nextp
.index loop||while file testing
If opening fails because the file exists, obey the tests given above for
existing files. However, to avoid looping in a situation where the file is
being continuously created and destroyed, the exists/not-exists loop is broken
after 10 repetitions, and the message is then frozen.
.nextp
If opening fails with any other error, defer delivery.
.nextp
.index file||locking
.index locking files
Once the file is open, unless both \use@_fcntl@_lock\ and \use@_flock@_lock\
are false, it is locked using \*fcntl()*\ or \*flock()*\ or both. If
\use@_mbx@_lock\ is false, an exclusive lock is requested in each case. 
However, if \use@_mbx@_lock\ is true,
Exim takes out a shared lock on the open file,
and an exclusive lock on the file whose name is
.display
/tmp/.<<device-number>>.<<inode-number>>
.endd
using the device and inode numbers of the open mailbox file, in accordance with
the MBX locking rules.

If Exim fails to lock the file, there are two possible courses of action,
depending on the value of the locking timeout. This is obtained from
\lock@_fcntl@_timeout\ or \lock@_flock@_timeout\, as appropriate.

If the timeout value is zero, the file is closed, Exim waits for
\lock@_interval\, and then goes back and re-opens the file as above and tries
to lock it again. This happens up to \lock@_retries\ times, after which the
delivery is deferred.

If the timeout has a value greater than zero, blocking calls to \*fcntl()*\ or
\*flock()*\ are used (with the given timeout), so there has already been some
waiting involved by the time locking fails. Nevertheless, Exim does not give up
immediately. It retries up to
.display
(lock@_retries * lock@_interval) / <<timeout>>
.endd
times (rounded up).
.endp

At the end of delivery, Exim closes the file (which releases the \*fcntl()*\
and/or \*flock()*\ locks) and then deletes the lock file if one was created.

.section Operational details for delivery to a new file
.rset SECTopdir "~~chapter.~~section"
.index delivery||to single file
.index `From' line
When the \directory\ option is set instead of \file\, each message is delivered
into a newly-created file or set of files. When \%appendfile%\ is activated 
directly from a \%redirect%\ router, neither \file\ nor \directory\ is normally 
set, because the path for delivery is supplied by the router. (See for example, 
the \%address@_file%\ transport in the default configuration.) In this case, 
delivery is to a new file if either the path name ends in \"/"\, or the 
\maildir@_format\ or \mailstore@_format\ option is set.

No locking is required while writing the message to a new file, so the various
locking options of the transport are ignored. The `From' line that by default
separates messages in a single file is not normally needed, nor is the escaping
of message lines that start with `From', and there is no need to ensure a
newline at the end of each message. Consequently, the default values for
\check@_string\, \message@_prefix\, and \message@_suffix\ are all unset when
any of \directory\, \maildir@_format\, or \mailstore@_format\ is set.

If Exim is required to check a \quota\ setting, it adds up the sizes of all the 
files in the delivery directory by default. However, you can specify a 
different directory by setting \quota@_directory\. Also, for maildir deliveries 
(see below) the \(maildirfolder)\ convention is honoured.


.index maildir format
.index mailstore format
There are three different ways in which delivery to individual files can be
done, controlled by the settings of the \maildir@_format\ and
\mailstore@_format\ options. Note that code to support maildir or mailstore
formats is not included in the binary unless \\SUPPORT@_MAILDIR\\ or
\\SUPPORT@_MAILSTORE\\, respectively, is set in \(Local/Makefile)\.

.index directory creation
In all three cases an attempt is made to create the directory and any necessary
sub-directories if they do not exist, provided that the \create@_directory\
option is set (the default). The location of a created directory can be
constrained by setting \create@_file\. A created directory's mode is given by
the \directory@_mode\ option. If creation fails, or if the \create@_directory\
option is not set when creation is required, delivery is deferred.


.section Maildir delivery
.rset SECTmaildirdelivery "~~chapter.~~section"
.index maildir format||description of
If the \maildir@_format\ option is true, Exim delivers each message by writing
it to a file whose name is \(tmp/<<stime>>.H<<mtime>>P<<pid>>.<<host>>)\ in the
given directory. If the delivery is successful, the file is renamed into the 
\(new)\ subdirectory.

In the file name, <<stime>> is the current time of day in seconds, and
<<mtime>> is the microsecond fraction of the time. After a maildir delivery,
Exim checks that the time-of-day clock has moved on by at least one microsecond
before terminating the delivery process. This guarantees uniqueness for the
file name. However, as a precaution, Exim calls \*stat()*\ for the file before
opening it. If any response other than \\ENOENT\\ (does not exist) is given,
Exim waits 2 seconds and tries again, up to \maildir@_retries\ times.

.index quota||in maildir delivery
.index maildir++
If Exim is required to check a \quota\ setting before a maildir delivery, and
\quota@_directory\ is not set, it looks for a file called \(maildirfolder)\ in
the maildir directory (alongside \(new)\, \(cur)\, \(tmp)\). If this exists,
Exim assumes the directory is a maildir++ folder directory, which is one level
down from the user's top level mailbox directory. This causes it to start at
the parent directory instead of the current directory when calculating the
amount of space used.


.section Using tags to record message sizes
If \maildir@_tag\ is set, the string is expanded for each delivery. 
When the maildir file is renamed into the \(new)\ sub-directory, the
tag is added to its name. However, if adding the tag takes the length of the
name to the point where the test \*stat()*\ call fails with \\ENAMETOOLONG\\,
the tag is dropped and the maildir file is created with no tag. 

Tags can be used to encode the size of files in their names; see
\quota@_size@_regex\ above for an example. The expansion of \maildir@_tag\ 
happens after the message has been written. The value of the \$message@_size$\
variable is set to the number of bytes actually written. If the expansion is
forced to fail, the tag is ignored, but a non-forced failure causes delivery to
be deferred. The expanded tag may contain any printing characters except `/'.
Non-printing characters in the string are ignored; if the resulting string is
empty, it is ignored. If it starts with an alphanumeric character, a leading
colon is inserted.


.em
.section Using a maildirsize file
.index quota||in maildir delivery
.index maildir format||\(maildirsize)\ file
If \maildir@_use@_size@_file\ is true, Exim implements the maildir++ rules for
storing quota and message size information in a file called \(maildirsize)\
within the maildir directory. If this file does not exist, Exim creates it,
setting the quota from the \quota\ option of the transport. If the maildir
directory itself does not exist, it is created before any attempt to write a
\(maildirsize)\ file.

The \(maildirsize)\ file is used to hold information about the sizes of
messages in the maildir, thus speeding up quota calculations. The quota value
in the file is just a cache; if the quota is changed in the transport, the new
value overrides the cached value when the next message is delivered. The cache
is maintained for the benefit of other programs that access the maildir and
need to know the quota.

If the \quota\ option in the transport is unset or zero, the \(maildirsize)\
file is maintained (with a zero quota setting), but no quota is imposed.

A regular expression is available for controlling which directories in the
maildir participate in quota calculations. See the description of the 
\maildir@_quota@_directory@_regex\ option above for details.
.nem


.section Mailstore delivery
.index mailstore format||description of
If the \mailstore@_format\ option is true, each message is written as two files
in the given directory. A unique base name is constructed from the message id
and the current delivery process, and the files that are written use this base
name plus the suffixes \(.env)\ and \(.msg)\. The \(.env)\ file contains the
message's envelope, and the \(.msg)\ file contains the message itself.

During delivery, the envelope is first written to a file with the suffix
\(.tmp)\. The \(.msg)\ file is then written, and when it is complete, the
\(.tmp)\ file is renamed as the \(.env)\ file. Programs that access messages in
mailstore format should wait for the presence of both a \(.msg)\ and a \(.env)\
file before accessing either of them. An alternative approach is to wait for
the absence of a \(.tmp)\ file.

The envelope file starts with any text defined by the \mailstore@_prefix\
option, expanded and terminated by a newline if there isn't one. Then follows
the sender address on one line, then all the recipient addresses, one per line.
There can be more than one recipient only if the \batch@_max\ option is set
greater than one. Finally, \mailstore@_suffix\ is expanded and the result
appended to the file, followed by a newline if it does not end with one.

If expansion of \mailstore@_prefix\ or \mailstore@_suffix\ ends with a forced
failure, it is ignored. Other expansion errors are treated as serious
configuration errors, and delivery is deferred.


.section Non-special new file delivery
If neither \maildir@_format\ nor \mailstore@_format\ is set, a single new file
is created directly in the named directory. For example, when delivering
messages into files in batched SMTP format for later delivery to some host (see
section ~~SECTbatchSMTP), a setting such as
.display asis
directory = /var/bsmtp/$host
.endd
might be used. A message is written to a file with a temporary name, which is
then renamed when the delivery is complete. The final name is obtained by
expanding the contents of the \directory@_file\ option.





.
.
.
.
. ============================================================================
.chapter The autoreply transport
.set runningfoot "autoreply transport"
.index transports||\%autoreply%\
.index \%autoreply%\ transport
The \%autoreply%\ transport is not a true transport in that it does not cause
the message to be transmitted. Instead, it generates another mail message. It
is usually run as the result of mail filtering, a `vacation' message being the
standard example. However, it can also be run directly from a router like any
other transport. To reduce the possibility of message cascades, messages
created by the \%autoreply%\ transport always have empty envelope sender
addresses, like bounce messages.

The parameters of the message to be sent can be specified in the configuration
by options described below. However, these are used only when the address
passed to the transport does not contain its own reply information. When the
transport is run as a consequence of a 
\mail\
or \vacation\ command in a filter file, the parameters of the message are
supplied by the filter, and passed with the address. The transport's options
that define the message are then ignored (so they are not usually set in this
case). The message is specified entirely by the filter or by the transport; it
is never built from a mixture of options. However, the \file@_optional\,
\mode\, and \return@_message\ options apply in all cases.

\%Autoreply%\ is implemented as a local transport. When used as a result of a
command in a user's filter file, \%autoreply%\ normally runs under the uid and
gid of the user, and with appropriate current and home directories (see chapter
~~CHAPenvironment).

There is a subtle difference between routing a message to a \%pipe%\ transport
that generates some text to be returned to the sender, and routing it to an
\%autoreply%\ transport. This difference is noticeable only if more than one
address from the same message is so handled. In the case of a pipe, the
separate outputs from the different addresses are gathered up and returned to
the sender in a single message, whereas if \%autoreply%\ is used, a separate
message is generated for each address that is passed to it.

Non-printing characters are not permitted in the header lines generated for the
message that \%autoreply%\ creates, with the exception of newlines that are
immediately followed by whitespace. If any non-printing characters are found, 
the transport defers.
Whether characters with the top bit set count as printing characters or not is
controlled by the \print@_topbitchars\ global option.

If any of the generic options for manipulating headers (for example,
\headers@_add\) are set on an \%autoreply%\ transport, they apply to the copy of
the original message that is included in the generated message when
\return@_message\ is set. They do not apply to the generated message itself.

If the \%autoreply%\ transport receives return code 2 from Exim when it submits
the message, indicating that there were no recipients, it does not treat this
as an error. This means that autoreplies sent to \$sender@_address$\ when this
is empty (because the incoming message is a bounce message) do not cause
problems. They are just discarded.


.section Private options for autoreply

.startconf
.index options||\%autoreply%\ transport
.conf bcc string$**$ unset
This specifies the addresses that are to receive `blind carbon copies' of the
message when the message is specified by the transport.

.conf cc string$**$ unset
This specifies recipients of the message and the contents of the ::Cc:: header
when the message is specified by the transport.

.conf file string$**$ unset
The contents of the file are sent as the body of the message when the message
is specified by the transport. If both \file\ and \text\ are set, the text
string comes first.

.conf file@_expand boolean false
If this is set, the contents of the file named by the \file\ option are
subjected to string expansion as they are added to the message.

.conf file@_optional boolean false
If this option is true, no error is generated if the file named by the \file\
option or passed with the address does not exist or cannot be read.

.conf from string$**$ unset
This specifies the contents of the ::From:: header when the message is specified
by the transport.

.conf headers string$**$ unset
This specifies additional RFC 2822 headers that are to be added to the message when
the message is specified by the transport. Several can be given by using `@\n'
to separate them. There is no check on the format.

.conf log string$**$ unset
This option names a file in which a record of every message sent is logged when
the message is specified by the transport.

.conf mode "octal integer" 0600
If either the log file or the `once' file has to be created, this mode is used.

.conf once string$**$ unset
This option names a file or DBM database in which a record of each 
::To:: recipient is kept when the message is specified by the transport.
\**Note**\: This does not apply to ::Cc:: or ::Bcc:: recipients.
If \once@_file@_size\ is not set, a DBM database is used, and it is allowed to
grow as large as necessary. If a potential recipient is already in the
database, no message is sent by default. However, if \once@_repeat\ specifies a
time greater than zero, the message is sent if that much time has elapsed since
a message was last sent to this recipient. If \once\ is unset, the message is
always sent.

If \once@_file@_size\ is set greater than zero, it changes the way Exim
implements the \once\ option. Instead of using a DBM file to record every
recipient it sends to, it uses a regular file, whose size will never get larger
than the given value. In the file, it keeps a linear list of recipient
addresses and times at which they were sent messages. If the file is full when
a new address needs to be added, the oldest address is dropped. If
\once@_repeat\ is not set, this means that a given recipient may receive
multiple messages, but at unpredictable intervals that depend on the rate of
turnover of addresses in the file. If \once@_repeat\ is set, it specifies a
maximum time between repeats.

.conf once@_file@_size integer 0
See \once\ above.

.conf once@_repeat time$**$ 0s
See \once\ above.
After expansion, the value of this option must be a valid time value.

.conf reply@_to string$**$ unset
This specifies the contents of the ::Reply-To:: header when the message is
specified by the transport.

.conf return@_message boolean false
If this is set, a copy of the original message is returned with the new
message, subject to the maximum size set in the \return@_size@_limit\ global
configuration option.

.conf subject string$**$ unset
This specifies the contents of the ::Subject:: header when the message is
specified by the transport.

.conf text string$**$ unset
This specifies a single string to be used as the body of the message when the
message is specified by the transport. If both \text\ and \file\ are set, the
text comes first.

.conf to string$**$ unset
This specifies recipients of the message and the contents of the ::To:: header
when the message is specified by the transport.

.endconf



.
.
.
.
. ============================================================================
.chapter The lmtp transport
.set runningfoot "lmtp transport"
.index transports||\%lmtp%\
.index \%lmtp%\ transport
.index LMTP||over a pipe
.index LMTP||over a socket
.rset CHAPLMTP "~~chapter"
The \%lmtp%\ transport runs the LMTP protocol (RFC 2033) over a pipe to a
specified command
or by interacting with a Unix domain socket.
This transport is something of a cross between the \%pipe%\ and \%smtp%\
transports. Exim also has support for using LMTP over TCP/IP; this is
implemented as an option for the \%smtp%\ transport. Because LMTP is expected
to be of minority interest, the default build-time configure in \(src/EDITME)\
has it commented out. You need to ensure that
.display asis
TRANSPORT_LMTP=yes
.endd
is present in your \(Local/Makefile)\ in order to have the \%lmtp%\ transport
included in the Exim binary.

The private options of the \%lmtp%\ transport are as follows:

.startconf
.index options||\%lmtp%\ transport

.conf batch@_id string$**$ unset
See the description of local delivery batching in chapter ~~CHAPbatching.

.conf batch@_max integer 1
This limits the number of addresses that can be handled in a single delivery.
Most LMTP servers can handle several addresses at once, so it is normally a
good idea to increase this value. See the description of local delivery
batching in chapter ~~CHAPbatching.

.conf command string$**$ unset
This option must be set if \socket\ is not set.
The string is a command which is run in a separate process. It is split up into
a command name and list of arguments, each of which is separately expanded (so
expansion cannot change the number of arguments). The command is run directly,
not via a shell. The message is passed to the new process using the standard
input and output to operate the LMTP protocol.

.conf socket string$**$ unset
This option must be set if \command\ is not set. The result of expansion must 
be the name of a Unix domain socket. The transport connects to the socket and 
delivers the message to it using the LMTP protocol.

.conf timeout time 5m
The transport is aborted if the created process 
or Unix domain socket
does not respond to LMTP commands or message input within this timeout.

.endconf

Here is an example of a typical LMTP transport:
.display asis
lmtp:
  driver = lmtp
  command = /some/local/lmtp/delivery/program
  batch_max = 20
  user = exim
.endd
This delivers up to 20 addresses at a time, in a mixture of domains if
necessary, running as the user \*exim*\.



.
.
.
.
. ============================================================================
.chapter The pipe transport
.rset CHAPpipetransport "~~chapter"
.set runningfoot "pipe transport"
.index transports||\%pipe%\
.index \%pipe%\ transport
The \%pipe%\ transport is used to deliver messages via a pipe to a command
running in another process. This can happen in one of two ways:
.numberpars $.
A router routes an address to a transport in the normal way, and the transport
is configured as a \%pipe%\ transport. In this case, \$local@_part$\ contains
the address (as usual), and the command which is run is specified by the
\command\ option on the transport. An example of this is the use of \%pipe%\ as
a pseudo-remote transport for passing messages to some other delivery mechanism
(such as UUCP).
.nextp
A router redirects an address directly to a pipe command (for example, from an
alias or forward file). In this case, \$local@_part$\ contains the local part
that was redirected, and \$address@_pipe$\ contains the text of the pipe
command itself. The \command\ option on the transport is ignored.
.endp

The \%pipe%\ transport is a non-interactive delivery method. Exim can also 
deliver messages over pipes using the LMTP interactive protocol. This is 
implemented by the \%lmtp%\ transport.

In the case when \%pipe%\ is run as a consequence of an entry in a local user's
\(.forward)\ file, the command runs under the uid and gid of that user. In
other cases, the uid and gid have to be specified explicitly, either on the
transport or on the router that handles the address. Current and `home'
directories are also controllable. See chapter ~~CHAPenvironment for details of
the local delivery environment.

.section Returned status and data
.index \%pipe%\ transport||returned data
If the command exits with a non-zero return code, the delivery is deemed to
have failed, unless either the \ignore@_status\ option is set (in which case
the return code is treated as zero), or the return code is one of those listed
in the \temp@_errors\ option, which are interpreted as meaning `try again
later'. In this case, delivery is deferred. Details of a permanent failure are
logged, but are not included in the bounce message, which merely contains
`local delivery failed'.

If the return code is greater than 128 and the command being run is a shell
script, it normally means that the script was terminated by a signal whose
value is the return code minus 128.

If Exim is unable to run the command (that is, if \*execve()*\ fails), the 
return code is set to 127. This is the value that a shell returns if it is 
asked to run a non-existent command. The wording for the log line suggests that 
a non-existent command may be the problem.

The \return@_output\ option can affect the result of a pipe delivery. If it is
set and the command produces any output on its standard output or standard
error streams, the command is considered to have failed, even if it gave a zero
return code or if \ignore@_status\ is set. The output from the command is
included as part of the bounce message. The \return@_fail@_output\ option is
similar, except that output is returned only when the command exits with a
failure return code, that is, a value other than zero or a code that matches
\temp@_errors\.


.section How the command is run
.rset SECThowcommandrun "~~chapter.~~section"
.index \%pipe%\ transport||path for command
The command line is (by default) broken down into a command name and arguments
by the \%pipe%\ transport itself. The \allow@_commands\ and \restrict@_to@_path\
options can be used to restrict the commands that may be run.
.index quoting||in pipe command
Unquoted arguments are delimited by white space. If an argument appears in
double quotes, backslash is interpreted as an escape character in the usual
way. If an argument appears in single quotes, no escaping is done.

String expansion is applied to the command line except when it comes from a
traditional \(.forward)\ file (commands from a filter file are expanded). The
expansion is applied to each argument in turn rather than to the whole line.
For this reason, any string expansion item that contains white space must be
quoted so as to be contained within a single argument. A setting such as
.display asis
command = /some/path ${if eq{$local_part}{postmaster}{xxx}{yyy}}
.endd
will not work, because the expansion item gets split between several
arguments. You have to write
.display asis
command = /some/path "${if eq{$local_part}{postmaster}{xxx}{yyy}}"
.endd
to ensure that it is all in one argument. The expansion is done in this way,
argument by argument, so that the number of arguments cannot be changed as a
result of expansion, and quotes or backslashes in inserted variables do not
interact with external quoting.

.index transport||filter
.index filter||transport filter
Special handling takes place when an argument consists of precisely the text
`$tt{@$pipe@_addresses}'. This is not a general expansion variable; the only
place this string is recognized is when it appears as an argument for a pipe or
transport filter command. It causes each address that is being handled to be
inserted in the argument list at that point $it{as a separate argument}. This
avoids any problems with spaces or shell metacharacters, and is of use when a
\%pipe%\ transport is handling groups of addresses in a batch.

After splitting up into arguments and expansion, the resulting command is run
in a subprocess directly from the transport, $it{not} under a shell. The
message that is being delivered is supplied on the standard input, and the
standard output and standard error are both connected to a single pipe that is
read by Exim. The \max@_output\ option controls how much output the command may
produce, and the \return@_output\ and \return@_fail@_output\ options control
what is done with it.

Not running the command under a shell (by default) lessens the security risks
in cases when a command from a user's filter file is built out of data that was
taken from an incoming message. If a shell is required, it can of course be
explicitly specified as the command to be run. However, there are circumstances
where existing commands (for example, in \(.forward)\ files) expect to be run
under a shell and cannot easily be modified. To allow for these cases, there is
an option called \use@_shell\, which changes the way the \%pipe%\ transport
works. Instead of breaking up the command line as just described, it expands it
as a single string and passes the result to \(/bin/sh)\. The
\restrict@_to@_path\ option and the \$pipe@_addresses$\ facility cannot be used
with \use@_shell\, and the whole mechanism is inherently less secure.


.section Environment variables
.rset SECTpipeenv "~~chapter.~~section"
.index \%pipe%\ transport||environment for command
.index environment for pipe transport
The environment variables listed below are set up when the command is invoked.
This list is a compromise for maximum compatibility with other MTAs. Note that
the \environment\ option can be used to add additional variables to this
environment.
.display flow
.tabs 20
DOMAIN              $t $rm{the domain of the address}
HOME                $t $rm{the home directory, if set}
HOST                $t $rm{the host name when called from a router (see below)}
LOCAL@_PART         $t $rm{see below}
LOCAL@_PART@_PREFIX $t $rm{see below}
LOCAL@_PART@_SUFFIX $t $rm{see below}
LOGNAME             $t $rm{see below}
MESSAGE@_ID         $t $rm{the message's id}
PATH                $t $rm{as specified by the \path\ option below}
QUALIFY@_DOMAIN     $t $rm{the sender qualification domain}
RECIPIENT           $t $rm{the complete recipient address}
SENDER              $t $rm{the sender of the message (empty if a bounce)}
SHELL               $t `$tt{/bin/sh}'
TZ                  $t $rm{the value of the \timezone\ option, if set}
USER                $t $rm{see below}
.endd

When a \%pipe%\ transport is called directly from (for example) an \%accept%\
router, \\LOCAL@_PART\\ is set to the local part of the address. When it is
called as a result of a forward or alias expansion, \\LOCAL@_PART\\ is set to
the local part of the address that was expanded. In both cases, any affixes are
removed from the local part, and made available in \\LOCAL@_PART@_PREFIX\\ and
\\LOCAL@_PART@_SUFFIX\\, respectively. \\LOGNAME\\ and \\USER\\ are set to the
same value as \\LOCAL@_PART\\ for compatibility with other MTAs.

.index \\HOST\\
\\HOST\\ is set only when a \%pipe%\ transport is called from a router that
associates hosts with an address, typically when using \%pipe%\ as a
pseudo-remote transport. \\HOST\\ is set to the first host name specified by
the router.

.index \\HOME\\
If the transport's generic \home@_directory\ option is set, its value is used
for the \\HOME\\ environment variable. Otherwise, a home directory may be set
by the router's \transport@_home@_directory\ option, which defaults to the
user's home directory if \check@_local@_user\ is set.

.section Private options for pipe
.index options||\%pipe%\ transport
.startconf

.conf allow@_commands "string list$**$" unset
.index \%pipe%\ transport||permitted commands
The string is expanded, and is then interpreted as a colon-separated list of
permitted commands. If \restrict@_to@_path\ is not set, the only commands
permitted are those in the \allow@_commands\ list. They need not be absolute
paths; the \path\ option is still used for relative paths. If
\restrict@_to@_path\ is set with \allow@_commands\, the command must either be
in the \allow@_commands\ list, or a name without any slashes that is found on
the path. In other words, if neither \allow@_commands\ nor \restrict@_to@_path\
is set, there is no restriction on the command, but otherwise only commands
that are permitted by one or the other are allowed. For example, if
.display asis
allow_commands = /usr/bin/vacation
.endd
and \restrict@_to@_path\ is not set, the only permitted command is
\(/usr/bin/vacation)\. The \allow@_commands\ option may not be set if
\use@_shell\ is set.

.conf batch@_id string$**$ unset
See the description of local delivery batching in chapter ~~CHAPbatching.

.conf batch@_max integer 1
This limits the number of addresses that can be handled in a single delivery.
See the description of local delivery batching in chapter ~~CHAPbatching.

.conf check@_string string unset
As \%pipe%\ writes the message, the start of each line is tested for matching
\check@_string\, and if it does, the initial matching characters are replaced
by the contents of \escape@_string\, provided both are set. The value of
\check@_string\ is a literal string, not a regular expression, and the case of
any letters it contains is significant. When \use@_bsmtp\ is set, the contents
of \check@_string\ and \escape@_string\ are forced to values that implement the
SMTP escaping protocol. Any settings made in the configuration file are
ignored.

.conf command string$**$ unset
This option need not be set when \%pipe%\ is being used to deliver to pipes
obtained directly from address redirections. In other cases, the option must be
set, to provide a command to be run. It need not yield an absolute path (see
the \path\ option below). The command is split up into separate arguments by
Exim, and each argument is separately expanded, as described in section
~~SECThowcommandrun above.

.conf environment string$**$ unset
.index \%pipe%\ transport||environment for command
.index environment for \%pipe%\ transport
This option is used to add additional variables to the environment in which the
command runs (see section ~~SECTpipeenv for the default list). Its value is a
string which is expanded, and then interpreted as a colon-separated list of
environment settings of the form `<<name>>=<<value>>'.

.conf escape@_string string unset
See \check@_string\ above.

.conf freeze@_exec@_fail boolean false
.index exec failure
.index failure of exec
.index \%pipe%\ transport||failure of exec
Failure to exec the command in a pipe transport is by default treated like
any other failure while running the command. However, if \freeze@_exec@_fail\
is set, failure to exec is treated specially, and causes the message to be
frozen, whatever the setting of \ignore@_status\.

.conf ignore@_status boolean false
If this option is true, the status returned by the subprocess that is set up to
run the command is ignored, and Exim behaves as if zero had been returned.
Otherwise, a non-zero status 
or termination by signal
causes an error return from the transport unless the status value is one of
those listed in \temp@_errors\; these cause the delivery to be deferred and
tried again later.

.conf log@_defer@_output boolean false
.index \%pipe%\ transport||logging output
If this option is set, and the status returned by the command is
one of the codes listed in \temp@_errors\ (that is, delivery was deferred),
and any output was produced, the first line of it is written to the main log.

.conf log@_fail@_output boolean false
If this option is set, and the command returns any output, and also ends with a
return code that is neither zero nor one of the return codes listed in
\temp@_errors\ (that is, the delivery failed), the first line of output is
written to the main log.

.conf log@_output boolean false
If this option is set and the command returns any output, the first line of
output is written to the main log, whatever the return code.

.conf max@_output integer 20K
This specifies the maximum amount of output that the command may produce on its
standard output and standard error file combined. If the limit is exceeded, the
process running the command is killed. This is intended as a safety measure to
catch runaway processes. The limit is applied independently of the settings of
the options that control what is done with such output (for example,
\return@_output\). Because of buffering effects, the amount of output may
exceed the limit by a small amount before Exim notices.

.conf message@_prefix string$**$ "see below"
The string specified here is expanded and output at the start of every message.
The default is unset if \use@_bsmtp\ is set. Otherwise it is
.display asis
message_prefix = \
  From ${if def:return_path{$return_path}{MAILER-DAEMON}}\
  ${tod_bsdinbox}\n
.endd
.index Cyrus
.index \tmail\
.index `From' line
This is required by the commonly used \(/usr/bin/vacation)\ program.
However, it must $it{not} be present if delivery is to the Cyrus IMAP server,
or to the \tmail\ local delivery agent. The prefix can be suppressed by setting
.display asis
message_prefix =
.endd

.conf message@_suffix string$**$ "see below"
The string specified here is expanded and output at the end of every message.
The default is unset if \use@_bsmtp\ is set. Otherwise it is a single newline.
The suffix can be suppressed by setting
.display asis
message_suffix =
.endd

.conf path string $tt{/usr/bin}
This option specifies the string that is set up in the \\PATH\\ environment
variable of the subprocess. If the \command\ option does not yield an absolute
path name, the command is sought in the \\PATH\\ directories, in the usual way.
\**Warning**\: This does not apply to a command specified as a transport 
filter.

.conf pipe@_as@_creator boolean false
.index uid (user id)||local delivery
If the generic \user\ option is not set and this option is true, the delivery
process is run under the uid that was in force when Exim was originally called
to accept the message. If the group id is not otherwise set (via the generic
\group\ option), the gid that was in force when Exim was originally called to
accept the message is used.

.conf restrict@_to@_path boolean false
When this option is set, any command name not listed in \allow@_commands\ must
contain no slashes. The command is searched for only in the directories listed
in the \path\ option. This option is intended for use in the case when a pipe
command has been generated from a user's \(.forward)\ file. This is usually
handled by a \%pipe%\ transport called \address@_pipe\.

.conf return@_fail@_output boolean false
If this option is true, and the command produced any output and ended with a
return code other than zero or one of the codes listed in \temp@_errors\ (that
is, the delivery failed), the output is returned in the bounce message.
However, if the message has a null sender (that is, it is itself a bounce
message), output from the command is discarded.

.conf return@_output boolean false
If this option is true, and the command produced any output, the delivery is
deemed to have failed whatever the return code from the command, and the output
is returned in the bounce message. Otherwise, the output is just discarded.
However, if the message has a null sender (that is, it is a bounce message),
output from the command is always discarded, whatever the setting of this
option.

.conf temp@_errors "string list" "see below"
.index \%pipe%\ transport||temporary failure
This option contains either a colon-separated list of numbers, or a single
asterisk. If \ignore@_status\ is false 
.em
and \return@_output\ is not set,
.nem
and the command exits with a non-zero return code, the failure is treated as
temporary and the delivery is deferred if the return code matches one of the
numbers, or if the setting is a single asterisk. Otherwise, non-zero return
codes are treated as permanent errors. The default setting contains the codes
defined by \\EX@_TEMPFAIL\\ and \\EX@_CANTCREAT\\ in \(sysexits.h)\. If Exim is
compiled on a system that does not define these macros, it assumes values of 75
and 73, respectively.

.conf timeout time 1h
If the command fails to complete within this time, it is killed. This normally
causes the delivery to fail. A zero time interval specifies no timeout. In
order to ensure that any subprocesses created by the command are also killed,
Exim makes the initial process a process group leader, and kills the whole
process group on a timeout. However, this can be defeated if one of the
processes starts a new process group.

.conf umask "octal integer" 022
This specifies the umask setting for the subprocess that runs the command.

.conf use@_bsmtp boolean false
.index envelope sender
If this option is set true, the \%pipe%\ transport writes messages in `batch
SMTP' format, with the envelope sender and recipient(s) included as SMTP
commands. If you want to include a leading \\HELO\\ command with such messages,
you can do so by setting the \message@_prefix\ option. See section
~~SECTbatchSMTP for details of batch SMTP.

.conf use@_crlf boolean false
.index carriage return
.index linefeed
This option causes lines to be terminated with the two-character CRLF sequence
(carriage return, linefeed) instead of just a linefeed character. In the case
of batched SMTP, the byte sequence written to the pipe is then an exact image
of what would be sent down a real SMTP connection.

The contents of the \message@_prefix\ and \message@_suffix\ options are written
verbatim, so must contain their own carriage return characters if these are
needed. Since the default values for both \message@_prefix\ and
\message@_suffix\ end with a single linefeed, their values
must
be changed to end with \"@\r@\n"\ if \use@_crlf\ is set.

.conf use@_shell boolean false
If this option is set, it causes the command to be passed to \(/bin/sh)\
instead of being run directly from the transport, as described in section
~~SECThowcommandrun. This is less secure, but is needed in some situations
where the command is expected to be run under a shell and cannot easily be
modified. The \allow@_commands\ and \restrict@_to@_path\ options, and the
`$tt{@$pipe@_addresses}' facility are incompatible with \use@_shell\. The
command is expanded as a single string, and handed to \(/bin/sh)\ as data for
its \-c-\ option.

.endconf

.section Using an external local delivery agent
.index local delivery||using an external agent
.index \*procmail*\
.index external local delivery
.index delivery||\*procmail*\
.index delivery||by external agent
The \%pipe%\ transport can be used to pass all messages that require local
delivery to a separate local delivery agent such as \procmail\. When doing
this, care must be taken to ensure that the pipe is run under an appropriate
uid and gid. In some configurations one wants this to be a uid that is trusted
by the delivery agent to supply the correct sender of the message. It may be
necessary to recompile or reconfigure the delivery agent so that it trusts an
appropriate user. The following is an example transport and router
configuration for \procmail\:
.display asis
# transport
procmail_pipe:
  driver = pipe
  command = /usr/local/bin/procmail -d $local_part
  return_path_add
  delivery_date_add
  envelope_to_add
  check_string = "From "
  escape_string = ">From "
  user = $local_part
  group = mail
.endd
.display asis
# router
procmail:
  driver = accept
  check_local_user
  transport = procmail_pipe
.endd

In this example, the pipe is run as the local user, but with the group set to
\*mail*\. An alternative is to run the pipe as a specific user such as \*mail*\
or \*exim*\, but in this case you must arrange for \procmail\ to trust that
user to supply a correct sender address. If you do not specify either a \group\
or a \user\ option, the pipe command is run as the local user. The home
directory is the user's home directory by default.

Note that the command that the pipe transport runs does $it{not} begin with
.display asis
IFS=" "
.endd
as shown in the \procmail\ documentation, because Exim does not by default use
a shell to run pipe commands.

.index Cyrus
The next example shows a transport and a router for a system where local
deliveries are handled by the Cyrus IMAP server.
.display asis
# transport
local_delivery_cyrus:
  driver = pipe
  command = /usr/cyrus/bin/deliver \
            -m ${substr_1:$local_part_suffix} -- $local_part
  user = cyrus
  group = mail
  return_output
  log_output
  message_prefix =
  message_suffix =
.endd
.display asis
# router
local_user_cyrus:
  driver = accept
  check_local_user
  local_part_suffix = .*
  transport = local_delivery_cyrus
.endd
Note the unsetting of \message@_prefix\ and \message@_suffix\, and the use of
\return@_output\ to cause any text written by Cyrus to be returned to the
sender.


.
.
.
.
. ============================================================================
.chapter The smtp transport
.rset CHAPsmtptrans "~~chapter"
.set runningfoot "smtp transport"
.index transports||\%smtp%\
.index \%smtp%\ transport
The \%smtp%\ transport delivers messages over TCP/IP connections using the SMTP
or LMTP protocol. The list of hosts to try can either be taken from the address
that is being processed (having been set up by the router), or specified
explicitly for the transport. Timeout and retry processing (see chapter
~~CHAPretry) is applied to each IP address independently.

.section Multiple messages on a single connection
The sending of multiple messages over a single TCP/IP connection can arise in
two ways:
.numberpars $.
If a message contains more than \max@_rcpt\ (see below) addresses that are
routed to the same host, more than one copy of the message has to be sent to
that host. In this situation, multiple copies may be sent in a single run of
the \%smtp%\ transport over a single TCP/IP connection. (What Exim actually does
when it has too many addresses to send in one message also depends on the value
of the global \remote@_max@_parallel\ option. Details are given in section
~~SECToutSMTPTCP.)
.nextp
.index hints database||remembering routing
When a message has been successfully delivered over a TCP/IP connection, Exim
looks in its hints database to see if there are any other messages awaiting a
connection to the same host. If there are, a new delivery process is started
for one of them, and the current TCP/IP connection is passed on to it. The new
process may in turn send multiple copies and possibly create yet another
process.
.endp

For each copy sent over the same TCP/IP connection, a sequence counter is
incremented, and if it ever gets to the value of \connection@_max@_messages\,
no further messages are sent over that connection.


.section Use of the @$host variable
.index \$host$\
.index \$host@_address$\
At the start of a run of the \%smtp%\ transport, the values of \$host$\ and
\$host@_address$\ are the name and IP address of the first host on the host list
passed by the router. However, when the transport is about to connect to a
specific host, and while it is connected to that host, \$host$\ and
\$host@_address$\ are set to the values for that host. These are the values
that are in force when the \helo@_data\, \hosts@_try@_auth\, \interface\,
\serialize@_hosts\, and the various TLS options are expanded.


.section Private options for smtp
The private options of the \%smtp%\ transport are as follows:

.index options||\%smtp%\ transport
.startconf
.conf allow@_localhost boolean false
.index local host||sending to
.index fallback||hosts specified on transport
When a host specified in \hosts\ or \fallback@_hosts\ (see below) turns out to
be the local host, or is listed in \hosts@_treat@_as@_local\, delivery is
deferred by default. However, if \allow@_localhost\ is set, Exim goes on to do
the delivery anyway. This should be used only in special cases when the
configuration ensures that no looping will result (for example, a differently
configured Exim is listening on the port to which the message is sent).

.conf authenticated@_sender string$**$ unset
.index Cyrus
When Exim has authenticated as a client, this option sets a value for the
\\AUTH=\\ item on outgoing \\MAIL\\ commands, overriding any existing
authenticated sender value. If the string expansion is forced to fail, the
option is ignored. Other expansion failures cause delivery to be deferred. If
the result of expansion is an empty string, that is also ignored.

If the SMTP session is not authenticated, the expansion of
\authenticated@_sender\ still happens (and can cause the delivery to be
deferred if it fails), but no \\AUTH=\\ item is added to \\MAIL\\ commands.

This option allows you to use the \%smtp%\ transport in LMTP mode to
deliver mail to Cyrus IMAP and provide the proper local part as the
`authenticated sender', via a setting such as:
.display asis
authenticated_sender = $local_part
.endd
This removes the need for IMAP subfolders to be assigned special ACLs to
allow direct delivery to those subfolders.

Because of expected uses such as that just described for Cyrus (when no
domain is involved), there is no checking on the syntax of the provided
value.

.conf command@_timeout time 5m
This sets a timeout for receiving a response to an SMTP command that has been
sent out. It is also used when waiting for the initial banner line from the
remote host. Its value must not be zero.

.conf connect@_timeout time 5m
This sets a timeout for the \*connect()*\ function, which sets up a TCP/IP call
to a remote host. A setting of zero allows the system timeout (typically
several minutes) to act. To have any effect, the value of this option must be
less than the system timeout. However, it has been observed that on some
systems there is no system timeout, which is why the default value for this
option is 5 minutes, a value recommended by RFC 1123.

.index SMTP||passed connection
.index SMTP||multiple deliveries
.index multiple SMTP deliveries
.conf connection@_max@_messages integer 500
This controls the maximum number of separate message deliveries that are sent
over a single TCP/IP connection. If the value is zero, there is no limit.
For testing purposes, this value can be overridden by the \-oB-\ command line
option.

.conf data@_timeout time 5m
This sets a timeout for the transmission of each block in the data portion of
the message. As a result, the overall timeout for a message depends on the size
of the message. Its value must not be zero. See also \final@_timeout\.

.conf delay@_after@_cutoff boolean true
This option controls what happens when all remote IP addresses for a given
domain have been inaccessible for so long that they have passed their retry
cutoff times.

In the default state, if the next retry time has not been reached for any of
them, the address is bounced without trying any deliveries. In other words,
Exim delays retrying an IP address after the final cutoff time until a new
retry time is reached, and can therefore bounce an address without ever trying
a delivery, when machines have been down for a long time. Some people are
unhappy at this prospect, so...

If \delay@_after@_cutoff\ is set false, Exim behaves differently. If all IP
addresses are past their final cutoff time, Exim tries to deliver to those
IP addresses that have not been tried since the message arrived. If there are
none, of if they all fail, the address is bounced. In other words, it does not
delay when a new message arrives, but immediately tries those expired IP
addresses that haven't been tried since the message arrived. If there is a
continuous stream of messages for the dead hosts, unsetting
\delay@_after@_cutoff\ means that there will be many more attempts to deliver
to them.

.conf dns@_qualify@_single boolean true
If the \hosts\ or \fallback@_hosts\ option is being used,
and the \gethostbyname\ option is false,
the \\RES@_DEFNAMES\\ resolver option is set. See the \qualify@_single\ option
in chapter ~~CHAPdnslookup for more details.

.conf dns@_search@_parents boolean false
.index \search@_parents\
If the \hosts\ or \fallback@_hosts\ option is being used, and the
\gethostbyname\ option is false, the \\RES@_DNSRCH\\ resolver option is set.
See the \search@_parents\ option in chapter ~~CHAPdnslookup for more details.


.conf fallback@_hosts "string list" unset
.index fallback||hosts specified on transport
String expansion is not applied to this option. The argument must be a
colon-separated list of host names or IP addresses. Fallback hosts can also be
specified on routers, which associate them with the addresses they process. As
for the \hosts\ option without \hosts@_override\, \fallback@_hosts\ specified
on the transport is used only if the address does not have its own associated
fallback host list. Unlike \hosts\, a setting of \fallback@_hosts\ on an
address is not overridden by \hosts@_override\. However, \hosts@_randomize\
does apply to fallback host lists.

If Exim is unable to deliver to any of the hosts for a particular address, and
the errors are not permanent rejections, the address is put on a separate
transport queue with its host list replaced by the fallback hosts, unless the
address was routed via MX records and the current host was in the original MX
list. In that situation, the fallback host list is not used.

Once normal deliveries are complete, the fallback queue is delivered by
re-running the same transports with the new host lists. If several failing
addresses have the same fallback hosts (and \max@_rcpt\ permits it), a single
copy of the message is sent.

The resolution of the host names on the fallback list is controlled by the
\gethostbyname\ option, as for the \hosts\ option. Fallback hosts apply
both to cases when the host list comes with the address and when it is taken
from \hosts\. This option provides a `use a smart host only if delivery fails'
facility.

.conf final@_timeout time 10m
This is the timeout that applies while waiting for the response to the final
line containing just `.' that terminates a message. Its value must not be zero.

.conf gethostbyname boolean false
If this option is true when the \hosts\ and/or \fallback@_hosts\ options are
being used, names are looked up using \*gethostbyname()*\ 
(or \*getipnodebyname()*\ when available)
instead of using the DNS. Of course, that function may in fact use the DNS, but
it may also consult other sources of information such as \(/etc/hosts)\.

.index \\HELO\\||argument, setting
.index \\EHLO\\||argument, setting
.conf helo@_data string$**$ $tt{@$primary@_hostname}
The value of this option is expanded, and used as the argument for the \\EHLO\\
or \\HELO\\ command that starts the outgoing SMTP session.

.conf hosts "string list$**$" unset
Hosts are associated with an address by a router such as \%dnslookup%\, which
finds the hosts by looking up the address domain in the DNS. However, addresses
can be passed to the \%smtp%\ transport by any router, and not all of them can
provide an associated host list. The \hosts\ option specifies a list of hosts
which are used if the address being processed does not have any hosts
associated with it. The hosts specified by \hosts\ are also used, whether or
not the address has its own hosts, if \hosts@_override\ is set.

The string is first expanded, before being interpreted as a colon-separated
list of host names or IP addresses. If the expansion fails, delivery is
deferred. Unless the failure was caused by the inability to complete a lookup,
the error is logged to the panic log as well as the main log. Host names are
looked up either by searching directly for address records in the DNS or by
calling \*gethostbyname()*\
(or \*getipnodebyname()*\ when available),
depending on the setting of the \gethostbyname\ option. When Exim is compiled
with IPv6 support, if a host that is looked up in the DNS has both IPv4 and
IPv6 addresses, both types of address are used.

During delivery, the hosts are tried in order, subject to their retry status,
unless \hosts@_randomize\ is set.

.conf hosts@_avoid@_esmtp "host list$**$" unset
.index ESMTP, avoiding use of
.index \\HELO\\||forcing use of
.index \\EHLO\\||avoiding use of
.index \\PIPELINING\\||avoiding the use of
This option is for use with broken hosts that announce ESMTP facilities (for
example, \\PIPELINING\\) and then fail to implement them properly. When a host
matches \hosts@_avoid@_esmtp\, Exim sends \\HELO\\ rather than \\EHLO\\ at the
start of the SMTP session. This means that it cannot use any of the ESMTP
facilities such as \\AUTH\\, \\PIPELINING\\, \\SIZE\\, and \\STARTTLS\\.

.conf hosts@_avoid@_tls "host list$**$" unset
.index TLS||avoiding for certain hosts
Exim will not try to start a TLS session when delivering to any host that
matches this list. See chapter ~~CHAPTLS for details of TLS.

.conf hosts@_max@_try integer 5
.index host||maximum number to try
.index limit||number of hosts tried
.index limit||number of MX tried
.index MX record||maximum tried
This option limits the number of IP addresses that are tried for any one
delivery
.em
in cases where there are temporary delivery errors.
.nem
Section ~~SECTvalhosmax describes in detail how the value of this option is
used.

.conf hosts@_nopass@_tls "host list$**$" unset
.index TLS||passing connection
.index multiple SMTP deliveries
.index TLS||multiple message deliveries
For any host that matches this list, a connection on which a TLS session has
been started will not be passed to a new delivery process for sending another
message on the same connection. See section ~~SECTmulmessam for an explanation
of when this might be needed.

.conf hosts@_override boolean false
If this option is set and the \hosts\ option is also set, any hosts that are
attached to the address are ignored, and instead the hosts specified by the
\hosts\ option are always used. This option does not apply to
\fallback@_hosts\.

.conf hosts@_randomize boolean false
.index randomized host list
.index host||list of, randomized
.index fallback||randomized hosts
If this option is set, and either the list of hosts is taken from the
\hosts\ or the \fallback@_hosts\ option, or the hosts supplied by the router
were not obtained from MX records (this includes fallback hosts from the
router), and were not randomizied by the router, the order of trying the hosts
is randomized each time the transport runs. Randomizing the order of a host
list can be used to do crude load sharing.

When \hosts@_randomize\ is true, a host list may be split into groups whose
order is separately randomized. This makes it possible to set up MX-like
behaviour. The boundaries between groups are indicated by an item that is just
\"+"\ in the host list. For example:
.display asis
hosts = host1:host2:host3:+:host4:host5
.endd
The order of the first three hosts and the order of the last two hosts is
randomized for each use, but the first three always end up before the last two.
If \hosts@_randomize\ is not set, a \"+"\ item in the list is ignored.

.index authentication||required by client
.conf hosts@_require@_auth "host list$**$" unset
This option provides a list of servers for which authentication must succeed
before Exim will try to transfer a message. If authentication fails for
servers which are not in this list, Exim tries to send unauthenticated. If
authentication fails for one of these servers, delivery is deferred. This
temporary error is detectable in the retry rules, so it can be turned into a
hard failure if required. See also \hosts@_try@_auth\, and chapter
~~CHAPSMTPAUTH for details of authentication.

.conf hosts@_require@_tls "host list$**$" unset
.index TLS||requiring for certain servers
Exim will insist on using a TLS session when delivering to any host that
matches this list. See chapter ~~CHAPTLS for details of TLS.
\**Note**\: This option affects outgoing mail only. To insist on TLS for 
incoming messages, use an appropriate ACL.

.index authentication||optional in client
.conf hosts@_try@_auth "host list$**$" unset
This option provides a list of servers to which, provided they announce
authentication support, Exim will attempt to authenticate as a client when it
connects. If authentication fails, Exim will try to transfer the message
unauthenticated. See also \hosts@_require@_auth\, and chapter ~~CHAPSMTPAUTH
for details of authentication.

.index bind IP address
.index IP address||binding
.conf interface "string list$**$" unset
This option specifies which interface to bind to when making an outgoing SMTP
call. The variables \$host$\ and \$host@_address$\ refer to the host to which a
connection is about to be made during the expansion of the string. Forced
expansion failure, or an empty string result causes the option to be ignored.
Otherwise, after expansion, 
.em
the string must be a list of IP addresses, colon-separated by default, but the
separator can be changed in the usual way.
.nem
For example:
.display asis
interface = <; 192.168.123.123 ; 3ffe:ffff:836f::fe86:a061
.endd
The first interface of the correct type (IPv4 or IPv6) is used for the outgoing
connection. If none of them are the correct type, the option is ignored. If
\interface\ is not set, or is ignored, the system's IP functions choose which
interface to use if the host has more than one.

.conf keepalive boolean true
.index keepalive||on outgoing connection
This option controls the setting of \\SO@_KEEPALIVE\\ on outgoing TCP/IP socket
connections. When set, it causes the kernel to probe idle connections
periodically, by sending packets with `old' sequence numbers. The other end of
the connection should send a acknowledgement if the connection is still okay or
a reset if the connection has been aborted. The reason for doing this is that
it has the beneficial effect of freeing up certain types of connection that can
get stuck when the remote host is disconnected without tidying up the TCP/IP
call properly. The keepalive mechanism takes several hours to detect
unreachable hosts.

.conf max@_rcpt integer 100
.index \\RCPT\\||maximum number of outgoing
This option limits the number of \\RCPT\\ commands that are sent in a single
SMTP message transaction. Each set of addresses is treated independently, and
so can cause parallel connections to the same host if \remote@_max@_parallel\
permits this.

.conf multi@_domain boolean true
When this option is set, the \%smtp%\ transport can handle a number of addresses
containing a mixture of different domains provided they all resolve to the same
list of hosts. Turning the option off restricts the transport to handling only
one domain at a time. This is useful if you want to use \$domain$\ in an
expansion for the transport, because it is set only when there is a single
domain involved in a remote delivery.

.conf port string$**$ "see below"
.index port||sending TCP/IP
.index TCP/IP||setting outgoing port
This option specifies the TCP/IP port on the server to which Exim connects. If
it begins with a digit it is taken as a port number; otherwise it is looked up
using \*getservbyname()*\. The default value is normally `smtp', but if
\protocol\ is set to `lmtp', the default is `lmtp'.
If the expansion fails, or if a port number cannot be found, delivery is 
deferred.


.conf protocol string "smtp"
.index LMTP||over TCP/IP
If this option is set to `lmtp' instead of `smtp', the default value for the
\port\ option changes to `lmtp', and the transport operates the LMTP protocol
(RFC 2033) instead of SMTP. This protocol is sometimes used for local
deliveries into closed message stores. Exim also has support for running LMTP
over a pipe to a local process -- see chapter ~~CHAPLMTP.

.conf retry@_include@_ip@_address boolean true
Exim normally includes both the host name and the IP address in the key it
constructs for indexing retry data after a temporary delivery failure. This
means that when one of several IP addresses for a host is failing, it gets
tried periodically (controlled by the retry rules), but use of the other IP
addresses is not affected.

However, in some dialup environments hosts are assigned a different IP address
each time they connect. In this situation the use of the IP address as part of
the retry key leads to undesirable behaviour. Setting this option false causes
Exim to use only the host name. This should normally be done on a separate
instance of the \%smtp%\ transport, set up specially to handle the dialup hosts.

.conf serialize@_hosts "host list$**$" unset
.index serializing connections
.index host||serializing connections
Because Exim operates in a distributed manner, if several messages for the same
host arrive at around the same time, more than one simultaneous connection to
the remote host can occur. This is not usually a problem except when there is a
slow link between the hosts. In that situation it may be helpful to restrict
Exim to one connection at a time. This can be done by setting
\serialize@_hosts\ to match the relevant hosts.

.index hints database||serializing deliveries to a host
Exim implements serialization by means of a hints database in which a record is
written whenever a process connects to one of the restricted hosts. The record
is deleted when the connection is completed. Obviously there is scope for
records to get left lying around if there is a system or program crash. To
guard against this, Exim ignores any records that are more than six hours old.

If you set up this kind of serialization, you should also arrange to delete the
relevant hints database whenever your system reboots. The names of the files
start with \(misc)\ and they are kept in the \(spool/db)\ directory. There
may be one or two files, depending on the type of DBM in use. The same files
are used for ETRN serialization.

.conf size@_addition integer 1024
.index SMTP||\\SIZE\\
.index message||size issue for transport filter
.index size||of message
.index transport||filter
.index filter||transport filter
If a remote SMTP server indicates that it supports the \\SIZE\\ option of the
\\MAIL\\ command, Exim uses this to pass over the message size at the start of
an SMTP transaction. It adds the value of \size@_addition\ to the value it
sends, to allow for headers and other text that may be added during delivery by
configuration options or in a transport filter. It may be necessary to increase
this if a lot of text is added to messages.

Alternatively, if the value of \size@_addition\ is set negative, it disables
the use of the \\SIZE\\ option altogether.

.conf tls@_certificate string$**$ unset
.index TLS||client certificate, location of
.index certificate||for client, location of
The value of this option must be the absolute path to a file which contains the
client's certificate, for use when sending a message over an encrypted
connection. The values of \$host$\ and \$host@_address$\ are set to the name
and address of the server during the expansion. See chapter ~~CHAPTLS for
details of TLS.

\**Note**\: This option must be set if you want Exim to use TLS when sending 
messages as a client. The global option of the same name specifies the 
certificate for Exim as a server; it is not automatically assumed that the same 
certificate should be used when Exim is operating as a client.

.em
.conf tls@_crl string$**$ unset
.index TLS||client certificate revocation list
.index certificate||revocation list for client
This option specifies a certificate revocation list. The expanded value must
be the name of a file that contains a CRL in PEM format.
.nem

.conf tls@_privatekey string$**$ unset
.index TLS||client private key, location of
The value of this option must be the absolute path to a file which contains the
client's private key, for use when sending a message over an encrypted
connection. The values of \$host$\ and \$host@_address$\ are set to the name
and address of the server during the expansion. 
If this option is unset, the private key is assumed to be in the same file as 
the certificate.
See chapter ~~CHAPTLS for details of TLS.

.conf tls@_require@_ciphers string$**$ unset
.index TLS||requiring specific ciphers
.index cipher||requiring specific
The value of this option must be a list of permitted cipher suites, for use
when setting up an 
.em
outgoing encrypted connection. (There is a global option of the same name for 
controlling incoming connections.)
.nem
The values of \$host$\ and \$host@_address$\ are set to the name and address of
the server during the expansion. See chapter ~~CHAPTLS for details of TLS; note
that this option is used in different ways by OpenSSL and GnuTLS (see section
~~SECTreqciphsslgnu).

.conf tls@_tempfail@_tryclear boolean true
When the server host is not in \hosts@_require@_tls\, and there is a problem in 
setting up a TLS session, this option determines whether or not Exim should try
to deliver the message unencrypted. If it is set false, delivery to the
current host is deferred; if there are other hosts, they are tried. If this
option is set true, Exim attempts to deliver unencrypted after a 4\*xx*\
response to \\STARTTLS\\. Also, if \\STARTTLS\\ is accepted, but the subsequent
TLS negotiation fails, Exim closes the current connection (because it is in an
unknown state), opens a new one to the same host, and then tries the delivery
in clear.

.conf tls@_verify@_certificates string$**$ unset
.index TLS||server certificate verification
.index certificate||verification of server
The value of this option must be the absolute path to a file containing
permitted server certificates, for use when setting up an encrypted connection.
Alternatively, if you are using OpenSSL, you can set
\tls@_verify@_certificates\ to the name of a directory containing certificate
files. This does not work with GnuTLS; the option must be set to the name of a
single file if you are using GnuTLS. The values of \$host$\ and
\$host@_address$\ are set to the name and address of the server during the
expansion of this option. See chapter ~~CHAPTLS for details of TLS.

.endconf


.section How the value of hosts@_max@_try is used
.rset SECTvalhosmax "~~chapter.~~section"
.index host||maximum number to try
.index limit||hosts, maximum number tried
The \hosts@_max@_try\ option limits the number of hosts that are tried
for a single delivery. However, despite the term `host' in its name, the option
actually applies to each IP address independently. In other words, a multihomed 
host is treated as several independent hosts, just as it is for retrying.

Many of the larger ISPs have multiple MX records which often point to
multihomed hosts. As a result, a list of a dozen or more IP addresses may be
created as a result of routing one of these domains.

Trying every single IP address on such a long list does not seem sensible; if
several at the top of the list fail, it is reasonable to assume there is some
problem that is likely to affect all of them. Roughly speaking, the value of
\hosts@_max@_try\ is the maximum number that are tried before deferring the 
delivery. However, the logic cannot be quite that simple.

Firstly, IP addresses that are skipped because their retry times have not
arrived do not count, and in addition, addresses that are past their retry
limits are also not counted, even when they are tried. This means that when
some IP addresses are past their retry limits, more than the value of
\hosts@_max@_retry\ may be tried. The reason for this behaviour is to ensure
that all IP addresses are considered before timing out an email address.

Secondly, when the \hosts@_max@_try\ limit is reached, Exim looks down the host
list to see if there is a subsequent host with a different (higher valued) MX.
If there is, that host is used next, and the current IP address is used but not
counted. This behaviour helps in the case of a domain with a retry rule that
hardly ever delays any hosts, as is now explained:

Consider the case of a long list of hosts with one MX value, and a few with a 
higher MX value. If \hosts@_max@_try\ is small (the default is 5) only a few
hosts at the top of the list are tried at first. With the default retry rule,
which specifies increasing retry times, the higher MX hosts are eventually
tried when those at the top of the list are skipped because they have not
reached their retry times.

However, it is common practice to put a fixed short retry time on domains for
large ISPs, on the grounds that their servers are rarely down for very long.
Unfortunately, these are exactly the domains that tend to resolve to long lists
of hosts. The short retry time means that the lowest MX hosts are tried every
time. The attempts may be in a different order because of random sorting, but
without the special MX check mentioned about, the higher MX hosts would never
be tried at all because the lower MX hosts are never all past their retry
times.

With the special check, Exim tries least one address from each MX value, even
if the \hosts@_max@_try\ limit has already been reached.






.
.
.
.
. ============================================================================
.chapter Address rewriting
.set runningfoot "address rewriting"
.rset CHAPrewrite ~~chapter
.index rewriting||addresses
There are some circumstances in which Exim automatically rewrites domains in
addresses. The two most common are when an address is given without a domain
(referred to as an `unqualified address') or when an address contains an
abbreviated domain that is expanded by DNS lookup.

Unqualified envelope addresses are accepted only for locally submitted
messages, or messages from hosts that match \sender@_unqualified@_hosts\ or
\recipient@_unqualified@_hosts\, respectively. Unqualified addresses in header
lines are qualified if they are in locally submitted messages, or messages from
hosts that are permitted to send unqualified envelope addresses. Otherwise,
unqualified addresses in header lines are neither qualified nor rewritten.

One situation in which Exim does $it{not} automatically rewrite a domain is
when it is the name of a CNAME record in the DNS. The older RFCs suggest that
such a domain should be rewritten using the `canonical' name, and some MTAs do
this. The new RFCs do not contain this suggestion.

.section Explicitly configured address rewriting
This chapter describes the rewriting rules that can be used in the
main rewrite section of the configuration file, and also in the generic
\headers@_rewrite\ option that can be set on any transport.

Some people believe that configured address rewriting is a Mortal Sin.
Others believe that life is not possible without it. Exim provides the
facility; you do not have to use it.

.em
The main rewriting rules that appear in the `rewrite' section of the
configuration file are applied to addresses in incoming messages, both envelope
addresses and addresses in header lines. Each rule specifies the types of
address to which it applies.
.nem

Rewriting of addresses in header lines applies only to those headers that
were received with the message, and, in the case of transport rewriting, those
that were added by a system filter. That is, it applies only to those headers
that are common to all copies of the message. Header lines that are added by
individual routers or transports (and which are therefore specific to
individual recipient addresses) are not rewritten.

In general, rewriting addresses from your own system or domain has some
legitimacy. Rewriting other addresses should be done only with great care and
in special circumstances. The author of Exim believes that rewriting should be
used sparingly, and mainly for `regularizing' addresses in your own domains.
Although it can sometimes be used as a routing tool, this is very strongly
discouraged.

There are two commonly encountered circumstances where rewriting is used, as
illustrated by these examples:
.numberpars $.
The company whose domain is \*hitch.fict.example*\ has a number of hosts that
exchange mail with each other behind a firewall, but there is only a single
gateway to the outer world. The gateway rewrites \*@*.hitch.fict.example*\ as
\*hitch.fict.example*\ when sending mail off-site.
.nextp
A host rewrites the local parts of its own users so that, for example,
\*fp42@@hitch.fict.example*\ becomes \*Ford.Prefect@@hitch.fict.example*\.
.endp

.em
.section When does rewriting happen?
.index rewriting||timing of
.index ~~ACL||rewriting addresses in
Configured address rewriting can take place at several different stages of a
message's processing. 

At the start of an ACL for \\MAIL\\, the sender address may have been rewritten 
by a special SMTP-time rewrite rule (see section ~~SECTrewriteS), but no
ordinary rewrite rules have yet been applied. If, however, the sender address
is verified in the ACL, it is rewritten before verification, and remains
rewritten thereafter. The subsequent value of \$sender@_address$\ is the
rewritten address. This also applies if sender verification happens in a
\\RCPT\\ ACL. Otherwise, when the sender address is not verified, it is
rewritten as soon as a message's header lines have been received.

Similarly, at the start of an ACL for \\RCPT\\, the current recipient's address
may have been rewritten by a special SMTP-time rewrite rule, but no ordinary
rewrite rules have yet been applied to it. However, the behaviour is different
from the sender address when a recipient is verified. The address is rewritten
for the verification, but the rewriting is not remembered at this stage. The
value of \$local@_part$\ and \$domain$\ after verification are always the same
as they were before (that is, they contain the unrewritten -- except for 
SMTP-time rewriting -- address).

Once a message's header lines have been received, all the envelope recipient 
addresses are permanently rewritten, and rewriting is also applied to the
addresses in the header lines (if configured).
.index \*local@_scan()*\ function||address rewriting, timing of
Thus, all the rewriting is completed before the \\DATA\\ ACL and
\*local@_scan()*\ functions are run.

When an address is being routed, either for delivery or for verification,
rewriting is applied immediately to child addresses that are generated by
redirection, unless \no@_rewrite\ is set on the router.
.nem

.index envelope sender, rewriting
.index rewriting||at transport time
At transport time, additional rewriting of addresses in header lines can be
specified by setting the generic \headers@_rewrite\ option on a transport. This
option contains rules that are identical in form to those in the rewrite
section of the configuration file. In addition, the outgoing envelope sender
can be rewritten by means of the \return@_path\ transport option. However, it
is not possible to rewrite envelope recipients at transport time.



.section Testing the rewriting rules that apply on input
.index rewriting||testing
.index testing||rewriting
Exim's input rewriting configuration appears in a part of the run time
configuration file headed by `begin rewrite'. It can be tested by the \-brw-\
command line option. This takes an address (which can be a full RFC 2822
address) as its argument. The output is a list of how the address would be
transformed by the rewriting rules for each of the different places it might
appear in an incoming message, that is, for each different header and for the
envelope sender and recipient fields. For example,
.display asis
exim -brw ph10@exim.workshop.example
.endd
might produce the output
.display asis
  sender: Philip.Hazel@exim.workshop.example
    from: Philip.Hazel@exim.workshop.example
      to: ph10@exim.workshop.example
      cc: ph10@exim.workshop.example
     bcc: ph10@exim.workshop.example
reply-to: Philip.Hazel@exim.workshop.example
env-from: Philip.Hazel@exim.workshop.example
  env-to: ph10@exim.workshop.example
.endd
which shows that rewriting has been set up for that address when used in any of
the source fields, but not when it appears as a recipient address. At the
present time, there is no equivalent way of testing rewriting rules that are
set for a particular transport.

.section Rewriting rules
.index rewriting||rules
The rewrite section of the configuration file consists of lines of rewriting
rules in the form
.display
<<source pattern>>  <<replacement>>  <<flags>>
.endd
Rewriting rules that are specified for the \headers@_rewrite\ generic transport
option are given as a colon-separated list. Each item in the list takes the
same form as a line in the main rewriting configuration
(except that any colons must be doubled, of course).

The formats of source patterns and replacement strings are described below.
Each is terminated by white space, unless enclosed in double quotes, in which
case normal quoting conventions apply inside the quotes. The flags are single
characters which may appear in any order. Spaces and tabs between them are
ignored.

For each address that could potentially be rewritten, the rules are scanned in
order, and replacements for the address from earlier rules can themselves be
replaced by later rules (but see the `q' and `R' flags).

The order in which addresses are rewritten is undefined, may change between
releases, and must not be relied on, with one exception: when a message is
received, the envelope sender is always rewritten first, before any header
lines are rewritten. For example, the replacement string for a rewrite of an
address in ::To:: must not assume that the message's address in ::From:: has (or
has not) already been rewritten. However, a rewrite of ::From:: may assume that
the envelope sender has already been rewritten.

The variables \$local@_part$\ and \$domain$\ can be used in the replacement
string to refer to the address that is being rewritten. Note that lookup-driven
rewriting can be done by a rule of the form
.display asis
*@*   ${lookup ...
.endd
where the lookup key uses \$1$\ and \$2$\ or \$local@_part$\ and \$domain$\ to
refer to the address that is being rewritten.

.section Rewriting patterns
.index rewriting||patterns
.index address list||in a rewriting pattern
The source pattern in a rewriting rule is any item which may appear in an
address list (see section ~~SECTaddresslist). It is in fact processed as a
single-item address list, which means that it is expanded before being tested
against the address.

Domains in patterns should be given in lower case. Local parts in patterns are 
case-sensitive. If you want to do case-insensitive matching of local parts, you 
can use a regular expression that starts with \"^(?i)"\.

.index numerical variables (\$1$\, \$2$\, etc)||in rewriting rules
After matching, the numerical variables \$1$\, \$2$\, etc. may be set,
depending on the type of match which occurred. These can be used in the
replacement string to insert portions of the incoming address. \$0$\ always
refers to the complete incoming address. When a regular expression is used, the
numerical variables are set from its capturing subexpressions. For other types
of pattern they are set as follows:

.numberpars $.
If a local part or domain starts with an asterisk, the numerical variables
refer to the character strings matched by asterisks, with \$1$\ associated with
the first asterisk, and \$2$\ with the second, if present. For example, if the
pattern
.display
*queen@@*.fict.example
.endd
is matched against the address \*hearts-queen@@wonderland.fict.example*\ then
.display asis
$0 = hearts-queen@wonderland.fict.example
$1 = hearts-
$2 = wonderland
.endd
Note that if the local part does not start with an asterisk, but the domain
does, it is \$1$\ that contains the wild part of the domain.
.nextp
If the domain part of the pattern is a partial lookup, the wild and fixed parts
of the domain are placed in the next available numerical variables. Suppose,
for example, that the address \*foo@@bar.baz.example*\ is processed by a
rewriting rule of the form
.display
*@@partial-dbm;/some/dbm/file    <<replacement string>>
.endd
and the key in the file that matches the domain is \"*.baz.example"\. Then
.display asis
$1 = foo
$2 = bar
$3 = baz.example
.endd
If the address \*foo@@baz.example*\ is looked up, this matches the same
wildcard file entry, and in this case \$2$\ is set to the empty string, but
\$3$\ is still set to \*baz.example*\. If a non-wild key is matched in a
partial lookup, \$2$\ is again set to the empty string and \$3$\ is set to the
whole domain. For non-partial domain lookups, no numerical variables are set.
.endp

.section Rewriting replacements
.index rewriting||replacements
If the replacement string for a rule is a single asterisk, addresses that
match the pattern and the flags are $it{not} rewritten, and no subsequent
rewriting rules are scanned. For example,
.display asis
hatta@lookingglass.fict.example  *  f
.endd
specifies that \*hatta@@lookingglass.fict.example*\ is never to be rewritten in
::From:: headers.

If the replacement string is not a single asterisk, it is expanded, and must
yield a fully qualified address. Within the expansion, the variables
\$local@_part$\ and \$domain$\ refer to the address that is being rewritten.
Any letters they contain retain their original case -- they are not lower
cased. The numerical variables are set up according to the type of pattern that
matched the address, as described above. If the expansion is forced to fail by
the presence of `fail' in a conditional or lookup item, rewriting by the
current rule is abandoned, but subsequent rules may take effect. Any other
expansion failure causes the entire rewriting operation to be abandoned, and an
entry written to the panic log.


.section Rewriting flags
There are three different kinds of flag that may appear on rewriting rules:
.numberpars $.
Flags that specify which headers and envelope addresses to rewrite: E, F, T, b,
c, f, h, r, s, t.
.nextp
A flag that specifies rewriting at SMTP time: S.
.nextp
Flags that control the rewriting process: Q, q, R, w.
.endp
For rules that are part of the \headers@_rewrite\ generic transport option,
E, F, T, and S are not permitted.


.section Flags specifying which headers and envelope addresses to rewrite
.index rewriting||flags
If none of the following flag letters, nor the `S' flag (see section
~~SECTrewriteS) are present, a main rewriting rule applies to all headers and
to both the sender and recipient fields of the envelope, whereas a
transport-time rewriting rule just applies to all headers. Otherwise, the
rewriting rule is skipped unless the relevant addresses are being processed.
.display
E       $rm{rewrite all envelope fields}
F       $rm{rewrite the envelope From field}
T       $rm{rewrite the envelope To field}
b       $rm{rewrite the ::Bcc:: header}
c       $rm{rewrite the ::Cc:: header}
f       $rm{rewrite the ::From:: header}
h       $rm{rewrite all headers}
r       $rm{rewrite the ::Reply-To:: header}
s       $rm{rewrite the ::Sender:: header}
t       $rm{rewrite the ::To:: header}
.endd
You should be particularly careful about rewriting ::Sender:: headers, and
restrict this to special known cases in your own domains.

.section The SMTP-time rewriting flag
.rset SECTrewriteS "~~chapter.~~section"
.index SMTP||rewriting malformed addresses
.index \\RCPT\\||rewriting argument of
.index \\MAIL\\||rewriting argument of
The rewrite flag `S' specifies a rewrite of incoming envelope addresses at SMTP
time, as soon as an address is received in a \\MAIL\\ or \\RCPT\\ command, and
before any other processing; even before syntax checking. The pattern is
required to be a regular expression, and it is matched against the whole of the
data for the command, including any surrounding angle brackets.

This form of rewrite rule allows for the handling of addresses that are not
compliant with RFCs 2821 and 2822 (for example, `bang paths' in batched SMTP
input). Because the input is not required to be a syntactically valid address,
the variables \$local@_part$\ and \$domain$\ are not available during the
expansion of the replacement string. The result of rewriting replaces the
original address in the \\MAIL\\ or \\RCPT\\ command.

.section Flags controlling the rewriting process
There are four flags which control the way the rewriting process works. These
take effect only when a rule is invoked, that is, when the address is of the
correct type (matches the flags) and matches the pattern:
.numberpars $.
If the `Q' flag is set on a rule, the rewritten address is permitted to be an
unqualified local part. It is qualified with \qualify@_recipient\. In the
absence of `Q' the rewritten address must always include a domain.
.nextp
If the `q' flag is set on a rule, no further rewriting rules are considered,
even if no rewriting actually takes place because of a `fail' in the expansion.
The `q' flag is not effective if the address is of the wrong type (does not
match the flags) or does not match the pattern.
.nextp
The `R' flag causes a successful rewriting rule to be re-applied to the new
address, up to ten times. It can be combined with the `q' flag, to stop
rewriting once it fails to match (after at least one successful rewrite).
.nextp
.index rewriting||whole addresses
When an address in a header is rewritten, the rewriting normally applies only
to the working part of the address, with any comments and RFC 2822 `phrase'
left unchanged. For example, rewriting might change
.display asis
From: Ford Prefect <fp42@restaurant.hitch.fict.example>
.endd
into
.display asis
From: Ford Prefect <prefectf@hitch.fict.example>
.endd
Sometimes there is a need to replace the whole address item, and this can be
done by adding the flag letter `w' to a rule. If this is set on a rule that
causes an address in a header line to be rewritten, the entire address is
replaced, not just the working part. The replacement must be a complete RFC
2822 address, including the angle brackets if necessary. If text outside angle
brackets contains a character whose value is greater than 126 or less than 32
(except for tab), the text is encoded according to RFC 2047.
The character set is taken from \headers@_charset\, which defaults to
ISO-8859-1.

When the `w' flag is set on a rule that causes an envelope address to be
rewritten, all but the working part of the replacement address is discarded.
.endp

.section Rewriting examples
Here is an example of the two common rewriting paradigms:
.display asis
*@*.hitch.fict.example  $1@hitch.fict.example
*@hitch.fict.example    ${lookup{$1}dbm{/etc/realnames}\
                     {$value}fail}@hitch.fict.example bctfrF
.endd
Note the use of `fail' in the lookup expansion in the second rule, forcing
the string expansion to fail if the lookup does not succeed. In this context it
has the effect of leaving the original address unchanged, but Exim goes on to
consider subsequent rewriting rules, if any, because the `q' flag is not
present in that rule. An alternative to `fail' would be to supply \$1$\
explicitly, which would cause the rewritten address to be the same as before,
at the cost of a small bit of processing. Not supplying either of these is an
error, since the rewritten address would then contain no local part.

The first example above replaces the domain with a superior, more general
domain. This may not be desirable for certain local parts. If the rule
.display asis
root@*.hitch.fict.example  *
.endd
were inserted before the first rule, rewriting would be suppressed for the
local part \*root*\ at any domain ending in \*hitch.fict.example*\.

Rewriting can be made conditional on a number of tests, by making use of
\${if$\ in the expansion item. For example, to apply a rewriting rule only to
messages that originate outside the local host:
.display asis
*@*.hitch.fict.example  "${if !eq {$sender_host_address}{}\
                         {$1@hitch.fict.example}fail}"
.endd
The replacement string is quoted in this example because it contains white
space.

.index rewriting||bang paths
.index bang paths||rewriting
Exim does not handle addresses in the form of `bang paths'. If it sees such an
address it treats it as an unqualified local part which it qualifies with the
local qualification domain (if the source of the message is local or if the
remote host is permitted to send unqualified addresses). Rewriting can
sometimes be used to handle simple bang paths with a fixed number of
components. For example, the rule
.display asis
\N^([^!]+)!(.*)@your.domain.example$\N   $2@$1
.endd
rewrites a two-component bang path \*host.name!user*\ as the domain address
\*user@@host.name*\. However, there is a security implication in using this as
a global rewriting rule for envelope addresses. It can provide a backdoor
method for using your system as a relay, because the incoming addresses appear
to be local. If the bang path addresses are received via SMTP, it is safer to
use the `S' flag to rewrite them as they are received, so that relay checking
can be done on the rewritten addresses.





.
.
.
.
. ============================================================================
.chapter Retry configuration
.set runningfoot "retry configuration"
.rset CHAPretry ~~chapter
.index retry||configuration, description of
.index configuration file||retry section
The `retry' section of the run time configuration file contains a list of retry
rules which control how often Exim tries to deliver messages that cannot be
delivered at the first attempt. If there are no retry rules, temporary errors
are treated as permanent. The \-brt-\ command line option can be used to test
which retry rule will be used for a given address or domain.

The most common cause of retries is temporary failure to deliver to a remote
host because the host is down, or inaccessible because of a network problem.
Exim's retry processing in this case is applied on a per-host (strictly, per IP
address) basis, not on a per-message basis. Thus, if one message has recently
been delayed, delivery of a new message to the same host is not immediately
tried, but waits for the host's retry time to arrive. If the \retry@_defer\ log
selector is set, the message
.index retry||time not reached
`retry time not reached' is written to the main log whenever a delivery is
skipped for this reason. Section ~~SECToutSMTPerr contains more details of the
handling of errors during remote deliveries.

Retry processing applies to routing as well as to delivering, except as covered
in the next paragraph. The retry rules do not distinguish between these
actions. It is not possible, for example, to specify different behaviour for
failures to route the domain \*snark.fict.example*\ and failures to deliver to
the host \*snark.fict.example*\. I didn't think anyone would ever need this
added complication, so did not implement it. However, although they share the
same retry rule, the actual retry times for routing and transporting a given
domain are maintained independently.

When a delivery is not part of a queue run (typically an immediate delivery on
receipt of a message), the routers are always run, and local deliveries are
always attempted, even if retry times are set for them. This makes for better
behaviour if one particular message is causing problems (for example, causing
quota overflow, or provoking an error in a filter file). If such a delivery
suffers a temporary failure, the retry data is updated as normal, and
subsequent delivery attempts from queue runs occur only when the retry time for
the local address is reached.


.section Retry rules
.index retry||rules
Each retry rule occupies one line and consists of three parts, separated by
white space: a pattern, an error name, and a list of retry parameters. The
pattern must be enclosed in double quotes if it contains white space. The rules
are searched in order until one is found whose pattern matches the failing host
or address.

The pattern is any single item that may appear in an address list (see section
~~SECTaddresslist). It is in fact processed as a one-item address list, which
means that it is expanded before being tested against the address that has
been delayed. Address list processing treats a plain domain name as if it were
preceded by `*@@', which makes it possible for many retry rules to start with
just a domain. For example,
.display asis
lookingglass.fict.example        *  F,24h,30m;
.endd
provides a rule for any address in the \*lookingglass.fict.example*\ domain,
whereas
.display asis
alice@lookingglass.fict.example  *  F,24h,30m;
.endd
applies only to temporary failures involving the local part \alice\.
In practice, almost all rules start with a domain name pattern without a local 
part.

.index regular expressions||in retry rules
\**Warning**\: If you use a regular expression in a routing rule, it must match 
a complete address, not just a domain, because that is how regular expressions 
work in address lists. 
.display
^@\Nxyz@\d+@\.abc@\.example@$@\N        *  G,1h,10m,2     \Wrong\
^@\N[^@@]+@@xyz@\d+@\.abc@\.example@$@\N  *  G,1h,10m,2     \Right\
.endd


.section Choosing which retry rule to use
When Exim is looking for a retry rule after a routing attempt has failed (for
example, after a DNS timeout), each line in the retry configuration is tested
against the complete address only if \retry__use@_local@_part\ is set for the
router. Otherwise, only the domain is used, except when matching against a
regular expression, when the local part of the address is replaced with `*'. A
domain on its own can match a domain pattern, or a pattern that starts with
`*@@'. By default, \retry@_use@_local@_part\ is true for routers where
\check@_local@_user\ is true, and false for other routers.

Similarly, when Exim is looking for a retry rule after a local delivery has
failed (for example, after a mailbox full error), each line in the retry
configuration is tested against the complete address only if
\retry@_use@_local@_part\ is set for the transport (it defaults true for all
local transports).

.em
When Exim is looking for a retry rule after a remote delivery attempt has
failed, what happens depends on the type of failure. After a 4\*xx*\ SMTP
response for a recipient address, the whole address is used when searching the
retry rules. The rule that is found is used to create a retry time for the 
failing address.

For a temporary error that is not related to an individual address,
.nem
(for example, a connection timeout), each line in the retry configuration is
checked twice. First, the name of the remote host is used as a domain name
(preceded by `*@@' when matching a regular expression). If this does not match
the line, the domain from the email address is tried in a similar fashion. For
example, suppose the MX records for \*a.b.c.example*\ are
.display asis
a.b.c.example  MX  5  x.y.z.example
               MX  6  p.q.r.example
               MX  7  m.n.o.example
.endd
and the retry rules are
.display asis
p.q.r.example    *      F,24h,30m;
a.b.c.example    *      F,4d,45m;
.endd
and a delivery to the host \*x.y.z.example*\ fails. The first rule matches
neither the host nor the domain, so Exim looks at the second rule. This does
not match the host, but it does match the domain, so it is used to calculate
the retry time for the host \*x.y.z.example*\. Meanwhile, Exim tries to deliver
to \*p.q.r.example*\. If this fails, the first retry rule is used, because it
matches the host.

In other words, failures to deliver to host \*p.q.r.example*\ use the first
rule to determine retry times, but for all the other hosts for the domain
\*a.b.c.example*\, the second rule is used. The second rule is also used if
routing to \*a.b.c.example*\ suffers a temporary failure.

.section Retry rules for specific errors
.index retry||specific errors, specifying
The second field in a retry rule is the name of a particular error, or an
asterisk, which matches any error. The errors that can be tested for are:
.numberpars " "
\*auth@_failed*\: authentication failed when trying to send to a host in the
\hosts@_require@_auth\ list in an \%smtp%\ transport
.nextp
\*refused@_MX*\: connection refused from a host obtained from an MX record
.nextp
\*refused@_A*\: connection refused from a host not obtained from an MX record
.nextp
\*refused*\: any connection refusal
.nextp
\*timeout@_connect@_MX*\: connection timeout from a host obtained from an MX
record
.nextp
\*timeout@_connect@_A*\: connection timeout from a host not obtained from an MX 
record
.nextp
\*timeout@_connect*\: any connection timeout
.nextp
\*timeout@_MX*\: any timeout from a host obtained from an MX
record
.nextp
\*timeout@_A*\: any timeout from a host not obtained from an MX 
record
.nextp
\*timeout*\: any timeout
.nextp
\*quota*\: quota exceeded in local delivery by \%appendfile%\
.nextp
.index quota||error testing in retry rule
.index retry||quota error testing
\*quota@_*\<<time>>: quota exceeded in local delivery, and the mailbox has not
been read for <<time>>. For example, \*quota@_4d*\ applies to a quota error
when the mailbox has not been read for four days.

.em
.index mailbox||time of last read
\**Warning**\: It is not always possible to determine a `time of last read' for
a mailbox:
.numberpars $.
If the mailbox is a single file, the time of last access is used.
.nextp
.index maildir format||time of last read
For a maildir delivery, the time of last modification of the \(new)\ 
subdirectory is used. As the mailbox is over quota, no new files will be 
created in the \(new)\ subdirectory, so any change is assumed to be the result 
of an MUA moving a new message to the \(cur)\ directory when it is first read.
.nextp
For other kinds of multi-file delivery, the time of last read cannot be
obtained, and so a retry rule that uses this type of error field is never
matched.
.endp
.nem
.endp
The quota errors apply both to system-enforced quotas and to Exim's own quota
mechanism in the \%appendfile%\ transport. The \*quota*\ error also applies
when a local delivery is deferred because a partition is full (the \\ENOSPC\\
error).


.section Retry rule parameters
.index retry||parameters in rules
The third field in a retry rule is a sequence of retry parameter sets,
separated by semicolons. Each set consists of
.display
<<letter>>,<<cutoff time>>,<<arguments>>
.endd
The letter identifies the algorithm for computing a new retry time; the cutoff
time is the time beyond which this algorithm no longer applies, and the
arguments vary the algorithm's action. The cutoff time is measured from the
time that the first failure for the domain (combined with the local part if
relevant) was detected, not from the time the message was received.
.index retry||algorithms
The available algorithms are:
.numberpars $.
\*F*\: retry at fixed intervals. There is a single time parameter specifying the
interval.
.nextp
\*G*\: retry at geometrically increasing intervals. The first argument specifies
a starting value for the interval, and the second a multiplier, which is used
to increase the size of the interval at each retry.
.endp
When computing the next retry time, the algorithm definitions are scanned in
order until one whose cutoff time has not yet passed is reached. This is then
used to compute a new retry time that is later than the current time. In the
case of fixed interval retries, this simply means adding the interval to the
current time. For geometrically increasing intervals, retry intervals are
computed from the rule's parameters until one that is greater than the previous
interval is found. The main configuration variable
.index limit||retry interval
.index retry||interval, maximum
.index \retry@_interval@_max\
\retry@_interval@_max\ limits the maximum interval between retries.

A single remote domain may have a number of hosts associated with it, and each
host may have more than one IP address. Retry algorithms are selected on the
basis of the domain name, but are applied to each IP address independently. If,
for example, a host has two IP addresses and one is unusable, Exim will
generate retry times for it and will not try to use it until its next retry
time comes. Thus the good IP address is likely to be tried first most of the
time.

.index hints database||use for retrying
Retry times are hints rather than promises. Exim does not make any attempt to
run deliveries exactly at the computed times. Instead, a queue runner process
starts delivery processes for delayed messages periodically, and these attempt
new deliveries only for those addresses that have passed their next retry time.
If a new message arrives for a deferred address, an immediate delivery attempt
occurs only if the address has passed its retry time. In the absence of new
messages, the minimum time between retries is the interval between queue runner
processes. There is not much point in setting retry times of five minutes if
your queue runners happen only once an hour, unless there are a significant
number of incoming messages (which might be the case on a system that is
sending everything to a smart host, for example).

The data in the retry hints database can be inspected by using the
\*exim@_dumpdb*\ or \*exim@_fixdb*\ utility programs (see chapter ~~CHAPutils). The
latter utility can also be used to change the data. The \*exinext*\ utility
script can be used to find out what the next retry times are for the hosts
associated with a particular mail domain, and also for local deliveries that
have been deferred.

.section Retry rule examples
Here are some example retry rules:
.display asis
alice@wonderland.fict.example quota_5d  F,7d,3h
wonderland.fict.example       quota_5d
wonderland.fict.example       *         F,1h,15m; G,2d,1h,2;
lookingglass.fict.example     *         F,24h,30m;
*                          refused_A F,2h,20m;
*                          *         F,2h,15m; G,16h,1h,1.5; F,5d,8h
.endd
The first rule sets up special handling for mail to
\*alice@@wonderland.fict.example*\ when there is an over-quota error and the
mailbox has not been read for at least 5 days. Retries continue every three
hours for 7 days. The second rule handles over-quota errors for all other local
parts at \*wonderland.fict.example*\; the absence of a local part has the same
effect as supplying `$*$@@'. As no retry algorithms are supplied, messages that
fail are bounced immediately if the mailbox has not been read for at least 5
days.

The third rule handles all other errors at \*wonderland.fict.example*\; retries
happen every 15 minutes for an hour, then with geometrically increasing
intervals until two days have passed since a delivery first failed. After the
first hour there is a delay of one hour, then two hours, then four hours, and
so on (this is a rather extreme example).

The fourth rule controls retries for the domain \*lookingglass.fict.example*\.
They happen every 30 minutes for 24 hours only. The remaining two rules handle
all other domains, with special action for connection refusal from hosts that
were not obtained from an MX record.

The final rule in a retry configuration should always have asterisks in the
first two fields so as to provide a general catch-all for any addresses that do
not have their own special handling. This example tries every 15 minutes for 2
hours, then with intervals starting at one hour and increasing by a factor of
1.5 up to 16 hours, then every 8 hours up to 5 days.


.section Timeout of retry data
.index timeout||of retry data
.index \retry@_data@_expire\
.index hints database||data expiry
.index retry||timeout of data
Exim timestamps the data that it writes to its retry hints database. When it
consults the data during a delivery it ignores any that is older than the value
set in \retry@_data@_expire\ (default 7 days). If, for example, a host hasn't
been tried for 7 days, Exim will try to deliver to it immediately a message
arrives, and if that fails, it will calculate a retry time as if it were
failing for the first time.

This improves the behaviour for messages routed to rarely-used hosts such as MX
backups. If such a host was down at one time, and happens to be down again when
Exim tries a month later, using the old retry data would imply that it had been
down all the time, which is not a justified assumption.

If a host really is permanently dead, this behaviour causes a burst of retries
every now and again, but only if messages routed to it are rare. It there is a
message at least once every 7 days the retry data never expires.



.section Long-term failures
.index delivery||failure, long-term
.index retry||after long-term failure
Special processing happens when an email address has been failing for so long
that the cutoff time for the last algorithm is reached. For example, using the
default retry rule:
.display asis
* * F,2h,15m; G,16h,1h,1.5; F,4d,6h
.endd
the cutoff time is four days. Reaching the retry cutoff is independent of how
long any specific message has been failing; it is the length of continuous
failure for the recipient address that counts. 

When the cutoff time is reached for a local delivery, or for all the IP
addresses associated with a remote delivery, a subsequent delivery failure
causes Exim to give up on the address, and a bounce message is generated.
In order to cater for new messages that use the failing address, a next retry
time is still computed from the final algorithm, and is used as follows:

For local deliveries, one delivery attempt is always made for any subsequent
messages. If this delivery fails, the address fails immediately. The
post-cutoff retry time is not used.

If the delivery is remote, there are two possibilities, controlled by the
.index \delay@_after@_cutoff\
\delay@_after@_cutoff\ option of the \%smtp%\ transport. The option is true by
default and in that case:
.numberpars " "
Until the post-cutoff retry time for one of the IP addresses is reached,
the failing email address is bounced immediately, without a delivery attempt
taking place. After that time, one new delivery attempt is made to those IP
addresses that are past their retry times, and if that still fails, the address
is bounced and new retry times are computed.
.endp

In other words, when all the hosts for a given email address have been failing
for a long time, Exim bounces rather then defers until one of the hosts' retry
times is reached. Then it tries once, and bounces if that attempt fails. This
behaviour ensures that few resources are wasted in repeatedly trying to deliver
to a broken destination, but if the host does recover, Exim will eventually
notice.

If \delay@_after@_cutoff\ is set false, Exim behaves differently. If all IP
addresses are past their final cutoff time, Exim tries to deliver to those IP
addresses that have not been tried since the message arrived. If there are
no suitable IP addresses, or if they all fail, the address is bounced. In other
words, it does not delay when a new message arrives, but tries the expired
addresses immediately, unless they have been tried since the message arrived.
If there is a continuous stream of messages for the failing domains, setting
\delay@_after@_cutoff\ false means that there will be many more attempts to
deliver to permanently failing IP addresses than when \delay@_after@_cutoff\ is
true.

.section Ultimate address timeout
.index retry||ultimate address timeout
An additional rule is needed to cope with cases where a host is intermittently
available, or when a message has some attribute that prevents its delivery when
others to the same address get through. In this situation, because some
messages are successfully delivered, the `retry clock' for the address keeps
getting restarted, and so a message could remain on the queue for ever. To
prevent this, if a message has been on the queue for longer than the cutoff
time of any applicable retry rule for a given address, a delivery is attempted
for that address, even if it is not yet time, and if this delivery fails, the
address is timed out. A new retry time is not computed in this case, so that
other messages for the same address are considered immediately.





.
.
.
.
. ============================================================================
.chapter SMTP authentication
.set runningfoot "SMTP authentication"
.rset CHAPSMTPAUTH "~~chapter"
.index SMTP||authentication configuration
.index authentication
The `authenticators' section of Exim's run time configuration is concerned with
SMTP authentication. This facility is an extension to the SMTP protocol,
described in RFC 2554, which allows a client SMTP host to authenticate itself
to a server. This is a common way for a server to recognize clients that
are permitted to use it as a relay. SMTP authentication is not of relevance to
the transfer of mail between servers that have no managerial connection with
each other.

.index \\AUTH\\||description of
Very briefly, the way SMTP authentication works is as follows:
.numberpars $.
The server advertises a number of authentication \*mechanisms*\ in response to 
the client's \\EHLO\\ command.
.nextp
The client issues an \\AUTH\\ command, naming a specific mechanism. The command
may, optionally, contain some authentication data.
.nextp
The server may issue one or more \*challenges*\, to which the client must send
appropriate responses. In simple authentication mechanisms, the challenges are
just prompts for user names and passwords. The server does not have to issue
any challenges -- in some mechanisms the relevant data may all be transmitted
with the \\AUTH\\ command.
.nextp
The server either accepts or denies authentication.
.nextp
If authentication succeeds, the client may optionally make use of the \\AUTH\\
option on the \\MAIL\\ command to pass an authenticated sender in subsequent
mail transactions. Authentication lasts for the remainder of the SMTP
connection.
.nextp
If authentication fails, the client may give up, or it may try a different
authentication mechanism, or it may try transferring mail over the
unauthenticated connection.
.endp
If you are setting up a client, and want to know which authentication
mechanisms the server supports, you can use Telnet to connect to port 25 (the
SMTP port) on the server, and issue an \\EHLO\\ command. The response to this
includes the list of supported mechanisms. For example:
.display
@$ $cb{telnet server.example 25}
Trying 192.168.34.25...
Connected to server.example.
Escape character is '@^]'.
220 server.example ESMTP Exim 4.20 ...
$cb{ehlo client.example}
250-server.example Hello client.example [10.8.4.5]
250-SIZE 52428800
250-PIPELINING
250-AUTH PLAIN
250 HELP
.endd
The second-last line of this example output shows that the server supports
authentication using the PLAIN mechanism. In Exim, the different authentication
mechanisms are configured by specifying \*authenticator*\ drivers. Like the
routers and transports, which authenticators are included in the binary is
controlled by build-time definitions. The following are currently available,
included by setting
.display asis
AUTH_CRAM_MD5=yes
AUTH_PLAINTEXT=yes
AUTH_SPA=yes
.endd
in \(Local/Makefile)\, respectively. The first of these supports the CRAM-MD5
authentication mechanism (RFC 2195), and the second can be configured to
support the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism,
which is not formally documented, but used by several MUAs. The third
authenticator supports Microsoft's \*Secure Password Authentication*\
mechanism.

The authenticators are configured using the same syntax as other drivers (see
section ~~SECTfordricon). If no authenticators are required, no authentication
section need be present in the configuration file. Each authenticator can in
principle have both server and client functions. When Exim is receiving SMTP
mail, it is acting as a server; when it is sending out messages over SMTP, it
is acting as a client. Authenticator configuration options are provided for use
in both these circumstances.

To make it clear which options apply to which situation, the prefixes
\server@_\ and \client@_\ are used on option names that are specific to either
the server or the client function, respectively. Server and client functions
are disabled if none of their options are set. If an authenticator is to be
used for both server and client functions, a single definition, using both sets
of options, is required. For example:
.display asis
cram:
  driver = cram_md5
  public_name = CRAM-MD5
  server_secret = ${if eq{$1}{ph10}{secret1}fail}
  client_name = ph10
  client_secret = secret2
.endd
The \server@_\ option is used when Exim is acting as a server, and the
\client@_\ options when it is acting as a client.

Descriptions of the individual authenticators are given in subsequent chapters.
The remainder of this chapter covers the generic options for the
authenticators, followed by general discussion of the way authentication works
in Exim.


.section Generic options for authenticators
.index authentication||generic options

.startconf
.index options||generic, for authenticators

.conf driver string unset
This option must always be set. It specifies which of the available
authenticators is to be used.

.conf public@_name string unset
This option specifies the name of the authentication mechanism that the driver
implements, and by which it is known to the outside world. These names should
contain only upper case letters, digits, underscores, and hyphens (RFC 2222),
but Exim in fact matches them caselessly. If \public@_name\ is not set, it
defaults to the driver's instance name.

.conf server@_advertise@_condition string$**$ unset
When a server is about to advertise an authentication mechanism, the condition
is expanded. If it yields the empty string, `0', `no', or `false', the
mechanism is not advertised. 
If the expansion fails, the mechanism is not advertised. If the failure was not 
forced, and was not caused by a lookup defer, the incident is logged.
See section ~~SECTauthexiser below for further discussion.

.conf server@_debug@_print string$**$ unset
If this option is set and authentication debugging is enabled (see the \-d-\
command line option), the string is expanded and included in the debugging
output when the authenticator is run as a server. This can help with checking
out the values of variables.
If expansion of the string fails, the error message is written to the debugging 
output, and Exim carries on processing.

.conf server@_set@_id string$**$ unset
When an Exim server successfully authenticates a client, this string is
expanded using data from the authentication, and preserved for any incoming
messages in the variable \$authenticated@_id$\. It is also included in the log
lines for incoming messages. For example, a user/password authenticator
configuration might preserve the user name that was used to authenticate, and
refer to it subsequently during delivery of the message.
If expansion fails, the option is ignored.

.conf server@_mail@_auth@_condition string$**$ unset
This option allows a server to discard authenticated sender addresses supplied
as part of \\MAIL\\ commands in SMTP connections that are authenticated by the 
driver on which \server__mail__auth@_condition\ is set. The option is not used
as part of the authentication process; instead its (unexpanded) value is
remembered for later use.
How it is used is described in the following section.
.endconf



.section The AUTH parameter on MAIL commands
.rset SECTauthparamail "~~chapter.~~section"
.index authentication||sender, authenticated
.index \\AUTH\\||on \\MAIL\\ command
When a client supplied an \\AUTH=\\ item on a \\MAIL\\ command, Exim applies 
the following checks before accepting it as the authenticated sender of the
message:
.numberpars $.
If the connection is not using extended SMTP (that is, \\HELO\\ was used rather 
than \\EHLO\\), the use of \\AUTH=\\ is a syntax error.
.nextp
If the value of the \\AUTH=\\ parameter is `@<@>', it is ignored.
.nextp
If \acl@_smtp@_mailauth\ is defined, the ACL it specifies is run. While it is
running, the value of \$authenticated@_sender$\ is set to the value obtained
from the \\AUTH=\\ parameter. If the ACL does not yield `accept', the value of
\$authenticated@_sender$\ is deleted. The \acl@_smtp@_mailauth\ ACL may not
return `drop' or `discard'. If it defers, a temporary error code (451) is given
for the \\MAIL\\ command.
.nextp
If \acl@_smtp@_mailauth\ is not defined, the value of the \\AUTH=\\ parameter
is accepted and placed in \$authenticated@_sender$\ only if the client has
authenticated.
.nextp
If the \\AUTH=\\ value was accepted by either of the two previous rules, and
the client has authenticated, and the authenticator has a setting for the
\server@_mail@_auth@_condition\, the condition is checked at this point. The
valued that was saved from the authenticator is expanded. If the expansion
fails, or yields an empty string, `0', `no', or `false', the value of
\$authenticated__sender$\ is deleted. If the expansion yields any other value,
the value of \$authenticated@_sender$\ is retained and passed on with the
message.
.endp

When \$authenticated@_sender$\ is set for a message, it is passed on to other
hosts to which Exim authenticates as a client. Do not confuse this value with
\$authenticated@_id$\, which is a string obtained from the authentication
process, and which is not usually a complete email address.

Whenever an \\AUTH=\\ value is ignored, the incident is logged. The ACL for
\\MAIL\\, if defined, is run after \\AUTH=\\ is accepted or ignored. It can
therefore make use of \$authenticated@_sender$\. The converse is not true: the
value of \$sender@_address$\ is not yet set up when the \acl@_smtp@_mailauth\
ACL is run.


.section Authentication on an Exim server
.rset SECTauthexiser "~~chapter.~~section"
.index authentication||on an Exim server
When Exim receives an \\EHLO\\ command, it advertises the public names of those 
authenticators that are configured as servers, subject to the following 
conditions:
.numberpars $.
The client host must match \auth@_advertise@_hosts\ (default $*$).
.nextp
It the \server@_advertise@_condition\ option is set, its expansion must not 
yield the empty string, `0', `no', or `false'.
.endp
The order in which the authenticators are defined controls the order in which 
the mechanisms are advertised.

Some mail clients (for example, some versions of Netscape) require the user to
provide a name and password for authentication whenever \\AUTH\\ is advertised,
even though authentication may not in fact be needed (for example, Exim may be
set up to allow unconditional relaying from the client by an IP address check).
You can make such clients more friendly by not advertising \\AUTH\\ to them.
For example, if clients on the 10.9.8.0/24 network are permitted (by the ACL
that runs for \\RCPT\\) to relay without authentication, you should set
.display asis
auth_advertise_hosts = ! 10.9.8.0/24
.endd
so that no authentication mechanisms are advertised to them.

The \server@_advertise@_condition\ controls the advertisement of individual
authentication mechanisms. For example, it can be used to restrict the
advertisement of a patricular mechanism to encrypted connections, by a setting
such as:
.display asis
server_advertise_condition = ${if eq{$tls_cipher}{}{no}{yes}}
.endd
If the session is encrypted, \$tls@_cipher$\ is not empty, and so the expansion 
yields `yes', which allows the advertisement to happen.

When an Exim server receives an \\AUTH\\ command from a client, it rejects it
immediately if \\AUTH\\ was not advertised in response to an earlier \\EHLO\\
command. This is the case if
.numberpars $.
The client host does not match \auth@_advertise@_hosts\; or
.nextp
No authenticators are configured with server options; or
.nextp
Expansion of \server@_advertise@_condition\ blocked the advertising of all the 
server authenticators.
.endp

Otherwise, Exim runs the ACL specified by \acl@_smtp@_auth\ in order
to decide whether to accept the command. If \acl@_smtp@_auth\ is not set,
\\AUTH\\ is accepted from any client host. 

If \\AUTH\\ is not rejected by the ACL, Exim searches its configuration for a
server authentication mechanism that was advertised in response to \\EHLO\\ and 
that matches the one named in the \\AUTH\\ command. If it finds one, it runs
the appropriate authentication protocol, and authentication either succeeds or
fails. If there is no matching advertised mechanism, the \\AUTH\\ command is
rejected with a 504 error.

When a message is received from an authenticated host, the value of
\$received@_protocol$\ is set to `asmtp' instead of `esmtp', and
\$sender@_host@_authenticated$\ contains the name (not the public name) of the
authenticator driver that successfully authenticated the client from which the
message was received. This variable is empty if there was no successful
authentication.



.section Testing server authentication
.index authentication||testing a server
.index \\AUTH\\||testing a server
.index base64 encoding||creating authentication test data
Exim's \-bh-\ option can be useful for testing server authentication
configurations. The data for the \\AUTH\\ command has to be sent using base64
encoding. A quick way to produce such data for testing is the following Perl
script:
.display asis
use MIME::Base64;
printf ("%s", encode_base64(eval "\"$ARGV[0]\""));
.endd
.index binary zero||in authentication data
This interprets its argument as a Perl string, and then encodes it. The
interpretation as a Perl string allows binary zeros, which are required for
some kinds of authentication, to be included in the data. For example, a
command line to run this script on such data might be
.display asis
encode '\0user\0password'
.endd
Note the use of single quotes to prevent the shell interpreting the
backslashes, so that they can be interpreted by Perl to specify characters
whose code value is zero. 

\**Warning 1**\: If either of the user or password strings starts with an octal
digit, you must use three zeros instead of one after the leading backslash. If
you do not, the octal digit that starts your string will be incorrectly
interpreted as part of the code for the first character.

\**Warning 2**\: If there are characters in the strings that Perl interprets 
specially, you must use a Perl escape to prevent them being misinterpreted. For 
example, a command such as
.display asis
encode '\0user@domain.com\0pas$$word'
.endd
gives an incorrect answer because of the unescaped `@@' and `@$' characters.

If you have the \mimencode\ command installed, another way to do produce
base64-encoded strings is to run the command
.display asis
echo -e -n `\0user\0password' | mimencode
.endd
The \-e-\ option of \echo\ enables the interpretation of backslash escapes in
the argument, and the \-n-\ option specifies no newline at the end of its
output. However, not all versions of \echo\ recognize these options, so you
should check your version before relying on this suggestion.


.section Authentication by an Exim client
.index authentication||on an Exim client
The \%smtp%\ transport has two options called \hosts@_require@_auth\ and
\hosts@_try@_auth\. When the \%smtp%\ transport connects to a server that
announces support for authentication, and the host matches an entry in either
of these options, Exim (as a client) tries to authenticate as follows:
.numberpars $.
For each authenticator that is configured as a client, it searches the
authentication mechanisms announced by the server for one whose name
matches the public name of the authenticator.
.nextp
When it finds one that matches, it runs the authenticator's client code.
The variables \$host$\ and \$host@_address$\ are available for any string
expansions that the client might do. They are set to the server's name and
IP address. If any expansion is forced to fail, the authentication attempt
is abandoned,
and Exim moves on to the next authenticator.
Otherwise an expansion failure causes delivery to be
deferred.
.nextp
If the result of the authentication attempt is a temporary error or a timeout,
Exim abandons trying to send the message to the host for the moment. It will
try again later. If there are any backup hosts available, they are tried in the
usual way.
.nextp
If the response to authentication is a permanent error (5xx code), Exim carries
on searching the list of authenticators and tries another one if possible. If
all authentication attempts give permanent errors, or if there are no attempts
because no mechanisms match
(or option expansions force failure),
what happens depends on whether the host matches \hosts@_require@_auth\ or
\hosts@_try@_auth\. In the first case, a temporary error is generated, and
delivery is deferred. The error can be detected in the retry rules, and thereby
turned into a permanent error if you wish. In the second case, Exim tries to
deliver the message unauthenticated.
.endp
.index \\AUTH\\||on \\MAIL\\ command
When Exim has authenticated itself to a remote server, it adds the \\AUTH\\
parameter to the \\MAIL\\ commands it sends, if it has an authenticated sender
for the message. 
If the message came from a remote host, the authenticated sender is the one 
that was receiving on an incoming \\MAIL\\ command, provided that the incoming 
connection was authenticated and the \server@_mail@_auth\ condition allowed the
authenticated sender to be retained. If a local process calls Exim to send a
message, the sender address that is built from the login name and
\qualify@_domain\ is treated as authenticated. However, if the
\authenticated@_sender\ option is set on the \%smtp%\ transport, it overrides
the authenticated sender that was received with the message.






.
.
.
.
. ============================================================================
.chapter The plaintext authenticator
.rset CHAPplaintext "~~chapter"
.set runningfoot "plaintext authenticator"
.index \%plaintext%\ authenticator
.index authenticators||\%plaintext%\
The \%plaintext%\ authenticator can be configured to support the PLAIN and
LOGIN authentication mechanisms, both of which transfer authentication data as
plain (unencrypted) text (though base64 encoded). The use of plain text is a
security risk. If you use one of these mechanisms without also making use of
SMTP encryption (see chapter ~~CHAPTLS) you should not use the same passwords
for SMTP connections as you do for login accounts.

.section Using plaintext in a server
When running as a server, \%plaintext%\ performs the authentication test by
expanding a string. It has the following options:

.startconf
.index options||\%plaintext%\ authenticator (server)

.conf server@_prompts string$**$ unset
The contents of this option, after expansion, must be a colon-separated list of
prompt strings. If expansion fails, a temporary authentication rejection is
given.

.conf server@_condition string$**$ unset
This option must be set in order to configure the driver as a server. Its use
is described below.

.endconf

.index \\AUTH\\||in \%plaintext%\ authenticator
.index binary zero||in \%plaintext%\ authenticator
.index numerical variables (\$1$\, \$2$\, etc)||in \%plaintext%\ authenticator
.index base64 encoding||in \%plaintext%\ authenticator
The data sent by the client with the \\AUTH\\ command, or in response to
subsequent prompts, is base64 encoded, and so may contain any byte values
when decoded. If any data is supplied with the command, it is treated as a
list of strings, separated by NULs (binary zeros), which are placed in the
expansion variables \$1$\, \$2$\, etc. If there are more strings in
\server@_prompts\ than the number of strings supplied with the \\AUTH\\
command, the remaining prompts are used to obtain more data. Each response from
the client may be a list of NUL-separated strings.

Once a sufficient number of data strings have been received,
\server@_condition\ is expanded.
If the expansion is forced to fail, authentication fails. Any other expansion
failure causes a temporary error code to be returned.
If the result of a successful expansion is an empty string, `0', `no', or
`false', authentication fails. If the result of the expansion is `1', `yes', or
`true', authentication succeeds and the generic \server@_set@_id\ option is
expanded and saved in \$authenticated@_id$\. For any other result, a temporary
error code is returned, with the expanded string as the error text.

\**Warning**\: If you use a lookup in the expansion to find the user's 
password, be sure to make the authentication fail if the user is unknown. 
There are good and bad examples at the end of the next section.


.section The PLAIN authentication mechanism
.index PLAIN authentication mechanism
.index authentication||PLAIN mechanism
.index binary zero||in \%plaintext%\ authenticator
The PLAIN authentication mechanism (RFC 2595) specifies that three strings be
sent as one item of data (that is, one combined string containing two NUL 
separators). The data is sent either as part of the \\AUTH\\ command, or
subsequently in response to an empty prompt from the server.

The second and third strings are a user name and a corresponding password.
Using a single fixed user name and password as an example, this could be
configured as follows:
.display asis
fixed_plain:
  driver = plaintext
  public_name = PLAIN
  server_prompts = : 
  server_condition = \
    ${if and {{eq{$2}{username}}{eq{$3}{mysecret}}}{yes}{no}}
  server_set_id = $2
.endd
The \server@_prompts\ setting specifies a single, empty prompt (empty items at
the end of a string list are ignored). If all the data comes as part of the
\\AUTH\\ command, as is commonly the case, the prompt is not used. This
authenticator is advertised in the response to \\EHLO\\ as
.display asis
250-AUTH PLAIN
.endd
and a client host can authenticate itself by sending the command
.display asis
AUTH PLAIN AHVzZXJuYW1lAG15c2VjcmV0
.endd
As this contains three strings (more than the number of prompts), no further
data is required from the client. Alternatively, the client may just send
.display asis
AUTH PLAIN
.endd
to initiate authentication, in which case the server replies with an empty 
prompt. The client must respond with the combined data string.

.em
The data string is base64 encoded, as required by the RFC. This example,
when decoded, is \"<<NUL>>username<<NUL>>mysecret"\, where <<NUL>> represents a
zero byte. This is split up into three strings, the first of which is empty.
The \server@_condition\ option in the authenticator checks that the second two
are \"username"\ and \"mysecret"\ respectively.

Having just one fixed user name and password, as in this example, is not very 
realistic, though for a small organization with only a handful of 
authenticating clients it could make sense.
.nem

A more sophisticated instance of this authenticator could use the user name in
\$2$\ to look up a password in a file or database, and maybe do an encrypted
comparison (see \crypteq\ in chapter ~~CHAPexpand). Here is a example of this
approach, where the passwords are looked up in a DBM file. \**Warning**\: This
is an incorrect example:
.display asis
server_condition = \
  ${if eq{$3}{${lookup{$2}dbm{/etc/authpwd}}}{yes}{no}}
.endd
The expansion uses the user name (\$2$\) as the key to look up a password,
which it then compares to the supplied password (\$3$\). Why is this example
incorrect? It works fine for existing users, but consider what happens if a
non-existent user name is given. The lookup fails, but as no success/failure
strings are given for the lookup, it yields an empty string. Thus, to defeat 
the authentication, all a client has to do is to supply a non-existent user 
name and an empty password. The correct way of writing this test is:
.display asis
server_condition = ${lookup{$2}dbm{/etc/authpwd}\
  {${if eq{$value}{$3}{yes}{no}}}{no}}    
.endd
In this case, if the lookup succeeds, the result is checked; if the lookup
fails, authentication fails. If \crypteq\ is being used instead of \eq\, the
first example is in fact safe, because \crypteq\ always fails if its second
argument is empty. However, the second way of writing the test makes the logic
clearer.


.section The LOGIN authentication mechanism
.index LOGIN authentication mechanism
.index authentication||LOGIN mechanism
The LOGIN authentication mechanism is not documented in any RFC, but is in use
in a number of programs. No data is sent with the \\AUTH\\ command. Instead, a
user name and password are supplied separately, in response to prompts. The
plaintext authenticator can be configured to support this as in this example:
.display asis
fixed_login:
  driver = plaintext
  public_name = LOGIN
  server_prompts = User Name : Password
  server_condition = \
    ${if and {{eq{$1}{username}}{eq{$2}{mysecret}}}{yes}{no}}
  server_set_id = $1
.endd
Because of the way plaintext operates, this authenticator accepts data supplied
with the \\AUTH\\ command (in contravention of the specification of LOGIN), but
if the client does not supply it (as is the case for LOGIN clients), the prompt
strings are used to obtain two data items.

Some clients are very particular about the precise text of the prompts. For
example, Outlook Express is reported to recognize only `Username:' and
`Password:'. Here is an example of a LOGIN authenticator which uses those
strings, and which uses the \ldapauth\ expansion condition to check the user
name and password by binding to an LDAP server:
.display asis
login:
  driver = plaintext
  public_name = LOGIN
  server_prompts = Username:: : Password::
  server_condition = ${if ldapauth \
.newline     
    {user="cn=${quote_ldap_dn:$1},ou=people,o=example.org" \
    pass=${quote:$2} \
.newline     
    ldap://ldap.example.org/}{yes}{no}}
  server_set_id = uid=$1,ou=people,o=example.org
.endd
Note the use of the \quote@_ldap@_dn\ operator to correctly quote the DN for
authentication. However, the basic \quote\ operator, rather than any of the
LDAP quoting operators, is the correct one to use for the password, because 
quoting is needed only to make the password conform to the Exim syntax. At the 
LDAP level, the password is an uninterpreted string.


.section Support for different kinds of authentication 
A number of string expansion features are provided for the purpose of
interfacing to different ways of user authentication. These include checking
traditionally encrypted passwords from \(/etc/passwd)\ (or equivalent), PAM,
Radius, \ldapauth\, and \*pwcheck*\. For details see section ~~SECTexpcond.



.section Using plaintext in a client
The \%plaintext%\ authenticator has just one client option:

.startconf
.index options||\%plaintext%\ authenticator (client)

.conf client@_send string$**$ unset
The string is a colon-separated list of authentication data strings. Each
string is independently expanded before being sent to the server. The first
string is sent with the \\AUTH\\ command; any more strings are sent in response
to prompts from the server.

\**Note**\: you cannot use expansion to create multiple strings, because
splitting takes priority and happens first.

Because the PLAIN authentication mechanism requires NUL (binary zero) bytes in
the data, further processing is applied to each string before it is sent. If
there are any single circumflex characters in the string, they are converted to
NULs. Should an actual circumflex be required as data, it must be doubled in
the string.

.endconf

This is an example of a client configuration that implements the PLAIN
authentication mechanism with a fixed user name and password:
.display asis
fixed_plain:
  driver = plaintext
  public_name = PLAIN
  client_send = ^username^mysecret
.endd
The lack of colons means that the entire text is sent with the \\AUTH\\
command, with the circumflex characters converted to NULs. A similar example
that uses the LOGIN mechanism is:
.display asis
fixed_login:
  driver = plaintext
  public_name = LOGIN
  client_send = : username : mysecret
.endd
The initial colon means that the first string is empty, so no data is sent with
the \\AUTH\\ command itself. The remaining strings are sent in response to
prompts.




.
.
.
.
. ============================================================================
.chapter The cram@_md5 authenticator
.set runningfoot "cram@_md5 authenticator"
.index \%cram@_md5%\ authenticator
.index authenticators||\%cram@_md5%\
.index CRAM-MD5 authentication mechanism
.index authentication||CRAM-MD5 mechanism
The CRAM-MD5 authentication mechanism is described in RFC 2195. The server
sends a challenge string to the client, and the response consists of a user
name and the CRAM-MD5 digest of the challenge string combined with a secret
string (password) which is known to both server and client. Thus, the secret
is not sent over the network as plain text, which makes this authenticator more
secure than \%plaintext%\. However, the downside is that the secret has to be
available in plain text at either end.

.section Using cram@_md5 as a server
This authenticator has one server option, which must be set to configure the
authenticator as a server:

.startconf
.index options||\%cram@_md5%\ authenticator (server)

.conf server@_secret string$**$ unset
.index numerical variables (\$1$\, \$2$\, etc)||in \%cram@_md5%\ authenticator
When the server receives the client's response, the user name is placed in
the expansion variable \$1$\, and \server@_secret\ is expanded to obtain the
password for that user. The server then computes the CRAM-MD5 digest that the
client should have sent, and checks that it received the correct string. If the
expansion of \server@_secret\ is forced to fail, authentication fails. If the
expansion fails for some other reason, a temporary error code is returned to
the client.

.endconf

For example, the following authenticator checks that the user name given by the
client is `ph10', and if so, uses `secret' as the password. For any other user
name, authentication fails.  
.display asis
fixed_cram:
  driver = cram_md5
  public_name = CRAM-MD5
  server_secret = ${if eq{$1}{ph10}{secret}fail}
  server_set_id = $1
.endd
If authentication succeeds, the setting of \server@_set@_id\ preserves the user
name in \$authenticated@_id$\.
A more tyical configuration might look up the secret string in a file, using
the user name as the key. For example:
.display asis
lookup_cram:
  driver = cram_md5
  public_name = CRAM-MD5
  server_secret = ${lookup{$1}lsearch{/etc/authpwd}{$value}fail}
  server_set_id = $1
.endd
Note that this expansion explicitly forces failure if the lookup fails
because \$1$\ contains an unknown user name.

.section Using cram@_md5 as a client
When used as a client, the \%cram@_md5%\ authenticator has two options:

.startconf
.index options||\%cram@_md5%\ authenticator (client)

.conf client@_name string$**$ "the primary host name"
This string is expanded, and the result used as the user name data when
computing the response to the server's challenge.

.conf client@_secret string$**$ unset
This option must be set for the authenticator to work as a client. Its value is
expanded and the result used as the secret string when computing the response.

.endconf

Different user names and secrets can be used for different servers by referring
to \$host$\ or \$host@_address$\ in the options.

Forced failure of either expansion string is treated as an indication that this
authenticator is not prepared to handle this case. Exim moves on to the next
configured client authenticator. Any other expansion failure causes Exim to
give up trying to send the message to the current server.

A simple example configuration of a \%cram@_md5%\ authenticator, using fixed
strings, is:
.display asis
fixed_cram:
  driver = cram_md5
  public_name = CRAM-MD5
  client_name = ph10
  client_secret = secret
.endd





.
.
.
.
. ============================================================================
.chapter The spa authenticator
.set runningfoot "spa authenticator"
.index \%spa%\ authenticator
.index authenticators||\%spa%\
.index authentication||Microsoft Secure Password
.index authentication||NTLM
.index Microsoft Secure Password Authentication
.index NTLM authentication
The \%spa%\ authenticator provides client support for Microsoft's \*Secure
Password Authentication*\ mechanism,
which is also sometimes known as NTLM (NT LanMan). The code for client side of
this authenticator was contributed by Marc Prud'hommeaux, and much of it is
taken from the Samba project (\?http://www.samba.org?\). The code for the
server side was subsequently contributed by Tom Kistner.

The mechanism works as follows:
.numberpars $.
After the \\AUTH\\ command has been accepted, the client sends an SPA
authentication request based on the user name and optional domain.
.nextp
The server sends back a challenge.
.nextp
The client builds a challenge response which makes use of the user's password
and sends it to the server, which then accepts or rejects it.
.endp
Encryption is used to protect the password in transit.


.section Using spa as a server
The \%spa%\ authenticator has just one server option:

.startconf
.index options||\%spa%\ authenticator (server)

.conf server@_password string$**$ unset
.index numerical variables (\$1$\, \$2$\, etc)||in \%spa%\ authenticator
This option is expanded, and the result must be the cleartext password for the 
authenticating user, whose name is at this point in \$1$\. For example:
.display asis
spa:
  driver = spa
  public_name = NTLM
  server_password = ${lookup{$1}lsearch{/etc/exim/spa_clearpass}}
.endd
If the expansion is forced to fail, authentication fails. Any other expansion 
failure causes a temporary error code to be returned.

.endconf



.section Using spa as a client
The \%spa%\ authenticator has the following client options:

.startconf
.index options||\%spa%\ authenticator (client)

.conf client@_domain string$**$ unset
This option specifies an optional domain for the authentication.

.conf client@_password string$**$ unset
This option specifies the user's password, and must be set.

.conf client@_username string$**$ unset
This option specifies the user name, and must be set.

.endconf

Here is an example of a configuration of this authenticator for use with the
mail servers at \*msn.com*\:
.display asis
msn:
  driver = spa
  public_name = MSN
  client_username = msn/msn_username
  client_password = msn_plaintext_password
  client_domain = DOMAIN_OR_UNSET
.endd






.
.
.
.
. ============================================================================
.chapter Encrypted SMTP connections using TLS/SSL
.set runningfoot "TLS encryption"
.rset CHAPTLS "~~chapter"
.index encryption||on SMTP connection
.index SMTP||encryption
.index TLS||on SMTP connection
.index OpenSSL
.index GnuTLS
.em
Support for TLS (Transport Layer Security), formerly known as SSL (Secure
Sockets Layer), is implemented by making use of the OpenSSL library or the
GnuTLS library (Exim requires GnuTLS release 1.0 or later).
.nem
There is no cryptographic code in the Exim distribution itself for implementing
TLS. In order to use this feature you must install OpenSSL or GnuTLS, and then
build a version of Exim that includes TLS support (see section
~~SECTinctlsssl). You also need to understand the basic concepts of encryption
at a managerial level, and in particular, the way that public keys, private
keys, and certificates are used.

RFC 2487 defines how SMTP connections can make use of encryption. Once a
connection is established, the client issues a \\STARTTLS\\ command. If the
server accepts this, the client and the server negotiate an encryption
mechanism. If the negotiation succeeds, the data that subsequently passes
between them is encrypted.

Exim also has support for legacy clients that do not use the \\STARTTLS\\
mechanism. Instead, they connect to a different port on the server (usually
called the `ssmtp' port), and expect to negotiate a TLS session as soon as the
connection to the server is established. The \-tls-on-connect-\ command line
option can be used to run an Exim server in this way from \*inetd*\, and it can
also be used to run a special daemon that operates in this manner (use \-oX-\
to specify the port).

Exim's ACLs can detect whether the current SMTP session is encrypted or not,
and if so, what cipher suite is in use, whether the client supplied a
certificate, and whether or not that certificate was verified. This makes it
possible for an Exim server to deny or accept certain commands based on the
encryption state.

\**Warning**\: certain types of firewall and certain anti-virus products can
disrupt TLS connections. You need to turn off SMTP scanning for these products
in order to get TLS to work.


.section OpenSSL vs GnuTLS
.index TLS||OpenSSL \*vs*\ GnuTLS
.rset SECTopenvsgnu "~~chapter.~~section"
The first TLS support in Exim was implemented using OpenSSL. Support for GnuTLS
followed later, when the first versions of GnuTLS were released. To build Exim
to use GnuTLS, you need to set
.display asis
USE_GNUTLS=yes
.endd
in Local/Makefile, in addition to
.display asis
SUPPORT_TLS=yes
.endd
You must also set \\TLS@_LIBS\\ and \\TLS@_INCLUDE\\ appropriately, so that the
include files and libraries for GnuTLS can be found.

There are some differences in usage when using GnuTLS instead of OpenSSL:
.numberpars $.
.em
The \tls@_verify@_certificates\ option must contain the name of a file, not the 
name of a directory (for OpenSSL it can be either).
.nem
.nextp
The \tls@_dhparam\ option is ignored, because early versions of GnuTLS had no
facility for varying its Diffie-Hellman parameters. I understand that this has 
changed, but Exim has not been updated to provide this facility.
.nextp
GnuTLS uses RSA and D-H parameters that take a substantial amount of
time to compute. It is unreasonable to re-compute them for every TLS
session. Therefore, Exim keeps this data in a file in its spool
directory, called \(gnutls-params)\. The file is owned by the Exim user and is
readable only by its owner. Every Exim process that start up GnuTLS reads the
RSA and D-H parameters from this file. If the file does not exist, the first
Exim process that needs it computes the data and writes it to a temporary file
which is renamed once it is complete. It does not matter if several Exim
processes do this simultaneously (apart from wasting a few resources). Once a
file is in place, new Exim processes immediately start using it.

For maximum security, the parameters that are stored in this file should be
recalculated periodically, the frequency depending on your paranoia level.
Arranging this is easy; just delete the file when you want new values to be
computed.
.nextp
.em
Distinguished Name (DN) strings reported by the OpenSSL library use a slash for 
separating fields; GnuTLS uses commas, in accordance with RFC 2253. This 
affects the value of the \$tls@_peerdn$\ variable.
.nem
.nextp
OpenSSL identifies cipher suites using hyphens as separators, for example:
DES-CBC3-SHA. GnuTLS uses underscores, for example: RSA@_ARCFOUR@_SHA. What is
more, OpenSSL complains if underscores are present in a cipher list. To make
life simpler, Exim changes underscores to hyhens for OpenSSL and hyphens to
underscores for GnuTLS when processing lists of cipher suites in the
.em
\tls@_require@_ciphers\ options (the global option and the \%smtp%\ transport 
option).
.nem
.nextp
.em
The \tls@_require@_ciphers\ options operate differently, as described in the
following section.
.nem
.endp

.em
.section Requiring specific ciphers in OpenSSL and GnuTLS
.rset SECTreqciphsslgnu "~~chapter.~~section"
.index TLS||requiring specific ciphers
.index \tls@_require@_ciphers\||OpenSSL \*vs*\ GnuTLS
This section documents the different ways the \tls@_require@_ciphers\ options
(the global option and the \%smtp%\ transport option) operate in OpenSSL and
GnuTLS.

There is a function in the OpenSSL library that can be passed a list of
cipher suites before the cipher negotiation takes place. This specifies which
ciphers are acceptable. The list is colon separated and may contain names like
DES-CBC3-SHA. Exim passes the expanded value of \tls@_require@_ciphers\
directly to this function call. The following quotation from
the OpenSSL documentation specifies what forms of item are allowed in the
cipher string:
.numberpars $.
It can consist of a single cipher suite such as RC4-SHA.
.nextp
It can represent a list of cipher suites containing a certain algorithm,
or cipher suites of a certain type. For example SHA1 represents all
ciphers suites using the digest algorithm SHA1 and SSLv3 represents all
SSL v3 algorithms.
.nextp
Lists of cipher suites can be combined in a single cipher string using
the + character. This is used as a logical and operation. For example
SHA1+DES represents all cipher suites containing the SHA1 and the DES
algorithms.
.nextp
Each cipher string can be optionally preceded by the characters \"!"\, \"-"\ or
\"+"\.
.numberpars " "
If \"!"\ is used then the ciphers are permanently deleted from the list. The
ciphers deleted can never reappear in the list even if they are explicitly
stated.
.nextp
If \"-"\ is used then the ciphers are deleted from the list, but some or all
of the ciphers can be added again by later options.
.nextp
If \"+"\ is used then the ciphers are moved to the end of the list. This
option doesn't add any new ciphers it just moves matching existing ones.
.nextp
If none of these characters is present then the string is just interpreted as a
list of ciphers to be appended to the current preference list. If the list
includes any ciphers already present they will be ignored: that is, they will
not moved to the end of the list.
.endp
.endp

The GnuTLS library does not have a combined function like OpenSSL. Instead,
it allows the caller to specify separate lists of key-exchange methods,
main cipher algorithms, and MAC algorithms. Unfortunately, these lists are
numerical, and the library does not have a function for turning names into
numbers. Consequently, the list of recognized names has to be built into
the application.

At present, Exim permits only the list of main cipher algorithms to be
changed. The \tls@_require@_ciphers\ option is in the same format as for
OpenSSL. Exim searches each item for the name of available algorithm. For
example, if the list contains RSA@_ARCFOUR@_SHA then ARCFOUR is recognized.

The cipher algorithms list starts out with a default set of algorithms. If
the first item in \tls@_require@_ciphers\ does \*not*\ start with an
exclamation mark, all the default items are deleted. Thus, only those specified
can be used. If the first item in \tls@_require@_ciphers\ \*does*\ start with
an exclamation mark, the defaults are left on the list.

Then, any item that starts with an exclamation mark causes the relevent
algorithms to be removed from the list, and any item that does not start
with an exclamation mark causes the relevant algorithms to be added to the
list. Thus,
.display asis
tls_require_ciphers = !RSA_ARCFOUR_SHA
.endd
allows all the defaults except those that use ARCFOUR, whereas
.display asis
tls_require_ciphers = AES : 3DES
.endd
allows only cipher suites that use AES and 3DES. The currently recognized
algorithms are: ARCFOUR@_128, ARCFOUR@_40, ARCFOUR (both of the preceding),
AES@_256, AES@_128, AES (both of the preceding), and 3DES.

Unrecognized algorithms are ignored. In a client, the order of the list
specifies a preference order for the algorithms.
.nem


.section Configuring an Exim server to use TLS
.index TLS||configuring an Exim server
When Exim has been built with TLS support, it advertises the availability of
the \\STARTTLS\\ command to client hosts that match \tls@_advertise@_hosts\,
but not to any others. The default value of this option is unset, which means
that \\STARTTLS\\ is not advertised at all. This default is chosen because you
need to set some other options in order to make TLS avaliable, and also it is
sensible for systems that want to use TLS only as a client.

If a client issues a \\STARTTLS\\ command and there is some configuration
problem in the server, the command is rejected with a 454 error. If the client
persists in trying to issue SMTP commands, all except \\QUIT\\ are rejected
with the error
.display asis
554 Security failure
.endd
If a \\STARTTLS\\ command is issued within an existing TLS session, it is
rejected with a 554 error code.

To enable TLS operations on a server, you must set \tls@_advertise@_hosts\ to
match some hosts. You can, of course, set it to $*$ to match all hosts.
However, this is not all you need to do. TLS sessions to a server won't work
without some further configuration at the server end.

It is rumoured that all existing clients that support TLS/SSL use RSA
encryption. To make this work you need to set, in the server,
.display asis
tls_certificate = /some/file/name
tls_privatekey = /some/file/name
.endd
The first file contains the server's X509 certificate, and the second contains
the private key that goes with it. These files need to be readable by the Exim
user, and must always be given as full path names. They can be the same file if
both the certificate and the key are contained within it. If \tls@_privatekey\
is not set, this is assumed to be the case. The certificate file may also
contain intermediate certificates that need to be sent to the client to enable
it to authenticate the server's certificate.

If you do not understand about certificates and keys, please try to find a
source of this background information, which is not Exim-specific. (There are a
few comments below in section ~~SECTcerandall.)

\**Note**\: These options do not apply when Exim is operating as a client -- 
they apply only in the case of a server. For a client, you must set the options 
of the same name in an \%smtp%\ transport.

With just these options, Exim will work as a server with clients such as
Netscape. It does not require the client to have a certificate (but see below
for how to insist on this). There is one other option that may be needed in
other situations. If
.display asis
tls_dhparam = /some/file/name
.endd
is set, the SSL library is initialized for the use of Diffie-Hellman ciphers
with the parameters contained in the file. This increases the set of cipher 
suites that the server supports. See the command
.display asis
openssl dhparam
.endd
for a way of generating this data.
At present, \tls@_dhparam\ is used only when Exim is linked with OpenSSL. It is 
ignored if GnuTLS is being used.

The strings supplied for these three options are expanded every time a client
host connects. It is therefore possible to use different certificates and keys
for different hosts, if you so wish, by making use of the client's IP address
in \$sender@_host@_address$\ to control the expansion. If a string expansion is
forced to fail, Exim behaves as if the option is not set.

.index cipher||logging
.index log||TLS cipher
The variable \$tls@_cipher$\ is set to the cipher suite that was negotiated for
an incoming TLS connection. It is included in the ::Received:: header of an
incoming message (by default -- you can, of course, change this), and it is
also included in the log line that records a message's arrival, keyed by `X=',
unless the \tls@_cipher\ log selector is turned off.
The \encrypted\ condition can be used to test for specific cipher suites in 
ACLs.

The ACLs that run for subsequent SMTP commands can check the name of the cipher
suite and vary their actions accordingly. The cipher suite names are those used
by OpenSSL. These may differ from the names used elsewhere. For example,
OpenSSL uses the name DES-CBC3-SHA for the cipher suite which in other contexts
is known as TLS@_RSA@_WITH@_3DES@_EDE@_CBC@_SHA. Check the OpenSSL
documentation for more details.


.section Requesting and verifying client certificates
.index certificate||verification of client
.index TLS||client certificate verification
If you want an Exim server to request a certificate when negotiating a TLS
session with a client, you must set either \tls@_verify@_hosts\ or
\tls@_try@_verify@_hosts\. You can, of course, set either of them to $*$ to
apply to all TLS connections. For any host that matches one of these options,
Exim requests a certificate as part of the setup of the TLS session. The
contents of the certificate are verified by comparing it with a list of
expected certificates. These must be available in a file or,
.em
for OpenSSL only (not GnuTLS), a directory, identified by
\tls@_verify@_certificates\.
.nem

A file can contain multiple certificates, concatenated end to end. If a
directory is used 
.em
(OpenSSL only), 
.nem
each certificate must be in a separate file, with a name (or a symbolic link)
of the form <<hash>>.0, where <<hash>> is a hash value constructed from the
certificate. You can compute the relevant hash by running the command
.display asis
openssl x509 -hash -noout -in /cert/file
.endd
where \(/cert/file)\ contains a single certificate.

The difference between \tls@_verify@_hosts\ and \tls@_try@_verify@_hosts\ is
what happens if the client does not supply a certificate, or if the certificate
does not match any of the certificates in the collection named by
\tls@_verify@_certificates\. If the client matches \tls@_verify@_hosts\, the
attempt to set up a TLS session is aborted, and the incoming connection is
dropped. If the client matches \tls@_try@_verify@_hosts\, the (encrypted) SMTP
session continues. ACLs that run for subsequent SMTP commands can detect the
fact that no certificate was verified, and vary their actions accordingly. For
example, you can insist on a certificate before accepting a message for
relaying, but not when the message is destined for local delivery.

When a client supplies a certificate (whether it verifies or not), the value of
the Distinguished Name of the certificate is made available in the variable
\$tls@_peerdn$\ during subsequent processing of the message.
.index log||distinguished name
Because it is often a long text string, it is not included in the log line or
::Received:: header by default. You can arrange for it to be logged, keyed by
`DN=', by setting the \tls@_peerdn\ log selector, and you can use
\received@_header@_text\ to change the ::Received:: header. When no certificate
is supplied, \$tls@_peerdn$\ is empty.

.em
.section Revoked certificates
.index TLS||revoked certificates
.index revocation list
.index certificate||revocation list
Certificate issuing authorities issue Certificate Revocation Lists (CRLs) when
certificates are revoked. If you have such a list, you can pass it to an Exim
server using the global option called \tls@_crl\ and to an Exim client using an
identically named option for the \%smtp%\ transport. In each case, the value of
the option is expanded and must then be the name of a file that contains a CRL
in PEM format.
.nem

.section Configuring an Exim client to use TLS
.index cipher||logging
.index log||TLS cipher
.index log||distinguished name
.index TLS||configuring an Exim client
The \tls@_cipher\ and \tls@_peerdn\ log selectors apply to outgoing SMTP
deliveries as well as to incoming, the latter one causing logging of the
server certificate's DN. The remaining client configuration for TLS is all
within the \%smtp%\ transport.

It is not necessary to set any options to have TLS work in the \%smtp%\
transport. If Exim is built with TLS support, and TLS is advertised by a
server, the \%smtp%\ transport always tries to start a TLS session. However,
this can be prevented by setting \hosts@_avoid@_tls\ (an option of the
transport) to a list of server hosts for which TLS should not be used.

If you do not want Exim to attempt to send messages unencrypted when an attempt
to set up an encrypted connection fails in any way, you can set
\hosts@_require@_tls\ to a list of hosts for which encryption is mandatory. For
those hosts, delivery is always deferred if an encrypted connection cannot be
set up. If there are any other hosts for the address, they are tried in the
usual way.

When the server host is not in \hosts@_require@_tls\, Exim may try to deliver
the message unencrypted. It always does this if the response to \\STARTTLS\\ is
a 5\*xx*\ code. For a temporary error code, or for a failure to negotiate a TLS
session after a success response code, what happens is controlled by the
\tls@_tempfail@_tryclear\ option of the \%smtp%\ transport. If it is false,
delivery to this host is deferred, and other hosts (if available) are tried. If
it is true, Exim attempts to deliver unencrypted after a 4\*xx*\ response to
\\STARTTLS\\, and if \\STARTTLS\\ is accepted, but the subsequent TLS
negotiation fails, Exim closes the current connection (because it is in an
unknown state), opens a new one to the same host, and then tries the delivery
unencrypted.


The \tls@_certificate\ and \tls@_privatekey\ options of the \%smtp%\ transport
provide the client with a certificate, which is passed to the server if it
requests it. If the server is Exim, it will request a certificate only if
\tls@_verify@_hosts\ or \tls@_try@_verify@_hosts\ matches the client.
\**Note**\: these options must be set in the \%smtp%\ transport for Exim to use 
TLS when it is operating as a client. Exim does not assume that a server
certificate (set by the global options of the same name) should also be used
when operating as a client.

If \tls@_verify@_certificates\ is set, it must name a file or,
.em
for OpenSSL only (not GnuTLS), a directory, that contains a collection of
expected server certificates. The client verifies the server's certificate
against this collection, taking into account any revoked certificates that are
in the list defined by \tls@_crl\.
.nem

If
\tls@_require@_ciphers\ is set on the \%smtp%\ transport, it must contain a
list of permitted cipher suites. If either of these checks fails, delivery to
the current host is abandoned, and the \%smtp%\ transport tries to deliver to
alternative hosts, if any.

All the TLS options in the \%smtp%\ transport are expanded before use, with
\$host$\ and \$host@_address$\ containing the name and address of the server to
which the client is connected. Forced failure of an expansion causes Exim to
behave as if the relevant option were unset.


.section Multiple messages on the same encrypted TCP/IP connection
.rset SECTmulmessam "~~chapter.~~section"
.index multiple SMTP deliveries with TLS
.index TLS||multiple message deliveries
Exim sends multiple messages down the same TCP/IP connection by starting up
an entirely new delivery process for each message, passing the socket from
one process to the next. This implementation does not fit well with the use
of TLS, because there is quite a lot of state information associated with a TLS
connection, not just a socket identification. Passing all the state information
to a new process is not feasible. Consequently, Exim shuts down an existing TLS
session before passing the socket to a new process. The new process may then
try to start a new TLS session, and if successful, may try to re-authenticate
if \\AUTH\\ is in use, before sending the next message.

The RFC is not clear as to whether or not an SMTP session continues in clear
after TLS has been shut down, or whether TLS may be restarted again later, as 
just described. However, if the server is Exim, this shutdown and
reinitialization works. It is not known which (if any) other servers operate
successfully if the client closes a TLS session and continues with unencrypted
SMTP, but there are certainly some that do not work. For such servers, Exim
should not pass the socket to another process, because the failure of the
subsequent attempt to use it would cause Exim to record a temporary host error,
and delay other deliveries to that host.

To test for this case, Exim sends an \\EHLO\\ command to the server after
closing down the TLS session. If this fails in any way, the connection is 
closed instead of being passed to a new delivery process, but no retry
information is recorded.

There is also a manual override; you can set \hosts@_nopass@_tls\ on the 
\%smtp%\ transport to match those hosts for which Exim should not pass 
connections to new processes if TLS has been used.



.section Certificates and all that
.rset SECTcerandall "~~chapter.~~section"
.index certificate||references to discussion
In order to understand fully how TLS works, you need to know about
certificates, certificate signing, and certificate authorities. This is not the
place to give a tutorial, especially as I do not know very much about it
myself. Some helpful introduction can be found in the FAQ for the SSL addition
to Apache, currently at
.display rm
\?http://www.modssl.org/docs/2.7/ssl@_faq.html@#ToC24?\
.endd
Other parts of the \*modssl*\ documentation are also helpful, and have
links to further files.
Eric Rescorla's book, \*SSL and TLS*\, published by Addison-Wesley (ISBN
0-201-61598-3), contains both introductory and more in-depth descriptions. 
Some sample programs taken from the book are available from
.display rm
\?http://www.rtfm.com/openssl-examples/?\
.endd

.section Certificate chains
The file named by \tls@_certificate\ may contain more than one
certificate. This is useful in the case where the certificate that is being
sent is validated by an intermediate certificate which the other end does
not have. Multiple certificates must be in the correct order in the file.
First the host's certificate itself, then the first intermediate
certificate to validate the issuer of the host certificate, then the next
intermediate certificate to validate the issuer of the first intermediate
certificate, and so on, until finally (optionally) the root certificate.
The root certificate must already be trusted by the recipient for
validation to succeed, of course, but if it's not preinstalled, sending the
root certificate along with the rest makes it available for the user to
install if the receiving end is a client MUA that can interact with a user.

.section Self-signed certificates
.index certificate||self-signed
You can create a self-signed certificate using the \*req*\ command provided
with OpenSSL, like this:
.display asis
openssl req -x509 -newkey rsa:1024 -keyout file1 -out file2 \
            -days 9999 -nodes
.endd
\(file1)\ and \(file2)\ can be the same file; the key and the certificate are
delimited and so can be identified independently. The \-days-\ option
specifies a period for which the certificate is valid. The \-nodes-\ option is
important: if you do not set it, the key is encrypted with a passphrase
that you are prompted for, and any use that is made of the key causes more
prompting for the passphrase. This is not helpful if you are going to use
this certificate and key in an MTA, where prompting is not possible.

A self-signed certificate made in this way is sufficient for testing, and
may be adequate for all your requirements if you are mainly interested in
encrypting transfers, and not in secure identification.

However, many clients require that the certificate presented by the server be a
user (also called `leaf' or `site') certificate, and not a self-signed
certificate. In this situation, the self-signed certificate described above
must be installed on the client host as a trusted root \*certification
authority*\ (CA), and the certificate used by Exim must be a user certificate
signed with that self-signed certificate.

For information on creating self-signed CA certificates and using them to sign
user certificates, see the \*General implementation overview*\ chapter of the
Open-source PKI book, available online at \?http://ospkibook.sourceforge.net/?\.



.
.
.
.
. ============================================================================
.chapter Access control lists
.set runningfoot "ACL"
.rset CHAPACL "~~chapter"
.index ~~ACL||description
.index control of incoming mail
.index message||controlling incoming
.index policy control||access control lists
Access Control Lists (ACLs) are defined in a separate section of the run time
configuration file, headed by `begin acl'. Each ACL definition starts with a
name, terminated by a colon. Here is a complete ACL section which contains just
one very small ACL:
.display asis
begin acl

small_acl:
  accept   hosts = one.host.only
.endd
You can have as many lists as you like in the ACL section, and the order in
which they appear does not matter. The lists are self-terminating.

The majority of ACLs are used to control Exim's behaviour when it receives
certain SMTP commands. This applies both to incoming TCP/IP connections, and
when a local process submits a message over a pipe (using the \-bs-\ option).
The most common use is for controlling which recipients are accepted in
incoming messages. In addition, you can also define an ACL that is used to
check local non-SMTP messages. The default configuration file contains an
example of a realistic ACL for checking \\RCPT\\ commands. This is discussed in
chapter ~~CHAPdefconfil.

.section Testing ACLs
The \-bh-\ command line option provides a way of testing your ACL configuration
locally by running a fake SMTP session with which you interact. The host
\*relay-test.mail-abuse.org*\ provides a service for checking your relaying
configuration (see section ~~SECTcheralcon for more details).


.section Specifying when ACLs are used
.index ~~ACL||options for specifying
In order to cause an ACL to be used, you have to name it in one of the relevant
options in the main part of the configuration. These options are:
.index \\AUTH\\||ACL for
.index \\DATA\\, ACL for
.index \\ETRN\\||ACL for
.index \\EXPN\\||ACL for
.index \\HELO\\||ACL for
.index \\EHLO\\||ACL for
.index \\MAIL\\||ACL for
.index \\RCPT\\||ACL for
.index \\STARTTLS\\, ACL for
.index \\VRFY\\||ACL for
.display
.tabs 20
.if !~~sys.fancy
.tabs 24
.fi
\acl@_not@_smtp\      $t $rm{ACL for non-SMTP messages}
\acl@_smtp@_auth\     $t $rm{ACL for \\AUTH\\}
\acl@_smtp@_connect\  $t $rm{ACL for start of SMTP connection}
\acl@_smtp@_data\     $t $rm{ACL after \\DATA\\}
\acl@_smtp@_etrn\     $t $rm{ACL for \\ETRN\\}
\acl@_smtp@_expn\     $t $rm{ACL for \\EXPN\\}
\acl@_smtp@_helo\     $t $rm{ACL for \\HELO\\ or \\EHLO\\}
\acl@_smtp@_mail\     $t $rm{ACL for \\MAIL\\}
.newline
\acl@_smtp@_mailauth\ $t $rm{ACL for the \\AUTH\\ parameter of \\MAIL\\}
.newline
\acl@_smtp@_rcpt\     $t $rm{ACL for \\RCPT\\}
\acl@_smtp@_starttls\ $t $rm{ACL for \\STARTTLS\\}
\acl@_smtp@_vrfy\     $t $rm{ACL for \\VRFY\\}
.endd
For example, if you set
.display asis
acl_smtp_rcpt = small_acl
.endd
the little ACL defined above is used whenever Exim receives a \\RCPT\\ command
in an SMTP dialogue. The majority of policy tests on incoming messages can be
done when \\RCPT\\ commands arrive. A rejection of \\RCPT\\ should cause the
sending MTA to give up on the recipient address contained in the \\RCPT\\
command, whereas rejection at other times may cause the client MTA to keep on 
trying to deliver the message. It is therefore recommended that you do as much 
testing as possible at \\RCPT\\ time.

However, you cannot test the contents of the message, for example, to verify
addresses in the headers, at \\RCPT\\ time. Such tests have to appear in the
ACL that is run after the message has been received, before the final response
to the \\DATA\\ command is sent. This is the ACL specified by
\acl@_smtp@_data\. At this time, it is no longer possible to reject individual
recipients. An error response should reject the entire message. Unfortunately,
it is known that some MTAs do not treat hard (5$it{xx}) errors correctly at
this point -- they keep the message on their queues and try again later, but
that is their problem, though it does waste some of your resources.

The ACL test specified by \acl@_smtp@_connect\ happens after the test specified
by \host__reject__connection\ (which is now an anomaly) and any TCP Wrappers
testing (if configured).

The non-SMTP ACL applies to all non-interactive incoming messages, that is, it
applies to batch SMTP as well as to non-SMTP messages. (Batch SMTP is not
really SMTP.) This ACL is run just before the \*local@_scan()*\ function. Any
kind of rejection is treated as permanent, because there is no way of sending a
temporary error for these kinds of message. Many of the ACL conditions (for
example, host tests, and tests on the state of the SMTP connection such as
encryption and authentication) are not relevant and are forbidden in this ACL.


.section ACL return codes
.index ~~ACL||return codes
The result of running an ACL is either `accept' or `deny', or, if some test
cannot be completed (for example, if a database is down), `defer'. These
results cause 2$it{xx}, 5$it{xx}, and 4$it{xx} return codes, respectively, to
be used in the SMTP dialogue. A fourth return, `error', occurs when there is an
error such as invalid syntax in the ACL. This also causes a 4$it{xx} return
code.

The ACLs that are relevant to message reception may also return `discard'. This
has the effect of `accept', but causes either the entire message or an
individual recipient address to be discarded. In other words, it is a
blackholing facility. Use it with great care.

If the ACL for \\MAIL\\ returns `discard', all recipients are discarded, and no
ACL is run for subsequent \\RCPT\\ commands. The effect of `discard' in a
\\RCPT\\ ACL is to discard just the one address. If there are no recipients
left when the message's data is received, the \\DATA\\ ACL is not run. A 
`discard' return from the \\DATA\\ or the non-SMTP ACL discards all the 
remaining recipients.

The \*local@_scan()*\ function is always run, even if there are no remaining 
recipients; it may create new recipients.


.section Unset ACL options
.index ~~ACL||unset options
.em
The default actions when any of the \acl@_$it{xxx}\ options are unset are not
all the same. \**Note**\: These defaults apply only when the relevant ACL is
not defined at all. For any defined ACL, the default action if control reaches
the end of the ACL statements is `deny'.
.nem

For \acl@_not@_smtp\, \acl@_smtp@_auth\, \acl@_smtp@_connect\,
\acl@_smtp@_data\, \acl@_smtp@_helo\, \acl__smtp__mail\, \acl@_smtp@_mailauth\,
and \acl@_smtp@_starttls\, the 
.em
action when the ACL is not defined is `accept'.

For the others (\acl@_smtp@_etrn\, \acl@_smtp@_expn\, \acl@_smtp@_rcpt\, and
\acl@_smtp@_vrfy\), the action when the ACL is not defined is `deny'.
.nem
This means that \acl@_smtp@_rcpt\ must be defined in order to receive any
messages over an SMTP connection. For an example, see the ACL in the default
configuration file.



.section Data for message ACLs
.index ~~ACL||data for message ACL
When an ACL for \\MAIL\\, \\RCPT\\, or \\DATA\\ is being run, the variables
that contain information about the host and the message's sender (for example,
\$sender@_host@_address$\ and \$sender@_address$\) are set, and can be used in
ACL statements. In the case of \\RCPT\\ (but not \\MAIL\\ or \\DATA\\),
\$domain$\ and \$local@_part$\ are set from the argument address.

When an ACL for the \\AUTH\\ parameter of \\MAIL\\ is being run, the variables 
that contain information about the host are set, but \$sender@_address$\ is not 
yet set.

The \$message@_size$\ variable is set to the value of the \\SIZE\\ parameter on
the \\MAIL\\ command at \\MAIL\\ and \\RCPT\\ time, or -1 if that parameter was
not given. 
Its value is updated to the true message size by the time the ACL after
\\DATA\\ is run.

The \$rcpt@_count$\ variable increases by one for each \\RCPT\\ command
received. The \$recipients@_count$\ variable increases by one each time a
\\RCPT\\ command is accepted, so while an ACL for \\RCPT\\ is being processed,
it contains the number of previously accepted recipients. At \\DATA\\ time,
\$rcpt@_count$\ contains the total number of \\RCPT\\ commands, and
\$recipients@_count$\ contains the total number of accepted recipients.



.section Data for non-message ACLs
.rset SECTdatfornon "~~chapter.~~section"
.index ~~ACL||data for non-message ACL
When an ACL for \\AUTH\\, \\ETRN\\, \\EXPN\\, 
\\STARTTLS\\,
or \\VRFY\\ is being run, the remainder of the SMTP command line is placed in
\$smtp@_command@_argument$\. This can be tested using a \condition\ condition.
For example, here is an ACL for use with \\AUTH\\, which insists that either
the session is encrypted, or the CRAM-MD5 authentication method is used. In
other words, it does not permit authentication methods that use cleartext
passwords on unencrypted connections.
.display asis
acl_check_auth:
  accept encrypted = *
  accept condition = ${if eq{${uc:$smtp_command_argument}}\
                      {CRAM-MD5}{yes}{no}}
  deny   message   = TLS encryption or CRAM-MD5 required
.endd
(Another way of applying this restriction is to arrange for the authenticators 
that use cleartext passwords not to be advertised when the connection is not 
encrypted. You can use the generic \server@_advertise@_condition\ authenticator 
option to do this.)


.section Use of the ACL selection options
.index ~~ACL||specifying which to use
The value of an \acl@_smtp@_$it{xxx}\ option is expanded before use, so you can
use different ACLs in different circumstances, and in fact the resulting string
does not have to be the name of a configured list. Having expanded the string,
Exim searches for an ACL as follows:
.numberpars $.
If the string begins with a slash, Exim attempts to open the file and read
its contents as an ACL. 
The lines are processed in the same way as lines in the Exim configuration
file. In particular, continuation lines are supported, blank lines are ignored,
as are lines whose first non-whitespace character is `@#'.
If the file does not exist or cannot be read, an error occurs (typically
causing a temporary failure of whatever caused the ACL to be run). For example:
.display asis
acl_smtp_data = /etc/acls/\
  ${lookup{$sender_host_address}lsearch\
  {/etc/acllist}{$value}{default}}
.endd
This looks up an ACL file to use on the basis of the host's IP address, falling
back to a default if the lookup fails. If an ACL is successfully read from a
file, it is retained in memory for the duration of the Exim process, so that it
can be re-used without having to re-read the file.
.nextp
If the string does not start with a slash, and does not contain any spaces,
Exim searches the ACL section of the configuration for a list whose name
matches the string.
.nextp
If no named ACL is found, or if the string contains spaces, Exim parses
the string as an inline ACL. This can save typing in cases where you just
want to have something like
.display asis
acl_smtp_vrfy = accept
.endd
in order to allow free use of the \\VRFY\\ command.
Such a string may contain newlines; it is processed in the same way as an ACL 
that is read from a file.
.endp


.section Format of an ACL
.index ~~ACL||format of
.index ~~ACL||verbs, definition of
An individual ACL consists of a number of statements. Each statement starts
with a verb, optionally followed by a number of conditions and other modifiers.
If all the conditions are met, the verb is obeyed. 
The same condition may be used (with different arguments) more than once in the 
same statement. This provides a means of specifying an `and' conjunction 
between conditions. For example:
.display asis
deny  dnslists = list1.example
      dnslists = list2.example
.endd

If there are no conditions, the verb is always obeyed. What happens if any of
the conditions are not met depends on the verb (and in one case, on a special
modifier). Not all the conditions make sense at every testing point. For
example, you cannot test a sender address in the ACL that is run for a \\VRFY\\
command.

The verbs are as follows:
.numberpars $.
\accept\: If all the conditions are met, the ACL returns `accept'. If any of
the conditions are not met, what happens depends on whether \endpass\ appears
among the conditions (for syntax see below). If the failing condition precedes
\endpass\, control is passed to the next ACL statement; if it follows
\endpass\, the ACL returns `deny'. Consider this statement, used to check a
\\RCPT\\ command:
.display asis
accept domains = +local_domains
       endpass
       verify = recipient
.endd
If the recipient domain does not match the \domains\ condition, control passes
to the next statement. If it does match, the recipient is verified, and the
command is accepted if verification succeeds. However, if verification fails,
the ACL yields `deny', because the failing condition is after \endpass\.
.nextp
\defer\: If all the conditions are met, the ACL returns `defer' which, in an 
SMTP session, causes a 4\*xx*\ response to be given. For a non-SMTP ACL, 
\defer\ is the same as \deny\, because there is no way of sending a temporary
error. For a \\RCPT\\ command, \defer\ is much the same as using a
\%redirect%\ router and \":defer:"\ while verifying, but the \defer\ verb can
be used in any ACL, and even for a recipient it might be a simpler approach.
.nextp
\deny\: If all the conditions are met, the ACL returns `deny'. If any of the
conditions are not met, control is passed to the next ACL statement. For
example,
.display asis
deny dnslists = blackholes.mail-abuse.org
.endd
rejects commands from hosts that are on a DNS black list.
.nextp
\discard\: This verb behaves like \accept\, except that it returns `discard' 
from the ACL instead of `accept'. It is permitted only on ACLs that are
concerned with receiving messages, and it causes recipients to be discarded.
If the \log@_message\ modifier is set when \discard\ operates, its contents are 
added to the line that is automatically written to the log. 

If \discard\ is used in an ACL for \\RCPT\\, just the one recipient is
discarded; if used for \\MAIL\\, \\DATA\\ or in the non-SMTP ACL, all the
message's recipients are discarded. Recipients that are discarded before
\\DATA\\ do not appear in the log line when the \log@_recipients\ log selector
is set.
.nextp
\drop\: This verb behaves like \deny\, except that an SMTP connection is
forcibly closed after the 5\*xx*\ error message has been sent. For example:
.display asis
drop   message   = I don't take more than 20 RCPTs
       condition = ${if > {$rcpt_count}{20}{yes}{no}}
.endd
There is no difference between \deny\ and \drop\ for the connect-time ACL. The
connection is always dropped after sending a 550 response.
.nextp
\require\: If all the conditions are met, control is passed to the next ACL
statement. If any of the conditions are not met, the ACL returns `deny'. For
example, when checking a \\RCPT\\ command,
.display asis
require verify = sender
.endd
passes control to subsequent statements only if the message's sender can be
verified. Otherwise, it rejects the command.
.nextp
.em
\warn\: If all the conditions are met, a header line is added to an incoming
message and/or a line is written to Exim's main log. In all cases, control
passes to the next ACL statement. The text of the added header line and the log
line are specified by modifiers; if they are not present, a \warn\ verb just
checks its conditions and obeys any `immediate' modifiers such as \set\ and
\logwrite\.

If any condition on a \warn\ statement cannot be completed (that is, there is
some sort of defer), no header is added and the configured log line is not
written. No further conditions or modifiers in the \warn\ statement are
processed. The incident is logged, but the ACL continues to be processed, from
the next statement onwards.

When testing an incoming message, the \message\ modifier can be used on a 
\warn\ statement to add an extra header line,
.nem
as in this example:
.display asis
warn message = X-blacklisted-at: $dnslist_domain
     dnslists = blackholes.mail-abuse.org : \
                dialup.mail-abuse.org
.endd
If an identical header line is requested several times (provoked, for example,
by multiple \\RCPT\\ commands), only one copy is actually added to the message.
.em
If the text of the \message\ modifier is not a valid header line, 
\"X-ACL-Warn:"\ is added to the front of it.
.nem

Header lines that are added by an ACL at \\MAIL\\ or \\RCPT\\ time are not
visible in string expansions in the ACL for subsequent \\RCPT\\ commands.
However they are visible in string expansions in the ACL that is run after
\\DATA\\. If you want to preserve data between \\MAIL\\ and \\RCPT\\ ACLs, you
can use ACL variables, as described in the next section. If a message is
rejected after \\DATA\\, all added header lines are included in the entry that
is written to the reject log.

If a \message\ modifier is present on a \warn\ verb in an ACL that is not 
testing an incoming message, it is ignored, and the incident is logged.

A \warn\ statement may use the \log@_message\ modifier to cause a line to be 
written to the main log when the statement's conditions are true. 
.em
Just as for \message\, if an identical log line is requested several times in 
the same message, only one copy is actually written to the log. If you want to
force duplicates to be written, use the \logwrite\ modifier instead.
.nem

When one of the \warn\ conditions is an address verification that fails, the
text of the verification failure message is in \$acl@_verify@_message$\. If you
want this logged, you must set it up explicitly. For example:
.display asis
warn   !verify = sender
        log_message = sender verify failed: $acl_verify_message
.endd
.endp

At the end of each ACL there is an implicit unconditional \deny\.

As you can see from the examples above, the conditions and modifiers are
written one to a line, with the first one on the same line as the verb, and
subsequent ones on following lines. If you have a very long condition, you can
continue it onto several physical lines by the usual @\ continuation mechanism.
It is conventional to align the conditions vertically.


.section ACL variables
.rset SECTaclvariables "~~chapter.~~section"
.index ~~ACL||variables
There are some special variables that can be set during ACL processing. They
can be used to pass information between different ACLs, different
invocations of the same ACL in the same SMTP connection, and between ACLs and
the routers, transports, and filters that are used to deliver a message.
There are two sets of these variables:
.numberpars $.
The values of \$acl@_c0$\ to \$acl@_c9$\ persist throughout an SMTP connection.
They are never reset. Thus, a value that is set while receiving one message is 
still available when receiving the next message on the same SMTP connection.
.nextp
The values of \$acl@_m0$\ to \$acl@_m9$\ persist only while a message is being
received. They are reset afterwards. They are also reset by \\MAIL\\, \\RSET\\,
\\EHLO\\, \\HELO\\, and after starting up a TLS session.
.endp
When a message is accepted, the current values of all the ACL variables are 
preserved with the message and are subsequently made available at delivery
time.

The ACL variables are set by modifier called \set\. For example:
.display asis
accept hosts = whatever
       set acl_m4 = some value
.endd
Note that the leading dollar sign is not used when naming a variable that is to
be set. If you want to set a variable without taking any action, you can use a
\warn\ verb without any other modifiers.


.section Condition and modifier processing
.index ~~ACL||conditions, processing
.index ~~ACL||modifiers, processing
An exclamation mark preceding a condition negates its result. For example,
.display asis
deny   domains = *.dom.example
      !verify = recipient
.endd
causes the ACL to return `deny' if the recipient domain ends in
\*dom.example*\, but the recipient address cannot be verified.

The arguments of conditions and modifiers are expanded. A forced failure
of an expansion causes a condition to be ignored, that is, it behaves as if the
condition is true. Consider these two statements:
.display asis
accept  senders = ${lookup{$host_name}lsearch\
                  {/some/file}{$value}fail}
accept  senders = ${lookup{$host_name}lsearch\
                  {/some/file}{$value}{}}
.endd
Each attempts to look up a list of acceptable senders. If the lookup succeeds,
the returned list is searched, but if the lookup fails the behaviour is
different in the two cases. The \fail\ in the first statement causes the
condition to be ignored, leaving no further conditions. The \accept\ verb
therefore succeeds. The second statement, however, generates an empty list when
the lookup fails. No sender can match an empty list, so the condition fails,
and therefore the \accept\ also fails.

ACL modifiers appear mixed in with conditions in ACL statements. Some of them
specify actions that are taken as the conditions for a statement are checked;
others specify text for messages that are used when access is denied or a
warning is generated.

The positioning of the modifiers in an ACL statement important, because the
processing of a verb ceases as soon as its outcome is known. Only those
modifiers that have already been encountered will take effect. For the \accept\
and \require\ statements, this means that processing stops as soon as a false
condition is met. For example, consider this use of the \message\ modifier:
.display asis
require message = Can't verify sender
        verify = sender
        message = Can't verify recipient
        verify = recipient
        message = This message cannot be used
.endd
If sender verification fails, Exim knows that the result of the statement is 
`deny', so it goes no further. The first \message\ modifier has been seen, so 
its text is used as the error message. If sender verification succeeds, but
recipient verification fails, the second message is used. If recipient
verification succeeds, the third message becomes `current', but is never used
because there are no more conditions to cause failure.

For the \deny\ verb, on the other hand, it is always the last \message\
modifier that is used, because all the conditions must be true for rejection to 
happen. Specifying more than one \message\ modifier does not make sense, and 
the message can even be specified after all the conditions. For example:
.display asis
deny   hosts = ...
      !senders = *@my.domain.example
       message = Invalid sender from client host
.endd
The `deny' result does not happen until the end of the statement is reached, by 
which time Exim has set up the message.


.section ACL modifiers
.rset SECTACLmodi "~~chapter.~~section"
.index ~~ACL||modifiers, list of
The ACL modifiers are as follows:

.startitems

.item "control = <<text>>"
.index message||submission
This modifier may appear only in ACLs for commands relating to incoming 
messages. It affects the subsequent processing of the message, provided that
the message is eventually accepted. 
.em
The text must be one of the words `freeze', `queue@_only', or `submission' (in 
the latter case, optionally followed by slash-delimited options). The first two
cause the message to be frozen or just queued (without immediate delivery),
respectively. The third tells Exim that this message is a submission from a
local MUA. In this case, Exim applies certain fixups to the message if
necessary. For example, it add a ::Date:: header line if one is not present.
Details are given in chapter ~~CHAPmsgproc.
.nem

Once one of these controls is set, it remains set for the message. For example,
if \control\ is used in a \\RCPT\\ ACL, it applies to the whole message, not
just the individual recipient. The \control\ modifier can be used in several
different ways. For example:
.numberpars $.
It can be at the end of an \accept\ statement:
.display asis
accept  ...some conditions...
        control = queue_only
.endd
In this case, the control is applied when this statement yields `accept'.
.nextp
It can be in the middle of an \accept\ statement:
.display asis
accept  ...some conditions...
        control = queue_only
        ...some more conditions...
.endd
If the first set of conditions are true, the control is applied, even if the 
statement does not accept because one of the second set of conditions is false.
In this case, some subsequent statement must yield `accept' for the control to
be relevant.
.nextp
It can be used with \warn\ to apply the control, leaving the
decision about accepting or denying to a subsequent verb. For
example:
.display asis
warn    ...some conditions...
        control = freeze
accept  ...
.endd
.em
This example of \warn\ does not contain \message\, \log@_message\, or
\logwrite\, so it does not add anything to the message and does not write a log
entry.
.nem
.endp

.item "delay = <<time>>"
.index \-bh-\ option
This modifier causes Exim to wait for the time interval before proceeding. The
time is given in the usual Exim notation. This modifier may appear in any ACL.
The delay happens as soon as the modifier is processed.
.em
However, when testing Exim using the \-bh-\ option, the delay is not actually 
imposed (an appropriate message is output).
.nem

Like \control\, \delay\ can be used with \accept\ or
\deny\, for example:
.display asis
deny    ...some conditions...
        delay = 30s
.endd
The delay happens if all the conditions are true, before the statement returns 
`deny'. Compare this with:
.display asis
deny    delay = 30s
        ...some conditions...
.endd
which waits for 30s before processing the conditions. The \delay\ modifier can
also be used with \warn\ and together with \control\:
.display
warn    ...some conditions...
        delay = 2m
        control = freeze
accept  ...
.endd

.item endpass
This modifier, which has no argument, is recognized only in \accept\
statements. It marks the boundary between the conditions whose failure causes
control to pass to the next statement, and the conditions whose failure causes
the ACL to return `deny'. See the description of \accept\ above.

.item "log@_message = <<text>>"
This modifier sets up a message that is used as part of the log message if the
ACL denies access
.em
or a \warn\ statement's conditions are true. 
.nem
For example:
.display asis
require log_message = wrong cipher suite $tls_cipher
        encrypted   = DES-CBC3-SHA
.endd
\log@_message\ adds to any underlying error message that may exist because of
the condition failure. For example, while verifying a recipient address, a
:::fail:: redirection might have already set up a message. Although the message
is usually defined before the conditions to which it applies, the expansion
does not happen until Exim decides that access is to be denied. This means that
any variables that are set by the condition are available for inclusion in the
message. For example, the \$dnslist@_<<xxx>>$\ variables are set after a DNS
black list lookup succeeds. If the expansion of \log@_message\ fails, or if the 
result is an empty string, the modifier is ignored.

If you want to use a \warn\ statement to log the result of an address
verification, you can use \$acl__verify__message$\ to include the verification
error message.

.em
If \log@_message\ is used with a \warn\ statement, `Warning:' is added to the
start of the logged message. If the same warning log message is requested more
than once while receiving  a single email message, only one copy is actually
logged. If you want to log multiple copies, use \logwrite\ instead of
\log@_message\. In the absence of \log@_message\ and \logwrite\, nothing is
logged for a succesful \warn\ statement.
.nem

If \log@_message\ is not present and there is no underlying error message (for
example, from the failure of address verification), but \message\ is present,
the \message\ text is used for logging rejections. However, if any text for
logging contains newlines, only the first line is logged. In the absence of
both \log@_message\ and \message\, a default built-in message is used for
logging rejections.

.item "logwrite = <<text>>"
.index log||in ACL, immediate
This modifier writes a message to a log file as soon as it is encountered when
processing an ACL. (Compare \log@_message\, which,
.em
except in the case of \warn\,
.nem
is used only if the ACL statement denies access.) The \logwrite\ modifier can
be used to log special incidents in ACLs. For example:
.display 
accept <<some special conditions>>
       control  = freeze
       logwrite = froze message because ...
.endd
By default, the message is written to the main log. However, it may begin
with a colon, followed by a comma-separated list of log names, and then
another colon, to specify exactly which logs are to be written. For
example:
.display asis
logwrite = :main,reject: text for main and reject logs
logwrite = :panic: text for panic log only
.endd

.item "message = <<text>>"
This modifier sets up a text string that is expanded and used as an error
message if the current statement causes the ACL to deny access. The expansion 
happens at the time Exim decides that access is to be denied, not at the time 
it processes \message\. If the expansion fails, or generates an empty string,
the modifier is ignored. For ACLs that are triggered by SMTP commands, the
message is returned as part of the SMTP error response.

The \message\ modifier is also used with the \warn\ verb to specify one or more
header lines to be added to an incoming message when all the conditions are 
true. 
If \message\ is used with \warn\ in an ACL that is not concerned with receiving
a message, it has no effect.

The text is literal; any quotes are taken as literals, but because the string
is expanded, backslash escapes are processed anyway. If the message contains
newlines, this gives rise to a multi-line SMTP response. Like \log@_message\,
the contents of \message\ are not expanded until after a condition has failed.

If \message\ is used on a statement that verifies an address, the message 
specified overrides any message that is generated by the verification process. 
However, the original message is available in the variable
\$acl@_verify@_message$\, so you can incorporate it into your message if you
wish. In particular, if you want the text from \:fail:\ items in \%redirect%\
routers to be passed back as part of the SMTP response, you should either not
use a \message\ modifier, or make use of \$acl@_verify@_message$\.

.item "set <<acl@_name>> = <<value>>"
This modifier puts a value into one of the ACL variables (see section 
~~SECTaclvariables).

.enditems




.section ACL conditions
.rset SECTaclconditions "~~chapter.~~section"
.index ~~ACL||conditions, list of
Not all conditions are relevant in all circumstances. For example, testing
senders and recipients does not make sense in an ACL that is being run as the
result of the arrival of an \\ETRN\\ command, and checks on message headers can
be done only in the ACLs specified by \acl@_smtp@_data\ 
and \acl__not__smtp\.
You can use the same condition (obviously with different parameters) more than 
once in the same ACL statement. This provides a way of specifying an `and' 
conjunction.
The conditions are as follows:

.startitems

.item "acl = <<name of acl or ACL string or file name >>"
.index ~~ACL||nested
.index ~~ACL||indirect
The possible values of the argument are the same as for the
\acl@_smtp@_$it{xxx}\ options. The named or inline ACL is run. If it returns
`accept' the condition is true; if it returns `deny' the condition is false; if
it returns `defer', the current ACL returns `defer'. 
If it returns `drop' and the outer condition denies access, the connection is 
dropped. If it returns `discard', the verb must be \accept\ or \discard\, and 
the action is taken immediately -- no further conditions are tested.

ACLs may be nested up to 20 deep; the limit exists purely to catch runaway
loops. This condition allows you to use different ACLs in different 
circumstances. For example, different ACLs can be used to handle \\RCPT\\
commands for different local users or different local domains.

.item "authenticated = <<string list>>"
.index authentication||ACL checking
.index ~~ACL||testing for authentication
If the SMTP connection is not authenticated, the condition is false. Otherwise,
the name of the authenticator is tested against the list. To test for
authentication by any authenticator, you can set
.display asis
authenticated = *
.endd

.item "condition = <<string>>"
.index customizing||ACL condition
.index ~~ACL||customized test
This feature allows you to make up custom conditions. If the result of
expanding the string is an empty string, the number zero, or one of the strings
`no' or `false', the condition is false. If the result is any non-zero number,
or one of the strings `yes' or `true', the condition is true. For any other
values, some error is assumed to have occured, and the ACL returns `defer'.

.item "dnslists = <<list of domain names and other data>>"
.index DNS list||in ACL
.index black list (DNS)
.index ~~ACL||testing a DNS list
This condition checks for entries in DNS black lists. These are also known as
`RBL lists', after the original Realtime Blackhole List, but note that the use
of the lists at \*mail-abuse.org*\ now carries a charge. 
There are too many different variants of this condition to describe briefly 
here. See sections ~~SECTmorednslists--~~SECTmorednslistslast for details.

.item "domains = <<domain list>>"
.index domain||ACL checking
.index ~~ACL||testing a recipient domain
This condition is relevant only after a \\RCPT\\ command. It checks that the
domain of the recipient address is in the domain list. If percent-hack
processing is enabled, it is done before this test is done. If the check
succeeds with a lookup, the result of the lookup is placed in \$domain@_data$\
until the next \domains\ test.

.item "encrypted = <<string list>>"
.index encryption||checking in an ACL
.index ~~ACL||testing for encryption
If the SMTP connection is not encrypted, the condition is false. Otherwise, the
name of the cipher suite in use is tested against the list. To test for
encryption without testing for any specific cipher suite(s), set
.display asis
encrypted = *
.endd

.item "hosts = << host list>>"
.index host||ACL checking
.index ~~ACL||testing the client host
This condition tests that the calling host matches the host list. If you have
name lookups or wildcarded host names and IP addresses in the same host list,
you should normally put the IP addresses first. For example, you could have:
.display asis
accept hosts = 10.9.8.7 : dbm;/etc/friendly/hosts
.endd
The reason for this lies in the left-to-right way that Exim processes lists.
It can test IP addresses without doing any DNS lookups, but when it reaches an
item that requires a host name, it fails if it cannot find a host name to
compare with the pattern. If the above list is given in the opposite order, the
\accept\ statement fails for a host whose name cannot be found, even if its
IP address is 10.9.8.7.

If you really do want to do the name check first, and still recognize the IP
address even if the name lookup fails, you can rewrite the ACL like this:
.display asis
accept hosts = dbm;/etc/friendly/hosts
accept hosts = 10.9.8.7
.endd
The default action on failing to find the host name is to assume that the host
is not in the list, so the first \accept\ statement fails. The second statement
can then check the IP address.

If a \hosts\ condition is satisfied by means of a lookup, the result
of the lookup is made available in the \$host@_data$\ variable. This
allows you, for example, to set up a statement like this:
.display asis
deny  hosts = net-lsearch;/some/file
      message = $host_data
.endd
which gives a custom error message for each denied host.

.item "local@_parts = <<local part list>>"
.index local part||ACL checking
.index ~~ACL||testing a local part
This condition is relevant only after a \\RCPT\\ command. It checks that the
local part of the recipient address is in the list. If percent-hack processing
is enabled, it is done before this test. If the check succeeds with a lookup,
the result of the lookup is placed in \$local@_part@_data$\ until the next
\local@_parts\ test.

.item "recipients = <<address list>>"
.index recipient||ACL checking
.index ~~ACL||testing a recipient
This condition is relevant only after a \\RCPT\\ command. It checks the entire
recipient address against a list of recipients.

.item "sender@_domains = <<domain list>>"
.index sender||ACL checking
.index ~~ACL||testing a sender domain
This condition tests the domain of the sender of the message against the given
domain list.
\**Note**\: the domain of the sender address is in
\$sender@_address@_domain$\. It is \*not*\ put in \$domain$\ during the testing 
of this condition. This is an exception to the general rule for testing 
domain lists. It is done this way so that, if this condition is used in an 
ACL for a \\RCPT\\ command, the recipient's domain (which is in \$domain$\) can
be used to influence the sender checking.

.item "senders = <<address list>>"
.index sender||ACL checking
.index ~~ACL||testing a sender
This condition tests the sender of the message against the given list. To test
for a bounce message, which has an empty sender, set
.display asis
senders = :
.endd

.item "verify = certificate"
.index TLS||client certificate verification
.index certificate||verification of client
.index ~~ACL||certificate verification
This condition is true in an SMTP session if the session is encrypted, and a
certificate was received from the client, and the certificate was verified. The
server requests a certificate only if the client matches \tls@_verify@_hosts\
or \tls@_try@_verify@_hosts\ (see chapter ~~CHAPTLS).

.item "verify = header@_sender/<<options>>"
.index ~~ACL||verifying sender in the header
.index header lines||verifying the sender in
.index sender||verifying in header
.index verifying||sender in header
This condition is relevant only in an ACL that is run after a message has been
received, that is, in an ACL specified by \acl@_smtp@_data\. It checks that
there is a verifiable sender address in at least one of the ::Sender::,
::Reply-To::, or ::From:: header lines. Details of address verification and the
options are given later, starting at section ~~SECTaddressverification. You can
combine this condition with the \senders\ condition to restrict it to bounce
messages only:
.display asis
deny    senders = :
        message = A valid sender header is required for bounces
       !verify  = header_sender
.endd

.item "verify = header@_syntax"
.index ~~ACL||verifying header syntax
.index header lines||verifying syntax
.index verifying||header syntax
This condition is relevant only in an ACL that is run after a message has been
received, that is, in an ACL specified by \acl@_smtp@_data\
or \acl@_not@_smtp\.
It checks the syntax of all header lines that can contain lists of addresses
(::Sender::, ::From::, ::Reply-To::, ::To::, ::Cc::, and ::Bcc::). 
Unqualified addresses (local parts without domains) are permitted only in
locally generated messages and from hosts that match
\sender@_unqualified@_hosts\ or \recipient@_unqualified@_hosts\, as
appropriate.

Note that this condition is a syntax check only. However, a common spamming
ploy is to send syntactically invalid headers such as
.display asis
To: @
.endd
and this condition can be used to reject such messages.

.item "verify = helo"
.index ~~ACL||verifying HELO/EHLO
.index \\HELO\\||verifying
.index \\EHLO\\||verifying
.index verifying||\\EHLO\\
.index verifying||\\HELO\\
This condition is true if a \\HELO\\ or \\EHLO\\ command has been received from
the client host, and its contents have been verified. Verification of these
commands does not happen by default. See the description of the
\helo@_verify@_hosts\ and \helo@_try@_verify@_hosts\ options for details of how
to request it.

.item "verify = recipient/<<options>>"
.index ~~ACL||verifying recipient
.index recipient||verifying
.index verifying||recipient
This condition is relevant only after a \\RCPT\\ command. It verifies the
current recipient. Details of address verification are given later, starting at
section ~~SECTaddressverification. After a recipient has been verified, the
value of \$address@_data$\ is the last value that was set while routing the
address. This applies even if the verification fails. When an address that is
being verified is redirected to a single address, verification continues with
the new address, and in that case, the subsequent value of \$address@_data$\ is
the value for the child address.


.item "verify = reverse@_host@_lookup"
.index ~~ACL||verifying host reverse lookup
.index host||verifying reverse lookup
This condition ensures that a verified host name has been looked up from the IP
address of the client host. (This may have happened already if the host name
was needed for checking a host list, or if the host matched \host@_lookup\.)
Verification ensures that the host name obtained from a reverse DNS lookup, or
one of its aliases, does, when it is itself looked up in the DNS, yield the
original IP address.

If this condition is used for a locally generated message (that is, when there 
is no client host involved), it always succeeds.


.item "verify = sender/<<options>>"
.index ~~ACL||verifying sender
.index sender||verifying
.index verifying||sender
This condition is relevant only after a 
\\MAIL\\ or \\RCPT\\ command, or after a message has been received (the 
\acl@_smtp@_data\ or \acl@_not@_smtp\ ACLs).
If the message's sender is empty (that is, this is a bounce message), the
condition is true. Otherwise, the sender address is verified. Details of
verification are given later, starting at section ~~SECTaddressverification.
Exim caches the result of sender verification, to avoid doing it more than once
per message.

.item "verify = sender=address/<<options>>"
This is a variation of the previous option, in which a modified address is
verified as a sender.

.enditems



.section Using DNS lists
.rset SECTmorednslists "~~chapter.~~section"
.index DNS list||in ACL
.index black list (DNS)
.index ~~ACL||testing a DNS list
In its simplest form, the \dnslists\ condition tests whether the calling host
is on a DNS list by looking up the inverted IP address in one or more DNS
domains. For example, if the calling host's IP address is 192.168.62.43, and
the ACL statement is
.display asis
deny dnslists = blackholes.mail-abuse.org : \
                dialups.mail-abuse.org
.endd
the following domains are looked up:
.display asis
43.62.168.192.blackholes.mail-abuse.org
43.62.168.192.dialups.mail-abuse.org                            
.endd
If a DNS lookup times out or otherwise fails to give a decisive answer, Exim
behaves as if the host is not on the relevant list. This is usually the
required action when \dnslists\ is used with \deny\ (which is the most common
usage), because it prevents a DNS failure from blocking mail. However, you can
change this behaviour by putting one of the following special items in the
list:
.index \"+include@_unknown"\
.index \"+exclude@_unknown"\
.index \"+defer@_unknown"\
.display
+include@_unknown    $rm{behave as if the item is on the list}
+exclude@_unknown    $rm{behave as if the item is not on the list (default)}
+defer@_unknown      $rm{give a temporary error}
.endd
Each of these applies to any subsequent items on the list. For example:
.display asis
deny dnslists = +defer_unknown : foo.bar.example
.endd

Testing the list of domains stops as soon as a match is found. If you want to
warn for one list and block for another, you can use two different statements:
.display asis
deny  dnslists = blackholes.mail-abuse.org
warn  message  = X-Warn: sending host is on dialups list
      dnslists = dialups.mail-abuse.org
.endd

DNS list lookups are cached by Exim for the duration of the SMTP session,
so a lookup based on the IP address is done at most once for any incoming
connection. Exim does not share information between multiple incoming
connections (but your local name server cache should be active).


.section DNS lists keyed on domain names
There are some lists that are keyed on domain names rather than inverted IP
addresses (see for example the \*domain based zones*\ link at
\?http://www.rfc-ignorant.org/?\). 
.em
No reversing of components is used with these lists.
.nem
You can change the name that is looked up in a DNS list by adding additional
data to a \dnslists\ item, introduced by a slash. For example,
.display asis
deny  message  = Sender's domain is listed at $dnslist_domain
      dnslists = dsn.rfc-ignorant.org/$sender_address_domain
.endd
This particular example is useful only in ACLs that are obeyed after the
\\RCPT\\ or \\DATA\\ commands, when a sender address is available. If (for
example) the message's sender is \*user@@tld.example*\ the name that is looked
up by this example is
.display asis
tld.example.dsn.rfc-ignorant.org
.endd
You can mix entries with and without additional data in the same \dnslists\
condition.

.section Data returned by DNS lists
DNS lists are constructed using address records in the DNS. The original RBL
just used the address 127.0.0.1 on the right hand side of each record, but the
RBL+ list and some other lists use a number of values with different meanings.
The values used on the RBL+ list are:
.display rm
.tabs 12
127.1.0.1 $t RBL
127.1.0.2 $t DUL
127.1.0.3 $t DUL and RBL
127.1.0.4 $t RSS
127.1.0.5 $t RSS and RBL
127.1.0.6 $t RSS and DUL
127.1.0.7 $t RSS and DUL and RBL
.endd
Some DNS lists may return more than one address record.

.section Variables set from DNS lists
When an entry is found in a DNS list, the variable \$dnslist@_domain$\
contains the name of the domain that matched, \$dnslist@_value$\ contains the
data from the entry, and \$dnslist@_text$\ contains the contents of any
associated TXT record. If more than one address record is returned by the DNS
lookup, all the IP addresses are included in \$dnslist@_value$\, separated by
commas and spaces.

You can use these variables in \message\ or \log@_message\ modifiers --
although these appear before the condition in the ACL, they are not expanded
until after it has failed. For example:
.display asis
deny    hosts = !+local_networks
        message = $sender_host_address is listed \
                  at $dnslist_domain
        dnslists = rbl-plus.mail-abuse.example
.endd


.section Additional matching conditions for DNS lists
If you add an equals sign and an IP address after a \dnslists\ domain name, you
can restrict its action to DNS records with a matching right hand side. For
example,
.display asis
deny dnslists = rblplus.mail-abuse.org=127.0.0.2
.endd
rejects only those hosts that yield 127.0.0.2. Without this additional data,
any address record is considered to be a match. If more than one address record
is found on the list, they are all checked for a matching right-hand side.

If you want to specify a constraining address and also change the name that is
looked up, the address list must be specified first. For example:
.display asis
deny dnslists = dsn.rfc-ignorant.org\
                =127.0.0.2/$sender_address_domain
.endd

More than one IP address may be given for checking, using a comma as a
separator. These are alternatives -- if any one of them matches, the \dnslists\
condition is true. For example:
.display asis
deny  dnslists = a.b.c=127.0.0.2,127.0.0.3
.endd

If the character `&' is used instead of `=', the comparison for each listed
IP address is done by a bitwise `and' instead of by an equality test. In
other words, the listed addresses are used as bit masks. The comparison is
true if all the bits in the mask are present in the address that is being
tested. For example:
.display asis
dnslists = a.b.c&0.0.0.3
.endd
matches if the address is \*x.x.x.*\3, \*x.x.x.*\7, \*x.x.x.*\11, etc. If you
want to test whether one bit or another bit is present (as opposed to both
being present), you must use multiple values. For example:
.display asis
dnslists = a.b.c&0.0.0.1,0.0.0.2
.endd
matches if the final component of the address is an odd number or two times
an odd number.


.section Negated DNS matching conditions
You can supply a negative list of IP addresses as part of a \dnslists\
condition. Whereas
.display asis
deny  dnslists = a.b.c=127.0.0.2,127.0.0.3
.endd
means `deny if the host is in the black list at the domain \*a.b.c*\ and the IP
address yielded by the list is either 127.0.0.2 or 127.0.0.3',
.display asis
deny  dnslists = a.b.c!=127.0.0.2,127.0.0.3
.endd
means `deny if the host is in the black list at the domain \*a.b.c*\ and the IP
address yielded by the list is not 127.0.0.2 and not 127.0.0.3'. In other
words, the result of the test is inverted if an exclamation mark appears before
the `=' (or the `&') sign.

\**Note**\: this kind of negation is not the same as negation in a domain,
host, or address list (which is why the syntax is different).

If you are using just one list, the negation syntax does not gain you much. The
previous example is precisely equivalent to
.display asis
deny  dnslists = a.b.c
     !dnslists = a.b.c=127.0.0.2,127.0.0.3
.endd
However, if you are using multiple lists, the negation syntax is clearer.
Consider this example:
.display asis
deny  dnslists = sbl.spamhaus.org : \
                 list.dsbl.org : \
                 dnsbl.njabl.org!=127.0.0.3 : \
                 relays.ordb.org
.endd
Using only positive lists, this would have to be:
.display asis
deny  dnslists = sbl.spamhaus.org : \
                 list.dsbl.org
deny  dnslists = dnsbl.njabl.org
     !dnslists = dnsbl.njabl.org=127.0.0.3
deny  dnslists = relays.ordb.org
.endd
which is less clear, and harder to maintain.



.section DNS lists and IPv6
.rset SECTmorednslistslast "~~chapter.~~section"
If Exim is asked to do a dnslist lookup for an IPv6 address, it inverts it 
nibble by nibble. For example, if the calling host's IP address is
3ffe:ffff:836f:0a00:000a:0800:200a:c031, Exim might look up
.display asis
1.3.0.c.a.0.0.2.0.0.8.0.a.0.0.0.0.0.a.0.f.6.3.8.
  f.f.f.f.e.f.f.3.blackholes.mail-abuse.org
.endd
(split over two lines here to fit on the page). Unfortunately, some of the DNS
lists contain wildcard records, intended for IPv4, that interact badly with
IPv6. For example, the DNS entry
.display asis
*.3.some.list.example.    A    127.0.0.1
.endd
is probably intended to put the entire 3.0.0.0/8 IPv4 network on the list. 
Unfortunately, it also matches the entire 3@:@:/124 IPv6 network.

You can exclude IPv6 addresses from DNS lookups by making use of a suitable 
\condition\ condition, as in this example:
.display asis
deny   condition = ${if isip4{$sender_host_address}{yes}{no}}
       dnslists  = some.list.example
.endd


.section Address verification
.rset SECTaddressverification "~~chapter.~~section"
.index verifying||address, options for
.index policy control||address verification
Several of the \verify\ conditions described in section ~~SECTaclconditions
cause addresses to be verified. These conditions can be followed by options
that modify the verification process. The options are separated from the
keyword and from each other by slashes, and some of them contain parameters.
For example:
.display asis
verify = sender/callout
verify = recipient/defer_ok/callout=10s,defer_ok
.endd
The first stage of verification is to run the address through the routers, in
`verify mode'. Routers can detect the difference between verification and
routing for delivery, and their actions can be varied by a number of generic
options such as \verify\ and \verify@_only\ (see chapter ~~CHAProutergeneric).

If there is a defer error while doing this verification routing, the ACL
normally returns `defer'. However, if you include \defer@_ok\ in the options,
the condition is forced to be true instead.

.section Callout verification
.rset SECTcallver "~~chapter.~~section"
.index verifying||address, by callout
.index callout||verification
.index SMTP||callout verification
For non-local addresses, routing verifies the domain, but is unable to do any
checking of the local part. There are situations where some means of verifying
the local part is desirable. One way this can be done is to make an SMTP
\*callback*\ to the sending host (for a sender address) or a \*callforward*\ to
a subsequent host (for a recipient address), to see if the host accepts the
address. We use the term \*callout*\ to cover both cases. This facility should
be used with care, because it can add a lot of resource usage to the cost of
verifying an address. However, Exim does cache the results of callouts, which
helps to reduce the cost. Details of caching are in the next section.

.em
Recipient callouts are usually used only between hosts that are controlled by 
the same administration. For example, a corporate gateway host could use 
callouts to check for valid recipients on an internal mailserver.
.nem
A successful callout does not guarantee that a real delivery to the address 
would succeed; on the other hand, a failing callout does guarantee that 
a delivery would fail.

If the \callout\ option is present on a condition that verifies an address, a
second stage of verification occurs if the address is successfully routed to
one or more remote hosts. The usual case is routing by a \%dnslookup%\ or a
\%manualroute%\ router, where the router specifies the hosts. However, if a 
router that does not set up hosts routes to an \%smtp%\ transport with a 
\hosts\ setting, the transport's hosts are used. If an \%smtp%\ transport has
\hosts@_override\ set, its hosts are always used, whether or not the router
supplies a host list.

The port that is used is taken from the transport, if it is specified and is a
remote transport. (For routers that do verification only, no transport need be
specified.) Otherwise, the default SMTP port is used. If a remote transport 
specifies an outgoing interface, this is used; otherwise the interface is not 
specified.

For a sender callout check, Exim makes SMTP connections to the remote hosts, to
test whether a bounce message could be delivered to the sender address. The
following SMTP commands are sent:
.display
HELO <<primary host name>>
MAIL FROM:@<@>
RCPT TO:<<the address to be tested>>
QUIT
.endd
\\LHLO\\ is used instead of \\HELO\\ if the transport's \protocol\ option is
set to `lmtp'. 

.em
A recipient callout check is similar. By default, it also uses an empty address 
for the sender. This default is chosen because most hosts do not make use of 
the sender address when verifying a recipient. Using the same address means 
that a single cache entry can be used for each recipient. Some sites, however, 
do make use of the sender address when verifying. These are catered for by the 
\use@_sender\ and \use@_postmaster\ options, described in the next section. 
.nem

If the response to the \\RCPT\\ command is a 2$it{xx} code, the verification
succeeds. If it is 5$it{xx}, the verification fails. For any other condition,
Exim tries the next host, if any. If there is a problem with all the remote
hosts, the ACL yields `defer', unless the \defer@_ok\ parameter of the
\callout\ option is given, in which case the condition is forced to succeed.


.section Additional parameters for callouts
.rset CALLaddparcall "~~chapter.~~section"
.index callout||timeout, specifying
The \callout\ option can be followed by an equals sign and a number of optional
parameters, separated by commas. For example:
.display asis
verify = recipient/callout=10s,defer_ok
.endd
The old syntax, which had \callout@_defer@_ok\ and \check@_postmaster\ as
separate verify options, is retained for backwards compatibility, but is now
deprecated. The additional parameters for \callout\ are as follows:

.numberpars $.
<<a time>>: This specifies the timeout that applies for the callout attempt to
each host. For example:
.display asis
verify = sender/callout=5s
.endd
The default is 30 seconds. The timeout is used for each response from the
remote host.
.nextp
.index callout||defer, action on
\defer@_ok\: Failure to contact any host, or any other kind of temporary error
is treated as success by the ACL. However, the cache is not updated in this
circumstance.
.nextp
.index callout||cache, suppressing
.index caching||callout, suppressing
\no@_cache\: The callout cache is neither read nor updated.
.nextp
.index callout||postmaster, checking
\postmaster\: A successful callout check is followed by a similar check for the
local part \*postmaster*\ at the same domain. If this address is rejected, the
callout fails. The result of the postmaster check is recorded in a cache
record; if it is a failure, this is used to fail subsequent callouts for the
domain without a connection being made, until the cache record expires.
.nextp
.index callout||`random' check
\random\: Before doing the normal callout check, Exim does a 
check for a `random' local part at the same domain. The local part is not
really random -- it is defined by the expansion of the option
\callout@_random@_local@_part\, which defaults to
.display asis
$primary_host_name-$tod_epoch-testing
.endd
The idea here is to try to determine whether the remote host accepts all local
parts without checking. If it does, there is no point in doing callouts for
specific local parts. If the `random' check succeeds, the result is saved in
a cache record, and used to force the current and subsequent callout checks to
succeed without a connection being made, until the cache record expires.
.nextp
.index callout||sender for recipient check
.em
\use@_postmaster\: This option applies to recipient callouts only. For example:
.display asis
deny  !verify = recipient/callout=use_postmaster
.endd
It causes a non-empty postmaster address to be used in the \\MAIL\\ command
when performing the callout. The local part of the address is \"postmaster"\
and the domain is the contents of \$qualify@_domain$\.
.nextp
\use@_sender\: This option applies to recipient callouts only. For example:
.display asis
require  verify = recipient/callout=use_sender
.endd
It causes the message's actual sender address to be used in the \\MAIL\\
command when performing the callout, instead of an empty address. The cache for 
such callouts is keyed by the sender/recipient combination; thus, for any given 
recipient, many more actual callouts are performed than when an empty sender or 
postmaster is used. This option should be set only when you know that the
called hosts make use of the sender when checking recipients.
.nem
.endp


.section Callout caching
.rset SECTcallvercache "~~chapter.~~section"
.index hints database||callout cache
.index callout||caching
.index caching||callout
Exim caches the results of callouts in order to reduce the amount of resources 
used, unless you specify the \no@_cache\ parameter with the \callout\ option.
A hints database called `callout' is used for the cache. Two different record 
types are used: one records the result of a callout check for a specific 
address, and the other records information that applies to the entire domain
(for example, that it accepts the local part \*postmaster*\).

When an original callout fails, a detailed SMTP error message is given about
the failure. However, for subsequent failures use the cache data, this message
is not available.

The expiry times for negative and positive address cache records are
independent, and can be set by the global options \callout@_negative@_expire\
(default 2h) and \callout@_positive@_expire\ (default 24h), respectively.

If a host gives a negative response to an SMTP connection, or rejects any
commands up to and including 
.display asis
MAIL FROM:<>
.endd
.em
(but not including the \\MAIL\\ command with a non-empty address),
.nem
any callout attempt is bound to fail. Exim remembers such failures in a
domain cache record, which it uses to fail callouts for the domain without
making new connections, until the domain record times out. There are two
separate expiry times for domain cache records:
\callout@_domain@_negative@_expire\ (default 3h) and
\callout__domain__positive@_expire\ (default 7d).

Domain records expire when the negative expiry time is reached if callouts
cannot be made for the domain, or if the postmaster check failed.
Otherwise, they expire when the positive expiry time is reached. This
ensures that, for example, a host that stops accepting `random' local parts
will eventually be noticed.

The callout caching mechanism is based entirely on the domain of the
address that is being tested. If the domain routes to several hosts, it is
assumed that their behaviour will be the same.


.section Sender address verification reporting
.index verifying||suppressing error details
When sender verification fails in an ACL, the details of the failure are
given as additional output lines before the 550 response to the relevant
SMTP command (\\RCPT\\ or \\DATA\\). For example, if sender callout is in use,
you might see:
.display asis
MAIL FROM:<xyz@abc.example>
250 OK
RCPT TO:<pqr@def.example>
550-Verification failed for <xyz@abc.example>
550-Called:   192.168.34.43
550-Sent:     RCPT TO:<xyz@abc.example>
550-Response: 550 Unknown local part xyz in <xyz@abc.example>
550 Sender verification failed
.endd
If more than one \\RCPT\\ command fails in the same way, the details are given
only for the first of them. However, some administrators do not want to send
out this much information. You can suppress the details by adding
`/no@_details' to the ACL statement that requests sender verification. For
example:
.display asis
verify = sender/no_details
.endd


.section Redirection while verifying
.index verifying||redirection while
.index address redirection||while verifying
A dilemma arises when a local address is redirected by aliasing or forwarding
during verification: should the generated addresses themselves be verified,
or should the successful expansion of the original address be enough to verify
it? Exim takes the following pragmatic approach:
.numberpars $.
When an incoming address is redirected to just one child address, verification
continues with the child address, and if that fails to verify, the original
verification also fails.
.nextp
When an incoming address is redirected to more than one child address,
verification does not continue. A success result is returned.
.endp
This seems the most reasonable behaviour for the common use of aliasing as a
way of redirecting different local parts to the same mailbox. It means, for
example, that a pair of alias entries of the form
.display asis
A.Wol:   aw123
aw123:   :fail: Gone away, no forwarding address
.endd
work as expected, with both local parts causing verification failure. When a
redirection generates more than one address, the behaviour is more like a
mailing list, where the existence of the alias itself is sufficient for
verification to succeed.


.section Using an ACL to control relaying
.rset SECTrelaycontrol "~~chapter.~~section"
.index ~~ACL||relay control
.index relaying||control by ACL
.index policy control||relay control
An MTA is said to \*relay*\ a message if it receives it from some host and
delivers it directly to another host as a result of a remote address contained
within it. Redirecting a local address via an alias or forward file and then
passing the message on to another host is not relaying,
.index `percent hack'
but a redirection as a result of the `percent hack' is.

Two kinds of relaying exist, which are termed `incoming' and `outgoing'. A host
which is acting as a gateway or an MX backup is concerned with incoming
relaying from arbitrary hosts to a specific set of domains. On the other hand,
a host which is acting as a smart host for a number of clients is concerned
with outgoing relaying from those clients to the Internet at large. Often the
same host is fulfilling both functions, as illustrated in the diagram below,
but in principle these two kinds of relaying are entirely independent. What is
not wanted is the transmission of mail from arbitrary remote hosts through your
system to arbitrary domains.
.if ~~sys.fancy
.figure "Controlled relaying" rm
.indent 0
.call aspic
centre ~~sys.linelength;
magnify 0.8;
boundingbox 30;
textdepth 16;
    boxwidth 120;
    boxdepth 44;
A:  box "Arbitrary" "remote hosts";
C:  ibox;
D:  box "Arbitrary" "domains";
    iline down 50 from bottom of C;
H:  box width 180 "Local host";
    iline down 50;
E:  ibox;
SH: box "Specific" "hosts";
SD: box join right to E "Specific" "domains";
    arcarrow clockwise from top of SH to bottom of D plus (-10,-4)
      via right of H plus (-20,0);
    arcarrow clockwise from bottom of A to top of SD plus (10,4)
      via left of H plus (20,0);

    ibox join left to right of H "$it{Outgoing}";
    goto H;
    ibox join right to left of H "$it{Incoming}";

L:  line dashed from right of A to top of H plus (-15,0);
    arc dashed to top of H plus (15,0);
    arrow dashed to left of D plus (-2,0);

    arrow dashed back up 72 right 32 from middle of L plus (8,0);
    text at end plus (0, 4) "$it{Not wanted}";
.endcall
.endfigure
.elif !~~html
.display asis
   --------------    -----------
   | Arbitrary  |    |Arbitrary|
   |remote hosts|    | domains |
   --------------    -----------
 I       v                ^       O
 n       v                ^       u
 c    ---v----------------^---    t
 o    |  v     Local      ^  |    g
 m    |  v      host      ^  |    o
 i    ---v----------------^---    i
 n       v                ^       n
 g       v                ^       g
      Specific         Specific
      domains           hosts
.endd
.else
[(IMG SRC="relaying.gif" alt="Controlled relaying")][(br)]
.fi

You can implement relay control by means of suitable statements in the ACL that
runs for each \\RCPT\\ command. For convenience, it is often easiest to use
Exim's named list facility to define the domains and hosts involved. For
example, suppose you want to do the following:
.numberpars $.
Deliver a number of domains to mailboxes on the local host (or process them
locally in some other way). Let's say these are \*my.dom1.example*\ and
\*my.dom2.example*\.
.nextp
Relay mail for a number of other domains for which you are the secondary MX.
These might be \*friend1.example*\ and \*friend2.example*\.
.nextp
Relay mail from the hosts on your local LAN, to whatever domains are involved.
Suppose your LAN is 192.168.45.0/24.
.endp
In the main part of the configuration, you put the following definitions:
.display asis
domainlist local_domains = my.dom1.example : my.dom2.example
domainlist relay_domains = friend1.example : friend2.example
hostlist   relay_hosts   = 192.168.45.0/24
.endd
Now you can use these definitions in the ACL that is run for every \\RCPT\\
command:
.display asis
acl_check_rcpt:
  accept domains = +local_domains : +relay_domains
  accept hosts   = +relay_hosts
.endd
The first statement accepts any \\RCPT\\ command that contains an address in
the local or relay domains. For any other domain, control passes to the second
statement, which accepts the command only if it comes from one of the relay
hosts. In practice, you will probably want to make your ACL more sophisticated
than this, for example, by including sender and recipient verification. The
default configuration includes a more comprehensive example, which is described
in chapter ~~CHAPdefconfil.


.section Checking a relay configuration
.rset SECTcheralcon "~~chapter.~~section"
.index relaying||checking control of
You can check the relay characteristics of your configuration in the same way 
that you can test any ACL behaviour for an incoming SMTP connection, by using 
the \-bh-\ option to run a fake SMTP session with which you interact.

For specifically testing for unwanted relaying, the host
\*relay-test.mail-abuse.org*\ provides a useful service. If you telnet to this 
host from the host on which Exim is running, using the normal telnet port, you 
will see a normal telnet connection message and then quite a long delay. Be 
patient. The remote host is making an SMTP connection back to your host, and 
trying a number of common probes to test for open relay vulnerability. The 
results of the tests will eventually appear on your terminal.




.
.
.
.
. ============================================================================
.chapter Adding a local scan function to Exim
.set runningfoot "local scan function"
.rset CHAPlocalscan "~~chapter"
.index \*local@_scan()*\ function||description of
.index customizing||input scan using C function
.index policy control||by local scan function

In these days of email worms, viruses, and ever-increasing spam, some sites
want to apply a lot of checking to messages before accepting them. You can do a
certain amount through string expansions and the \condition\ condition in the
ACL that runs after the SMTP \\DATA\\ command or the ACL for non-SMTP messages
(see chapter ~~CHAPACL), but this has its limitations. 

.index \exiscan\
An increasingly popular way of doing additional checking is to make use of the 
Exiscan patch for Exim, which adds ACL conditions that perform body scans of 
various kinds. This is available from
.if ~~html
[(A HREF="http://duncanthrax.net/exiscan-acl/")]
/?http://duncanthrax.net/exiscan-acl/?\.
[(/A)]
.else
\?http:@/@/duncanthrax.net/exiscan-acl/?\.
.fi

To allow for even more general checking that can be customized to a site's own
requirements, there is the possibility of linking Exim with a private message
scanning function, written in C. If you want to run code that is written in
something other than C, you can of course use a little C stub to call it.

The local scan function is run once for every incoming message, at the point 
when Exim is just about to accept the message.
It can therefore be used to control non-SMTP messages from local processes as
well as messages arriving via SMTP.

Exim applies a timeout to calls of the local scan function, and there is an
option called \local@_scan@_timeout\ for setting it. The default is 5 minutes.
Zero means `no timeout'. 
Exim also sets up signal handlers for SIGSEGV, SIGILL, SIGFPE, and SIGBUS
before calling the local scan function, so that the most common types of crash
are caught. If the timeout is exceeded or one of those signals is caught, the
incoming message is rejected with a temporary error if it is an SMTP message.
For a non-SMTP message, the message is dropped and Exim ends with a non-zero
code. The incident is logged on the main and reject logs.


.section Building Exim to use a local scan function
.index \*local@_scan()*\ function||building Exim to use
To make use of the local scan function feature, you must tell Exim where your
function is before building Exim, by setting \\LOCAL@_SCAN@_SOURCE\\ in your
\(Local/Makefile)\. A recommended place to put it is in the \(Local)\
directory, so you might set
.display asis
LOCAL_SCAN_SOURCE=Local/local_scan.c
.endd
for example. The function must be called \*local@_scan()*\. It is called by
Exim after it has received a message, when the success return code is about to
be sent. This is after all the ACLs have been run. The return code from your
function controls whether the message is actually accepted or not. There is a
commented template function (that just accepts the message) in the file
\(src/local@_scan.c)\.

If you want to make use of Exim's run time configuration file to set options 
for your \*local@_scan()*\ function, you must also set
.display asis
LOCAL_SCAN_HAS_OPTIONS=yes
.endd
in \(Local/Makefile)\ (see section ~~SECTconoptloc below).



.section API for local@_scan()
.rset SECTapiforloc "~~chapter.~~section"
.index \*local@_scan()*\ function||API description
You must include this line near the start of your code:
.display asis
#include "local_scan.h"
.endd
This header file defines a number of variables and other values, and the
prototype for the function itself. Exim is coded to use unsigned char values
almost exclusively, and one of the things this header defines is a shorthand
for \"unsigned char"\ called \"uschar"\. 
It also contains the following macro definitions, to simplify casting character 
strings and pointers to character strings:
.display asis
#define CS   (char *)
#define CCS  (const char *)
#define CSS  (char **)
#define US   (unsigned char *)
#define CUS  (const unsigned char *)
#define USS  (unsigned char **)
.endd

The function prototype for \*local@_scan()*\ is:
.display asis
extern int local_scan(int fd, uschar **return_text);
.endd
The arguments are as follows:
.numberpars $.
\fd\ is a file descriptor for the file that contains the body of the message
(the -D file). 
The file is open for reading and writing, but updating it is not recommended.
\**Warning**\: You must \*not*\ close this file descriptor.

The descriptor is positioned at character 19 of the file, which is the first
character of the body itself, because the first 19 characters are the message
id followed by \"-D"\ and a newline. If you rewind the file, you should use the
macro \\SPOOL@_DATA@_START@_OFFSET\\ to reset to the start of the data, just in
case this changes in some future version.

.nextp
\return@_text\ is an address which you can use to return a pointer to a text
string at the end of the function. The value it points to on entry is NULL.
.endp
The function must return an \int\ value which is one of the following macros:
.numberpars $.
\"LOCAL@_SCAN@_ACCEPT"\

The message is accepted. If you pass back a string of text, it is saved with
the message, and made available in the variable \$local@_scan@_data$\. No
newlines are permitted (if there are any, they are turned into spaces) and the
maximum length of text is 1000 characters.
.nextp
\"LOCAL@_SCAN@_ACCEPT@_FREEZE"\

This behaves as \\LOCAL@_SCAN@_ACCEPT\\, except that the accepted message is 
queued without immediate delivery, and is frozen.
.nextp
\"LOCAL@_SCAN@_ACCEPT@_QUEUE"\

This behaves as \\LOCAL@_SCAN@_ACCEPT\\, except that the accepted message is 
queued without immediate delivery.
.nextp
\"LOCAL@_SCAN@_REJECT"\

The message is rejected; the returned text is used as an error message which is
passed back to the sender and which is also logged. Newlines are permitted --
they cause a multiline response for SMTP rejections, but are converted to
\"@\n"\ in log lines.
If no message is given, `Administrative prohibition' is used.
.nextp
\"LOCAL@_SCAN@_TEMPREJECT"\

The message is temporarily rejected; the returned text is used as an error
message as for \\LOCAL@_SCAN@_REJECT\\. If no message is given, `Temporary
local problem' is used.
.nextp
\"LOCAL@_SCAN@_REJECT@_NOLOGHDR"\

This behaves as \\LOCAL@_SCAN@_REJECT\\, except that the header of the rejected
message is not written to the reject log. It has the effect of unsetting the
\rejected@_header\ log selector for just this rejection. If \rejected@_header\
is already unset (see the discussion of the \log@_selection\ option in section
~~SECTlogselector), this code is the same as \\LOCAL@_SCAN@_REJECT\\.

.nextp
\"LOCAL@_SCAN@_TEMPREJECT@_NOLOGHDR"\

This code is a variation of \\LOCAL@_SCAN@_TEMPREJECT\\ in the same way that
\\LOCAL__SCAN__REJECT__NOLOGHDR\\ is a variation of \\LOCAL@_SCAN@_REJECT\\.
.endp

If the message is not being received by interactive SMTP, rejections are
reported by writing to \stderr\ or by sending an email, as configured by the
\-oe-\ command line options.


.section Configuration options for local@_scan()
.rset SECTconoptloc "~~chapter.~~section"
.index \*local@_scan()*\ function||configuration options
It is possible to have option settings in the main configuration file
that set values in static variables in the \*local@_scan()*\ module. If you
want to do this, you must have the line
.display asis
LOCAL_SCAN_HAS_OPTIONS=yes
.endd
in your \(Local/Makefile)\ when you build Exim. (This line is in
\(OS/Makefile-Default)\, commented out). Then, in the \*local@_scan()*\ source
file, you must define static variables to hold the option values, and a table to
define them. 

The table must be a vector called \local@_scan@_options\, of type
\"optionlist"\. Each entry is a triplet, consisting of a name, an option type,
and a pointer to the variable that holds the value. The entries must appear in
alphabetical order. Following \local@_scan@_options\ you must also define a
variable called \local@_scan@_options@_count\ that contains the number of
entries in the table. Here is a short example, showing two kinds of option:
.display asis
static int my_integer_option = 42;
static uschar *my_string_option = US"a default string";

optionlist local_scan_options[] = {
  { "my_integer", opt_int,       &my_integer_option },
  { "my_string",  opt_stringptr, &my_string_option }
};
int local_scan_options_count =
  sizeof(local_scan_options)/sizeof(optionlist);
.endd
The values of the variables can now be changed from Exim's runtime
configuration file by including a local scan section as in this example:
.display asis
begin local_scan
my_integer = 99
my_string = some string of text...
.endd
The available types of option data are as follows:

.startitems

.item opt@_bool
This specifies a boolean (true/false) option. The address should point to
a variable of type \"BOOL"\, which will be set to \\TRUE\\ or \\FALSE\\, which 
are macros that are defined as `1' and `0', respectively. If you want to detect
whether such a variable has been set at all, you can initialize it to
\\TRUE@_UNSET\\. (BOOL variables are integers underneath, so can hold more than
two values.)

.item "opt@_fixed"
This specifies a fixed point number, such as is used for load averages.
The address should point to a variable of type \"int"\. The value is stored
multiplied by 1000, so, for example, 1.4142 is truncated and stored as 1414.

.item "opt@_int"
This specifies an integer; the address should point to a variable of type 
\"int"\. The value may be specified in any of the integer formats accepted by
Exim.

.item "opt@_mkint"
This is the same as \opt@_int\, except that when such a value is output in a
\-bP-\ listing, if it is an exact number of kilobytes or megabytes, it is
printed with the suffix K or M.

.item "opt@_octint"
This also specifies an integer, but the value is always interpeted as an
octal integer, whether or not it starts with the digit zero, and it is
always output in octal.

.item "opt@_stringptr"
This specifies a string value; the address must be a pointer to a
variable that points to a string (for example, of type \"uschar $*$"\).

.item "opt@_time"
This specifies a time interval value. The address must point to a variable of
type \"int"\. The value that is placed there is a number of seconds.

.enditems

If the \-bP-\ command line option is followed by \"local@_scan"\, Exim prints
out the values of all the \*local@_scan()*\ options.


.section Available Exim variables
.index \*local@_scan()*\ function||available Exim variables
The header \(local@_scan.h)\ gives you access to a number of C variables.
These are the only ones that are guaranteed to be maintained from release to
release. Note, however, that you can obtain the value of any Exim variable by
calling \*expand@_string()*\. The exported variables are as follows:

.startitems

.item "unsigned int debug@_selector"
This variable is set to zero when no debugging is taking place. Otherwise, it
is a bitmap of debugging selectors. Two bits are identified for use in
\*local@_scan()*\; they are defined as macros:
.numberpars $.
The \"D@_v"\ bit is set when \-v-\ was present on the command line. This is a
testing option that is not privileged -- any caller may set it. All the
other selector bits can be set only by admin users.
.nextp
The \"D@_local@_scan"\ bit is provided for use by \*local@_scan()*\; it is set
by the \"+local@_scan"\ debug selector. It is not included in the default set
of debugging bits.
.endp
Thus, to write to the debugging output only when \"+local@_scan"\ has been
selected, you should use code like this:
.display asis
if ((debug_selector & D_local_scan) != 0) 
  debug_printf("xxx", ...);
.endd

.item "uschar *expand@_string@_message"
After a failing call to \*expand@_string()*\ (returned value NULL), the
variable \expand__string__message\ contains the error message, zero-terminated.

.item "header@_line *header@_list"
A pointer to a chain of header lines. The \header@_line\ structure is discussed
below.

.item "header@_line *header@_last"
A pointer to the last of the header lines.

.item "uschar *headers@_charset"
The value of the \headers@_charset\ configuration option.

.item "BOOL host@_checking"
This variable is TRUE during a host checking session that is initiated by the 
\-bh-\ command line option.

.item "uschar *interface@_address"
The IP address of the interface that received the message, as a string. This
is NULL for locally submitted messages.

.item "int interface@_port"
The port on which this message was received.

.item "uschar *message@_id"
This variable contains the message id for the incoming message as a 
zero-terminated string.


.item "uschar *received@_protocol"
The name of the protocol by which the message was received.

.item "int recipients@_count"
The number of accepted recipients.

.item "recipient@_item *recipients@_list"
.index recipient||adding in local scan
.index recipient||removing in local scan
The list of accepted recipients, held in a vector of length
\recipients@_count\. The \recipient@_item\ structure is discussed below. You
can add additional recipients by calling \*receive@_add@_recipient()*\ (see
below). You can delete recipients by removing them from the vector and adusting
the value in \recipients@_count\. In particular, by setting \recipients@_count\
to zero you remove all recipients. If you then return the value
\"LOCAL@_SCAN@_ACCEPT"\, the message is accepted, but immediately blackholed.
To replace the recipients, set \recipients@_count\ to zero and then call 
\*receive@_add@_recipient()*\ as often as needed.

.item "uschar *sender@_address"
The envelope sender address. For bounce messages this is the empty string.

.item "uschar *sender@_host@_address"
The IP address of the sending host, as a string. This is NULL for
locally-submitted messages.

.item "uschar *sender@_host@_authenticated"
The name of the authentication mechanism that was used, or NULL if the message
was not received over an authenticated SMTP connection.

.item "uschar *sender@_host@_name"
The name of the sending host, if known.

.item "int sender@_host@_port"
The port on the sending host.

.item "BOOL smtp@_input"
This variable is TRUE for all SMTP input, including BSMTP.

.item "BOOL smtp@_batched@_input"
This variable is TRUE for BSMTP input.

.item "int store@_pool"
The contents of this variable control which pool of memory is used for new 
requests. See section ~~SECTmemhanloc for details.

.enditems


.section Structure of header lines
The \header@_line\ structure contains the members listed below.
You can add additional header lines by calling the \*header@_add()*\ function
(see below). You can cause header lines to be ignored (deleted) by setting
their type to $*$.

.startitems

.item "struct header@_line *next"
A pointer to the next header line, or NULL for the last line.

.item "int type"
A code identifying certain headers that Exim recognizes. The codes are printing
characters, and are documented in chapter ~~CHAPspool of this manual. Notice in
particular that any header line whose type is $*$ is not transmitted with the
message. This flagging is used for header lines that have been rewritten, or
are to be removed (for example, ::Envelope-sender:: header lines.) Effectively,
$*$ means `deleted'.

.item "int slen"
The number of characters in the header line, including the terminating and any
internal newlines.

.item "uschar *text"
A pointer to the text of the header. It always ends with a newline, followed by
a zero byte. Internal newlines are preserved.

.enditems



.section Structure of recipient items
The \recipient@_item\ structure contains these members:

.startitems

.item "uschar *address"
This is a pointer to the recipient address as it was received.

.item "int pno"
This is used in later Exim processing when top level addresses are created
by the \one@_time\ option. It is not relevant at the time \*local@_scan()*\ is
run and 
must always contain -1 at this stage.

.item "uschar *errors@_to"
If this value is not NULL, bounce messages caused by failing to deliver to the 
recipient are sent to the address it contains. In other words, it overrides the
envelope sender for this one recipient. (Compare the \errors@_to\ generic
router option.) 
If a \*local@_scan()*\ function sets an \errors@_to\ field to an unqualified
address, Exim qualifies it using the domain from \qualify@_recipient\.
When \*local@_scan()*\ is called, the \errors@_to\ field is NULL for all
recipients.
.enditems


.section Available Exim functions
.index \*local@_scan()*\ function||available Exim functions
The header \(local@_scan.h)\ gives you access to a number of Exim functions.
These are the only ones that are guaranteed to be maintained from release to
release:

.startitems

.item "pid@_t child@_open(uschar **argv, uschar **envp, int newumask, int *infdptr, int *outfdptr, BOOL make@_leader)"
This function creates a child process that runs the command specified by
\argv\. The environment for the process is specified by \envp\, which can be 
NULL if no environment variables are to be passed. A new umask is supplied for
the process in \newumask\.

Pipes to the standard input and output of the new process are set up
and returned to the caller via the \infdptr\ and \outfdptr\ arguments. The
standard error is cloned to the standard output. If there are any file
descriptors `in the way' in the new process, they are closed. If the final 
argument is TRUE, the new process is made into a process group leader.

The function returns the pid of the new process, or -1 if things go wrong.


.item "int child@_close(pid@_t pid, int timeout)"
This function waits for a child process to terminate, or for a timeout (in
seconds) to expire. A timeout value of zero means wait as long as it takes. The
return value is as follows:
.numberpars $.
>= 0

The process terminated by a normal exit and the value is the process ending
status.
.nextp
< 0 and > --256

The process was terminated by a signal and the value is the negation of the
signal number.
.nextp
--256

The process timed out.
.nextp
--257

The was some other error in wait(); \errno\ is still set.
.endp


.item "pid@_t child@_open@_exim(int *fd)"
This function provide you with a means of submitting a new message to
Exim. (Of course, you can also call \(/usr/sbin/sendmail)\ yourself if you
want, but this packages it all up for you.) The function creates a pipe,
forks a subprocess that is running
.display asis
exim -t -oem -oi -f <>
.endd
and returns to you (via the \"int *"\ argument) a file descriptor for the pipe
that is connected to the standard input. The yield of the function is the PID
of the subprocess. You can then write a message to the file descriptor, with
recipients in ::To::, ::Cc::, and/or ::Bcc:: header lines. 

When you have finished, call \*child@_close()*\ to wait for the process to
finish and to collect its ending status. A timeout value of zero is usually
fine in this circumstance. Unless you have made a mistake with the recipient
addresses, you should get a return code of zero.

.item "void debug@_printf(char *, ...)"
This is Exim's debugging function, with arguments as for \*(printf()*\. The 
output is written to the standard error stream. If no debugging is selected,
calls to \*debug@_printf()*\ have no effect. Normally, you should make calls 
conditional on the \"local@_scan"\ debug selector by coding like this:
.display asis
if ((debug_selector & D_local_scan) != 0) 
  debug_printf("xxx", ...);
.endd

.item "uschar *expand@_string(uschar *string)"
This is an interface to Exim's string expansion code. The return value is the
expanded string, or NULL if there was an expansion failure.
The C variable \expand@_string@_message\ contains an error message after an 
expansion failure. If expansion does not change the string, the return value is 
the pointer to the input string. Otherwise, the return value points to a new
block of memory that was obtained by a call to \*store@_get()*\. See section
~~SECTmemhanloc below for a discussion of memory handling.

.item "void header@_add(int type, char *format, ...)"
This function allows you to add additional header lines. The first argument is
the type, and should normally be a space character. The second argument is a
format string and any number of substitution arguments as for \*sprintf()*\.
You may include internal newlines if you want, and you must ensure that the
string ends with a newline.

.item "uschar *lss@_b64encode(uschar *cleartext, int length)"
.index base64 encoding||functions for \*local@_scan()*\ use
This function base64-encodes a string, which is passed by address and length.
The text may contain bytes of any value, including zero. The result is passed
back in dynamic memory that is obtained by calling \*store@_get()*\. It is
zero-terminated.

.item "int lss@_b64decode(uschar *codetext, uschar **cleartext)"
This function decodes a base64-encoded string. Its arguments are a
zero-terminated base64-encoded string and the address of a variable that is set
to point to the result, which is in dynamic memory. The length of the
decoded string is the yield of the function. If the input is invalid base64
data, the yield is -1. A zero byte is added to the end of the output string to
make it easy to interpret as a C string (assuming it contains no zeros of its
own). The added zero byte is not included in the returned count.

.item "int lss@_match@_domain(uschar *domain, uschar *list)"
This function checks for a match in a domain list. Domains are always
matched caselessly. The return value is one of the following:
.display
OK     $rm{match succeeded}
FAIL   $rm{match failed}
DEFER  $rm{match deferred}
.endd
DEFER is usually caused by some kind of lookup defer, such as the
inability to contact a database.

.item "int lss@_match@_local@_part(uschar *localpart, uschar *list, BOOL caseless)"
This function checks for a match in a local part list. The third argument
controls case-sensitivity. The return values are as for 
\*lss@_match@_domain()*\.

.item "int lss@_match@_address(uschar *address, uschar *list, BOOL caseless)"
This function checks for a match in an address list. The third argument
controls the case-sensitivity of the local part match. The domain is always
matched caselessly. The return values are as for \*lss@_match@_domain()*\.

.item "int lss@_match@_host(uschar *host@_name, uschar *host@_address, uschar *list)"
This function checks for a match in a host list. The most common usage is
expected to be
.display asis
lss_match_host(sender_host_name, sender_host_address, ...)
.endd
An empty address field matches an empty item in the host list. If the
host name is NULL, the name corresponding to \$sender@_host@_address$\ is
automatically looked up if a host name is required to match an item in the
list. The return values are as for \*lss@_match@_domain()*\, but in addition,
\*lss@_match@_host()*\ returns ERROR in the case when it had to look up a host
name, but the lookup failed.

.item "void log@_write(unsigned int selector, int which, char *format, ...)"
This function writes to Exim's log files. The first argument should be zero (it
is concerned with \log@_selector\). The second argument can be \"LOG@_MAIN"\ or
\"LOG@_REJECT"\ or 
\"LOG@_PANIC"\ or the inclusive `or' of any combination of them. It specifies
to which log or logs the message is written.
The remaining arguments are a format and relevant insertion arguments. The
string should not contain any newlines, not even at the end.


.item "void receive@_add@_recipient(uschar *address, int pno)"
This function adds an additional recipient to the message. The first argument
is the recipient address. If it is unqualified (has no domain), it is qualified
with the \qualify@_recipient\ domain. The second argument must always be -1.

This function does not allow you to specify a private \errors@_to\ address (as 
described with the structure of \recipient@_item\ above), because it pre-dates 
the addition of that field to the structure. However, it is easy to add such a 
value afterwards. For example:
.display asis
receive_add_recipient(US"monitor@mydom.example", -1);
recipients_list[recipients_count-1].errors_to = 
  US"postmaster@mydom.example";
.endd

.item "uschar *rfc2047@_decode(uschar *string, BOOL lencheck, uschar *target, int zeroval, int *lenptr, uschar **error)"
This function decodes strings that are encoded according to RFC 2047. Typically
these are the contents of header lines. First, each encoded `word' is decoded
from the Q or B encoding into a byte-string. Then, if provided with the name of
a charset encoding, and if the \*iconv()*\ function is available, an attempt is
made  to translate the result to the named character set. If this fails, the
binary string is returned with an error message.

The first argument is the string to be decoded. If \lencheck\ is TRUE, the 
maximum MIME word length is enforced. The third argument is the target 
encoding, or NULL if no translation is wanted.
                
.index binary zero||in RFC 2047 decoding
If a binary zero is encountered in the decoded string, it is replaced by the
contents of the \zeroval\ argument. For use with Exim headers, the value must
not be 0 because header lines are handled as zero-terminated strings.

The function returns the result of processing the string, zero-terminated; if
\lenptr\ is not NULL, the length of the result is set in the variable to which
it points. When \zeroval\ is 0, \lenptr\ should not be NULL.

If an error is encountered, the function returns NULL and uses the \error\ 
argument to return an error message. The variable pointed to by \error\ is set 
to NULL if there is no error; it may be set non-NULL even when the function 
returns a non-NULL value if decoding was successful, but there was a problem 
with translation.


.item "int smtp@_fflush(void)"
This function is used in conjunction with \*smtp@_printf()*\, as described 
below.

.item "void smtp@_printf(char *, ...)"
The arguments of this function are like \*printf()*\; it writes to the SMTP
output stream. You should use this function only when there is an SMTP output
stream, that is, when the incoming message is being received via interactive
SMTP. This is the case when \smtp@_input\ is TRUE and \smtp@_batched@_input\ is
FALSE. If you want to test for an incoming message from another host (as
opposed to a local process that used the \-bs-\ command line option), you can
test the value of \sender@_host@_address\, which is non-NULL when a remote host
is involved.

If an SMTP TLS connection is established, \*smtp@_printf()*\ uses the TLS
output function, so it can be used for all forms of SMTP connection.

Strings that are written by \*smtp@_printf()*\ from within \*local@_scan()*\
must start with an appropriate response code: 550 if you are going to return
\\LOCAL@_SCAN@_REJECT\\, 451 if you are going to return
\\LOCAL@_SCAN@_TEMPREJECT\\, and 250 otherwise. Because you are writing the
initial lines of a multi-line response, the code must be followed by a hyphen
to indicate that the line is not the final response line. You must also ensure
that the lines you write terminate with CRLF. For example:
.display asis
smtp_printf("550-this is some extra info\r\n");
return LOCAL_SCAN_REJECT;
.endd
Note that you can also create multi-line responses by including newlines in
the data returned via the \return@_text\ argument. The added value of using
\*smtp@_printf()*\ is that, for instance, you could introduce delays between
multiple output lines.

The \*smtp@_printf()*\ function does not return any error indication, because it
does not automatically flush pending output, and therefore does not test
the state of the stream. (In the main code of Exim, flushing and error
detection is done when Exim is ready for the next SMTP input command.) If
you want to flush the output and check for an error (for example, the
dropping of a TCP/IP connection), you can call \*smtp@_fflush()*\, which has no
arguments. It flushes the output stream, and returns a non-zero value if there
is an error.

.item "void *store@_get(int)"
This function accesses Exim's internal store (memory) manager. It gets a new
chunk of memory whose size is given by the argument. Exim bombs out if it ever
runs out of memory. See the next section for a discussion of memory handling.

.item "void *store@_get@_perm(int)"
This function is like \*store@_get()*\, but it always gets memory from the 
permanent pool. See the next section for a discussion of memory handling.

.item "uschar *string@_copy(uschar *string)"
.item "uschar *string@_copyn(uschar *string, int length)" 0
.item "uschar *string@_sprintf(char *format, ...)" 0
These three functions create strings using Exim's dynamic memory facilities.
The first makes a copy of an entire string. The second copies up to a maximum
number of characters, indicated by the second argument. The third uses a format
and insertion arguments to create a new string. In each case, the result is a
pointer to a new string
in the current memory pool. See the next section for more discussion.

.enditems



.section More about Exim's memory handling
.rset SECTmemhanloc "~~chapter.~~section"
.index \*local@_scan()*\ function||memory handling
No function is provided for freeing memory, because that is never needed. 
The dynamic memory that Exim uses when receiving a message is automatically
recycled if another message is received by the same process (this applies only 
to incoming SMTP connections -- other input methods can supply only one message 
at a time). After receiving the last message, a reception process terminates.

Because it is recycled, the normal dynamic memory cannot be used for holding
data that must be preserved over a number of incoming messages on the same SMTP
connection. However, Exim in fact uses two pools of dynamic memory; the second
one is not recycled, and can be used for this purpose.

If you want to allocate memory that remains available for subsequent messages 
in the same SMTP connection, you should set
.display asis
store_pool = POOL_PERM
.endd
before calling the function that does the allocation. There is no need to 
restore the value if you do not need to; however, if you do want to revert to 
the normal pool, you can either restore the previous value of \store@_pool\ or
set it explicitly to \\POOL@_MAIN\\.

The pool setting applies to all functions that get dynamic memory, including
\*expand@_string()*\, \*store@_get()*\, and the \*string@_xxx()*\ functions.
There is also a convenience function called \*store@_get@_perm()*\ that gets a
block of memory from the permanent pool while preserving the value of
\store@_pool\.





.
.
.
.
. ============================================================================
.chapter System-wide message filtering
.set runningfoot "system filtering"
.rset CHAPsystemfilter "~~chapter"
.index filter||system filter
.index filtering all mail
.index system filter
The previous chapters (on ACLs and the local scan function) describe checks
that can be applied to messages before they are accepted by a host. There is
also a mechanism for checking messages once they have been received, but before
they are delivered. This is called the $it{system filter}.

The system filter operates in a similar manner to users' filter files, but it
is run just once per message (however many recipients the message has). 
It should not normally be used as a substitute for routing, because \deliver\ 
commands in a system router provide new envelope recipient addresses.
The system filter must be an Exim filter. It cannot be a Sieve filter.

The system filter is run at the start of a delivery attempt, before any routing
is done. If a message fails to be completely delivered at the first attempt,
the system filter is run again at the start of every retry.
If you want your filter to do something only once per message, you can make use
of the \first@_delivery\ condition in an \if\ command in the filter to prevent 
it happening on retries.

\**Warning**\: Because the system filter runs just once, variables that are
specific to individual recipient addresses, such as \$local@_part$\ and
\$domain$\, are not set, and the `personal' condition is not meaningful. If you
want to run a centrally-specified filter for each recipient address
independently, you can do so by setting up a suitable \%redirect%\ router, as
described in section ~~SECTperaddfil below.

.section Specifying a system filter
.index uid (user id)||system filter
.index gid (group id)||system filter
The name of the file that contains the system filter must be specified by
setting \system@_filter\. If you want the filter to run under a uid and gid
other than root, you must also set \system@_filter@_user\ and
\system@_filter@_group\ as appropriate. For example:
.display asis
system_filter = /etc/mail/exim.filter
system_filter_user = exim
.endd
If a system filter generates any deliveries directly to files or pipes (via the
\save\ or \pipe\ commands), transports to handle these deliveries must be
specified by setting \system@_filter@_file@_transport\ and
\system@_filter@_pipe@_transport\, respectively. Similarly,
\system@_filter@_reply@_transport\ must be set to handle any messages generated
by the \reply\ command.

.section Testing a system filter
You can run simple tests of a system filter in the same way as for a user
filter, but you should use \-bF-\ rather than \-bf-\, so that features that
are permitted only in system filters are recognized.

.section Contents of a system filter
The language used to specify system filters is the same as for users' filter
files. It is described in the separate end-user document \*Exim's interface to
mail filtering*\. However, there are some additional features that are
available only in system filters; these are described in subsequent sections.
If they are encountered in a user's filter file or when testing with \-bf-\,
they cause errors.

.index frozen messages||manual thaw, testing in filter
There are two special conditions which, though available in users' filter
files, are designed for use in system filters. The condition \first@_delivery\
is true only for the first attempt at delivering a message, and
\manually@_thawed\ is true only if the message has been frozen, and
subsequently thawed by an admin user. An explicit forced delivery counts as a
manual thaw, but thawing as a result of the \auto__thaw\ setting does not.

\**Warning**\: If a system filter uses the \first@_delivery\ condition to
specify an `unseen' (non-significant) delivery, and that delivery does not
succeed, it will not be tried again.
If you want Exim to retry an unseen delivery until it succeeds, you should 
arrange to set it up every time the filter runs.

When a system filter finishes running, the values of the variables \$n0$\ --
\$n9$\ are copied into \$sn0$\ -- \$sn9$\ and are thereby made available to
users' filter files. Thus a system filter can, for example, set up `scores' to
which users' filter files can refer.


.section Additional variable for system filters
The expansion variable \$recipients$\, containing a list of all the recipients
of the message (separated by commas and white space), is available in system
filters. It is not available in users' filters for privacy reasons.


.section Defer, freeze, and fail commands for system filters
.index freezing messages
.index message||freezing
.index message||forced failure
.index \fail\||in system filter
.index \freeze\ in system filter
.index \defer\ in system filter
There are three extra commands (\defer\, \freeze\ and \fail\) which are always
available in system filters, but are not normally enabled in users' filters.
(See the \allow@_defer\, 
\allow@_freeze\ and \allow@_fail\ options for the \%redirect%\ router.) These
commands can optionally be followed by the word \text\ and a string containing
an error message, for example:
.display asis
fail text "this message looks like spam to me"
.endd
The keyword \text\ is optional if the next character is a double quote. 

The \defer\ command defers delivery of the original recipients of the message. 
The \fail\ command causes all the original recipients to be failed, and a
bounce message to be created. The \freeze\ command suspends all delivery
attempts for the original recipients. In all cases, any new deliveries that are
specified by the filter are attempted as normal after the filter has run.

The \freeze\ command is ignored if the message has been manually unfrozen and
not manually frozen since. This means that automatic freezing by a system
filter can be used as a way of checking out suspicious messages. If a message
is found to be all right, manually unfreezing it allows it to be delivered.

.index log||\fail\ command log line
.index \fail\||log line, reducing
The text given with a fail command is used as part of the bounce message as
well as being written to the log. If the message is quite long, this can fill
up a lot of log space when such failures are common. To reduce the size of the
log message, Exim interprets the text in a special way if it starts with the
two characters \"@<@<"\ and contains \"@>@>"\ later. The text between these two
strings is written to the log, and the rest of the text is used in the bounce
message. For example:
.display asis
fail "<<filter test 1>>Your message is rejected \
     because it contains attachments that we are \
     not prepared to receive."
.endd

.index loop||caused by \fail\
Take great care with the \fail\ command when basing the decision to fail on the
contents of the message, because the bounce message will of course include the
contents of the original message and will therefore trigger the \fail\ command
again (causing a mail loop) unless steps are taken to prevent this. Testing the
\error@_message\ condition is one way to prevent this. You could use, for
example
.display asis
if $message_body contains "this is spam" and not error_message
  then fail text "spam is not wanted here" endif
.endd
though of course that might let through unwanted bounce messages. The
alternative is clever checking of the body and/or headers to detect bounces
generated by the filter.

The interpretation of a system filter file ceases after a 
\defer\, 
\freeze\, or \fail\ command is obeyed. However, any deliveries that were set up
earlier in the filter file are honoured, so you can use a sequence such as
.display asis
mail ...
freeze
.endd
to send a specified message when the system filter is freezing (or deferring or 
failing) a message. The normal deliveries for the message do not, of course,
take place.


.section Adding and removing headers in a system filter
.index header lines||adding in system filter
.index header lines||removing in system filter
.index filter||header lines, adding/removing
Two filter commands that are available only in system filters are:
.display asis
headers add <<string>>
headers remove <<string>>
.endd
The argument for the \headers add\ is a string which is expanded and then added
to the end of the message's headers. It is the responsibility of the filter
maintainer to make sure it conforms to RFC 2822 syntax. Leading white space is
ignored, and if the string is otherwise empty, or if the expansion is forced to
fail, the command has no effect.

If the message is not delivered at the first attempt, header lines that were
added by the system filter are stored with the message, and so are still 
present at the next delivery attempt. For that reason, it is usual to make the
\headers add\ command conditional on \first@_delivery\.

.em
You can use `@\n' within the string, followed by white space, to specify
continued header lines. More than one header may be added in one command by
including `@\n' within the string without any following white space. For
example:
.display asis
headers add "X-header-1: ....\n  \
             continuation of X-header-1 ...\n\
             X-header-2: ...."
.endd
Note that the header line continuation white space after the first newline must
be placed before the backslash that continues the input string, because white 
space after input continuations is ignored.

Header lines that are added by a system filter are visible to users' filter
files and to all routers and transports. 
.nem

The argument for \headers remove\ is a colon-separated list of header names.
This command applies only to those headers that are stored with the message;
those that are added at delivery time (such as ::Envelope-To:: and
::Return-Path::) cannot be removed by this means.
If there is more than one header with the same name, they are all removed.


.section Setting an errors address in a system filter
.index envelope sender
In a system filter, if a \deliver\ command is followed by
.display
errors@_to <<some address>>
.endd
in order to change the envelope sender (and hence the error reporting) for that
delivery, any address may be specified. (In a user filter, only the current
user's address can be set.) For example, if some mail is being monitored, you
might use
.display asis
unseen deliver monitor@spying.example errors_to root@local.example
.endd
to take a copy which would not be sent back to the normal error reporting
address if its delivery failed.


.section Per-address filtering
.rset SECTperaddfil "~~chapter.~~section"
In contrast to the system filter, which is run just once per message for each
delivery attempt, it is also possible to set up a system-wide filtering
operation that runs once for each recipient address. In this case, variables
such as \$local@_part$\ and \$domain$\ can be used, and indeed, the choice of
filter file could be made dependent on them. This is an example of a router
which implements such a filter:
.display asis
central_filter:
.newline
.em
  check_local_user
.newline
.nem   
  driver = redirect
  domains = +local_domains
  file = /central/filters/$local_part
  no_verify
  allow_filter
  allow_freeze
.endd
.em
The filter is run in a separate process under its own uid. Therefore, either
\check@_local@_user\ must be set (as above), in which case the filter is run as 
the local user, or the \user\ option must be used to specify which user to use. 
If both are set, \user\ overrides.
.nem

Care should be taken to ensure that none of the commands in the filter file
specify a significant delivery if the message is to go on to be delivered to
its intended recipient. The router will not then claim to have dealt with the
address, so it will be passed on to subsequent routers to be delivered in the
normal way.





.
.
.
.
. ============================================================================
.chapter Customizing bounce and warning messages
.set runningfoot "customizing messages"
.rset CHAPemsgcust "~~chapter"
When a message fails to be delivered, or remains on the queue for more than a
configured amount of time, Exim sends a message to the original sender, or
to an alternative configured address. The text of these messages is built into
the code of Exim, but it is possible to change it, either by adding a single
string, or by replacing each of the paragraphs by text supplied in a file.

The ::From:: and ::To:: header lines are automatically generated; you can cause 
a ::Reply-To:: line to be added by setting the \errors@_reply@_to\ option. Exim 
also adds the line
.display asis
Auto-Submitted: auto-generated
.endd
to all warning and bounce messages,

.section Customizing bounce messages
.index customizing||bounce message
.index bounce message||customizing
If \bounce@_message@_text\ is set, its contents are included in the default
message immediately after `This message was created automatically by mail
delivery software.' The string is not expanded. It is not used if
\bounce@_message@_file\ is set.

When \bounce@_message@_file\ is set, it must point to a template file for
constructing error messages. The file consists of a series of text items,
separated by lines consisting of exactly four asterisks. If the file cannot be
opened, default text is used and a message is written to the main and panic
logs. If any text item in the file is empty, default text is used for that
item.

Each item of text that is read from the file is expanded, and there are two
expansion variables which can be of use here: \$bounce@_recipient$\ is set to
the recipient of an error message while it is being created, and
\$return@_size@_limit$\ contains the value of the \return@_size@_limit\ option,
rounded to a whole number.

The items must appear in the file in the following order:
.numberpars $.
The first item is included in the headers, and should include at least a
::Subject:: header. Exim does not check the syntax of these headers.
.nextp
The second item forms the start of the error message. After it, Exim lists the
failing addresses with their error messages.
.nextp
The third item is used to introduce any text from pipe transports that is to be
returned to the sender. It is omitted if there is no such text.
.nextp
The fourth item is used to introduce the copy of the message that is returned
as part of the error report.
.nextp
The fifth item is added after the fourth one if the returned message is
truncated because it is bigger than \return@_size@_limit\.
.nextp
The sixth item is added after the copy of the original message.
.endp
The default state (\bounce@_message@_file\ unset) is equivalent to the
following file, in which the sixth item is empty. The ::Subject:: line has been
split into two here in order to fit it on the page:
.if ~~sys.fancy
.display flow asis
.fontgroup 0
.font 54
.else
.rule
.display flow asis
.linelength 80em
.indent 0
.fi
Subject: Mail delivery failed
  ${if eq{$sender_address}{$bounce_recipient}{: returning message to sender}}
****
This message was created automatically by mail delivery software.

A message ${if eq{$sender_address}{$bounce_recipient}{that you sent }{sent by

  <$sender_address>

}}could not be delivered to all of its recipients.
The following address(es) failed:
****
The following text was generated during the delivery attempt(s):
****
------ This is a copy of the message, including all the headers. ------
****
------ The body of the message is $message_size characters long; only the first
------ $return_size_limit or so are included here.
****
.endd
.if !~~sys.fancy
.rule
.fi

.section Customizing warning messages
.rset SECTcustwarn "~~chapter.~~section"
.index customizing||warning message
.index warning of delay||customizing the message
The option 
\warn@_message@_file\ 
can be pointed at a template file for use when
warnings about message delays are created. In this case there are only three
text sections:
.numberpars $.
The first item is included in the headers, and should include at least a
::Subject:: header. Exim does not check the syntax of these headers.
.nextp
The second item forms the start of the warning message. After it, Exim lists
the delayed addresses.
.nextp
The third item then ends the message.
.endp
The default state is equivalent to the following file, except that the line 
starting `A message' has been split here, in order to fit it on the page:
.if ~~sys.fancy
.display asis
.fontgroup 0
.font 54
.else
.rule
.display asis
.linelength 80em
.indent 0
.fi
.newline
Subject: Warning: message $message_id delayed $warn_message_delay
****
This message was created automatically by mail delivery software.

A message ${if eq{$sender_address}{$warn_message_recipients}
  {that you sent }{sent by

  <$sender_address>

}}has not been delivered to all of its recipients after
more than $warn_message_delay on the queue on $primary_hostname.
.newline

The message identifier is:     $message_id
The subject of the message is: $h_subject
The date of the message is:    $h_date

The following address(es) have not yet been delivered:
****
No action is required on your part. Delivery attempts will continue for
some time, and this warning may be repeated at intervals if the message
remains undelivered. Eventually the mail delivery software will give up,
and when that happens, the message will be returned to you.
.endd
.if !~~sys.fancy
.rule
.fi
except that in the default state the subject and date lines are omitted if no
appropriate headers exist. During the expansion of this file,
\$warn@_message@_delay$\
is set to the delay time in one of the forms `<<n>> minutes'
or `<<n>> hours', and 
\$warn@_message@_recipients$\
contains a list of recipients for the warning message. There may be more than
one if there are multiple addresses with different \errors@_to\ settings on the
routers that handled them.




.
.
.
. ============================================================================
.chapter Some common configuration requirements
.set runningfoot "common configuration requirements"
.rset CHAPcomconreq "~~chapter"
This chapter discusses some configuration requirements that seem to be fairly
common. More examples and discussion can be found in the Exim book.


.section Sending mail to a smart host
.index smart host||example router
If you want to send all mail for non-local domains to a `smart host', you
should replace the default \%dnslookup%\ router with a router which does the
routing explicitly:
.display asis
send_to_smart_host:
  driver = manualroute
  route_list = !+local_domains smart.host.name
  transport = remote_smtp
.endd
You can use the smart host's IP address instead of the name if you wish.


.section Using Exim to handle mailing lists
.rset SECTmailinglists "~~chapter.~~section"
.index mailing lists
Exim can be used to run simple mailing lists, but for large and/or complicated
requirements, the use of additional specialized mailing list software such as
Majordomo or Mailman is recommended.

The \%redirect%\ router can be used to handle mailing lists where each list
is maintained in a separate file, which can therefore be managed by an
independent manager. The \domains\ router option can be used to run these
lists in a separate domain from normal mail. For example:
.display asis
lists:
  driver = redirect
  domains = lists.example
  file = /usr/lists/$local_part
  forbid_pipe
  forbid_file
  errors_to = $local_part-request@lists.example
  no_more
.endd
This router is skipped for domains other than \*lists.example*\. For addresses
in that domain, it looks for a file that matches the local part. If there is no
such file, the router declines, but because \no@_more\ is set, no subsequent
routers are tried, and so the whole delivery fails.

The \forbid@_pipe\ and \forbid@_file\ options prevent a local part from being
expanded into a file name or a pipe delivery, which is usually inappropriate in
a mailing list.

.index \errors@_to\
The \errors@_to\ option specifies that any delivery errors caused by addresses
taken from a mailing list are to be sent to the given address rather than the
original sender of the message. However, before acting on this, Exim verifies
the error address, and ignores it if verification fails.

For example, using the configuration above, mail sent to
\*dicts@@lists.example*\ is passed on to those addresses contained in
\(/usr/lists/dicts)\, with error reports directed to
\*dicts-request@@lists.example*\, provided that this address can be verified.
There could be a file called \(/usr/lists/dicts-request)\ containing
the address(es) of this particular list's manager(s), but other approaches,
such as setting up an earlier router (possibly using the \local@_part@_prefix\
or \local@_part@_suffix\ options) to handle addresses of the form \owner-xxx\
or \xxx-request\, are also possible.


.section Syntax errors in mailing lists
.index mailing lists||syntax errors in
If an entry in redirection data contains a syntax error, Exim normally defers
delivery of the original address. That means that a syntax error in a mailing
list holds up all deliveries to the list. This may not be appropriate when a
list is being maintained automatically from data supplied by users, and the
addresses are not rigorously checked.

If the \skip@_syntax@_errors\ option is set, the \%redirect%\ router just skips
entries that fail to parse, noting the incident in the log. If in addition
\syntax@_errors@_to\ is set to a verifiable address, a message is sent to it
whenever a broken address is skipped. It is usually appropriate to set
\syntax@_errors@_to\ to the same address as \errors@_to\.


.section Re-expansion of mailing lists
.index mailing lists||re-expansion of
Exim remembers every individual address to which a message has been delivered,
in order to avoid duplication, but it normally stores only the original
recipient addresses with a message. If all the deliveries to a mailing list
cannot be done at the first attempt, the mailing list is re-expanded when the
delivery is next tried. This means that alterations to the list are taken into
account at each delivery attempt, so addresses that have been added to
the list since the message arrived will therefore receive a copy of the
message, even though it pre-dates their subscription.

If this behaviour is felt to be undesirable, the \one@_time\ option can be set
on the \%redirect%\ router. If this is done, any addresses generated by the
router that fail to deliver at the first attempt are added to the message as
`top level' addresses, and the parent address that generated them is marked
`delivered'. Thus, expansion of the mailing list does not happen again at the
subsequent delivery attempts. The disadvantage of this is that if any of the
failing addresses are incorrect, correcting them in the file has no effect on
pre-existing messages.

The original top-level address is remembered with each of the generated
addresses, and is output in any log messages. However, any intermediate parent
addresses are not recorded. This makes a difference to the log only if the
\all@_parents\ selector is set, but for mailing lists there is normally only
one level of expansion anyway.


.section Closed mailing lists
.index mailing lists||closed
The examples so far have assumed open mailing lists, to which anybody may
send mail. It is also possible to set up closed lists, where mail is accepted
from specified senders only. This is done by making use of the generic
\senders\ option to restrict the router that handles the list.

The following example uses the same file as a list of recipients and as a list
of permitted senders. It requires three routers:
.display asis
lists_request:
  driver = redirect
  domains = lists.example
  local_part_suffix = -request
  file = /usr/lists/$local_part$local_part_suffix
  no_more

lists_post:
  driver = redirect
  domains = lists.example
  senders = ${if exists {/usr/lists/$local_part}\
             {lsearch;/usr/lists/$local_part}{*}}
  file = /usr/lists/$local_part
  forbid_pipe
  forbid_file
  errors_to = $local_part-request@lists.example
  no_more

lists_closed:
  driver = redirect
  domains = lists.example
  allow_fail 
  data = :fail: $local_part@lists.example is a closed mailing list
.endd
All three routers have the same \domains\ setting, so for any other domains,
they are all skipped. The first router runs only if the local part ends in
\@-request\. It handles messages to the list manager(s) by means of an open
mailing list.

The second router runs only if the \senders\ precondition is satisfied. It
checks for the existence of a list that corresponds to the local part, and then
checks that the sender is on the list by means of a linear search. It is
necessary to check for the existence of the file before trying to search it,
because otherwise Exim thinks there is a configuration error. If the file does
not exist, the expansion of \senders\ is $*$, which matches all senders. This
means that the router runs, but because there is no list, declines, and
\no@_more\ ensures that no further routers are run. The address fails with an
`unrouteable address' error.

The third router runs only if the second router is skipped, which happens when
a mailing list exists, but the sender is not on it. This router forcibly fails
the address, giving a suitable error message.



.section Virtual domains
.rset SECTvirtualdomains "~~chapter.~~section"
.index virtual domains
.index domain||virtual
The phrase \*virtual domain*\ is unfortunately used with two rather different
meanings:
.numberpars $.
A domain for which there are no real mailboxes; all valid local parts are
aliases for other email addresses. Common examples are organizational
top-level domains and `vanity' domains.
.nextp
One of a number of independent domains that are all handled by the same host,
with mailboxes on that host, but where the mailbox owners do not necessarily
have login accounts on that host.
.endp
The first usage is probably more common, and does seem more `virtual' than the
second. This kind of domain can be handled in Exim with a straightforward
aliasing router. One approach is to create a separate alias file for each
virtual domain. Exim can test for the existence of the alias file to determine
whether the domain exists. The \%dsearch%\ lookup type is useful here, leading
to a router of this form:
.display asis
virtual:
  driver = redirect
  domains = dsearch;/etc/mail/virtual
  data = ${lookup{$local_part}lsearch{/etc/mail/virtual/$domain}}
  no_more
.endd
The \domains\ option specifies that the router is to be skipped, unless there
is a file in the \(/etc/mail/virtual)\ directory whose name is the same as the
domain that is being processed. When the router runs, it looks up the local
part in the file to find a new address (or list of addresses). The \no@_more\
setting ensures that if the lookup fails (leading to \data\ being an empty
string), Exim gives up on the address without trying any subsequent routers.

This one router can handle all the virtual domains because the alias file names
follow a fixed pattern. Permissions can be arranged so that appropriate people
can edit the different alias files. A successful aliasing operation results in
a new envelope recipient address, which is then routed from scratch.

The other kind of `virtual' domain can also be handled in a straightforward
way. One approach is to create a file for each domain containing a list of
valid local parts, and use it in a router like this:
.display asis
my_domains:
  driver = accept
  domains = dsearch;/etc/mail/domains
  local_parts = lsearch;/etc/mail/domains/$domain
  transport = my_mailboxes
.endd
The address is accepted if there is a file for the domain, and the local part
can be found in the file. The \domains\ option is used to check for the file's
existence because \domains\ is tested before the \local@_parts\ option (see
section ~~SECTrouprecon). You can't use \require@_files\, because that option
is tested after \local@_parts\. The transport is as follows:
.display asis
my_mailboxes:
  driver = appendfile
  file = /var/mail/$domain/$local_part
  user = mail
.endd
This uses a directory of mailboxes for each domain. The \user\ setting is
required, to specify which uid is to be used for writing to the mailboxes.

The configuration shown here is just one example of how you might support this
requirement. There are many other ways this kind of configuration can be set
up, for example, by using a database instead of separate files to hold all the
information about the domains.


.section Multiple user mailboxes
.rset SECTmulbox "~~chapter.~~section"
.index multiple mailboxes
.index mailbox||multiple
.index local part||prefix
.index local part||suffix
Heavy email users often want to operate with multiple mailboxes, into which
incoming mail is automatically sorted. A popular way of handling this is to
allow users to use multiple sender addresses, so that replies can easily be
identified. Users are permitted to add prefixes or suffixes to their local
parts for this purpose. The wildcard facility of the generic router options
\local@_part@_prefix\ and \local@_part@_suffix\ can be used for this. For
example, consider this router:
.display asis
userforward:
  driver = redirect
  check_local_user
  file = $home/.forward
  local_part_suffix = -*
  local_part_suffix_optional
  allow_filter
.endd
It runs a user's \(.forward)\ file for all local parts of the form
\*username-$*$*\. Within the filter file the user can distinguish different
cases by testing the variable \$local@_part@_suffix$\. For example:
.display asis
if $local_part_suffix contains -special then
  save /home/$local_part/Mail/special
endif
.endd
If the filter file does not exist, or does not deal with such addresses, they
fall through to subsequent routers, and, assuming no subsequent use of the
\local@_part@_suffix\ option is made, they presumably fail. Thus, users have
control over which suffixes are valid.

Alternatively, a suffix can be used to trigger the use of a different
\(.forward)\ file -- which is the way a similar facility is implemented in
another MTA:
.display asis
userforward:
  driver = redirect
  check_local_user
  file = $home/.forward$local_part_suffix
  local_part_suffix = -*
  local_part_suffix_optional
  allow_filter
.endd
If there is no suffix, \(.forward)\ is used; if the suffix is \*-special*\, for
example, \(.forward-special)\ is used. Once again, if the appropriate file
does not exist, or does not deal with the address, it is passed on to
subsequent routers, which could, if required, look for an unqualified
\(.forward)\ file to use as a default.


.section Simplified vacation processing
.index vacation processing
The traditional way of running the \*vacation*\ program is for a user to set up
a pipe command in a \(.forward)\ file
(see section ~~SECTspecitredli for syntax details).
This is prone to error by inexperienced users. There are two features of Exim
that can be used to make this process simpler for users:
.numberpars $.
A local part prefix such as `vacation-' can be specified on a router which
can cause the message to be delivered directly to the \*vacation*\ program, or
alternatively can use Exim's \%autoreply%\ transport. The contents of a user's
\(.forward)\ file are then much simpler. For example:
.display asis
spqr, vacation-spqr
.endd
.nextp
The \require@_files\ generic router option can be used to trigger a
vacation delivery by checking for the existence of a certain file in the
user's home directory. The \unseen\ generic option should also be used, to
ensure that the original delivery also proceeds. In this case, all the user has
to do is to create a file called, say, \(.vacation)\, containing a vacation
message.
.endp
Another advantage of both these methods is that they both work even when the
use of arbitrary pipes by users is locked out.


.section Taking copies of mail
.index message||copying every
Some installations have policies that require archive copies of all messages to
be made. A single copy of each message can easily be taken by an appropriate
command in a system filter, which could, for example, use a different file for
each day's messages.

There is also a shadow transport mechanism that can be used to take copies of
messages that are successfully delivered by local transports, one copy per
delivery. This could be used, $it{inter alia}, to implement automatic
notification of delivery by sites that insist on doing such things.


.section Intermittently connected hosts
.index intermittently connected hosts
It has become quite common (because it is cheaper) for hosts to connect to the
Internet periodically rather than remain connected all the time. The normal
arrangement is that mail for such hosts accumulates on a system that is
permanently connected.

Exim was designed for use on permanently connected hosts, and so it is not
particularly well-suited to use in an intermittently connected environment.
Nevertheless there are some features that can be used.

.section Exim on the upstream server host
It is tempting to arrange for incoming mail for the intermittently connected
host to remain on Exim's queue until the client connects. However, this
approach does not scale very well. Two different kinds of waiting message are
being mixed up in the same queue -- those that cannot be delivered because of
some temporary problem, and those that are waiting for their destination host
to connect. This makes it hard to manage the queue, as well as wasting
resources, because each queue runner scans the entire queue.

A better approach is to separate off those messages that are waiting for an
intermittently connected host. This can be done by delivering these messages
into local files in batch SMTP, `mailstore', or other envelope-preserving
format, from where they are transmitted by other software when their
destination connects. This makes it easy to collect all the mail for one host
in a single directory, and to apply local timeout rules on a per-message basis
if required.

On a very small scale, leaving the mail on Exim's queue can be made to work. If
you are doing this, you should configure Exim with a long retry period for the
intermittent host. For example:
.display
cheshire.wonderland.fict.example    *   F,5d,24h
.endd
This stops a lot of failed delivery attempts from occurring, but Exim remembers
which messages it has queued up for that host. Once the intermittent host comes
online, forcing delivery of one message (either by using the \-M-\ or \-R-\
options, or by using the \\ETRN\\ SMTP command (see section ~~SECTETRN)
causes all the queued up messages to be delivered, often down a single SMTP
connection. While the host remains connected, any new messages get delivered
immediately.

If the connecting hosts do not have fixed IP addresses, that is, if a host is
issued with a different IP address each time it connects, Exim's retry
mechanisms on the holding host get confused, because the IP address is normally
used as part of the key string for holding retry information. This can be
avoided by unsetting \retry__include__ip__address\ on the \%smtp%\ transport.
Since this has disadvantages for permanently connected hosts, it is best to
arrange a separate transport for the intermittently connected ones.


.section Exim on the intermittently connected client host
The value of \smtp@_accept@_queue@_per@_connection\ should probably be
increased, or even set to zero (that is, disabled) on the intermittently
connected host, so that all incoming messages down a single connection get
delivered immediately.

.index SMTP||passed connection
.index SMTP||multiple deliveries
.index multiple SMTP deliveries
Mail waiting to be sent from an intermittently connected host will probably
not have been routed, because without a connection DNS lookups are not
possible. This means that if a normal queue run is done at connection time,
each message is likely to be sent in a separate SMTP session. This can be
avoided by starting the queue run with a command line option beginning with
\-qq-\ instead of \-q-\. In this case, the queue is scanned twice. In the first
pass, routing is done but no deliveries take place. The second pass is a normal
queue run; since all the messages have been previously routed, those destined
for the same host are likely to get sent as multiple deliveries in a single
SMTP connection.





.
.
.
.
. ============================================================================
.chapter SMTP processing
.set runningfoot "smtp processing"
.rset CHAPSMTP ~~chapter
.index SMTP||processing details
.index LMTP||processing details
Exim supports a number of different ways of using the SMTP protocol, and its
LMTP variant, which is an interactive protocol for transferring messages into a
closed mail store application. This chapter contains details of how SMTP is
processed. For incoming mail, the following are available:
.numberpars $.
SMTP over TCP/IP (Exim daemon or \*inetd*\);
.nextp
SMTP over the standard input and output (the \-bs-\ option);
.nextp
Batched SMTP on the standard input (the \-bS-\ option).
.endp
For mail delivery, the following are available:
.numberpars $.
SMTP over TCP/IP (the \%smtp%\ transport);
.nextp
LMTP over TCP/IP (the \%smtp%\ transport with the \protocol\ option set to
`lmtp');
.nextp
LMTP over a pipe to a process running in the local host (the \%lmtp%\
transport);
.nextp
Batched SMTP to a file or pipe (the \%appendfile%\ and \%pipe%\ transports with
the \use@_bsmtp\ option set).
.endp
\*Batched SMTP*\ is the name for a process in which batches of messages are
stored in or read from files (or pipes), in a format in which SMTP commands are
used to contain the envelope information.


.section Outgoing SMTP and LMTP over TCP/IP
.rset SECToutSMTPTCP "~~chapter.~~section"
.index SMTP||outgoing over TCP/IP
.index outgoing SMTP over TCP/IP
.index LMTP||over TCP/IP
.index outgoing LMTP over TCP/IP
.index \\EHLO\\
.index \\HELO\\
.index \\SIZE\\ option on \\MAIL\\ command
Outgoing SMTP and LMTP over TCP/IP is implemented by the \%smtp%\ transport.
The \protocol\ option selects which protocol is to be used, but the actual
processing is the same in both cases.

If, in response to its \\EHLO\\ command, Exim is told that the \\SIZE\\
parameter is supported, it adds \\SIZE\\=<<n>> to each subsequent \\MAIL\\
command. The value of <<n>> is the message size plus the value of the
\size@_addition\ option (default 1024) to allow for additions to the message
such as per-transport header lines, or changes made in a
.index transport||filter
.index filter||transport filter
transport filter. If \size@_addition\ is set negative, the use of \\SIZE\\ is
suppressed.

If the remote server advertises support for \\PIPELINING\\, Exim uses the
pipelining extension to SMTP (RFC 2197) to reduce the number of TCP/IP packets
required for the transaction.

If the remote server advertises support for the \\STARTTLS\\ command, and Exim
was built to support TLS encryption, it tries to start a TLS session unless the
server matches \hosts@_avoid@_tls\. See chapter ~~CHAPTLS for more details.

If the remote server advertises support for the \\AUTH\\ command, Exim scans
the authenticators configuration for any suitable client settings, as described
in chapter ~~CHAPSMTPAUTH.

.index carriage return
.index linefeed
Responses from the remote host are supposed to be terminated by CR followed by
LF. However, there are known to be hosts that do not send CR characters, so in
order to be able to interwork with such hosts, Exim treats LF on its own as a
line terminator.

If a message contains a number of different addresses, all those with the same
characteristics (for example, the same envelope sender) that resolve to the
same set of hosts, in the same order, are sent in a single SMTP transaction,
even if they are for different domains, unless there are more than the setting
of the \max@_rcpts\ option in the \%smtp%\ transport allows, in which case they
are split into groups containing no more than \max@_rcpts\ addresses each. If
\remote@_max@_parallel\ is greater than one, such groups may be sent in
parallel sessions. The order of hosts with identical MX values is not
significant when checking whether addresses can be batched in this way.

When the \%smtp%\ transport suffers a temporary failure that is not
message-related, Exim updates its transport-specific database, which contains
records indexed by host name that remember which messages are waiting for each
particular host. It also updates the retry database with new retry times.
.index hints database||retry keys
Exim's retry hints are based on host name plus IP address, so if one address of
a multi-homed host is broken, it will soon be skipped most of the time.
See the next section for more detail about error handling.

.index SMTP||passed connection
.index SMTP||batching over TCP/IP
When a message is successfully delivered over a TCP/IP SMTP connection, Exim
looks in the hints database for the transport to see if there are any queued
messages waiting for the host to which it is connected. If it finds one, it
creates a new Exim process using the \-MC-\ option (which can only be used by a
process running as root or the Exim user) and passes the TCP/IP socket to it so
that it can deliver another message using the same socket. The new process does
only those deliveries that are routed to the connected host, and may in turn
pass the socket on to a third process, and so on.

The \connection@_max@_messages\ option of the \%smtp%\ transport can be used to
limit the number of messages sent down a single TCP/IP connection.
.index asterisk||after IP address
The second and subsequent messages delivered down an existing connection are
identified in the main log by the addition of an asterisk after the closing
square bracket of the IP address.



.section Errors in outgoing SMTP
.rset SECToutSMTPerr "~~chapter.~~section"
.index error||in outgoing SMTP
.index SMTP||errors in outgoing
.index host||error
Three different kinds of error are recognized for outgoing SMTP: host errors,
message errors, and recipient errors.
.numberpars
A host error is not associated with a particular message or with a
particular recipient of a message. The host errors are:
.numberpars $.
Connection refused or timed out,
.nextp
Any error response code on connection,
.nextp
Any error response code to \\EHLO\\ or \\HELO\\,
.nextp
Loss of connection at any time, except after `.',
.nextp
I/O errors at any time,
.nextp
Timeouts during the session, other than in response to \\MAIL\\, \\RCPT\\ or
the `.' at the end of the data.
.endp
For a host error, a permanent error response on connection, or in response to
\\EHLO\\, causes all addresses routed to the host to be failed. Any other host
error causes all addresses to be deferred, and retry data to be created for the
host. It is not tried again, for any message, until its retry time arrives. If
the current set of addresses are not all delivered in this run (to some
alternative host), the message is added to the list of those waiting for this
host, so if it is still undelivered when a subsequent successful delivery is
made to the host, it will be sent down the same SMTP connection.
.nextp
.index message||error
A message error is associated with a particular message when sent to a
particular host, but not with a particular recipient of the message. The
message errors are:
.numberpars $.
Any error response code to \\MAIL\\, \\DATA\\, or the `.' that terminates
the data,
.nextp
Timeout after \\MAIL\\,
.nextp
Timeout
or loss of connection after the `.' that terminates the data. A timeout after
the \\DATA\\ command itself is treated as a host error, as is loss of
connection at any other time.
.endp
For a message error, a permanent error response (5$it{xx}) causes all addresses
to be failed, and a delivery error report to be returned to the sender. A
temporary error response (4$it{xx}), or one of the timeouts, causes all
addresses to be deferred. Retry data is not created for the host, but instead,
a retry record for the combination of host plus message id is created. The
message is not added to the list of those waiting for this host. This ensures
that the failing message will not be sent to this host again until the retry
time arrives. However, other messages that are routed to the host are not
affected, so if it is some property of the message that is causing the error,
it will not stop the delivery of other mail.

If the remote host specified support for the \\SIZE\\ parameter in its response
to \\EHLO\\, Exim adds SIZE=$it{nnn} to the \\MAIL\\ command, so an
over-large message will cause a message error because the error arrives as a
response to \\MAIL\\.
.nextp
.index recipient||error
A recipient error is associated with a particular recipient of a message. The
recipient errors are:
.numberpars $.
Any error response to \\RCPT\\,
.nextp
Timeout after \\RCPT\\.
.endp
For a recipient error, a permanent error response (5$it{xx}) causes the
recipient address to be failed, and a bounce message to be returned to the
sender. A temporary error response (4$it{xx}) or a timeout causes the failing
address to be deferred, and routing retry data to be created for it. This is
used to delay processing of the address in subsequent queue runs, until its
routing retry time arrives. This applies to all messages, but because it
operates only in queue runs, one attempt will be made to deliver a new message
to the failing address before the delay starts to operate. This ensures that,
if the failure is really related to the message rather than the recipient
(`message too big for this recipient' is a possible example), other messages
have a chance of getting delivered. If a delivery to the address does succeed,
the retry information gets cleared, so all stuck messages get tried again, and
the retry clock is reset.

The message is not added to the list of those waiting for this host. Use of the
host for other messages is unaffected, and except in the case of a timeout,
other recipients are processed independently, and may be successfully delivered
in the current SMTP session. After a timeout it is of course impossible to
proceed with the session, so all addresses get deferred. However, those other
than the one that failed do not suffer any subsequent retry delays. Therefore,
if one recipient is causing trouble, the others have a chance of getting
through when a subsequent delivery attempt occurs before the failing
recipient's retry time.
.endp

In all cases, if there are other hosts (or IP addresses) available for the
current set of addresses (for example, from multiple MX records), they are
tried in this run for any undelivered addresses, subject of course to their
own retry data. In other words, recipient error retry data does not take effect
until the next delivery attempt.

Some hosts have been observed to give temporary error responses to every
\\MAIL\\ command at certain times (`insufficient space' has been seen). It
would be nice if such circumstances could be recognized, and defer data for the
host itself created, but this is not possible within the current Exim design.
What actually happens is that retry data for every (host, message) combination
is created.

The reason that timeouts after \\MAIL\\ and \\RCPT\\ are treated specially is
that these can sometimes arise as a result of the remote host's verification
procedures. Exim makes this assumption, and treats them as if a temporary error
response had been received. A timeout after `.' is treated specially because it
is known that some broken implementations fail to recognize the end of the
message if the last character of the last line is a binary zero. Thus, it is
helpful to treat this case as a message error.

Timeouts at other times are treated as host errors, assuming a problem with the
host, or the connection to it. If a timeout after \\MAIL\\, \\RCPT\\,
or `.' is really a connection problem, the assumption is that at the next try
the timeout is likely to occur at some other point in the dialogue, causing it
then to be treated as a host error.

There is experimental evidence that some MTAs drop the connection after the
terminating `.' if they do not like the contents of the message for some
reason, in contravention of the RFC, which indicates that a 5$it{xx} response
should be given. That is why Exim treats this case as a message rather than a
host error, in order not to delay other messages to the same host.




.section Variable Envelope Return Paths (VERP)
.index VERP
.index Variable Envelope Return Paths
.index envelope sender
Variable Envelope Return Paths -- see
\?ftp://koobera.math.uic.edu/www/proto/verp.txt?\ -- can be supported in Exim
by using the \return@_path\ generic transport option to rewrite the return path
at transport time. For example, the following could be used on an \%smtp%\
transport:
.display asis
return_path = \
  ${if match {$return_path}{^(.+?)-request@your.dom.example\$}\
  {$1-request=$local_part%$domain@your.dom.example}fail}
.endd
This has the effect of rewriting the return path (envelope sender) on all
outgoing SMTP messages, if the local part of the original return path ends in
`-request', and the domain is \*your.dom.example*\. The rewriting inserts the
local part and domain of the recipient into the return path. Suppose, for
example, that a message whose return path has been set to
\*somelist-request@@your.dom.example*\ is sent to
\*subscriber@@other.dom.example*\. In the transport, the return path is
rewritten as
.display asis
somelist-request=subscriber%other.dom.example@your.dom.example
.endd
For this to work, you must arrange for outgoing messages that have `-request'
in their return paths to have just a single recipient. This can be done by
setting
.display asis
max_rcpt = 1
.endd
in the \%smtp%\ transport. Otherwise a single copy of a message might be
addressed to several different recipients in the same domain, in which case
\$local@_part$\ is not available (because it is not unique). Of course, if you
do start sending out messages with this kind of return path, you must also
configure Exim to accept the bounce messages that come back to those paths.
Typically this would be done by setting an \local@_part@_suffix\ option for a
suitable router.

The overhead incurred in using VERP depends very much on the size of the
message, the number of recipient addresses that resolve to the same remote
host, and the speed of the connection over which the message is being sent. If
a lot of addresses resolve to the same host and the connection is slow, sending
a separate copy of the message for each address may take substantially longer
than sending a single copy with many recipients (for which VERP cannot be
used).


.section Incoming SMTP messages over TCP/IP
.index SMTP||incoming over TCP/IP
.index incoming SMTP over TCP/IP
.index inetd
.index daemon
Incoming SMTP messages can be accepted in one of two ways: by running a
listening daemon, or by using \*inetd*\. In the latter case, the entry in
\(/etc/inetd.conf)\ should be like this:
.display asis
smtp  stream  tcp  nowait  exim  /opt/exim/bin/exim  in.exim  -bs
.endd
Exim distinguishes between this case and the case of a locally running user
agent using the \-bs-\ option by checking whether or not the standard input is
a socket. When it is, either the port must be privileged (less than 1024), or
the caller must be root or the Exim user. If any other user passes a socket
with an unprivileged port number, Exim prints a message on the standard error
stream and exits with an error code.

By default, Exim does not make a log entry when a remote host connects or
disconnects (either via the daemon or \*inetd*\), unless the disconnection is
unexpected. It can be made to write such log entries by setting the
\smtp@_connection\ log selector.

.index carriage return
.index linefeed
Commands from the remote host are supposed to be terminated by CR followed by
LF. However, there are known to be hosts that do not send CR characters. In
order to be able to interwork with such hosts, Exim treats LF on its own as a
line terminator.
Furthermore, because common code is used for receiving messages from all
sources, a CR on its own is also interpreted as a line terminator. However, the
sequence `CR, dot, CR' does not terminate incoming SMTP data.

.index \\EHLO\\||invalid data
.index \\HELO\\||invalid data
One area that sometimes gives rise to problems concerns the \\EHLO\\ or
\\HELO\\ commands. Some clients send syntactically invalid versions of these
commands, which Exim rejects by default. (This is nothing to do with verifying
the data that is sent, so \helo@_verify@_hosts\ is not relevant.) You can tell
Exim not to apply a syntax check by setting \helo@_accept@_junk@_hosts\ to
match the broken hosts that send invalid commands.

.index \\SIZE\\ option on \\MAIL\\ command
.index \\MAIL\\||\\SIZE\\ option
The amount of disk space available is checked whenever \\SIZE\\ is received on
a \\MAIL\\ command, independently of whether \message@_size@_limit\ or
\check@_spool@_space\ is configured, unless \smtp__check__spool__space\ is set
false. A temporary error is given if there is not enough space. If
\check@_spool@_space\ is set, the check is for that amount of space plus the
value given with \\SIZE\\, that is, it checks that the addition of the incoming
message will not reduce the space below the threshold.

When a message is successfully received, Exim includes the local message id in
its response to the final `.' that terminates the data. If the remote host logs
this text it can help with tracing what has happened to a message.

The Exim daemon can limit the number of simultaneous incoming connections it is
prepared to handle (see the \smtp@_accept@_max\ option). It can also limit the
number of simultaneous incoming connections from a single remote host (see the
\smtp@_accept@_max@_per@_host\ option). Additional connection attempts are
rejected using the SMTP temporary error code 421.

The Exim daemon does not rely on the \\SIGCHLD\\ signal to detect when a
subprocess has finished, as this can get lost at busy times. Instead, it looks
for completed subprocesses every time it wakes up. Provided there are other
things happening (new incoming calls, starts of queue runs), completed
processes will be noticed and tidied away. On very quiet systems you may
sometimes see a `defunct' Exim process hanging about. This is not a problem; it
will be noticed when the daemon next wakes up.

When running as a daemon, Exim can reserve some SMTP slots for specific hosts,
and can also be set up to reject SMTP calls from non-reserved hosts at times of
high system load -- for details see the \smtp@_accept@_reserve\,
\smtp@_load@_reserve\, and \smtp@_reserve@_hosts\ options. The load check
applies in both the daemon and \*inetd*\ cases.

Exim normally starts a delivery process for each message received, though this
can be varied by means of the \-odq-\ command line option and the
\queue@_only\, \queue@_only@_file\, and \queue@_only@_load\ options. The number
of simultaneously running delivery processes started in this way from SMTP
input can be limited by the \smtp__accept__queue\ and
\smtp__accept__queue__per__connection\ options. When either limit is reached,
subsequently received messages are just put on the input queue without starting
a delivery process.

The controls that involve counts of incoming SMTP calls (\smtp@_accept@_max\,
\smtp@_accept@_queue\, \smtp__accept__reserve\) are not available when Exim is
started up from the \*inetd*\ daemon, because in that case each connection is
handled by an entirely independent Exim process. Control by load average is,
however, available with \*inetd*\.

Exim can be configured to verify addresses in incoming SMTP commands as they
are received. See chapter ~~CHAPACL for details. It can also be configured to
rewrite addresses at this time -- before any syntax checking is done. See
section ~~SECTrewriteS.

Exim can also be configured to limit the rate at which a client host submits
\\MAIL\\ and \\RCPT\\ commands in a single SMTP session. See the
\smtp@_ratelimit@_hosts\ option.


.section Unrecognized SMTP commands
.index SMTP||unrecognized commands
If Exim receives more than \smtp@_max@_unknown@_commands\ unrecognized SMTP
commands during a single SMTP connection, it drops the connection after sending
the error response to the last command. The default value for
\smtp@_max@_unknown@_commands\ is 3. This is a defence against some kinds of
abuse that subvert web servers into making connections to SMTP ports; in these
circumstances, a number of non-SMTP lines are sent first.

.section Syntax and protocol errors in SMTP commands
.index SMTP||syntax errors
.index SMTP||protocol errors
A syntax error is detected if an SMTP command is recognized, but there is 
something syntactically wrong with its data, for example, a malformed email
address in a \\RCPT\\ command. Protocol errors include invalid command
sequencing such as \\RCPT\\ before \\MAIL\\. If Exim receives more than 
\smtp@_max@_synprot@_errors\ such commands during a single SMTP connection, it 
drops the connection after sending the error response to the last command. The 
default value for \smtp__max__synprot__errors\ is 3. This is a defence against 
broken clients that loop sending bad commands (yes, it has been seen).


.section Use of non-mail SMTP commands
.index SMTP||non-mail commands
The `non-mail' SMTP commands are those other than \\MAIL\\, \\RCPT\\, and
\\DATA\\. Exim counts such commands, and drops the connection if there are too
many of them in a single SMTP session. This action catches some
denial-of-service attempts and things like repeated failing \\AUTH\\s, or a mad
client looping sending \\EHLO\\. The global option \smtp@_accept@_max@_nonmail\
defines what `too many' means. Its default value is 10.

When a new message is expected, one occurrence of \\RSET\\ is not counted. This
allows a client to send one \\RSET\\ between messages (this is not necessary,
but some clients do it). Exim also allows one uncounted occurence of \\HELO\\
or \\EHLO\\, and one occurrence of \\STARTTLS\\ between messages. After
starting up a TLS session, another \\EHLO\\ is expected, and so it too is not
counted.

The first occurrence of \\AUTH\\ in a connection, or immediately following
\\STARTTLS\\ is also not counted. Otherwise, all commands other than \\MAIL\\,
\\RCPT\\, \\DATA\\, and \\QUIT\\ are counted.

You can control which hosts are subject to the limit set by
\smtp@_accept@_max@_nonmail\ by setting
\smtp@_accept@_max@_nonmail@_hosts\. The default value is \"$*$"\, which makes 
the limit apply to all hosts. This option means that you can exclude any
specific badly-behaved hosts that you have to live with.



.section The \\VRFY\\ and \\EXPN\\ commands
When Exim receives a \\VRFY\\ or \\EXPN\\ command on a TCP/IP connection, it
runs the ACL specified by \acl@_smtp@_vrfy\ or \acl@_smtp@_expn\ (as
appropriate) in order to decide whether the command should be accepted or not.
If no ACL is defined, the command is rejected.

.index \\VRFY\\||processing
When \\VRFY\\ is accepted, it runs exactly the same code as when Exim is
called with the \-bv-\ option.
.index \\EXPN\\||processing
When \\EXPN\\ is accepted, a single-level expansion of the address is done.
\\EXPN\\ is treated as an `address test' (similar to the \-bt-\ option) rather
than a verification (the \-bv-\ option). If an unqualified local part is given
as the argument to \\EXPN\\, it is qualified with \qualify@_domain\. Rejections
of \\VRFY\\ and \\EXPN\\ commands are logged on the main and reject logs, and
\\VRFY\\ verification failures are logged on the main log for consistency with
\\RCPT\\ failures.


.section The \\ETRN\\ command
.rset SECTETRN "~~chapter.~~section"
.index \\ETRN\\||processing
RFC 1985 describes an SMTP command called \\ETRN\\ that is designed to
overcome the security problems of the \\TURN\\ command (which has fallen into
disuse). When Exim receives an \\ETRN\\ command on a TCP/IP connection, it runs
the ACL specified by \acl@_smtp@_etrn\ in order to decide whether the command
should be accepted or not. If no ACL is defined, the command is rejected.

The \\ETRN\\ command is concerned with `releasing' messages that are awaiting
delivery to certain hosts. As Exim does not organize its message queue by host,
the only form of \\ETRN\\ that is supported by default is the one where the
text starts with the `@#' prefix, in which case the remainder of the text is
specific to the SMTP server. A valid \\ETRN\\ command causes a run of Exim with
the \-R-\ option to happen, with the remainder of the \\ETRN\\ text as its
argument. For example,
.display asis
ETRN #brigadoon
.endd
runs the command
.display asis
exim -R brigadoon
.endd
which causes a delivery attempt on all messages with undelivered addresses
containing the text `brigadoon'. When \smtp@_etrn@_serialize\ is set (the
default), Exim prevents the simultaneous execution of more than one queue run
for the same argument string as a result of an \\ETRN\\ command. This stops
a misbehaving client from starting more than one queue runner at once.

.index hints database||\\ETRN\\ serialization
Exim implements the serialization by means of a hints database in which a
record is written whenever a process is started by \\ETRN\\, and deleted when
the process completes. However, Exim does not keep the SMTP session waiting for
the \\ETRN\\ process to complete. Once \\ETRN\\ is accepted, the client is sent
a `success' return code. Obviously there is scope for hints records to get left
lying around if there is a system or program crash. To guard against this, Exim
ignores any records that are more than six hours old.

.index \smtp@_etrn@_command\
For more control over what \\ETRN\\ does, the \smtp@_etrn@_command\ option can
used. This specifies a command that is run whenever \\ETRN\\ is received,
whatever the form of its argument. For
example:
.display asis
smtp_etrn_command = /etc/etrn_command $domain $sender_host_address
.endd
The string is split up into arguments which are independently expanded. The
expansion variable \$domain$\ is set to the argument of the \\ETRN\\ command,
and no syntax checking is done on the contents of this argument. Exim does not
wait for the command to complete, so its status code is not checked. Exim runs
under its own uid and gid when receiving incoming SMTP, so it is not possible
for it to change them before running the command.


.section Incoming local SMTP
.index SMTP||local incoming
Some user agents use SMTP to pass messages to their local MTA using the
standard input and output, as opposed to passing the envelope on the command
line and writing the message to the standard input. This is supported by the
\-bs-\ option. This form of SMTP is handled in the same way as incoming
messages over TCP/IP (including the use of ACLs), except that the envelope
sender given in a \\MAIL\\ command is ignored unless the caller is trusted. In
an ACL you can detect this form of SMTP input by testing for an empty host
identification. It is common to have this as the first line in the ACL that
runs for \\RCPT\\ commands:
.display asis
accept hosts = :
.endd
This accepts SMTP messages from local processes without doing any other tests.


.section Outgoing batched SMTP
.rset SECTbatchSMTP "~~chapter.~~section"
.index SMTP||batched outgoing
.index batched SMTP output
Both the \%appendfile%\ and \%pipe%\ transports can be used for handling batched
SMTP. Each has an option called \use@_bsmtp\ which causes messages to be output
in BSMTP format. No SMTP responses are possible for this form of delivery. All
it is doing is using SMTP commands as a way of transmitting the envelope along
with the message.

The message is written to the file or pipe preceded by the SMTP commands
\\MAIL\\ and \\RCPT\\, and followed by a line containing a single dot. Lines in
the message that start with a dot have an extra dot added. The SMTP command
\\HELO\\ is not normally used. If it is required, the \message@_prefix\ option
can be used to specify it.

Because \%appendfile%\ and \%pipe%\ are both local transports, they accept only
one recipient address at a time by default. However, you can arrange for them
to handle several addresses at once by setting the \batch@_max\ option. When
this is done for BSMTP, messages may contain multiple \\RCPT\\ commands. See
chapter ~~CHAPbatching for more details.

When one or more addresses are routed to a BSMTP transport by a router that
sets up a host list, the name of the first host on the list is available to the
transport in the variable \$host$\. Here is an example of such a transport and
router:
.display asis
begin routers
route_append:
  driver = manualroute
  transport = smtp_appendfile
  route_list = domain.example  batch.host.example

begin transports
smtp_appendfile:
  driver = appendfile
  directory = /var/bsmtp/$host
  batch_max = 1000
  use_bsmtp
  user = exim
.endd
This causes messages addressed to \*domain.example*\ to be written in BSMTP
format to \(/var/bsmtp/batch.host.example)\, with only a single copy of each
message (unless there are more than 1000 recipients).


.section Incoming batched SMTP
.rset SECTincomingbatchedSMTP "~~chapter.~~section"
.index SMTP||batched incoming
.index batched SMTP input
The \-bS-\ command line option causes Exim to accept one or more messages by
reading SMTP on the standard input, but to generate no responses. If the caller
is trusted, the senders in the \\MAIL\\ commands are believed; otherwise the
sender is always the caller of Exim. Unqualified senders and receivers are not
rejected (there seems little point) but instead just get qualified. \\HELO\\
and \\EHLO\\ act as \\RSET\\; \\VRFY\\, \\EXPN\\, \\ETRN\\ and  \\HELP\\, act
as \\NOOP\\; \\QUIT\\ quits.

No policy checking is done for BSMTP input. That is, no ACL is run at anytime.
In this respect it is like non-SMTP local input.

If an error is detected while reading a message, including a missing `.' at
the end, Exim gives up immediately. It writes details of the error to the
standard output in a stylized way that the calling program should be able to
make some use of automatically, for example:
.display asis
554 Unexpected end of file
Transaction started in line 10
Error detected in line 14
.endd
It writes a more verbose version, for human consumption, to the standard error
file, for example:
.display asis
An error was detected while processing a file of BSMTP input.
The error message was:

  501 '>' missing at end of address

The SMTP transaction started in line 10.
The error was detected in line 12.
The SMTP command at fault was:

   rcpt to:<malformed@in.com.plete

1 previous message was successfully processed.
The rest of the batch was abandoned.
.endd
The return code from Exim is zero only if there were no errors. It is 1 if some
messages were accepted before an error was detected, and 2 if no messages were
accepted.




.
.
.
.
. ============================================================================
.chapter Message processing
.set runningfoot "message processing"
.rset CHAPmsgproc "~~chapter"
.index message||general processing
Exim performs various transformations on the sender and recipient addresses of
all messages that it handles, and also on the messages' header lines. Some of
these are optional and configurable, while others always take place. All of
this processing, except rewriting as a result of routing, and the addition or
removal of header lines while delivering, happens when a message is received,
before it is placed on Exim's queue.

Some of the automatic processing takes place 
.em
by default
.nem
only for `locally-originated' messages. This adjective is used to describe
messages that are not received over TCP/IP, but instead are passed to an Exim
process on its standard input. This includes the interactive `local SMTP' case
that is set up by the \-bs-\ command line option. \**Note**\: messages received
over TCP/IP on the loopback interface (127.0.0.1 or @:@:1) are not considered
to be locally-originated. Exim does not treat the loopback interface specially
in any way.

.em
.index message||submission
Processing that happens automatically for locally-originated messages can also 
be requested for other messages. This is done by obeying the modifier
.display asis
control = submission
.endd
in one of the ACLs that are run for an incoming message (see section
~~SECTACLmodi). This makes Exim treat the message as a local submission, and is 
normally used when the source of the message is known to be an MUA running on a 
client host (as opposed to an MTA). In the descriptions below, the term
`submission mode' is used to describe this state.

When a ::From:: or ::Sender:: header is generated in submission mode, the value 
of \qualify@_domain\ is used by default. However, it is possible to specify 
another domain by a setting such as
.display asis
control = submission/domain=some.other.domain
.endd
.nem



.section Line endings
.rset SECTlineendings "~~chapter.~~section"
.index line endings
.index carriage return
.index linefeed
RFC 2821 specifies that CRLF (two characters: carriage-return, followed by 
linefeed) is the line ending for messages transmitted over the Internet using
SMTP over TCP/IP. However, within individual operating systems, different
conventions are used. For example, Unix-like systems use just LF, but others
use CRLF or just CR.

Exim was designed for Unix-like systems, and internally, it stores messages 
using the system's convention of a single LF as a line terminator. When 
receiving a message, all line endings are translated to this standard format. 
Originally, it was thought that programs that passed messages directly to an 
MTA within an operating system would use that system's convention. Experience 
has shown that this is not the case; for example, there are Unix applications
that use CRLF in this circumstance. For this reason, and for compatibility with 
other MTAs, the way Exim handles line endings for all messages is now as 
follows:
.numberpars $.
LF not preceded by CR is treated as a line ending.
.nextp
CR is treated as a line ending; if it is immediately followed by LF, the LF 
is ignored.
.nextp
The sequence `CR, dot, CR' does not terminate an incoming SMTP message,
nor a local message in the state where a line containing only a dot is a
terminator.
.nextp
If a bare CR is encountered within a header line, an extra space is added after
the line terminator so as not to end the header line. The reasoning behind this
is that bare CRs in header lines are most likely either to be mistakes, or
people trying to play silly games.
.nextp
.em
If the first header line received in a message ends with CRLF, a subsequent 
bare LF in a header line is treated in the same way as a bare CR in a header 
line. 
.nem
.endp



.section Unqualified addresses
.index unqualified addresses
.index address||qualification
By default, Exim expects every address it receives from an external host to be
fully qualified. Unqualified addresses cause negative responses to SMTP
commands. However, because SMTP is used as a means of transporting messages
from MUAs running on personal workstations, there is sometimes a requirement to
accept unqualified addresses from specific hosts or IP networks.

Exim has two options that separately control which hosts may send unqualified
sender or receipient addresses in SMTP commands, namely
\sender__unqualified__hosts\ and \recipient__unqualified__hosts\. In both
cases, if an unqualified address is accepted, it is qualified by adding the
value of \qualify__domain\ or \qualify__recipient\, as appropriate.
.index \qualify@_domain\
.index \qualify@_recipient\


.section The UUCP From line
.index `From' line
.index UUCP||`From' line
.index sender||address
.index \uucp@_from@_pattern\
.index \uucp@_from@_sender\
.index envelope sender
.index Sendmail compatibility||`From' line
Messages that have come from UUCP (and some other applications) often begin
with a line containing the envelope sender and a timestamp, following the word
`From'. Examples of two common formats are:
.display asis
From a.oakley@berlin.mus Fri Jan  5 12:35 GMT 1996
From f.butler@berlin.mus Fri, 7 Jan 97 14:00:00 GMT
.endd
This line precedes the RFC 2822 header lines. For compatibility with Sendmail,
Exim recognizes such lines at the start of messages that are submitted to it
via the command line (that is, on the standard input). It does not recognize
such lines in incoming SMTP messages, unless the sending host matches
\ignore@_fromline@_hosts\ or the \-bs-\ option was used for a local message and
\ignore@_fromline@_local\ is set. The recognition is controlled by a regular
expression that is defined by the \uucp@_from@_pattern\ option, whose default
value matches the two common cases shown above and puts the address that
follows `From' into \$1$\.

.index numerical variables (\$1$\, \$2$\, etc)||in `From ' line handling
When the caller of Exim for a non-SMTP message that contains a `From' line is a
trusted user, the message's sender address is constructed by expanding the
contents of \uucp@_sender@_address\, whose default value is `@$1'. This is then
parsed as an RFC 2822 address. If there is no domain, the local part is
qualified with \qualify@_domain\ unless it is the empty string. However, if the
command line \-f-\ option is used, it overrides the `From' line.

If the caller of Exim is not trusted, the `From' line is recognized, but the
sender address is not changed. This is also the case for incoming SMTP messages
that are permitted to contain `From' lines.

Only one `From' line is recognized. If there is more than one, the second is
treated as a data line that starts the body of the message, as it is not valid
as a header line. This also happens if a `From' line is present in an incoming
SMTP message from a source that is not permitted to send them.


.section Resent- header lines
.index \Resent@-\ header lines
RFC 2822 makes provision for sets of header lines starting with the string
\"Resent-"\ to be added to a message when it is resent by the original
recipient to somebody else. These headers are ::Resent-Date::, ::Resent-From::,
::Resent-Sender::, ::Resent-To::, ::Resent-Cc::, ::Resent-Bcc:: and
::Resent-Message-ID::. The RFC says:

\*Resent fields are strictly informational. They MUST NOT be used in the normal
processing of replies or other such automatic actions on messages.*\

This leaves things a bit vague as far as other processing actions such as
address rewriting are concerned. Exim treats \Resent@-\ header lines as
follows:
.numberpars $.
A ::Resent-From:: line that just contains the login id of the submitting user
is automatically rewritten in the same way as ::From:: (see below).
.nextp
If there's a rewriting rule for a particular header line, it is also applied to
\Resent@-\ header lines of the same type. For example, a rule that rewrites
::From:: also rewrites ::Resent-From::.
.nextp
For local messages, if ::Sender:: is removed on input, ::Resent-Sender:: is also
removed.
.nextp
For a locally-submitted message,
if there are any \Resent@-\ header lines but no ::Resent-Date::,
::Resent-From::, or ::Resent-Message-Id::, they are added as necessary. It is
the contents of ::Resent-Message-Id:: (rather than ::Message-Id::) which are
included in log lines in this case.
.nextp
The logic for adding ::Sender:: is duplicated for ::Resent-Sender:: when any
\Resent@-\ header lines are present.
.endp


.section The Auto-Submitted: header line
Whenever Exim generates a bounce or a delay warning message, it includes the 
header line
.display asis
Auto-Submitted: auto-generated
.endd


.section The Bcc: header line
.index ::Bcc:: header line
If Exim is called with the \-t-\ option, to take recipient addresses from a
message's header, it removes any ::Bcc:: header line that may exist (after
extracting its addresses). If \-t-\ is not present on the command line, any
existing ::Bcc:: is not removed.

.section The Date: header line
.index ::Date:: header line
If a locally-generated 
.em
or submission-mode
.nem
message has no ::Date:: header line, Exim adds one, using the current date and
time.

.section The Delivery-date: header line
.index ::Delivery-date:: header line
.index \delivery@_date@_remove\
::Delivery-date:: header lines are not part of the standard RFC 2822 header
set. Exim can be configured to add them to the final delivery of messages. (See
the generic \delivery@_date@_add\ transport option.) They should not be present
in messages in transit. If the \delivery@_date@_remove\ configuration option is
set (the default), Exim removes ::Delivery-date:: header lines from incoming
messages.

.section The Envelope-to: header line
.index ::Envelope-to:: header line
.index \envelope@_to@_remove\
::Envelope-to:: header lines are not part of the standard RFC 2822 header set.
Exim can be configured to add them to the final delivery of messages. (See the
generic \envelope@_to@_add\ transport option.) They should not be present in
messages in transit. If the \envelope@_to@_remove\ configuration option is set
(the default), Exim removes ::Envelope-to:: header lines from incoming
messages.

.section The From: header line
.index ::From:: header line
.index Sendmail compatibility||`From' line
.em
If a submission-mode message does not contain a ::From:: header line, Exim adds 
one if either of the following conditions is true:
.numberpars alpha
The envelope sender address is not empty (that is, this is not a bounce 
message); the added header line copies the envelope sender address.
.nextp
The SMTP session is authenticated and \$authenticated@_id$\ is not empty; the 
added header's local part is \$authenticated@_id$\ and the domain is 
the domain specified on the submission control, or \$qualify@_domain$\ if that 
is not set.
.endp
A non-empty envelope sender takes precedence.
.nem

If a locally-generated incoming message does not contain a ::From:: header
line, Exim adds one containing the sender's address. The calling user's login
name and full name are used to construct the address, as described in section
~~SECTconstr. They are obtained from the password data by calling
\*getpwuid()*\ (but see the \unknown@_login\ configuration option). The address
is qualified with \qualify@_domain\.

For compatibility with Sendmail, if an incoming, non-SMTP message has a
::From:: header line containing just the unqualified login name of the calling
user, this is replaced by an address containing the user's login name and full
name as described in section ~~SECTconstr.

.section The Message-ID: header line
.index ::Message-ID:: header line
If a locally-generated
.em
or submission-mode
.nem
incoming message does not contain a ::Message-ID:: or ::Resent-Message-ID::
header line, Exim adds one to the message. If there are any ::Resent-:: headers
in the message, it creates ::Resent-Message-ID::. The id is constructed from
Exim's internal message id, preceded by the letter E to ensure it starts with a
letter, and followed by @@ and the primary host name. Additional information
can be included in this header line by setting the
.index \message@_id@_header@_text\
\message@_id@_header@_text\ and/or \message__id__header__domain\ options.


.section The Received: header line
.index ::Received:: header line
A ::Received:: header line is added at the start of every message. The contents
are defined by the \received@_header@_text\ configuration option, and Exim
automatically adds a semicolon and a timestamp to the configured string.

.em
The ::Received:: header is generated as soon as the message's header lines have 
been received. At this stage, the timestamp in the ::Received:: header line is 
the time that the message started to be received. This is the value that is 
seen by the \\DATA\\ ACL and by the \*local@_scan()*\ function.

Once a message is accepted, the timestamp in the ::Received:: header line is 
changed to the time of acceptance, which is (apart from a small delay while the 
-H spool file is written) the earliest time at which delivery could start.
.nem 


.section The Return-path: header line
.index ::Return-path:: header line
.index \return@_path@_remove\
::Return-path:: header lines are defined as something an MTA may insert when
it does the final delivery of messages. (See the generic \return@_path@_add\
transport option.) Therefore, they should not be present in messages in
transit. If the \return@_path@_remove\ configuration option is set (the
default), Exim removes ::Return-path:: header lines from incoming messages.


.section The Sender: header line
.rset SECTthesenhea "~~chapter.~~section"
.index ::Sender:: header line
For a locally-originated message from an untrusted user, Exim may remove an
existing ::Sender:: header line, and it may add a new one. You can modify these
actions by setting \local@_sender@_retain\ true or \local@_from@_check\ false.

When a local message is received from an untrusted user and
\local@_from@_check\ is true (the default), a check is made to see if the
address given in the ::From:: header line is the correct (local) sender of the
message. The address that is expected has the login name as the local part and
the value of \qualify@_domain\ as the domain. Prefixes and suffixes for the
local part can be permitted by setting \local@_from@_prefix\ and
\local@_from@_suffix\ appropriately. If ::From:: does not contain the correct
sender, a ::Sender:: line is added to the message.

If you set \local@_from@_check\ false, this checking does not occur. However,
the removal of an existing ::Sender:: line still happens, unless you also set
\local@_sender@_retain\ to be true. It is not possible to set both of these
options true at the same time.

.em
By default, no processing of ::Sender:: header lines is done for messages
received by TCP/IP or for messages submitted by trusted users. However, when a 
message is received over TCP/IP in submission mode, ::Sender:: header lines are 
always removed. If the SMTP session is authenticated, and \$authenticated@_id$\ 
is not empty, a sender address is created with \$authenticated@_id$\ as the 
local part and either the domain specified in the submission control or, if 
that is not specified, \$qualify@_domain$\ as the domain. This is compared with
the address in the ::From:: header line. If they are different, a ::Sender::
header line is added. Prefixes and suffixes for the local part in ::From:: can
be permitted by setting \local@_from@_prefix\ and \local@_from@_suffix\
appropriately.
.nem


.section Adding and removing header lines
.index header lines||adding
.index header lines||removing
.rset SECTheadersaddrem "~~chapter.~~section"
When a message is delivered, the addition and removal of header lines can be
specified on any of the routers and transports, and also in the system filter.
Changes specified in the system filter affect all deliveries of a message.

Header changes specified on a router affect all addresses handled by that
router, and also any new addresses it generates. If an address passes through
several routers, the changes are cumulative. When a message is processed by a
transport, the message's original set of header lines is output, except for
those named in any \headers@_remove\ options that the address has encountered
as it was processed, and any in the transport's own \headers@_remove\ option.
Then the new header lines from \headers@_add\ options are output.


.section Constructed addresses
.rset SECTconstr "~~chapter.~~section"
.index address||constructed
.index constructed address
When Exim constructs a sender address for a locally-generated message, it uses
the form
.display
<<user name>> <$$<<login>>@@<<qualify@_domain>>$$>
.endd
For example:
.display asis
Zaphod Beeblebrox <zaphod@end.univ.example>
.endd
The user name is obtained from the \-F-\ command line option if set, or
otherwise by looking up the calling user by \*getpwuid()*\ and extracting the
`gecos' field from the password entry. If the `gecos' field contains an
ampersand character, this is replaced by the login name with the first letter
upper cased, as is conventional in a number of operating systems. See the
\gecos@_name\ option for a way to tailor the handling of the `gecos' field. The
\unknown@_username\ option can be used to specify user names in cases when
there is no password file entry.

In all cases, the user name is made to conform to RFC 2822 by quoting all or
parts of it if necessary. In addition, if it contains any non-printing
characters, it is encoded as described in RFC 2047, which defines a way of
including non-ASCII characters in header lines. 
The value of the \headers@_charset\ option specifies the name of the encoding 
that is used (the characters are assumed to be in this encoding).
The setting of \print@_topbitchars\ controls whether characters with the top
bit set (that is, with codes greater than 127) count as printing characters or
not.


.section Case of local parts
.index case of local parts
.index local part||case of
RFC 2822 states that the case of letters in the local parts of addresses cannot
be assumed to be non-significant. Exim preserves the case of local parts of
addresses, but by default it uses a lower-cased form when it is routing,
because on most Unix systems, usernames are in lower case and case-insensitive
routing is required. However, any particular router can be made to use the
original case for local parts by setting the \caseful@_local@_part\ generic
router option.

.index mixed-case login names
If you must have mixed-case user names on your system, the best way to proceed,
assuming you want case-independent handling of incoming email, is to set up
your first router to convert incoming local parts in your domains to the
correct case by means of a file lookup. For example:
.display asis
correct_case:
  driver = redirect
  domains = +local_domains
  data = ${lookup{$local_part}cdb\
              {/etc/usercased.cdb}{$value}fail}\
              @$domain
.endd
For this router, the local part is forced to lower case by the default action
(\caseful@_local@_part\ is not set). The lower-cased local part is used to look
up a new local part in the correct case. If you then set \caseful@_local@_part\
on any subsequent routers which process your domains, they will operate on
local parts with the correct case in a case-sensitive manner.


.section Dots in local parts
.index dot||in local part
.index local part||dots in
RFC 2822 forbids empty components in local parts. That is, an unquoted local
part may not begin or end with a dot, nor have two consecutive dots in the
middle. However, it seems that many MTAs do not enforce this, so Exim permits
empty components for compatibility.


.section Rewriting addresses
.index rewriting||addresses
Rewriting of sender and recipient addresses, and addresses in headers, can
happen automatically, or as the result of configuration options, as described
in chapter ~~CHAPrewrite. The headers that may be affected by this are ::Bcc::,
::Cc::, ::From::, ::Reply-To::, ::Sender::, and ::To::.

Automatic rewriting includes qualification, as mentioned above. The other case
in which it can happen is when an incomplete non-local domain is given. The
routing process may cause this to be expanded into the full domain name. For
example, a header such as
.display asis
To: hare@teaparty
.endd
might get rewritten as
.display asis
To: hare@teaparty.wonderland.fict.example
.endd
Rewriting as a result of routing is the one kind of message processing that
does not happen at input time, as it cannot be done until the address has
been routed.

Strictly, one should not do $it{any} deliveries of a message until all its
addresses have been routed, in case any of the headers get changed as a
result of routing. However, doing this in practice would hold up many
deliveries for unreasonable amounts of time, just because one address could not
immediately be routed. Exim therefore does not delay other deliveries when
routing of one or more addresses is deferred.





.
.
.
.
. ============================================================================
.chapter Log files
.set runningfoot "log files"
.rset CHAPlog "~~chapter"
.index log||types of
.index log||general description
Exim writes three different logs, referred to as the main log, the reject log,
and the panic log:
.numberpars $.
.index main log
The main log records the arrival of each message and each delivery in a single
line in each case. The format is as compact as possible, in an attempt to keep
down the size of log files. Two-character flag sequences make it easy to pick
out these lines. A number of other events are recorded in the main log. Some of
them are optional, in which case the \log@_selector\ option controls whether
they are included or not. A Perl script called \*eximstats*\, which does simple
analysis of main log files, is provided in the Exim distribution (see section
~~SECTmailstat).
.nextp
.index reject log
The reject log records information from messages that are rejected as a result
of a configuration option (that is, for policy reasons). 
.em
The first line of each rejection is a copy of the line that is also written to
the main log. Then, if the message's header has been read at the time the log
is written, its contents are written to this log. Only the original header
lines are available; header lines added by ACLs are not logged. You can use the
reject log to check that your policy controls are working correctly; on a busy
host this may be easier than scanning the main log for rejection messages. You
can suppress the writing of the reject log by setting \write@_rejectlog\ false.
.nem
.nextp
.index panic log
.index system log
When certain serious errors occur, Exim writes entries to its panic log. If the
error is sufficiently disastrous, Exim bombs out afterwards. Panic log entries
are usually written to the main log as well, but can get lost amid the mass of
other entries. The panic log should be empty under normal circumstances. It is
therefore a good idea to check it (or to have a \*cron*\ script check it)
regularly, in order to become aware of any problems. When Exim cannot open its
panic log, it tries as a last resort to write to the system log (syslog). This
is opened with LOG@_PID+LOG@_CONS and the facility code of LOG@_MAIL. The
message itself is written at priority LOG@_CRIT.
.endp
Every log line starts with a timestamp, in the format shown in this example:
.display asis
2001-09-16 16:09:47 SMTP connection from [127.0.0.1] closed by QUIT
.endd
By default, the timestamps are in the local timezone. There are two 
ways of changing this:
.numberpars $.
You can set the \timezone\ option to a different time zone; in particular, if
you set
.display asis
timezone = UTC
.endd
the timestamps will be in UTC (aka GMT).
.nextp
If you set \log@_timezone\ true, the time zone is added to the timestamp, for 
example:
.display asis
2003-04-25 11:17:07 +0100 Start queue run: pid=12762
.endd
.endp



.section Where the logs are written
.rset SECTwhelogwri "~~chapter.~~section"
.index log||destination
.index log||to file
.index log||to syslog
.index syslog
The logs may be written to local files, or to syslog, or both. However, it
should be noted that many syslog implementations use UDP as a transport, and
are therefore unreliable in the sense that messages are not guaranteed to
arrive at the loghost, nor is the ordering of messages necessarily maintained.
It has also been reported that on large log files (tens of megabytes) you may
need to tweak syslog to prevent it syncing the file with each write -- on Linux
this has been seen to make syslog take 90% plus of CPU time.

The destination for Exim's logs is configured by setting \\LOG@_FILE@_PATH\\ in
\(Local/Makefile)\ or by setting \log@_file@_path\ in the run time
configuration. This latter string is expanded, so it can contain, for example,
references to the host name:
.display asis
log_file_path = /var/log/$primary_hostname/exim_%slog
.endd
It is generally advisable, however, to set the string in \(Local/Makefile)\
rather than at run time, because then the setting is available right from the
start of Exim's execution. Otherwise, if there's something it wants to log
before it has read the configuration file (for example, an error in the
configuration file) it will not use the path you want, and may not be able to
log at all.

The value of \\LOG@_FILE@_PATH\\ or \log@_file@_path\ is a colon-separated
list, currently limited to at most two items. This is one option where the
facility for changing a list separator may not be used. The list must always be
colon-separated. If an item in the list is `syslog' then syslog is used;
otherwise the item must either be an absolute path, containing \"%s"\ at the
point where `main', `reject', or `panic' is to be inserted, or be empty,
implying the use of a default path.

When Exim encounters an empty item in the list, it searches the list defined by
\\LOG@_FILE@_PATH\\, and uses the first item it finds that is neither empty nor
`syslog'. This means that an empty item in \log@_file@_path\ can be used to
mean `use the path specified at build time'. It no such item exists, log files
are written in the \(log)\ subdirectory of the spool directory. This is
equivalent to the setting:
.display asis
log_file_path = $spool_directory/log/%slog
.endd
If you do not specify anything at build time or run time, that is where the 
logs are written.

A log file path may also contain \"%D"\ if datestamped log file names are in
use -- see section ~~SECTdatlogfil below.

Here are some examples of possible settings:
.display
.tabs 42
LOG@_FILE@_PATH=syslog                      $t $rm{syslog only}
LOG@_FILE@_PATH=:syslog                     $t $rm{syslog and default path}
LOG@_FILE@_PATH=syslog : /usr/log/exim@_%s  $t $rm{syslog and specified path}
LOG@_FILE@_PATH=/usr/log/exim@_%s           $t $rm{specified path only}
.endd
If there are more than two paths in the list, the first is used and a panic
error is logged.


.section Logging to local files that are periodically `cycled'
.index log||cycling local files
.index cycling logs
.index \*exicyclog*\
.index log||local files, writing to
Some operating systems provide centralized and standardised methods for cycling
log files. For those that do not, a utility script called \*exicyclog*\ is
provided (see section ~~SECTcyclogfil). This renames and compresses the main
and reject logs each time it is called. The maximum number of old logs to keep
can be set. It is suggested this script is run as a daily \*cron*\ job.

An Exim delivery process opens the main log when it first needs to write to it,
and it keeps the file open in case subsequent entries are required -- for
example, if a number of different deliveries are being done for the same
message. However, remote SMTP deliveries can take a long time, and this means
that the file may be kept open long after it is renamed if \*exicyclog*\ or
something similar is being used to rename log files on a regular basis. To
ensure that a switch of log files is noticed as soon as possible, Exim calls
\*stat()*\ on the main log's name before reusing an open file, and if the file
does not exist, or its inode has changed, the old file is closed and Exim
tries to open the main log from scratch. Thus, an old log file may remain open
for quite some time, but no Exim processes should write to it once it has been
renamed.


.section Datestamped log files
.rset SECTdatlogfil "~~chapter.~~section"
.index log||datestamped files
Instead of cycling the main and reject log files by renaming them
periodically, some sites like to use files whose names contain a datestamp,
for example, \(mainlog-20031225)\. The datestamp is in the form \(yyyymmdd)\.
Exim has support for this way of working. It is enabled by setting the
\log@_file@_path\ option to a path that includes \"%D"\ at the point where the
datestamp is required. For example:
.display asis
log_file_path = /var/spool/exim/log/%slog-%D
log_file_path = /var/log/exim-%s-%D.log
log_file_path = /var/spool/exim/log/%D-%slog
.endd
As before, \"%s"\ is replaced by `main' or `reject'; the following are examples
of names generated by the above examples:
.display asis
/var/spool/exim/log/mainlog-20021225
/var/log/exim-reject-20021225.log
/var/spool/exim/log/20021225-mainlog
.endd
When this form of log file is specified, Exim automatically switches to new
files at midnight. It does not make any attempt to compress old logs; you
will need to write your own script if you require this. You should not
run \*exicyclog*\ with this form of logging.

The location of the panic log is also determined by \log@_file@_path\, but it
is not datestamped, because rotation of the panic log does not make sense.
When generating the name of the panic log, \"%D"\ is removed from the string.
In addition, if it immediately follows a slash, a following non-alphanumeric
character is removed; otherwise a preceding non-alphanumeric character is
removed. Thus, the three examples above would give these panic log names:
.display asis
/var/spool/exim/log/paniclog
/var/log/exim-panic.log
/var/spool/exim/log/paniclog
.endd


.section Logging to syslog
.index log||syslog, writing to
The use of syslog does not change what Exim logs or the format of its messages,
except in one respect. If \syslog@_timestamp\ is set false, the timestamps on
Exim's log lines are omitted when these lines are sent to syslog. Apart from
that, the same strings are written to syslog as to log files. The syslog
`facility' is set to \\LOG@_MAIL\\, and the program name to `exim'
by default, but you can change these by setting the \syslog@_facility\ and
\syslog@_processname\ options, respectively. If Exim was compiled with
\\SYSLOG@_LOG@_PID\\ set in \(Local/Makefile)\ (this is the default in 
\(src/EDITME)\), then, on systems that permit it (all except ULTRIX), the
\\LOG@_PID\\ flag is set so that the \*syslog()*\ call adds the pid as well as
the time and host name to each line.
The three log streams are mapped onto syslog priorities as follows:
.numberpars " "
\*mainlog*\ is mapped to \\LOG@_INFO\\
.nextp
\*rejectlog*\ is mapped to \\LOG@_NOTICE\\
.nextp
\*paniclog*\ is mapped to \\LOG@_ALERT\\
.endp
Many log lines are written to both \*mainlog*\ and \*rejectlog*\, and some are 
written to both \*mainlog*\ and \*paniclog*\, so there will be duplicates if
these are routed by syslog to the same place. You can suppress this duplication 
by setting \syslog@_duplication\ false.

Exim's log lines can sometimes be very long, and some of its \*rejectlog*\
entries contain multiple lines when headers are included. To cope with both
these cases, entries written to syslog are split into separate \*syslog()*\
calls at each internal newline, and also after a maximum of 
870 data characters. (This allows for a total syslog line length of 1024, when
additions such as timestamps are added.) If you are running a syslog
replacement that can handle lines longer than the 1024 characters allowed by
RFC 3164, you should set
.display asis
SYSLOG_LONG_LINES=yes
.endd
in \(Local/Makefile)\ before building Exim. That stops Exim from splitting long 
lines, but it still splits at internal newlines in \*reject*\ log entries.

To make it easy to re-assemble split lines later, each component of a split
entry starts with a string of the form `[<<n>>/<<m>>]' or `[<<n>>@\<<m>>]'
where <<n>> is the component number and <<m>> is the total number of components
in the entry. The / delimiter is used when the line was split because it was
too long; if it was split because of an internal newline, the @\ delimiter is
used. For example, supposing the length limit to be 70 instead of 1000, the
following would be the result of a typical rejection message to \*mainlog*\
(LOG@_INFO), each line in addition being preceded by the time, host name, and
pid as added by syslog:
.display
.indent 0
$smc{[1/3] 2002-09-16 16:09:43 16RdAL-0006pc-00 rejected from [127.0.0.1] (ph10):
[2/3]  syntax error in 'From' header when scanning for sender: missing or ma
[3/3] lformed local part in "<>" (envelope sender is <ph10@@cam.example>)}
.endd
The same error might cause the following lines to be written to `rejectlog'
(LOG@_NOTICE):
.display flow
.indent 0
$smc{[1/14] 2002-09-16 16:09:43 16RdAL-0006pc-00 rejected from [127.0.0.1] (ph10):
[2/14]  syntax error in 'From' header when scanning for sender: missing or ma
[3@\14] lformed local part in "@<@>" (envelope sender is <ph10@@cam.example>)
[4@\14] Recipients: ph10@@some.domain.cam.example
[5@\14] P Received: from [127.0.0.1] (ident=ph10)
[6@\14]        by xxxxx.cam.example with smtp (Exim 4.00)
[7@\14]        id 16RdAL-0006pc-00
[8@\14]        for ph10@@cam.example; Mon, 16 Sep 2002 16:09:43 +0100
[9@\14] F From: @<@>
[10@\14]   Subject: this is a test header
[11@\14]   X-something: this is another header
[12@\14] I Message-Id: <E16RdAL-0006pc-00@@xxxxx.cam.example>
[13@\14] B Bcc:
[14/14]   Date: Mon, 16 Sep 2002 16:09:43 +0100}
.endd
Log lines that are neither too long nor contain newlines are written to syslog
without modification.

If only syslog is being used, the Exim monitor is unable to provide a log tail
display, unless syslog is routing \*mainlog*\ to a file on the local host and
the environment variable \\EXIMON@_LOG@_FILE@_PATH\\ is set to tell the monitor
where it is.


.section Log line flags
One line is written to the main log for each message received, and for each
successful, unsuccessful, and delayed delivery. These lines can readily be
picked out by the distinctive two-character flags that immediately follow the
timestamp. The flags are:
.display
.tabs 6
<=    $t $rm{message arrival}
=>    $t $rm{normal message delivery}
->    $t $rm{additional address in same delivery}
*>    $t $rm{delivery suppressed by \-N-\}
**    $t $rm{delivery failed; address bounced}
==    $t $rm{delivery deferred; temporary problem}
.endd


.section Logging message reception
.index log||reception line
The format of the single-line entry in the main log that is written for every
message received is shown in the basic example below, which is split over
several lines in order to fit it on the page:
.display
.indent 0
2002-10-31 08:57:53 16ZCW1-0005MB-00 <= kryten@@dwarf.fict.example
  H=mailer.fict.example [192.168.123.123] U=exim
  P=smtp S=5678 id=<<incoming message id>>
.endd
The address immediately following `<=' is the envelope sender address. A bounce
message is shown with the sender address `<>', and if it is locally generated,
this is followed by an item of the form
.display
R=<<message id>>
.endd
which is a reference to the message that caused the bounce to be sent.

.index \\HELO\\
.index \\EHLO\\
For messages from other hosts, the H and U fields identify the remote host and
record the RFC 1413 identity of the user that sent the message, if one was
received. The number given in square brackets is the IP address of the sending
host. If there is a single, unparenthesized  host name in the H field, as
above, it has been verified to correspond to the IP address (see the
\host@_lookup\ option). If the name is in parentheses, it was the name quoted
by the remote host in the SMTP \\HELO\\ or \\EHLO\\ command, and has not been
verified. If verification yields a different name to that given for \\HELO\\ or
\\EHLO\\, the verified name appears first, followed by the \\HELO\\ or \\EHLO\\
name in parentheses.

Misconfigured hosts (and mail forgers) sometimes put an IP address, with or
without brackets, in the \\HELO\\ or \\EHLO\\ command, leading to entries in
the log containing text like these examples:
.display
H=(10.21.32.43) [192.168.8.34]
H=([10.21.32.43]) [192.168.8.34]
.endd
This can be confusing. Only the final address in square brackets can be relied
on.

For locally generated messages (that is, messages not received over TCP/IP),
the H field is omitted, and the U field contains the login name of the caller
of Exim.

.index authentication||logging
.index \\AUTH\\||logging
For all messages, the P field specifies the protocol used to receive the
message. This is set to `asmtp' for messages received from hosts which have
authenticated themselves using the SMTP \\AUTH\\ command. In this case there is
an additional item A= followed by the name of the authenticator that was used.
If an authenticated identification was set up by the authenticator's
\server@_set@_id\ option, this is logged too, separated by a colon from the
authenticator name.

The id field records the existing message id, if present.
.index size||of message
The size of the received message is given by the S field. When the message is
delivered, headers may get removed or added, so that the size of delivered
copies of the message may not correspond with this value (and indeed may be
different to each other).

The \log@_selector\ option can be used to request the logging of additional
data when a message is received. See section ~~SECTlogselector below.


.section Logging deliveries
.index log||delivery line
The format of the single-line entry in the main log that is written for every
delivery is shown in one of the examples below, for local and remote deliveries,
respectively. Each example has been split into two lines in order to fit
it on the page:
.display
.indent 0
2002-10-31 08:59:13 16ZCW1-0005MB-00 => marv <marv@@hitch.fict.example>
  R=localuser T=local@_delivery
2002-10-31 09:00:10 16ZCW1-0005MB-00 => monk@@holistic.fict.example
  R=dnslookup T=remote@_smtp H=holistic.fict.example [192.168.234.234]
.endd
For ordinary local deliveries, the original address is given in angle brackets
after the final delivery address, which might be a pipe or a file. If
intermediate address(es) exist between the original and the final address, the
last of these is given in parentheses after the final address. The R and T
fields record the router and transport that were used to process the address.

If a shadow transport was run after a successful local delivery, the log line
for the successful delivery has an item added on the end, of the form
.display
ST=<<shadow transport name>>
.endd
If the shadow transport did not succeed, the error message is put in
parentheses afterwards.

When more than one address is included in a single delivery (for example, two
SMTP \\RCPT\\ commands in one transaction) the second and subsequent
addresses are flagged with `$tt{@-@>}' instead of `$tt{@=@>}'. When two or more
messages are delivered down a single SMTP connection, an asterisk follows the
IP address in the log lines for the second and subsequent messages.

The generation of a reply message by a filter file gets logged as a `delivery'
to the addressee, preceded by `>'.

The \log@_selector\ option can be used to request the logging of additional
data when a message is delivered. See section ~~SECTlogselector below.


.section Discarded deliveries
.index discarded messages
.index message||discarded
.index delivery||discarded, logging
When a message is discarded as a result of the command `seen finish' being
obeyed in a filter file which generates no deliveries, a log entry of the form
.display
2002-12-10 00:50:49 16auJc-0001UB-00 => discarded
  <low.club@@bridge.example> R=userforward
.endd
is written, to record why no deliveries are logged. When a message is discarded
because it is aliased to `:blackhole:' the log line is like this:
.display asis
1999-03-02 09:44:33 10HmaX-0005vi-00 => :blackhole:
  <hole@nowhere.example> R=blackhole_router
.endd


.section Deferred deliveries
When a delivery is deferred, a line of the following form is logged:
.display
.indent 0
2002-12-19 16:20:23 16aiQz-0002Q5-00 == marvin@@endrest.example
  R=dnslookup T=smtp defer (146): Connection refused
.endd
In the case of remote deliveries, the error is the one that was given for the
last IP address that was tried. Details of individual SMTP failures are also
written to the log, so the above line would be preceded by something like
.display
.indent 0
2002-12-19 16:20:23 16aiQz-0002Q5-00 Failed to connect to
  mail1.endrest.example [192.168.239.239]: Connection refused
.endd
When a deferred address is skipped because its retry time has not been reached,
a message is written to the log, but this can be suppressed by setting an
appropriate value in \log@_selector\.


.section Delivery failures
.index delivery||failure, logging
If a delivery fails because an address cannot be routed, a line of the
following form is logged:
.display asis
.indent 0
1995-12-19 16:20:23 0tRiQz-0002Q5-00 ** jim@trek99.example
  <jim@trek99.example>: unknown mail domain
.endd
If a delivery fails at transport time, the router and transport are shown, and 
the response from the remote host is included, as in this example:
.display asis
.indent 0
2002-07-11 07:14:17 17SXDU-000189-00 ** ace400@pb.example R=dnslookup
.newline
.em
  T=remote_smtp: SMTP error from remote mailer after pipelined
.newline
.nem    
  RCPT TO:<ace400@pb.example>: host pbmail3.py.example 
  [192.168.63.111]: 553 5.3.0 <ace400@pb.example>... 
  Addressee unknown
.endd
.em
The word `pipelined' indicates that the SMTP \\PIPELINING\\ extension was being 
used. See \hosts@_avoid@_esmtp\ in the \%smtp%\ transport for a way of 
disabling \\PIPELINING\\.
.nem

The log lines for all forms of delivery failure are flagged with \"**"\.


.section Fake deliveries
.index delivery||fake, logging
If a delivery does not actually take place because the \-N-\ option has been
used to suppress it, a normal delivery line is written to the log, except that
`=>' is replaced by `$*$>'.


.section Completion
A line of the form
.display
2002-10-31 09:00:11 16ZCW1-0005MB-00 Completed
.endd
is written to the main log when a message is about to be removed from the spool
at the end of its processing.



.section Summary of Fields in Log Lines
.index log||summary of fields
A summary of the field identifiers that are used in log lines is shown in
the following table:
.display flow
.tabs 8
A          $t $rm{authenticator name (and optional id)}
C          $t $rm{SMTP confirmation on delivery}
.newline
.em
CV         $t $rm{certificate verification status}
DN         $t $rm{distinguished name from peer certificate}
DT         $t $rm{time taken for a delivery}
.newline
.nem
F          $t $rm{sender address (on delivery lines)}
H          $t $rm{host name and IP address}
.newline
.em
I          $t $rm{local interface used}
.newline
.nem
id         $t $rm{message id for incoming message}
P          $t $rm{on \"<="\ lines: protocol used}
.newline
.em
           $t $rm{on \"=>"\ lines: return path}
QT         $t $rm{time spent on queue}            
.newline
.nem
R          $t $rm{on \"<="\ lines: reference for local bounce}
           $t $rm{on \"=>"\ lines: router name}
S          $t $rm{size of message}
ST         $t $rm{shadow transport name}
T          $t $rm{on \"<="\ lines: message subject (topic)}
           $t $rm{on \"=>"\ lines: transport name}
U          $t $rm{local user or RFC 1413 identity}
X          $t $rm{TLS cipher suite}
.endd


.section Other log entries
Various other types of log entry are written from time to time. Most should be
self-explanatory. Among the more common are:
.numberpars $.
.index retry||time not reached
\*retry time not reached*\##An address previously suffered a temporary error
during routing or local delivery, and the time to retry has not yet arrived.
This message is not written to an individual message log file unless it happens
during the first delivery attempt.
.nextp
\*retry time not reached for any host*\##An address previously suffered
temporary errors during remote delivery, and the retry time has not yet arrived
for any of the hosts to which it is routed.
.nextp
.index spool directory||file locked
\*spool file locked*\##An attempt to deliver a message cannot proceed because
some other Exim process is already working on the message. This can be quite
common if queue running processes are started at frequent intervals. The
\*exiwhat*\ utility script can be used to find out what Exim processes are
doing.
.nextp
.em
.index error||ignored
\*error ignored*\##There are several circumstances that give rise to this 
message:
.numberpars " "
Exim failed to deliver a bounce message whose age was greater than 
\ignore__bounce__errors__after\. The bounce was discarded.
.nextp
A filter file set up a delivery using the `noerror' option, and the delivery 
failed. The delivery was discarded.
.nextp
A delivery set up by a router configured with 
.display asis
errors_to = <>
.endd
failed. The delivery was discarded.
.endp 
.nem
.endp



.section Reducing or increasing what is logged
.rset SECTlogselector "~~chapter.~~section"
.index log||selectors
By setting the \log@_selector\ global option, you can disable some of Exim's
default logging, or you can request additional logging. The value of
\log@_selector\ is made up of names preceded by plus or minus characters. For
example:
.display asis
log_selector = +arguments -retry_defer
.endd
The list of optional log items is in the following table, with the default
selection marked by asterisks:
.display flow
.tabs 32
 address@_rewrite           $t $rm{address rewriting}
 all@_parents               $t $rm{all parents in => lines}
 arguments                  $t $rm{command line arguments}
*connection@_reject         $t $rm{connection rejections}
*delay@_delivery            $t $rm{immediate delivery delayed (message queued)}
.newline
.em
 deliver@_time              $t $rm{time taken to perform delivery}
.newline
.nem
 delivery@_size             $t $rm{add S=nnn to => lines}
*dnslist@_defer             $t $rm{defers of DNS list (aka RBL) lookups}
*etrn                       $t $rm{ETRN commands}
*host@_lookup@_failed       $t $rm{as it says}
.newline
.em
 ident@_timeout             $t $rm{timeout for ident connection}
.newline
.nem
 incoming@_interface        $t $rm{incoming interface on <= lines}
 incoming@_port             $t $rm{incoming port on <= lines}
*lost@_incoming@_connection $t $rm{as it says (includes timeouts)}
.newline
.em
 outgoing@_port             $t $rm{add remote port to => lines}
.newline
.nem
*queue@_run                 $t $rm{start and end queue runs}
.newline
.em
 queue@_time                $t $rm{time on queue}
.newline
.nem
 received@_recipients       $t $rm{recipients on <= lines}
 received@_sender           $t $rm{sender on <= lines}
*rejected@_header           $t $rm{header contents on reject log}
*retry@_defer               $t $rm{`retry time not reached'}
.newline
.em
 return@_path@_on@_delivery $t $rm{put return path on => and ** lines}
.newline
.nem
 sender@_on@_delivery       $t $rm{add sender to => lines}
*size@_reject               $t $rm{rejection because too big}
*skip@_delivery             $t $rm{`message is frozen', `spool file is locked'}
.newline
.em
 smtp@_confirmation         $t $rm{SMTP confirmation on => lines}
.newline
.nem  
 smtp@_connection           $t $rm{SMTP connections}
 smtp@_incomplete@_transaction $t $rm{incomplete SMTP transactions}
 smtp@_protocol@_error      $t $rm{SMTP protocol errors}
 smtp@_syntax@_error        $t $rm{SMTP syntax errors}
 subject                    $t $rm{contents of ::Subject:: on <= lines}
.newline
.em
 tls@_certificate@_verified $t $rm{certificate verification status}
.newline
.nem
*tls@_cipher                $t $rm{TLS cipher suite on <= and => lines}
 tls@_peerdn                $t $rm{TLS peer DN on <= and => lines}

 all                        $t $rm{all of the above}
.endd
More details on each of these items follows:
.numberpars $.
.index log||rewriting
.index rewriting||logging
\address@_rewrite\: This applies both to global rewrites and per-transport
rewrites,
.em
but not to rewrites in filters run as an unprivileged user (because such users 
cannot access the log).
.nem
.nextp
.index log||full parentage
\all@_parents\: Normally only the original and final addresses are logged on
delivery lines; with this selector, intermediate parents are given in
parentheses between them.
.nextp
.index log||Exim arguments
.index Exim arguments, logging
\arguments\: This causes Exim to write the arguments with which it was called
to the main log,
preceded by the current working directory.
This is a debugging feature, added to make it easier to find out how certain
MUAs call \(/usr/sbin/sendmail)\. The logging does not happen if Exim has given
up root privilege because it was called with the \-C-\ or \-D-\ options. 
Arguments that are empty or that contain whitespace are quoted. Non-printing 
characters are shown as escape sequences.
This facility cannot log unrecognized arguments, because the arguments are
checked before the configuration file is read. The only way to log such cases
is to interpose a script such as \(util/logargs.sh)\ between the caller and
Exim.
.nextp
.index log||connection rejections
\connection@_reject\: A log entry is written whenever an incoming SMTP
connection is rejected, for whatever reason.
.nextp
.index log||delayed delivery
.index delayed delivery, logging
\delay@_delivery\: A log entry is written whenever a delivery process is not
started for an incoming message because the load is too high or too many
messages were received on one connection. Logging does not occur if no delivery
process is started because \queue@_only\ is set or \-odq-\ was used.
.nextp
.em
.index log||delivery duration
\deliver@_time\: For each delivery, the amount of real time it has taken to
perform the actual delivery is logged as DT=<<time>>, for example, \"DT=1s"\.
.nem
.nextp
.index log||message size on delivery
.index size||of message
\delivery@_size\: For each delivery, the size of message delivered is added to
the `=>' line, tagged with S=.
.nextp
.index log||dnslist defer
.index DNS list||logging defer
.index black list (DNS)
\dnslist@_defer\: A log entry is written if an attempt to look up a host in a
DNS black list suffers a temporary error.
.nextp
.index log||ETRN commands
.index \\ETRN\\||logging
\etrn\: Every legal ETRN command that is received is logged, before the ACL is
run to determine whether or not it is actually accepted. An invalid ETRN
command, or one received within a message transaction is not logged by this
selector (see \smtp@_syntax@_error\ and \smtp@_protocol@_error\).
.nextp
.index log||host lookup failure
\host@_lookup@_failed\: When a lookup of a host's IP addresses fails to find
any addresses, or when a lookup of an IP address fails to find a host name, a
log line is written. This logging does not apply to direct DNS lookups when
routing email addresses, but it does apply to `byname' lookups.
.nextp
.em
.index log||ident timeout
.index RFC 1413||logging timeout
\ident@_timeout\: A log line is written whenever an attempt to connect to a
client's ident port times out.
.nem
.nextp
.index log||incoming interface
.index interface||logging
\incoming@_interface\: The interface on which a message was received is added
to the `<=' line as an IP address in square brackets, tagged by I= and followed
by a colon and the port number.
.em
The local interface and port are also added to other SMTP log
lines, for example `SMTP connection from', and to rejection lines.
.nem
.nextp
.index log||incoming remote port
.index port||logging remote
.index TCP/IP||logging incoming remote port
\incoming@_port\: The remote port number from which a message was received is
added to log entries and ::Received:: header lines, following the IP address in
square brackets, and separated from it by a colon. This is implemented by
changing the value that is put in the \$sender@_fullhost$\ and
\$sender@_rcvhost$\ variables. Recording the remote port number has become more
important with the widening use of NAT (see RFC 2505).
.nextp
.index log||dropped connection
\lost@_incoming@_connection\: A log line is written when an incoming SMTP
connection is unexpectedly dropped.
.nextp
.em
.index log||outgoing remote port
.index port||logging outgoint remote
.index TCP/IP||logging ougtoing remote port
\outgoing@_port\: The remote port number is added to delivery log lines (those
containing => tags) following the IP address. This option is not included in
the default setting, because for most ordinary configurations, the remote port
number is always 25 (the SMTP port).
.nem
.nextp
.index log||queue run
.index queue runner||logging
\queue@_run\: The start and end of every queue run are logged.
.nextp
.em
.index log||queue time
\queue@_time\: The amount of time the message has been in the queue on the
local host is logged as QT=<<time>>, for example, \"QT=3m45s"\. The clock
starts when Exim starts to receive the message, so it includes reception time
as well as the delivery time of the current address.
.nem
.nextp
.index log||recipients
\received@_recipients\: The recipients of a message are listed in the main log
as soon as the message is received. The list appears at the end of the log line
that is written when a message is received, preceded by the word `for'. The
addresses are listed after they have been qualified, but before any rewriting
has taken place.
Recipients that were discarded by an ACL for \\MAIL\\ or \\RCPT\\ do not appear
in the list.
.nextp
.index log||sender reception
\received@_sender\: The unrewritten original sender of a message is added to
the end of the log line that records the message's arrival, after the word
`from' (before the recipients if \received@_recipients\ is also set).
.nextp
.index log||header lines for rejection
\rejected@_header\: If a message's header has been received at the time a
rejection is written to the reject log, the complete header is added to the
log. Header logging can be turned off individually for messages that are
rejected by the \*local@_scan()*\ function (see section ~~SECTapiforloc).
.nextp
.index log||retry defer
\retry@_defer\: A log line is written if a delivery is deferred because a retry
time has not yet been reached. However, this `retry time not reached' message
is always omitted from individual message logs after the first delivery
attempt.
.nextp
.index log||return path
.em
\return@_path@_on@_delivery\: The return path that is being transmitted with 
the message is included in delivery and bounce lines, using the tag P=.
.nem
.nextp
.index log||sender on delivery
\sender@_on@_delivery\: The message's sender address is added to every delivery
and bounce line, tagged by F= (for `from').
.em
This is the original sender that was received with the message; it is not 
necessarily the same as the outgoing return path.
.nem
.nextp
.index log||size rejection
\size@_reject\: A log line is written whenever a message is rejected because it
is too big.
.nextp
.index log||frozen messages, skipped
.index frozen messages||logging skipping
\skip@_delivery\: A log line is written whenever a message is skipped during a
queue run because it is frozen or because another process is already delivering
it.
.nextp
.index log||smtp confirmation
.index SMTP||logging confirmation
\smtp@_confirmation\: The response to the final `.' in the SMTP dialogue for
outgoing messages is added to delivery log lines in the form `C="<<text>>"'. A
number of MTAs (including Exim) return an identifying string in this response.
.nextp
.index log||SMTP connections
.index SMTP||logging connections
\smtp@_connection\: A log line is written whenever an SMTP connection is
established or closed. (By contrast, \lost@_incoming@_connection\ applies only
when the closure is unexpected.) This applies to connections from local
processes that use \-bs-\ as well as to TCP/IP connections. If a connection is
dropped in the middle of a message, a log line is always written, whether this
selector is set or not, but otherwise nothing is written at the start and end
of connections unless this selector is enabled. 

For TCP/IP connections to an Exim daemon, the current number of connections is
included in the log message for each new connection, but note that the count is
reset if the daemon is restarted.
Also, because connections are closed (and the closure is logged) in 
subprocesses, the count may not include connections that have been closed but 
whose termination the daemon has not yet noticed. Thus, while it is possible to 
match up the opening and closing of connections in the log, the value of the 
logged counts may not be entirely accurate.
.nextp
.index log||SMTP transaction, incomplete
.index SMTP||logging incomplete transactions
\smtp@_incomplete@_transaction\: When a mail transaction is aborted by
\\RSET\\, \\QUIT\\, loss of connection, or otherwise, the incident is logged,
and the message sender plus any accepted recipients are included in the log
line. This can provide evidence of dictionary attacks.
.nextp
.index log||SMTP protocol error
.index SMTP||logging protocol error
\smtp@_protocol@_error\: A log line is written for every SMTP protocol error
encountered.
.em
Exim does not have perfect detection of all protocol errors because of 
transmission delays and the use of pipelining. If \\PIPELINING\\ has been 
advertised to a client, an Exim server assumes that the client will use it, and 
therefore it does not count `expected' errors (for example, \\RCPT\\ received
after rejecting \\MAIL\\) as protocol errors.
.nem
.nextp
.index SMTP||logging syntax errors
.index SMTP||syntax errors, logging
.index SMTP||unknown command, logging
.index log||unknown SMTP command
.index log||SMTP syntax error
\smtp@_syntax@_error\: A log line is written for every SMTP syntax error
encountered. An unrecognized command is treated as a syntax error. For an
external connection, the host identity is given; for an internal connection
using \-bs-\ the sender identification (normally the calling user) is given.
.nextp
.index log||subject
.index subject, logging
\subject\: The subject of the message is added to the arrival log line,
preceded by `T=' (T for `topic', since S is already used for `size').
Any MIME `words' in the subject are decoded. The \print@_topbitchars\ option 
specifies whether characters with values greater than 127 should be logged 
unchanged, or whether they should be rendered as escape sequences.
.nextp
.index log||certificate verification
.em
\tls@_certificate@_verified\: An extra item is added to <= and => log lines
when TLS is in use. The item is \"CV=yes"\ if the peer's certificate was
verified, and \"CV=no"\ if not.
.nem
.nextp
.index log||TLS cipher
.index TLS||logging cipher
\tls@_cipher\: When a message is sent or received over an encrypted connection,
the cipher suite used is added to the log line, preceded by X=.
.nextp
.index log||TLS peer DN
.index TLS||logging peer DN
\tls@_peerdn\: When a message is sent or received over an encrypted connection,
and a certificate is supplied by the remote host, the peer DN is added to the
log line, preceded by DN=.
.endp

.section Message log
.index message||log file for
.index log||message log, description of 
In addition to the general log files, Exim writes a log file for each message
that it handles. The names of these per-message logs are the message ids, and
.index \(msglog)\ directory
they are kept in the \(msglog)\ sub-directory of the spool directory. Each
message log contains copies of the log lines that apply to the message. This
makes it easier to inspect the status of an individual message without having
to search the main log. A message log is deleted when processing of the message
is complete,
.index \preserve@_message@_logs\
unless \preserve__message__logs\ is set, but this should be used only with
great care because they can fill up your disk very quickly.

On a heavily loaded system, it may be desirable to disable the use of 
per-message logs, in order to reduce disk I/O. This can be done by setting the 
\message@_logs\ option false.



.
.
.
. ============================================================================
.chapter Exim utilities
.set runningfoot "utilities"
.rset CHAPutils ~~chapter
.index utilities
A number of utility scripts and programs are supplied with Exim and are
described in this chapter. There is also the Exim Monitor, which is covered in
the next chapter. The utilities described here are:

. This duplication seems to be the only way to arrange that the cross-
. references are omitted in the Texinfo version. They look horribly ugly.

.if ~~texinfo
.display rm
.tabs 22
\*exiwhat*\           $t $rm{list what Exim processes are doing}
.newline
\*exiqgrep*\          $t $rm{grep the queue}
.newline
\*exiqsumm*\          $t $rm{summarize the queue}
\*exigrep*\           $t $rm{search the main log}
\*exipick*\           $t $rm{select messages on various criteria}
\*exicyclog*\         $t $rm{cycle (rotate) log files}
\*eximstats*\         $t $rm{extract statistics from the log}
\*exim@_checkaccess*\ $t $rm{check address acceptance from given IP}
\*exim@_dbmbuild*\    $t $rm{build a DBM file}
\*exinext*\           $t $rm{extract retry information}
\*exim@_dumpdb*\      $t $rm{dump a hints database}
\*exim@_tidydb*\      $t $rm{clean up a hints database}
\*exim@_fixdb*\       $t $rm{patch a hints database}
\*exim@_lock*\        $t $rm{lock a mailbox file}
.endd
.
.else
.
.display rm
.tabs 22
~~SECTfinoutwha  \*exiwhat*\           $t $rm{list what Exim processes are doing}
.newline
~~SECTgreptheque  \*exiqgrep*\         $t $rm{grep the queue}
.newline
~~SECTsumtheque  \*exiqsumm*\          $t $rm{summarize the queue}
~~SECTextspeinf  \*exigrep*\           $t $rm{search the main log}
.newline
.em
~~SECTexipick  \*exipick*\           $t $rm{select messages on various criteria}
.newline
.nem
~~SECTcyclogfil  \*exicyclog*\         $t $rm{cycle (rotate) log files}
~~SECTmailstat  \*eximstats*\         $t $rm{extract statistics from the log}
~~SECTcheckaccess  \*exim@_checkaccess*\ $t $rm{check address acceptance from given IP}
~~SECTdbmbuild  \*exim@_dbmbuild*\    $t $rm{build a DBM file}
~~SECTfinindret  \*exinext*\           $t $rm{extract retry information}
~~SECThindatmai  \*exim@_dumpdb*\      $t $rm{dump a hints database}
~~SECThindatmai  \*exim@_tidydb*\      $t $rm{clean up a hints database}
~~SECThindatmai  \*exim@_fixdb*\       $t $rm{patch a hints database}
~~SECTmailboxmaint  \*exim@_lock*\     $t $rm{lock a mailbox file}
.endd
.fi

.section Finding out what Exim processes are doing (exiwhat)
.rset SECTfinoutwha "~~chapter.~~section"
.index \*exiwhat*\
.index process, querying
.index \\SIGUSR1\\
On operating systems that can restart a system call after receiving a signal
(most modern OS), an Exim process responds to the \\SIGUSR1\\ signal by writing
a line describing what it is doing to the file \(exim-process.info)\ in the
Exim spool directory. The \*exiwhat*\ script sends the signal to all Exim
processes it can find, having first emptied the file. It then waits for one
second to allow the Exim processes to react before displaying the results.
In order to run \*exiwhat*\ successfully you have to have sufficient privilege to
send the signal to the Exim processes, so it is normally run as root.

Unfortunately, the \*ps*\ command which \*exiwhat*\ uses to find Exim processes
varies in different operating systems. Not only are different options used,
but the format of the output is different. For this reason, there are some
system configuration options that configure exactly how \*exiwhat*\ works. If it
doesn't seem to be working for you, check the following compile-time options:
.display
EXIWHAT@_PS@_CMD     $rm{the command for running \*ps*\}
EXIWHAT@_PS@_ARG     $rm{the argument for \*ps*\}
EXIWHAT@_EGREP@_ARG  $rm{the argument for \*egrep*\ to select from \*ps*\ output}
EXIWHAT@_KILL@_ARG   $rm{the argument for the \*kill*\ command}
.endd
An example of typical output from \*exiwhat*\ is
.display
.indent 0
  164 daemon: -q1h, listening on port 25
10483 running queue: waiting for 0tAycK-0002ij-00 (10492)
10492 delivering 0tAycK-0002ij-00 to mail.ref.example [10.19.42.42]
  (editor@@ref.example)
10592 handling incoming call from [192.168.243.242]
10628 accepting a local non-SMTP message
.endd
The first number in the output line is the process number. The third line has
been split here, in order to fit it on the page.


.section Selective queue listing (exiqgrep)
.rset SECTgreptheque "~~chapter.~~section"
.index \*exiqgrep*\
.index queue||grepping
This utility is a Perl script contributed by Matt Hubbard. It runs
.display asis
exim -bpu
.endd
to obtain a queue listing with undelivered recipients only, and then greps the 
output to select messages that match given criteria. The following selection 
options are available:

.startoptions

.option f <<regex>>
Match the sender address. The field that is tested is enclosed in angle 
brackets, so you can test for bounce messages with 
.display asis
exiqgrep -f '^<>$'
.endd

.option r <<regex>>
Match a recipient address. The field that is tested is not enclosed in angle 
brackets.

.option s <<regex>>
Match against the size field.

.option y <<seconds>>
Match messages that are younger than the given time.

.option o <<seconds>>
Match messages that are older than the given time.

.option z
Match only frozen messages.

.option x
Match only non-frozen messages.

.endoptions

The following options control the format of the output:

.startoptions

.option c
Display only the count of matching messages.

.option l
Long format -- display the full message information as output by Exim. This is
the default.

.option i
Display message ids only.

.option b
Brief format -- one line per message.

.option R
Display messages in reverse order.

.endoptions

There is one more option, \-h-\, which outputs a list of options.


.section Summarising the queue (exiqsumm)
.rset SECTsumtheque "~~chapter.~~section"
.index \*exiqsumm*\
.index queue||summary
The \*exiqsumm*\ utility is a Perl script which reads the output of \*exim
-bp*\ and produces a summary of the messages on the queue. Thus, you use it by
running a command such as
.display asis
exim -bp | exiqsumm
.endd
The output consists of one line for each domain that has messages waiting for
it, as in the following example:
.display asis
  3   2322   74m   66m  msn.com.example
.endd
Each line lists the number of 
pending deliveries for a domain, their total volume, and the length of time
that the oldest and the newest messages have been waiting. Note that the number 
of pending deliveries is greater than the number of messages when messages 
have more than one recipient.

A summary line is output at the end. By default the output is sorted on the
domain name, but \*exiqsumm*\ has the options \-a-\ and \-c-\, which cause the
output to be sorted by oldest message and by count of messages, respectively.

The output of \*exim -bp*\ contains the original addresses in the message, so
this also applies to the output from \*exiqsumm*\. No domains from addresses
generated by aliasing or forwarding are included (unless the \one@_time\ option
of the \%redirect%\ router has been used to convert them into `top level'
addresses).



.section Extracting specific information from the log (exigrep)
.rset SECTextspeinf "~~chapter.~~section"
.index \*exigrep*\
.index log||extracts, grepping for
The \*exigrep*\ utility is a Perl script that searches one or more main log
files for entries that match a given pattern. When it finds a match, it
extracts all the log entries for the relevant message, not just those that
match the pattern. Thus, \*exigrep*\ can extract complete log entries for a
given message, or all mail for a given user, or for a given host, for example.

.em
If a matching log line is not associated with a specific message, it is always
included in \*exigrep*\'s output.
.nem
The usage is:
.display asis
exigrep [-l] [-t<n>] <pattern> [<log file>] ...
.endd
The \-t-\ argument specifies a number of seconds. It adds an additional 
condition for message selection. Messages that are complete are shown only if 
they spent more than <<n>> seconds on the queue.

The \-l-\ flag means `literal', that is, treat all characters in the
pattern as standing for themselves. Otherwise the pattern must be a Perl
regular expression. The pattern match is case-insensitive. If no file names are
given on the command line, the standard input is read.

If the location of a \*zcat*\ command is known from the definition of
\\ZCAT@_COMMAND\\ in \(Local/Makefile)\, \*exigrep*\ automatically passes any
file whose name ends in \\COMPRESS@_SUFFIX\\ through \*zcat*\ as it searches
it.

.em
.section Selecting messages by various criteria (exipick)
.rset SECTexipick "~~chapter.~~section"
.index \*exipick*\
John Jetmore's \*exipick*\ utility is included in the Exim distribution. It
lists messages from the queue according to a variety of criteria. For details,
run:
.display asis
exipick --help
.endd
.nem


.section Cycling log files (exicyclog)
.rset SECTcyclogfil "~~chapter.~~section"
.index log||cycling local files
.index cycling logs
.index \*exicyclog*\
The \*exicyclog*\ script can be used to cycle (rotate) \*mainlog*\ and
\*rejectlog*\ files. This is not necessary if only syslog is being used,
or if you are using log files with datestamps in their names (see section
~~SECTdatlogfil).
Some operating systems have their own standard mechanisms for log cycling, and
these can be used instead of \*exicyclog*\ if preferred.

Each time \*exicyclog*\ is run the file names get `shuffled down' by one. If the
main log file name is \(mainlog)\ (the default) then when \*exicyclog*\ is run
\(mainlog)\ becomes \(mainlog.01)\, the previous \(mainlog.01)\ becomes
\(mainlog.02)\ and so on, up to a limit which is set in the script, and which
defaults to 10. Reject logs are handled similarly.

If no \(mainlog)\ file exists, the script does nothing. Files that `drop off'
the end are deleted. All files with numbers greater than 01 are compressed,
using a compression command which is configured by the \\COMPRESS@_COMMAND\\
setting in \(Local/Makefile)\. It is usual to run \*exicyclog*\ daily from a
root \crontab\ entry of the form
.display
1 0 * * * su exim -c /usr/exim/bin/exicyclog
.endd
assuming you have used the name `exim' for the Exim user. You can run
\*exicyclog*\ as root if you wish, but there is no need.


.section Mail statistics (eximstats)
.rset SECTmailstat "~~chapter.~~section"
.index statistics
.index \*eximstats*\
A Perl script called \*eximstats*\ is provided for extracting statistical
information from log files. The output is either plain text, or HTML.
Exim log files are also suported by the \*Lire*\ system produced by the 
LogReport Foundation (\?http://www.logreport.org?\).

The \*eximstats*\ script has been hacked about quite a bit over time. The
latest version is the result of some extensive revision by Steve Campbell. A
lot of information is given by default, but there are options for suppressing
various parts of it. Following any options, the arguments to the script are a
list of files, which should be main log files. For example:
.display asis
eximstats -nr /var/spool/exim/log/mainlog.01
.endd
By default, \*eximstats*\ extracts information about the number and volume of
messages received from or delivered to various hosts. The information is sorted
both by message count and by volume, and the top fifty hosts in each category
are listed on the standard output. Similar information, based on email
addresses or domains instead of hosts can be requested by means of various
options. For messages delivered and received locally, similar statistics are
also produced per user.

The output also includes total counts and statistics about delivery errors, and
histograms showing the number of messages received and deliveries made in each
hour of the day. A delivery with more than one address in its envelope (for
example, an SMTP transaction with more than one \\RCPT\\ command) is counted
as a single delivery by \*eximstats*\.

Though normally more deliveries than receipts are reported (as messages may
have multiple recipients), it is possible for \*eximstats*\ to report more
messages received than delivered, even though the queue is empty at the start
and end of the period in question. If an incoming message contains no valid
recipients, no deliveries are recorded for it. A bounce message is handled as
an entirely separate message.

\*eximstats*\ always outputs a grand total summary giving the volume and number
of messages received and deliveries made, and the number of hosts involved in
each case. It also outputs the number of messages that were delayed (that is,
not completely delivered at the first attempt), and the number that had at
least one address that failed.

The remainder of the output is in sections that can be independently disabled
or modified by various options. It consists of a summary of deliveries by
transport, histograms of messages received and delivered per time interval
(default per hour), information about the time messages spent on the queue,
a list of relayed messages, lists of the top fifty sending hosts, local
senders, destination hosts, and destination local users by count and by volume,
and a list of delivery errors that occurred.

The relay information lists messages that were actually relayed, that is, they
came from a remote host and were directly delivered to some other remote host,
without being processed (for example, for aliasing or forwarding) locally.

The options for \*eximstats*\ are as follows:

.startoptions
.index \*eximstats*\||options
.option bydomain
The `league tables' are computed on the basis of the superior domains of the
sending hosts instead of the sending and receiving hosts. This option may be
combined with \-byhost-\ and/or \-byemail-\.

.option byedomain
This is a synonym for \-byemaildomain-\.

.option byemail
The `league tables' are computed on the basis of complete email addresses,
instead of sending and receiving hosts. This option may be combined with
\-byhost-\ and/or \-bydomain-\.

.option byemaildomain
The `league tables' are computed on the basis of the sender's email domain 
instead of the sending and receiving hosts. This option may be combined with
\-byhost-\, \-bydomain-\, or \-byemail-\.

.option byhost
The `league tables' are computed on the basis of sending and receiving hosts.
This is the default option. It may be combined with \-bydomain-\ and/or
\-byemail-\.

.option cache
Cache results of \*timegm()*\ lookups. This results in a significant speedup
when processing hundreds of thousands of messages, at a cost of increasing the
memory utilisation.

.option chartdir <<dir>>
When \-charts-\ is specified, create the charts in the directory <<dir>>.

.option chartrel <<dir>>
When \-charts-\ is specified, this option specifies the relative directory for
the \"img src="\ tags from where to include the charts.

.option charts
Create graphical charts to be displayed in HTML output. This requires the
\"GD"\, \"GDTextUtil"\, and \"GDGraph"\ Perl modules, which can be obtained
from \?http://www.cpan.org/modules/01modules.index.html?\.

To install these, download and unpack them, then use the normal Perl
installation procedure:
.display asis
perl Makefile.PL
make
make test
make install
.endd

.option d
This is a debug flag. It causes \*eximstats*\ to output the \*eval()*\'d parser
to the standard output, which makes it easier to trap errors in the eval
section. Remember to add one to the line numbers to allow for the title.


.option help
Show help information about \*eximstats*\' options.

.option h <<n>>
This option controls the histograms of messages received and deliveries per
time interval. By default the time interval is one hour. If \-h0-\ is given,
the histograms are suppressed; otherwise the value of <<n>> gives the number of
divisions per hour. Valid values are 0, 1, 2, 3, 5, 10, 15, 20, 30 or 60, so
\-h2-\ sets an interval of 30 minutes, and the default is equivalent to \-h1-\.

.option html
Output the results in HTML instead of plain text.

.option merge
This option causes \*eximstats*\ to merge old reports into a combined report.
When this option is used, the input files must be outputs from previous calls 
to \*eximstats*\, not raw log files. For example, you could produce a set of
daily reports and a weekly report by commands such as
.display asis
eximstats mainlog.sun > report.sun.txt
eximstats mainlog.mon > report.mon.txt
eximstats mainlog.tue > report.tue.txt
eximstats mainlog.wed > report.wed.txt
eximstats mainlog.thu > report.thu.txt
eximstats mainlog.fri > report.fri.txt
eximstats mainlog.sat > report.sat.txt
eximstats -merge -html report.*.txt > weekly_report.html
.endd
You can merge text or html reports and output the results as text or html. You
can use all the normal \*eximstats*\ output options, but only data included in
the original reports can be shown. When merging reports, some loss of accuracy
may occur in the `league tables', towards the ends of the lists. The order of
items in the `league tables' may vary when the data volumes round to the same
value.

.option ne
Suppress the display of information about failed deliveries (errors).

.option nr
Suppress information about messages relayed through this host.

.option nr /pattern/
Suppress information about relayed messages that match the pattern, which is
matched against a string of the following form (split over two lines here in
order to fit it on the page):
.display asis
H=<host> [<ip address>] A=<sender address> =>
  H=<host> A=<recipient address>
.endd
for example
.display asis
H=in.host [1.2.3.4] A=from@some.where.example =>
  H=out.host A=to@else.where.example
.endd
The sending host name appears in parentheses if it has not been verified as
matching the IP address. The mail addresses are taken from the envelope, not
the headers. This option allows you to screen out hosts whom you are happy to
have using your host as a relay.

.option nt
Suppress the statistics about delivery by transport.

.option nt/<<pattern>>/
Suppress the statistics about delivery by any transport whose name matches the 
pattern. If you are using one transport to send all messages to a scanning 
mechanism before doing the real delivery, this feature can be used to omit that 
transport from your normal statistics (on the grounds that it is of no
interest).


.option "pattern" "#<<description>>#/<<pattern>>/"
Count lines matching specified patterns and show them in
the results. For example:
.display asis
-pattern 'Refused connections' '/refused connection/'
.endd
This option can be specified multiple times. 

.option q0
Suppress information about times messages spend on the queue.

.option q <<n1>>...
This option sets an alternative list of time intervals for the queueing
information. The values are separated by commas and are in seconds, but can
involve arithmetic multipliers, so for example you can set 3$*$60 to specify 3
minutes. A setting such as
.display asis
-q60,5*60,10*60
.endd
causes \*eximstats*\ to give counts of messages that stayed on the queue for less
than one minute, less than five minutes, less than ten minutes, and over ten
minutes.

.option t <<n>>
Sets the `top' count to <<n>>. This controls the listings of the `top <<n>>'
hosts and users by count and volume. The default is 50, and setting 0
suppresses the output altogether.

.option tnl
Omit local information from the `top' listings.

.option t@_remote@_users
Include remote users in the `top' listings.

.endoptions


.section Checking access policy (exim@_checkaccess)
.rset SECTcheckaccess "~~chapter.~~section"
.index \*exim@_checkaccess*\
.index policy control||checking access
.index checking access
The \-bh-\ command line argument allows you to run a fake SMTP session with
debugging output, in order to check what Exim is doing when it is applying
policy controls to incoming SMTP mail. However, not everybody is sufficiently
familiar with the SMTP protocol to be able to make full use of \-bh-\, and
sometimes you just want to answer the question \*Does this address have
access?*\ without bothering with any further details.

The \*exim@_checkaccess*\ utility is a `packaged' version of \-bh-\. It takes
two arguments, an IP address and an email address:
.display asis
exim_checkaccess 10.9.8.7 A.User@a.domain.example
.endd
The utility runs a call to Exim with the \-bh-\ option, to test whether the
given email address would be accepted in a \\RCPT\\ command in a TCP/IP
connection from the host with the given IP address. The output of the utility
is either the word `accepted', or the SMTP error response, for example:
.display asis
Rejected:
  550 Relay not permitted
.endd
When running this test, the utility uses \"<>"\ as the envelope sender address
for the \\MAIL\\ command, but you can change this by providing additional
options. These are passed directly to the Exim command. For example, to specify
that the test is to be run with the sender address \*himself@@there.example*\
you can use:
.display asis
exim_checkaccess 10.9.8.7 A.User@a.domain.example \
                 -f himself@there.example
.endd
Note that these additional Exim command line items must be given after the two
mandatory arguments.

Because the \exim@_checkaccess\ uses \-bh-\, it does not perform callouts while
running its checks. You can run checks that include callouts by using \-bhc-\, 
but this is not yet available in a `packaged' form.


.section Making DBM files (exim@_dbmbuild)
.rset SECTdbmbuild "~~chapter.~~section"
.index DBM||building dbm files
.index building DBM files
.index \*exim@_dbmbuild*\
.index lower casing
.index binary zero||in lookup key
The \*exim@_dbmbuild*\ program reads an input file containing keys and data in
the format used by the \%lsearch%\ lookup (see section ~~SECTsinglekeylookups).
It writes a DBM file using the lower-cased alias names as keys and the
remainder of the information as data. The lower-casing can be prevented by
calling the program with the \-nolc-\ option.

A terminating zero is included as part of the key string. This is expected by
the \%dbm%\ lookup type. However, if the option \-nozero-\ is given,
\*exim@_dbmbuild*\ creates files without terminating zeroes in either the key
strings or the data strings. The \%dbmnz%\ lookup type can be used with such
files.

The program requires two arguments: the name of the input file (which can be a
single hyphen to indicate the standard input), and the name of the output file.
It creates the output under a temporary name, and then renames it if all went
well.
.index \\USE@_DB\\
If the native DB interface is in use (\\USE@_DB\\ is set in a compile-time
configuration file -- this is common in free versions of Unix) the two file
names must be different, because in this mode the Berkeley DB functions create
a single output file using exactly the name given. For example,
.display asis
exim_dbmbuild /etc/aliases /etc/aliases.db
.endd
reads the system alias file and creates a DBM version of it in
\(/etc/aliases.db)\.

In systems that use the \*ndbm*\ routines (mostly proprietary versions of Unix),
two files are used, with the suffixes \(.dir)\ and \(.pag)\. In this
environment, the suffixes are added to the second argument of
\*exim@_dbmbuild*\, so it can be the same as the first. This is also the case
when the Berkeley functions are used in compatibility mode (though this is not
recommended), because in that case it adds a \(.db)\ suffix to the file name.

If a duplicate key is encountered, the program outputs a warning, and when it
finishes, its return code is 1 rather than zero, unless the \-noduperr-\ option
is used. By default, only the first of a set of duplicates is used -- this
makes it compatible with \%lsearch%\ lookups. There is an option \-lastdup-\
which causes it to use the data for the last duplicate instead. There is also
an option \-nowarn-\, which stops it listing duplicate keys to \stderr\. For
other errors, where it doesn't actually make a new file, the return code is 2.



.section Finding individual retry times (exinext)
.rset SECTfinindret "~~chapter.~~section"
.index retry||times
.index \*exinext*\
A utility called \*exinext*\ (mostly a Perl script) provides the ability to fish
specific information out of the retry database. Given a mail domain (or a
complete address), it looks up the hosts for that domain, and outputs any retry
information for the hosts or for the domain. At present, the retry information
is obtained by running \*exim@_dumpdb*\ (see below) and post-processing the
output. For example:
.display asis
$ exinext piglet@milne.fict.example
kanga.milne.fict.example:192.168.8.1 error 146: Connection refused
  first failed: 21-Feb-1996 14:57:34
  last tried:   21-Feb-1996 14:57:34
  next try at:  21-Feb-1996 15:02:34
roo.milne.fict.example:192.168.8.3 error 146: Connection refused
  first failed: 20-Jan-1996 13:12:08
  last tried:   21-Feb-1996 11:42:03
  next try at:  21-Feb-1996 19:42:03
  past final cutoff time
.endd
You can also give \*exinext*\ a local part, without a domain, and it
will give any retry information for that local part in your default domain.
A message id can be used to obtain retry information pertaining to a specific
message. This exists only when an attempt to deliver a message to a remote host
suffers a message-specific error (see section ~~SECToutSMTPerr). \*exinext*\ is
not particularly efficient, but then it isn't expected to be run very often.

.em
The \*exinext*\ utility calls Exim to find out information such as the location
of the spool directory. The utility has \-C-\ and \-D-\ options, which are
passed on to the \*exim*\ commands. The first specifies an alternate Exim
configuration file, and the second sets macros for use within the configuration
file. These features are mainly to help in testing, but might also be useful in
environments where more than one configuration file is in use.
.nem



.section Hints database maintenance (exim@_dumpdb, exim@_fixdb, exim@_tidydb)
.rset SECThindatmai "~~chapter.~~section"
.index hints database||maintenance
.index maintaining Exim's hints database
Three utility programs are provided for maintaining the DBM files that Exim
uses to contain its delivery hint information. Each program requires two
arguments. The first specifies the name of Exim's spool directory, and the
second is the name of the database it is to operate on. These are as
follows:
.numberpars $.
\*retry*\: the database of retry information
.nextp
\*wait-*\<<transport name>>: databases of information about messages waiting
for remote hosts
.nextp
.em
\*callout*\: the callout cache
.nem
.nextp
\*misc*\: other hints data 
.endp
.em
The \*misc*\ database is used for
.numberpars alpha
Serializing \\ETRN\\ runs (when \smtp@_etrn@_serialize\ is set)
.nextp
Serializing delivery to a specific host (when \serialize@_hosts\ is set in an 
\%smtp%\ transport)
.endp
.nem
.index \*exim@_dumpdb*\
The entire contents of a database are written to the standard output by the
\*exim@_dumpdb*\ program, which has no options or arguments other than the
spool and database names. For example, to dump the retry database:
.display asis
exim_dumpdb /var/spool/exim retry
.endd
Two lines of output are produced for each entry:
.display
  T:mail.ref.example:192.168.242.242 146 77 Connection refused
31-Oct-1995 12:00:12  02-Nov-1995 12:21:39  02-Nov-1995 20:21:39 *
.endd
The first item on the first line is the key of the record. It starts with one
of the letters R, or T, depending on whether it refers to a routing or
transport retry. For a local delivery, the next part is the local address; for
a remote delivery it is the name of the remote host, followed by its failing IP
address (unless \no@_retry@_include@_ip@_address\ is set on the \%smtp%\
transport). 
.em
If the remote port is not the standard one (port 25), it is added to the IP 
address.
.nem
Then there follows an error code, an additional error code, and a
textual description of the error.

The three times on the second line are the time of first failure, the time of
the last delivery attempt, and the computed time for the next attempt. The line
ends with an asterisk if the cutoff time for the last retry rule has been
exceeded.

Each output line from \*exim@_dumpdb*\ for the \*wait-*\$it{xxx} databases
consists of a host name followed by a list of ids for messages that are or were
waiting to be delivered to that host. If there are a very large number for any
one host, continuation records, with a sequence number added to the host name,
may be seen. The data in these records is often out of date, because a message
may be routed to several alternative hosts, and Exim makes no effort to keep
cross-references.

.index \*exim@_tidydb*\
The \*exim@_tidydb*\ utility program is used to tidy up the contents of the
hints databases. If run with no options, it removes all records from a database
that are more than 30 days old. The cutoff date can be altered by means of the
\-t-\ option, which must be followed by a time. For example, to remove all
records older than a week from the retry database:
.display asis
exim_tidydb -t 7d /var/spool/exim retry
.endd
Both the \*wait-*\$it{xxx} and \*retry*\ databases contain items that involve
message ids. In the former these appear as data in records keyed by host --
they were messages that were waiting for that host -- and in the latter they
are the keys for retry information for messages that have suffered certain
types of error. When \*exim@_tidydb*\ is run, a check is made to ensure that
message ids in database records are those of messages that are still on the
queue. Message ids for messages that no longer exist are removed from
\*wait-*\$it{xxx} records, and if this leaves any records empty, they are
deleted. For the \*retry*\ database, records whose keys are non-existent message
ids are removed. The \*exim@_tidydb*\ utility outputs comments on the standard
output whenever it removes information from the database.

Removing records from a DBM file does not normally make the file smaller, but
all the common DBM libraries are able to re-use the space that is released.
It is therefore suggested that \*exim@_tidydb*\ be run periodically on all the
hints databases, but at a quiet time of day, because it requires a database to
be locked (and therefore inaccessible to Exim) while it does its work.

.index \*exim@_fixdb*\
The \*exim@_fixdb*\ program is a utility for interactively modifying databases.
Its main use is for testing Exim, but it might also be occasionally useful for
getting round problems in a live system. It has no options, and its interface
is somewhat crude. On entry, it prompts for input with a right angle-bracket. A
key of a database record can then be entered, and the data for that record is
displayed.

If `d' is typed at the next prompt, the entire record is deleted. For all
except the \*retry*\ database, that is the only operation that can be carried
out. For the \*retry*\ database, each field is output preceded by a number, and
data for individual fields can be changed by typing the field number followed
by new data, for example:
.display asis
> 4 951102:1000
.endd
resets the time of the next delivery attempt. Time values are given as a
sequence of digit pairs for year, month, day, hour, and minute. Colons can be
used as optional separators.



.section Mailbox maintenance (exim@_lock)
.rset SECTmailboxmaint "~~chapter.~~section"
.index mailbox||maintenance
.index \*exim@_lock*\
.index locking mailboxes
The \*exim@_lock*\ utility locks a mailbox file using the same algorithm as
Exim. For a discussion of locking issues, see section ~~SECTopappend.
\*Exim@_lock*\ can be used to prevent any modification of a mailbox by Exim or
a user agent while investigating a problem. The utility requires the name of
the file as its first argument. If the locking is successful, the second
argument is run as a command (using C's \*system()*\ function); if there is no
second argument, the value of the SHELL environment variable is used; if this
is unset or empty, \(/bin/sh)\ is run. When the command finishes, the mailbox
is unlocked and the utility ends. The following options are available:

.startoptions

.option fcntl
Use \*fcntl()*\ locking on the open mailbox.

.option flock
Use \*flock()*\ locking on the open mailbox, provided the operating system 
supports it.

.option interval
This must be followed by a number, which is a number of seconds; it sets the
interval to sleep between retries (default 3).

.option lockfile
Create a lock file before opening the mailbox.

.option mbx
Lock the mailbox using MBX rules.

.option q
Suppress verification output.

.option retries
This must be followed by a number; it sets the number of times to try to get
the lock (default 10).

.option restore@_time
This option causes \exim@_lock\ to restore the modified and read times to the
locked file before exiting. This allows you to access a locked mailbox (for
example, to take a backup copy) without disturbing the times that the user
subsequently sees.

.option timeout
This must be followed by a number, which is a number of seconds; it sets a
timeout to be used with a blocking \*fcntl()*\ lock. If it is not set (the
default), a non-blocking call is used.

.option v
Generate verbose output.

.endoptions

If none of \-fcntl-\, 
\-flock-\,
\-lockfile-\ or \-mbx-\ are given, the default is to create a lock file and
also to use \*fcntl()*\ locking on the mailbox, which is the same as Exim's
default. The use of 
\-flock-\ 
or \-fcntl-\ requires that the file be writeable; the use of
\-lockfile-\ requires that the directory containing the file be writeable.
Locking by lock file does not last for ever; Exim assumes that a lock file is
expired if it is more than 30 minutes old.

The \-mbx-\ option can be used with either or both of \-fcntl-\ or \-flock-\. 
It assumes \-fcntl-\ by default.
MBX locking causes a shared lock to be taken out on the open mailbox, and an
exclusive lock on the file \(/tmp/.$it{n}.$it{m})\ where $it{n} and $it{m} are
the device number and inode number of the mailbox file. When the locking is
released, if an exclusive lock can be obtained for the mailbox, the file in
\(/tmp)\ is deleted.

The default output contains verification of the locking that takes place. The
\-v-\ option causes some additional information to be given. The \-q-\ option
suppresses all output except error messages.

A command such as
.display asis
exim_lock /var/spool/mail/spqr
.endd
runs an interactive shell while the file is locked, whereas
.display
exim@_lock -q /var/spool/mail/spqr @<@<End
<<some commands>>
End
.endd
runs a specific non-interactive sequence of commands while the file is locked,
suppressing all verification output. A single command can be run by a command
such as
.display asis
exim_lock -q /var/spool/mail/spqr \
  "cp /var/spool/mail/spqr /some/where"
.endd
Note that if a command is supplied, it must be entirely contained within the
second argument -- hence the quotes.



.
.
.
.
. ============================================================================
.chapter The Exim monitor
.set runningfoot "monitor"
.rset CHAPeximon ~~chapter
.index monitor
.index Exim monitor
.index X-windows
.index \*eximon*\
.index Local/eximon.conf
.index \(exim@_monitor/EDITME)\
The Exim monitor is an application which displays in an X window information
about the state of Exim's queue and what Exim is doing. An admin user can
perform certain operations on messages from this GUI interface; however all
such facilities are also available from the command line, and indeed, the
monitor itself makes use of the command line to perform any actions requested.


.section Running the monitor
The monitor is started by running the script called \*eximon*\. This is a shell
script that sets up a number of environment variables, and then runs the
binary called \(eximon.bin)\. The default appearance of the monitor window can
be changed by editing the \(Local/eximon.conf)\ file created by editing
\(exim@_monitor/EDITME)\. Comments in that file describe what the various
parameters are for.

The parameters that get built into the \*eximon*\ script can be overridden for a
particular invocation by setting up environment variables of the same names,
preceded by `$tt{EXIMON@_}'. For example, a shell command such as
.display asis
EXIMON_LOG_DEPTH=400 eximon
.endd
(in a Bourne-compatible shell) runs \*eximon*\ with an overriding setting of the
\\LOG@_DEPTH\\ parameter. If \\EXIMON@_LOG@_FILE@_PATH\\ is set in the
environment, it overrides the Exim log file configuration. This makes it
possible to have \*eximon*\ tailing log data that is written to syslog, provided
that MAIL.INFO syslog messages are routed to a file on the local host.

X resources can be used to change the appearance of the window in the normal
way. For example, a resource setting of the form
.display asis
Eximon*background: gray94
.endd
changes the colour of the background to light grey rather than white. The
stripcharts are drawn with both the data lines and the reference lines in
black. This means that the reference lines are not visible when on top of the
data. However, their colour can be changed by setting a resource called
`highlight' (an odd name, but that's what the Athena stripchart widget uses).
For example, if your X server is running Unix, you could set up lighter
reference lines in the stripcharts by obeying
.display asis
xrdb -merge <<End
Eximon*highlight: gray
End
.endd

.index admin user
In order to see the contents of messages on the queue, and to operate on them,
\*eximon*\ must either be run as root or by an admin user.

The monitor's window is divided into three parts. The first contains one or
more stripcharts and two action buttons, the second contains a `tail' of the
main log file, and the third is a display of the queue of messages awaiting
delivery, with two more action buttons. The following sections describe these
different parts of the display.



.section The stripcharts
.index stripchart
The first stripchart is always a count of messages on the queue. Its name can
be configured by setting \\QUEUE@_STRIPCHART@_NAME\\ in the
\(Local/eximon.conf)\ file. The remaining stripcharts are defined in the
configuration script by regular expression matches on log file entries, making
it possible to display, for example, counts of messages delivered to certain
hosts or using certain transports. The supplied defaults display counts of
received and delivered messages, and of local and SMTP deliveries. The default
period between stripchart updates is one minute; this can be adjusted by a
parameter in the \(Local/eximon.conf)\ file.

The stripchart displays rescale themselves automatically as the value they are
displaying changes. There are always 10 horizontal lines in each chart; the
title string indicates the value of each division when it is greater than one.
For example, `x2' means that each division represents a value of 2.

It is also possible to have a stripchart which shows the percentage fullness of
a particular disk partition, which is useful when local deliveries are confined
to a single partition.
.index \statvfs\ function
This relies on the availability of the \*statvfs()*\ function or equivalent in
the operating system. Most, but not all versions of Unix that support Exim have
this. For this particular stripchart, the top of the chart always represents
100%, and the scale is given as `x10%'. This chart is configured by setting
\\SIZE@_STRIPCHART\\ and (optionally) \\SIZE@_STRIPCHART@_NAME\\ in the
\(Local/eximon.conf)\ file.



.section Main action buttons
.index size||of monitor window
.index monitor window size
.index window size
Below the stripcharts there is an action button for quitting the monitor. Next
to this is another button marked `Size'. They are placed here so that shrinking
the window to its default minimum size leaves just the queue count stripchart
and these two buttons visible. Pressing the `Size' button causes the window to
expand to its maximum size, unless it is already at the maximum, in which case
it is reduced to its minimum.

When expanding to the maximum, if the window cannot be fully seen where it
currently is, it is moved back to where it was the last time it was at full
size. When it is expanding from its minimum size, the old position is
remembered, and next time it is reduced to the minimum it is moved back there.

The idea is that you can keep a reduced window just showing one or two
stripcharts at a convenient place on your screen, easily expand it to show
the full window when required, and just as easily put it back to what it was.
The idea is copied from what the \*twm*\ window manager does for its
\*f.fullzoom*\ action. The minimum size of the window can be changed by setting
the \\MIN@_HEIGHT\\ and \\MIN@_WIDTH\\ values in \(Local/eximon.conf)\.

Normally, the monitor starts up with the window at its full size, but it can be
built so that it starts up with the window at its smallest size, by setting
\\START@_SMALL\\=yes in \(Local/eximon.conf)\.


.section The log display
.index log||tail of, in monitor
The second section of the window is an area in which a display of the tail of
the main log is maintained. 
To save space on the screen, the timestamp on each log line is shortened by
removing the date and, if \log@_timezone\ is set, the timezone.
The log tail is not available when the only destination for logging data is
syslog, unless the syslog lines are routed to a local file whose name is passed
to \*eximon*\ via the \\EXIMON@_LOG@_FILE@_PATH\\ environment variable.

The log sub-window has a scroll bar at its lefthand side which can be used to
move back to look at earlier text, and the up and down arrow keys also have a
scrolling effect. The amount of log that is kept depends on the setting of
\\LOG@_BUFFER\\ in \(Local/eximon.conf)\, which specifies the amount of memory
to use. When this is full, the earlier 50% of data is discarded -- this is much
more efficient than throwing it away line by line. The sub-window also has a
horizontal scroll bar for accessing the ends of long log lines. This is the
only means of horizontal scrolling; the right and left arrow keys are not
available. Text can be cut from this part of the window using the mouse in the
normal way. The size of this subwindow is controlled by parameters in the
configuration file \(Local/eximon.conf)\.

Searches of the text in the log window can be carried out by means of the ^R
and ^S keystrokes, which default to a reverse and a forward search,
respectively. The search covers only the text that is displayed in the window.
It cannot go further back up the log.

The point from which the search starts is indicated by a caret marker. This is
normally at the end of the text in the window, but can be positioned explicitly
by pointing and clicking with the left mouse button, and is moved automatically
by a successful search. If new text arrives in the window when it is scrolled
back, the caret remains where it is, but if the window is not scrolled back,
the caret is moved to the end of the new text.

Pressing ^R or ^S pops up a window into which the search text can be typed.
There are buttons for selecting forward or reverse searching, for carrying out
the search, and for cancelling. If the `Search' button is pressed, the search
happens and the window remains so that further searches can be done. If the
`Return' key is pressed, a single search is done and the window is closed. If
^C is typed the search is cancelled.

The searching facility is implemented using the facilities of the Athena text
widget. By default this pops up a window containing both `search' and `replace'
options. In order to suppress the unwanted `replace' portion for eximon, a
modified version of the \TextPop\ widget is distributed with Exim. However, the
linkers in BSDI and HP-UX seem unable to handle an externally provided version
of \TextPop\ when the remaining parts of the text widget come from the standard
libraries. The compile-time option \\EXIMON@_TEXTPOP\\ can be unset to cut out
the modified \TextPop\, making it possible to build Eximon on these systems, at
the expense of having unwanted items in the search popup window.


.section The queue display
.index queue||display in monitor
The bottom section of the monitor window contains a list of all messages that
are on the queue, which includes those currently being received or delivered,
as well as those awaiting delivery. The size of this subwindow is controlled by
parameters in the configuration file \(Local/eximon.conf)\, and the frequency
at which it is updated is controlled by another parameter in the same file --
the default is 5 minutes, since queue scans can be quite expensive. However,
there is an `Update' action button just above the display which can be used to
force an update of the queue display at any time.

When a host is down for some time, a lot of pending mail can build up for it,
and this can make it hard to deal with other messages on the queue. To help
with this situation there is a button next to `Update' called `Hide'. If
pressed, a dialogue box called `Hide addresses ending with' is put up. If you
type anything in here and press `Return', the text is added to a chain of such
texts, and if every undelivered address in a message matches at least one
of the texts, the message is not displayed.

If there is an address that does not match any of the texts, all the addresses
are displayed as normal. The matching happens on the ends of addresses so, for
example, \*cam.ac.uk*\ specifies all addresses in Cambridge, while
\*xxx@@foo.com.example*\ specifies just one specific address. When any hiding
has been set up, a button called `Unhide' is displayed. If pressed, it cancels
all hiding. Also, to ensure that hidden messages do not get forgotten, a hide
request is automatically cancelled after one hour.

While the dialogue box is displayed, you can't press any buttons or do anything
else to the monitor window. For this reason, if you want to cut text from the
queue display to use in the dialogue box, you have to do the cutting before
pressing the `Hide' button.

The queue display contains, for each unhidden queued message, the length of
time it has been on the queue, the size of the message, the message id, the
message sender, and the first undelivered recipient, all on one line. If it is
a bounce message, the sender is shown as `<>'. If there is more than one
recipient to which the message has not yet been delivered, subsequent ones are
listed on additional lines, up to a maximum configured number, following which
an ellipsis is displayed. Recipients that have already received the message are
not shown.
.index frozen messages||display
If a message is frozen, an asterisk is displayed at the left-hand side.

The queue display has a vertical scroll bar, and can also be scrolled by means
of the arrow keys. Text can be cut from it using the mouse in the normal way.
The text searching facilities, as described above for the log window, are also
available, but the caret is always moved to the end of the text when the queue
display is updated.


.section The queue menu
.index queue||menu in monitor
If the \shift\ key is held down and the left button is clicked when the mouse
pointer is over the text for any message, an action menu pops up, and the first
line of the queue display for the message is highlighted. This does not affect
any selected text.

If you want to use some other event for popping up the menu, you can set the
\\MENU@_EVENT\\ parameter in \(Local/eximon.conf)\ to change the default, or
set \\EXIMON@_MENU@_EVENT\\ in the environment before starting the monitor. The
value set in this parameter is a standard X event description. For example, to
run eximon using \ctrl\ rather than \shift\ you could use
.display asis
EXIMON_MENU_EVENT='Ctrl<Btn1Down>' eximon
.endd
The title of the menu is the message id, and it contains entries which act as
follows:
.numberpars $.
\*message log*\: The contents of the message log for the message are displayed in
a new text window.
.nextp
\*headers*\: Information from the spool file that contains the envelope
information and headers is displayed in a new text window. See chapter
~~CHAPspool for a description of the format of spool files.
.nextp
\*body*\: The contents of the spool file containing the body of the message are
displayed in a new text window. There is a default limit of 20,000 bytes to the
amount of data displayed. This can be changed by setting the \\BODY@_MAX\\
option at compile time, or the \\EXIMON@_BODY@_MAX\\ option at run time.
.nextp
\*deliver message*\: A call to Exim is made using the \-M-\ option to request
delivery of the message. This causes an automatic thaw if the message is
frozen. The \-v-\ option is also set, and the output from Exim is displayed in
a new text window. The delivery is run in a separate process, to avoid holding
up the monitor while the delivery proceeds.
.nextp
\*freeze message*\: A call to Exim is made using the \-Mf-\ option to request
that the message be frozen.
.nextp
.index thawing messages
.index unfreezing messages
.index frozen messages||thawing
\*thaw message*\: A call to Exim is made using the \-Mt-\ option to request that
the message be thawed.
.nextp
.index delivery||forcing failure
\*give up on msg*\: A call to Exim is made using the \-Mg-\ option to request
that Exim gives up trying to deliver the message. A bounce message is generated
for any remaining undelivered addresses.
.nextp
\*remove message*\: A call to Exim is made using the \-Mrm-\ option to request
that the message be deleted from the system without generating a bounce
message.
.nextp
\*add recipient*\: A dialog box is displayed into which a recipient address can
be typed. If the address is not qualified and the \\QUALIFY@_DOMAIN\\ parameter
is set in \(Local/eximon.conf)\, the address is qualified with that domain.
Otherwise it must be entered as a fully qualified address. Pressing \\RETURN\\
causes a call to Exim to be made using the \-Mar-\ option to request that an
additional recipient be added to the message, unless the entry box is empty, in
which case no action is taken.
.nextp
\*mark delivered*\: A dialog box is displayed into which a recipient address can
be typed. If the address is not qualified and the \\QUALIFY@_DOMAIN\\ parameter
is set in \(Local/eximon.conf)\, the address is qualified with that domain.
Otherwise it must be entered as a fully qualified address. Pressing \\RETURN\\
causes a call to Exim to be made using the \-Mmd-\ option to mark the given
recipient address as already delivered, unless the entry box is empty, in which
case no action is taken.
.nextp
\*mark all delivered*\: A call to Exim is made using the \-Mmad-\ option to mark
all recipient addresses as already delivered.
.nextp
\*edit sender*\: A dialog box is displayed initialized with the current sender's
address. Pressing \\RETURN\\ causes a call to Exim to be made using the \-Mes-\
option to replace the sender address, unless the entry box is empty, in which
case no action is taken. If you want to set an empty sender (as in bounce
messages), you must specify it as `<>'. Otherwise, if the address is not
qualified and the \\QUALIFY@_DOMAIN\\ parameter is set in
\(Local/eximon.conf)\, the address is qualified with that domain.
.endp
When a delivery is forced, a window showing the \-v-\ output is displayed. In
other cases when a call to Exim is made, if there is any output from Exim (in
particular, if the command fails) a window containing the command and the
output is displayed. Otherwise, the results of the action are normally apparent
from the log and queue displays. However, if you set \\ACTION@_OUTPUT\\=yes in
\(Local/eximon.conf)\, a window showing the Exim command is always opened, even
if no output is generated.

The queue display is automatically updated for actions such as freezing and
thawing, unless \\ACTION@_QUEUE@_UPDATE\\=no has been set in
\(Local/eximon.conf)\. In this case the `Update' button has to be used to force
an update of the display after one of these actions.

In any text window that is displayed as result of a menu action, the normal
cut-and-paste facility is available, and searching can be carried out using ^R
and ^S, as described above for the log tail window.






.
.
.
.
. ============================================================================
.chapter Security considerations
.set runningfoot "security"
.rset CHAPsecurity ~~chapter
.index security
This chapter discusses a number of issues concerned with security, some of
which are also covered in other parts of this manual.

For reasons that this author does not understand, some people have promoted
Exim as a `particularly secure' mailer. Perhaps it is because of the existence
of this chapter in the documentation. However, the intent of the chapter is
simply to describe the way Exim works in relation to certain security concerns,
not to make any specific claims about the effectiveness of its security as
compared with other MTAs.

What follows is a description of the way Exim is supposed to be. Best efforts
have been made to try to ensure that the code agrees with the theory, but an
absence of bugs can never be guaranteed. Any that are reported will get fixed
as soon as possible.

.section Building a more `hardened' Exim
.index security||build-time features
There are a number of build-time options that can be set in \(Local/Makefile)\
to create Exim binaries that are `harder' to attack, in particular by a rogue
Exim administrator who does not have the root password, or by someone who has
penetrated the Exim (but not the root) account. These options are as follows:
.numberpars $.
\\ALT@_CONFIG@_PREFIX\\ can be set to a string that is required to match the
start of any file names used with the \-C-\ option. When it is set, these file
names are also not allowed to contain the sequence `/../'. (However, if the
value of the \-C-\ option is identical to the value of \\CONFIGURE@_FILE\\ in
\(Local/Makefile)\, Exim ignores \-C-\ and proceeds as usual.) There is no
default setting for \ALT@_CONFIG@_PREFIX\.

If the permitted configuration files are confined to a directory to
which only root has access, this guards against someone who has broken
into the Exim account from running a privileged Exim with an arbitrary
configuration file, and using it to break into other accounts.
.nextp
If \\ALT@_CONFIG@_ROOT@_ONLY\\ is defined, root privilege is retained for \-C-\
and \-D-\ only if the caller of Exim is root. Without it, the Exim user may
also use \-C-\ and \-D-\ and retain privilege. Setting this option locks out
the possibility of testing a configuration using \-C-\ right through message
reception and delivery, even if the caller is root. The reception works, but by
that time, Exim is running as the Exim user, so when it re-execs to regain
privilege for the delivery, the use of \-C-\ causes privilege to be lost.
However, root can test reception and delivery using two separate commands.
\\ALT@_CONFIG@_ROOT@_ONLY\\ is not set by default.
.nextp
If \\DISABLE@_D@_OPTION\\ is defined, the use of the \-D-\ command line option
is disabled.
.nextp
\\FIXED@_NEVER@_USERS\\ can be set to a colon-separated list of users that are
never to be used for any deliveries. This is like the \never@_users\ runtime
option, but it cannot be overridden; the runtime option adds additional users
to the list. The default setting is `root'; this prevents a non-root user who
is permitted to modify the runtime file from using Exim as a way to get root.
.endp


.section Root privilege
.index setuid
.index root privilege
The Exim binary is normally setuid to root, which means that it gains root
privilege (runs as root) when it starts execution. In some special cases (for
example, when the daemon is not in use and there are no local deliveries), it
may be possible to run Exim setuid to some user other than root. This is
discussed in the next section. However, in most installations, root privilege
is required for two things:
.numberpars $.
To set up a socket connected to the standard SMTP port (25) when initialising
the listening daemon. If Exim is run from \*inetd*\, this privileged action is
not required.
.nextp
To be able to change uid and gid in order to read users' \(.forward)\ files and
perform local deliveries as the receiving user or as specified in the
configuration.
.endp
It is not necessary to be root to do any of the other things Exim does, such as
receiving messages and delivering them externally over SMTP, and it is
obviously more secure if Exim does not run as root except when necessary.
For this reason, a user and group for Exim to use must be defined in
\(Local/Makefile)\. These are known as `the Exim user' and `the Exim group'.
Their values can be changed by the run time configuration, though this is not
recommended. Often a user called \*exim*\ is used, but some sites use \*mail*\
or another user name altogether.

Exim uses \*setuid()*\ whenever it gives up root privilege. This is a permanent
abdication; the process cannot regain root afterwards. Prior to release 4.00,
\*seteuid()*\ was used in some circumstances, but this is no longer the case.

After a new Exim process has interpreted its command line options, it changes
uid and gid in the following cases:
.numberpars $.
.index \-C-\ option
.index \-D-\ option
If the \-C-\ option is used to specify an alternate configuration file, or if
the \-D-\ option is used to define macro values for the configuration, and the
calling process is not running as root or the Exim user, the uid and gid are
changed to those of the calling process.
However, if \\ALT@_CONFIG@_ROOT@_ONLY\\ is defined in \(Local/Makefile)\, only 
root callers may use \-C-\ and \-D-\ without losing privilege, and if 
\\DISABLE@_D@_OPTION\\ is set, the \-D-\ option may not be used at all.
.nextp
.index \-be-\ option
.index \-bf-\ option
.index \-bF-\ option
If the expansion test option (\-be-\) or one of the filter testing options
(\-bf-\ or \-bF-\) are used, the uid and gid are changed to those of the
calling process.
.nextp
If the process is not a daemon process or a queue runner process or a delivery
process or a process for testing address routing (started with \-bt-\), the uid
and gid are changed to the Exim user and group. This means that Exim always
runs under its own uid and gid when receiving messages. This also applies when
testing address verification 
.index \-bv-\ option
.index \-bh-\ option
(the \-bv-\ option) and testing incoming message policy controls (the \-bh-\
option).
.nextp
For a daemon, queue runner, delivery, or address testing process, the uid
remains as root at this stage, but the gid is changed to the Exim group.
.endp
The processes that initially retain root privilege behave as follows:
.numberpars $.
A daemon process changes the gid to the Exim group and the uid to the Exim user
after setting up one or more listening sockets. The \*initgroups()*\ function
is called, so that if the Exim user is in any additional groups, they will be
used during message reception.
.nextp
A queue runner process retains root privilege throughout its execution. Its job
is to fork a controlled sequence of delivery processes.
.nextp
A delivery process retains root privilege throughout most of its execution,
but any actual deliveries (that is, the transports themselves) are run in
subprocesses which always change to a non-root uid and gid. For local
deliveries this is typically the uid and gid of the owner of the mailbox; for
remote deliveries, the Exim uid and gid are used. Once all the delivery
subprocesses have been run, a delivery process changes to the Exim uid and gid
while doing post-delivery tidying up such as updating the retry database and
generating bounce and warning messages.

While the recipient addresses in a message are being routed, the delivery
process runs as root. However, if a user's filter file has to be processed,
this is done in a subprocess that runs under the individual user's uid and
gid. A system filter is run as root unless \system@_filter@_user\ is set.
.nextp
A process that is testing addresses (the \-bt-\ option) runs as root so that
the routing is done in the same environment as a message delivery.
.endp


.section Running Exim without privilege
.index privilege, running without
.index unprivileged running
.index root privilege||running without
Some installations like to run Exim in an unprivileged state for more of its
operation, for added security. Support for this mode of operation is provided
by the global option \deliver@_drop@_privilege\. When this is set, the uid and
gid are changed to the Exim user and group at the start of a delivery process
(and also queue runner and address testing processes). This means that address
routing is no longer run as root, and the deliveries themselves cannot change
to any other uid.

Leaving the binary setuid to root, but setting \deliver@_drop@_privilege\ means
that the daemon can still be started in the usual way, and it can respond
correctly to SIGHUP because the re-invocation regains root privilege.

An alternative approach is to make Exim setuid to the Exim user and also setgid
to the Exim group.
If you do this, the daemon must be started from a root process. (Calling
Exim from a root process makes it behave in the way it does when it is setuid
root.) However, the daemon cannot restart itself after a SIGHUP signal because
it cannot regain privilege.

It is still useful to set \deliver@_drop@_privilege\ in this case, because it
stops Exim from trying to re-invoke itself to do a delivery after a message has
been received. Such a re-invocation is a waste of resources because it has no
effect.

If restarting the daemon is not an issue (for example, if \*inetd*\ is being
used instead of a daemon), having the binary setuid to the Exim user seems a
clean approach, but there is one complication:

In this style of operation, Exim is running with the real uid and gid set to
those of the calling process, and the effective uid/gid set to Exim's values.
Ideally, any association with the calling process' uid/gid should be dropped,
that is, the real uid/gid should be reset to the effective values so as to
discard any privileges that the caller may have. While some operating systems
have a function that permits this action for a non-root effective uid, quite a
number of them do not. Because of this lack of standardization, Exim does not
address this problem at this time.

For this reason, the recommended approach for `mostly unprivileged' running is
to keep the Exim binary setuid to root, and to set \deliver@_drop@_privilege\.
This also has the advantage of allowing a daemon to be used in the most
straightforward way.

If you configure Exim not to run delivery processes as root, there are a
number of restrictions on what you can do:
.numberpars $.
You can deliver only as the Exim user/group. You should  explicitly use the
\user\ and \group\ options to override routers or local transports that
normally deliver as the recipient. This makes sure that configurations that
work in this mode function the same way in normal mode. Any implicit or
explicit specification of another user causes an error.
.nextp
Use of \(.forward)\ files is severely restricted, such that it is usually
not worthwhile to include them in the configuration.
.nextp
Users who wish to use \(.forward)\ would have to make their home directory and
the file itself accessible to the Exim user. Pipe and append-to-file entries,
and their equivalents in Exim filters, cannot be used. While they could be
enabled in the Exim user's name, that would be insecure and not very useful.
.nextp
Unless the local user mailboxes are all owned by the Exim user (possible in
some POP3 or IMAP-only environments):
.numberpars $*$
They must be owned by the Exim group and be writable by that group. This
implies you must set \mode\ in the appendfile configuration, as well as the
mode of the mailbox files themselves.
.nextp
You must set \no@_check@_owner\, since most or all of the files will not be
owned by the Exim user.
.nextp
You must set \file@_must@_exist\, because Exim cannot set the owner correctly
on a newly created mailbox when unprivileged. This also implies that new
mailboxes need to be created manually.
.endp
.endp
These restrictions severely restrict what can be done in local deliveries.
However, there are no restrictions on remote deliveries. If you are running a
gateway host that does no local deliveries, setting \deliver@_drop@_privilege\
gives more security at essentially no cost.


.section Delivering to local files
Full details of the checks applied by \%appendfile%\ before it writes to a file
are given in chapter ~~CHAPappendfile.


.section IPv4 source routing
.index source routing||in IP packets
.index IP source routing
Many operating systems suppress IP source-routed packets in the kernel, but
some cannot be made to do this, so Exim does its own check. It logs incoming
IPv4 source-routed TCP calls, and then drops them. Things are all different in
IPv6. No special checking is currently done.


.section The VRFY, EXPN, and ETRN commands in SMTP
Support for these SMTP commands is disabled by default. If required, they can
be enabled by defining suitable ACLs.



.section Privileged users
.index trusted user
.index admin user
.index privileged user
.index user||trusted
.index user||admin
Exim recognises two sets of users with special privileges. Trusted users are
able to submit new messages to Exim locally, but supply their own sender
addresses and information about a sending host. For other users submitting
local messages, Exim sets up the sender address from the uid, and doesn't
permit a remote host to be specified.

.index \-f-\ option
However, an untrusted user is permitted to use the \-f-\ command line option in
the special form \-f @<@>-\ to indicate that a delivery failure for the message
should not cause an error report. This affects the message's envelope, but it
does not affect the ::Sender:: header. Untrusted users may also be permitted to
use specific forms of address with the \-f-\ option by setting the
\untrusted@_set@_sender\ option.

Trusted users are used to run processes that receive mail messages from some
other mail domain and pass them on to Exim for delivery either locally, or over
the Internet. Exim trusts a caller that is running as root, as the Exim user,
as any user listed in the \trusted@_users\ configuration option, or under any
group listed in the \trusted@_groups\ option.

Admin users are permitted to do things to the messages on Exim's queue. They
can freeze or thaw messages, cause them to be returned to their senders, remove
them entirely, or modify them in various ways. In addition, admin users can run
the Exim monitor and see all the information it is capable of providing, which
includes the contents of files on the spool.

.index \-M-\ option
.index \-q-\ option
By default, the use of the \-M-\ and \-q-\ options to cause Exim to attempt
delivery of messages on its queue is restricted to admin users. This
restriction can be relaxed by setting the \no@_prod@_requires@_admin\ option.
Similarly, the use of \-bp-\ (and its variants) to list the contents of the
queue is also restricted to admin users. This restriction can be relaxed by
setting \no@_queue@_list@_requires@_admin\.

Exim recognises an admin user if the calling process is running as root or as
the Exim user or if any of the groups associated with the calling process is
the Exim group. It is not necessary actually to be running under the Exim
group. However, if admin users who are not root or the Exim user are to access
the contents of files on the spool via the Exim monitor (which runs
unprivileged), Exim must be built to allow group read access to its spool
files.


.section Spool files
.index spool directory||files
Exim's spool directory and everything it contains is owned by the Exim user and
set to the Exim group. The mode for spool files is defined in the
\(Local/Makefile)\ configuration file, and defaults to 0640. This means that
any user who is a member of the Exim group can access these files.


.section Use of argv[0]
Exim examines the last component of \argv[0]\, and if it matches one of a set
of specific strings, Exim assumes certain options. For example, calling Exim
with the last component of \argv[0]\ set to `rsmtp' is exactly equivalent to
calling it with the option \-bS-\. There are no security implications in this.


.section Use of %f formatting
The only use made of `%f' by Exim is in formatting load average values. These
are actually stored in integer variables as 1000 times the load average.
Consequently, their range is limited and so therefore is the length of the
converted output.


.section Embedded Exim path
Exim uses its own path name, which is embedded in the code, only when it needs
to re-exec in order to regain root privilege. Therefore, it is not root when it
does so. If some bug allowed the path to get overwritten, it would lead to an
arbitrary program's being run as exim, not as root.


.section Use of sprintf()
.index \*sprintf()*\
A large number of occurrences of `sprintf' in the code are actually calls to
\*string@_sprintf()*\, a function that returns the result in malloc'd store.
The intermediate formatting is done into a large fixed buffer by a function
that runs through the format string itself, and checks the length of each
conversion before performing it, thus preventing buffer overruns.

The remaining uses of \*sprintf()*\ happen in controlled circumstances where
the output buffer is known to be sufficiently long to contain the converted
string.


.section Use of debug@_printf() and log@_write()
Arbitrary strings are passed to both these functions, but they do their
formatting by calling the function \*string@_vformat()*\, which runs through
the format string itself, and checks the length of each conversion.


.section Use of strcat() and strcpy()
These are used only in cases where the output buffer is known to be large
enough to hold the result.




.
.
.
.
. ============================================================================
.chapter Format of spool files
.set runningfoot "spool file format"
.rset CHAPspool ~~chapter
.index format||spool files
.index spool directory||format of files
.index spool||files, format of
.index spool||files, editing
A message on Exim's queue consists of two files, whose names are the message id
followed by -D and -H, respectively. The data portion of the message is kept in
the -D file on its own. The message's envelope, status, and headers are all
kept in the -H file, whose format is described in this chapter. Each of these
two files contains the final component of its own name as its first line. This
is insurance against disk crashes where the directory is lost but the files
themselves are recoverable.

.em
Some people are tempted into editing -D files in order to modify messages. You
need to be extremely careful if you do this; it is not recommended and you are
on your own if you do it. Here are some of the pitfalls:
.numberpars $.
You must use the \*exim@_lock*\ utility to ensure that Exim does not try to
deliver the message while you are fiddling with it. The lock is implemented
by opening the -D file and taking out a write lock on it. If you update the
file in place, the lock will be retained. If you write a new file and rename
it, the lock will be lost at the instant of rename.
.nextp
If you change the number of lines in the file, the value of
\$body@_linecount$\, which is stored in the -H file, will be incorrect.
.nextp
If the message is in MIME format, you must take care not to break it.
.nextp
If the message is cryptographically signed, any change will invalidate the 
signature.
.endp
.nem

Files whose names end with -J may also be seen in the \(input)\ directory (or
its subdirectories when \split@_spool@_directory\ is set). These are journal
files, used to record addresses to which the message has been delivered during
the course of a delivery run. At the end of the run, the -H file is updated,
and the -J file is deleted.

.section Format of the -H file
.index uid (user id)||in spool file
.index gid (group id)||in spool file
The second line of the -H file contains the login name for the uid of the
process that called Exim to read the message, followed by the numerical uid and
gid. For a locally generated message, this is normally the user who sent the
message. For a message received over TCP/IP, it is normally the Exim user.

The third line of the file contains the address of the message's sender as
transmitted in the envelope, contained in angle brackets. The sender address is
empty for bounce messages. For incoming SMTP mail, the sender address is given
in the \\MAIL\\ command. For locally generated mail, the sender address is
created by Exim from the login name of the current user and the configured
\qualify@_domain\. However, this can be overridden by the \-f-\ option or a
leading `From' line if the caller is trusted, or if the supplied address is
`@<@>' or an address that matches \untrusted@_set@_senders\.

The fourth line contains two numbers. The first is the time that the message
was received, in the conventional Unix form -- the number of seconds since the
start of the epoch. The second number is a count of the number of messages
warning of delayed delivery that have been sent to the sender.

There follow a number of lines starting with a hyphen. These can appear in any
order, and are omitted when not relevant:
.numberpars $.
.em
\-acl <<number>> <<length>>-\: A line of this form is present for every ACL 
variable that is not empty. The number identifies the variable; the 
\acl@_c\*x*\$$\ variables are numbered 0--9 and the \acl@_m\*x*\$$\ variables 
are numbered 10--19. The length is the length of the data string for the 
variable. The string itself starts at the beginning of the next line, and is
followed by a newline character. It may contain internal newlines.
.nextp
\-allow@_unqualified@_recipient-\: This is present if unqualified recipient 
addresses are permitted in header lines (to stop such addresses from being 
qualified if rewriting occurs at transport time). Local messages that were 
input using \-bnq-\ and remote messages from hosts that match 
\recipient@_unqualified@_hosts\ set this flag.
.nextp
\-allow@_unqualified@_sender-\: This is present if unqualified sender 
addresses are permitted in header lines (to stop such addresses from being 
qualified if rewriting occurs at transport time). Local messages that were 
input using \-bnq-\ and remote messages from hosts that match 
\sender@_unqualified@_hosts\ set this flag.
.nem
.nextp
\-auth@_id <<text>>-\: The id information for a message received on an
authenticated SMTP connection -- the value of the \$authenticated@_id$\
variable.
.nextp
\-auth@_sender <<address>>-\: The address of an authenticated sender -- the
value of the \$authenticated@_sender$\ variable.
.nextp
\-body@_linecount <<number>>-\: This records the number of lines in the body of
the message, and is always present.
.nextp
\-deliver@_firsttime-\: This is written when a new message is first added to
the spool. When the spool file is updated after a deferral, it is omitted.
.nextp
.index frozen messages||spool data
\-frozen <<time>>-\: The message is frozen, and the freezing happened at
<<time>>.
.nextp
\-helo@_name <<text>>-\: This records the host name as specified by a remote
host in a \\HELO\\ or \\EHLO\\ command.
.nextp
\-host@_address <<address>>.<<port>>-\: This records the IP address of the host
from which the message was received and the remote port number that was used.
It is omitted for locally generated messages.
.nextp
\-host@_auth <<text>>-\: If the message was received on an authenticated SMTP
connection, this records the name of the authenticator -- the value of the
\$sender@_host@_authenticated$\ variable.
.nextp
\-host@_lookup@_failed-\: This is present if an attempt to look up the sending
host's name from its IP address failed. It corresponds to the
\$host@_lookup@_failed$\ variable.
.nextp
.index DNS||reverse lookup
.index reverse DNS lookup
\-host@_name <<text>>-\: This records the name of the remote host from which
the message was received, if the host name was looked up from the IP address
when the message was being received. It is not present if no reverse lookup was
done.
.nextp
\-ident <<text>>-\: For locally submitted messages, this records the login of
the originating user, unless it was a trusted user and the \-oMt-\ option was
used to specify an ident value. For messages received over TCP/IP, this records
the ident string supplied by the remote host, if any.
.nextp
\-interface@_address <<address>>.<<port>>-\: This records the IP address of the
local interface and the port number through which a message was received from a
remote host. It is omitted for locally generated messages.
.nextp
\-local-\: The message is from a local sender.
.nextp
\-localerror-\: The message is a locally-generated bounce message.
.nextp
\-local@_scan <<string>>-\: This records the data string that was
returned by the \*local@_scan()*\ function when the message was received -- the
value of the \$local@_scan@_data$\ variable. It is omitted if no data was
returned.
.nextp
\-manual@_thaw-\: The message was frozen but has been thawed manually, that is,
by an explicit Exim command rather than via the auto-thaw process.
.nextp
\-N-\: A testing delivery process was started using the \-N-\ option to
suppress any actual deliveries, but delivery was deferred. At any further
delivery attempts, \-N-\ is assumed.
.nextp
\-received@_protocol-\: This records the value of the \$received@_protocol$\
variable, which contains the name of the protocol by which the message was
received.
.nextp
\-sender@_set@_untrusted-\: The envelope sender of this message was set by an
untrusted local caller (used to ensure that the caller is displayed in queue
listings).
.nextp
\-tls@_certificate@_verified-\: A TLS certificate was received from the client 
that sent this message, and the certificate was verified by the server.
.nextp
\-tls@_cipher <<cipher name>>-\: When the message was received over an
encrypted connection, this records the name of the cipher suite that was used.
.nextp
\-tls@_peerdn <<peer DN>>-\: When the message was received over an encrypted
connection, and a certificate was received from the client, this records the
Distinguished Name from that certificate.
.endp

Following the options there is a list of those addresses to which the message
is not to be delivered. This set of addresses is initialized from the command
line when the \-t-\ option is used and \extract__addresses__remove__arguments\
is set; otherwise it starts out empty. Whenever a successful delivery is made,
the address is added to this set. The addresses are kept internally as a
balanced binary tree, and it is a representation of that tree which is written
to the spool file. If an address is expanded via an alias or forward file, the
original address is added to the tree when deliveries to all its child
addresses are complete.

If the tree is empty, there is a single line in the spool file containing just
the text `XX'. Otherwise, each line consists of two letters, which are either Y
or N, followed by an address. The address is the value for the node of the
tree, and the letters indicate whether the node has a left branch and/or a
right branch attached to it, respectively. If branches exist, they immediately
follow. Here is an example of a three-node tree:
.display asis
YY darcy@austen.fict.example
NN alice@wonderland.fict.example
NN editor@thesaurus.ref.example
.endd
After the non-recipients tree, there is a list of the message's recipients.
This is a simple list, preceded by a count. It includes all the original
recipients of the message, including those to whom the message has already been
delivered. In the simplest case, the list contains one address per line. For
example:
.display asis
4
editor@thesaurus.ref.example
darcy@austen.fict.example
rdo@foundation
alice@wonderland.fict.example
.endd
However, when a child address has been added to the top-level addresses as a
result of the use of the \one@_time\ option on a \%redirect%\ router, each line
is of the following form:
.display
<<top-level address>> <<errors@_to address>> <<length>>,<<parent number>>@#<<flag bits>>
.endd
The 01 flag bit indicates the presence of the three other fields that follow
the top-level address. Other bits may be used in future to support additional
fields. The <<parent number>> is the offset in the recipients list of the
original parent of the `one time' address. The first two fields are the
envelope sender that is associated with this address and its length. If the
length is zero, there is no special envelope sender (there are then two space
characters in the line). A non-empty field can arise from a \%redirect%\ router
that has an \errors@_to\ setting.


A blank line separates the envelope and status information from the headers
which follow. A header may occupy several lines of the file, and to save effort
when reading it in, each header is preceded by a number and an identifying
character. The number is the number of characters in the header, including any
embedded newlines and the terminating newline. The character is one of the
following:
.display
.tabs 9
<<blank>>  $t $rm{header in which Exim has no special interest}
#B      $t $rm{::Bcc:: header}
#C      $t $rm{::Cc:: header}
#F      $t $rm{::From:: header}
#I      $t $rm{::Message-id:: header}
#P      $t $rm{::Received:: header -- P for `postmark'}
#R      $t $rm{::Reply-To:: header}
#S      $t $rm{::Sender:: header}
#T      $t $rm{::To:: header}
#*      $t $rm{replaced or deleted header}
.endd
Deleted or replaced (rewritten) headers remain in the spool file for debugging
purposes. They are not transmitted when the message is delivered. Here is a
typical set of headers:
.display asis
111P Received: by hobbit.fict.example with local (Exim 4.00)
        id 14y9EI-00026G-00; Fri, 11 May 2001 10:28:59 +0100
049  Message-Id: <E14y9EI-00026G-00@hobbit.fict.example>
038* X-rewrote-sender: bb@hobbit.fict.example
042* From: Bilbo Baggins <bb@hobbit.fict.example>
049F From: Bilbo Baggins <B.Baggins@hobbit.fict.example>
099* To: alice@wonderland.fict.example, rdo@foundation,
 darcy@austen.fict.example, editor@thesaurus.ref.example
109T To: alice@wonderland.fict.example, rdo@foundation.fict.example,
 darcy@austen.fict.example, editor@thesaurus.ref.example
038  Date: Fri, 11 May 2001 10:28:59 +0100
.endd
The asterisked headers indicate that the envelope sender, ::From:: header, and
::To:: header have been rewritten, the last one because routing expanded the
unqualified domain \*foundation*\.

.
.
.
.
. ============================================================================
.chapter Adding new drivers or lookup types
.set runningfoot "adding drivers"
.index adding drivers
.index new drivers, adding
.index drivers||adding new
The following actions have to be taken in order to add a new router, transport,
authenticator, or lookup type to Exim:
.numberpars
Choose a name for the driver or lookup type that does not conflict with any
existing name; I will use `newdriver' in what follows.
.nextp
Add to \(src/EDITME)\ the line
.display
<<type>>@_NEWDRIVER=yes
.endd
where <<type>> is \\ROUTER\\, \\TRANSPORT\\, \\AUTH\\, or \\LOOKUP\\. If the
code is not to be included in the binary by default, comment this line out. You
should also add any relevant comments about the driver or lookup type.
.nextp
Add to \(src/config.h.defaults)\ the line
.display
@#define <<type>>@_NEWDRIVER
.endd
.nextp
Edit \(src/drtables.c)\, adding conditional code to pull in the private header
and create a table entry as is done for all the other drivers and lookup types.
.nextp
Edit \(Makefile)\ in the appropriate sub-directory (\(src/routers)\,
\(src/transports)\, \(src/auths)\, or \(src/lookups)\); add a line for the new
driver or lookup type and add it to the definition of OBJ.
.nextp
Create \(newdriver.h)\ and \(newdriver.c)\ in the appropriate sub-directory of
\(src)\.
.nextp
Edit \(scripts/MakeLinks)\ and add commands to link the \(.h)\ and \(.c)\ files
as for other drivers and lookups.
.endp
Then all you need to do is write the code! A good way to start is to make a
proforma by copying an existing module of the same type, globally changing all
occurrences of the name, and cutting out most of the code. Note that any
options you create must be listed in alphabetical order, because the tables are
searched using a binary chop procedure.

There is a \(README)\ file in each of the sub-directories of \(src)\ describing
the interface that is expected.

.
.
.
.
. ============================================================================
. Fudge for the index page number. We want it to be on a right-hand page.
.
.set indexpage ~~sys.pagenumber + 1
.if even ~~indexpage
.set indexpage ~~indexpage + 1
.fi
.if ~~sgcal
.%index Index$e~~indexpage--
.fi
.
.
. End of Exim specification