. $Cambridge: exim/doc/doc-src/spec.src,v 1.6 2005/01/27 15:00:38 ph10 Exp $ . .set version "4.50" .set previousversion "4.40" .set versionmonth "February" .set versionyear "2005" .set ACL "ACL" . The last of those is to make ACL index entries easier to type. It is put . up here so that it gets picked up by the HTML converter, which otherwise . skips to the first chapter. A longer version is set below for use in the . printed index. .set sgcal true .set html false .set texinfo false .if !set style .library "a4ps" .linelength ~~sys.linelength + 0.2in .set newlinelength ~~sys.linelength .emphasis ~~sys.linelength + 0.1in .pagedepth ~~sys.pagedepth - 0.2in .bindfont 51 "atl/Times-Bold" 9 .bindfont 52 "atl/Times-Roman" 9 .bindfont 53 "atl/Times-Roman" 7 .bindfont 54 "atl/Courier" 9 .bindfont 55 "atl/Courier-Bold" ~~maintypesize .bindfont 56 "atl/Times-Italic" 7 .bindfont 57 "atl/Times-Bold" 7 .bindfont 58 "atl/Symbol" 7 .set ssspaceb 1.50 .if ~~sgcal . 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This is used for the printed index. See setting above for . the HTML index value. .set ACL "access control lists (ACLs)" . ====================================================== .push .disable filling .justify centre .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 .space 2ld .if ~~sgcal .fontgroup 1 .fi $c$rm{Copyright (c) University of Cambridge ~~versionyear} .if ~~sgcal .fontgroup 0 .font 0 .fi .pop .newpage . Blank verso for title page .space 1ld .newpage . Set up for actual text pages .page 1 . The first one to prevent a warning from sgfr . set runningfoot "~~chapter" .set runningfoot "" .if ~~sys.fancy .footdepth 2ld .foot .if "~~runningfoot" == "" .set rhs "" .else .set rhs "~~runningfoot (~~chapter)" .fi .set lhs "Exim ~~version" .linelength ~~newlinelength $it{~~lhs}$c[~~sys.pagenumber]$e$it{~~rhs} .endfoot .fi . . . . . ============================================================================ .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) .elif !~~html $c"If I have seen further it is by standing on the shoulders of giants." .newline $e (Isaac Newton) .else \*If I have seen further it is by standing on the shoulders of giants.*\ (Isaac Newton). .fi .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. Specifications of new features that are not yet in this manual are placed in the file \(doc/NewStuff)\ in the Exim distribution. .em Some features may be classified as `experimental'. These may change incompatibly while they are developing, or even be withdrawn. For this reason, they are not documented in this manual. Information about experimental features can be found in the file \(doc/experimental.txt)\. .nem 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} .newline .em \(experimental.txt)\ $t $rm{documentation of experimental features} .nem .newline \(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} \(Exim4.upgrade)\ $t $rm{upgrade notes from release 3 to release 4} .endd The main specification and the specification of the filtering language are also available in other formats (HTML, PostScript, PDF, and Texinfo). Section ~~SECTavail below tells you how to get hold of these. .section FTP and web sites .index web site .index FTP site .em The primary distribution site for Exim is currently the University of Cambridge's FTP site, whose contents are described in \*Where to find the Exim distribution*\ below. In addition, there is a .if ~~html [(A HREF="http://www.exim.org/")] .fi web site .if ~~html [(/A)] .fi and an .if ~~html [(A HREF="ftp://ftp.exim.org/")] .fi FTP site .if ~~html [(/A)] .fi at \exim.org\. These are now also hosted at the University of Cambridge. The \exim.org\ site was previously hosted for a number of years by Energis Squared, formerly Planet Online Ltd, whose support I gratefully acknowledge. As well as Exim distribution tar files, the Exim web site contains a number of differently formatted versions of the documentation, including the .index FAQ .if ~~html [(A HREF="FAQ.html")] .fi FAQ .if ~~html [(/A)] .fi in both text and HTML formats. The HTML version comes with a keyword-in-context index. A recent addition to the online information is the .index wiki .if ~~html [(A HREF="http://www.exim.org/eximwiki/")] Exim wiki. [(/A)] .else Exim wiki (\?http://www.exim.org/eximwiki/?\). .fi We hope that this will make it easier for Exim users to contribute examples, tips, and know-how for the benefit of others. .nem .section Mailing lists .index mailing lists||for Exim users The following are the two main Exim 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. .em .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 This is mirrored by .display rm .if ! ~~sys.fancy .indent 0 .fi \?ftp://ftp.exim.org/pub/exim?\ .endd The file references that follow are relative to the \(exim)\ directories at these sites. There are now quite a number of independent mirror sites around the world. Those that I know about are listed in the file called \(Mirrors)\. Within the \(exim)\ directory there are subdirectories called \(exim3)\ (for previous Exim 3 distributions), \(exim4)\ (for the latest Exim 4 distributions), and \(Testing)\ for testing versions. 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 currently 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 \(Public-Key)\. 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 For each released version, the log of changes is made separately available in a separate file in the directory \(ChangeLogs)\ 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 in these files: .display rm \(exim4/FAQ.txt.gz)\ \(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 into the file \(exim4/WishList)\. 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 \(Contrib)\ that contains miscellaneous files contributed to the Exim community by Exim users. There is also a collection of contributed configuration examples in \(exim4/config.samples.tar.gz)\. These samples are referenced from the FAQ. .nem .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 .em Although Exim does have basic 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. If you compile Exim with the content-scanning extension, straightforward interfaces to a number of common scanners are provided. .nem .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 or a `non-delivery report' (NDR). 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) 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 (at the time he contributed it) 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 .space 1ld .nextp .em Many people have contributed code fragments, some large, some small, that were not covered by any specific licence requirements. It is assumed that the contributors are happy to see their code incoporated into Exim under the GPL. .nem .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 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 from a remote host. 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 .em When Exim is compiled with the content-scanning extension, facilities are provided in the ACL mechanism for passing the message to external virus and/or spam scanning software. The result of such a scan is passed back to the ACL, which can then use it to decide what to do with the message. .nem .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 .em Using the \*local@_scan()*\ mechanism is another way of calling external scanner software. The \SA-Exim\ add-on package works this way. It does not require Exim to be compiled with the content-scanning extension. .nem .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 -sgcal -nv 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. The order in which deliveries are done is not defined, except that all local deliveries happen before any remote deliveries. .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 content scanning||specifying at build time .em Exim's interfaces for calling virus and spam scanning sofware directly from access control lists are not compiled by default. If you want to include these facilities, you need to set .display asis WITH_CONTENT_SCAN=yes .endd in your \(Local/Makefile)\. For details of the facilities themselves, see chapter ~~CHAPexiscan. .nem .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@_ports\ runtime option and 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. .em Two different types of DNS record for handling IPv6 addresses have been defined. AAAA records (analagous to A records for IPv4) are in use, and are currently seen as the mainstream. Another record type called A6 was proposed as better than AAAA because it had more flexibility. However, it was felt to be over-complex, and its status was reduced to `experimental'. It is not known if anyone is actually using A6 records. Exim has support for A6 records, but this is included only if you set \\SUPPORT@_A6=YES\\ in \(Local/Makefile)\. The support has not been tested for some time. .nem .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. \**Warning**\: The \-j-\ (parallel) flag must not be used with \*make*\; the building process fails if it is set. 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-)\<> \(Local/Makefile)\ \(Local/Makefile-)\<> \(Local/Makefile-)\<> \(Local/Makefile-)\<>-<> \(OS/Makefile-Base)\ .endd .index \(Local/Makefile)\ where <> is the operating system type and <> 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 <> and <> 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 (\(OS/Makefile-<>)\) 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-<>)\, 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-<>)\ 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-<>)\. 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-)\<> \(Local/eximon.conf)\ \(Local/eximon.conf-)\<> \(Local/eximon.conf-)\<> \(Local/eximon.conf-)\<>-<> .endd .index \(Local/eximon.conf)\ As with Exim itself, the final three files need not exist, and in this case the \(OS/eximon.conf-<>)\ 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 \(Local/Makefile)\ and the Texinfo source of the documentation is found in the source tree, running \*make install*\ automatically builds the info files and installs them. .section Setting up the spool directory .index spool directory||creating When it starts up, Exim tries to create its spool directory if it does not exist. The Exim uid and gid are used for the owner and group of the spool directory. Sub-directories are automatically created in the spool directory as necessary. .section Testing .index testing||installation Having installed Exim, you can check that the run time configuration file is syntactically valid by running the following command, which assumes that the Exim binary directory is within your \\PATH\\ environment variable: .display exim -bV .endd If there are any errors in the configuration file, Exim outputs error messages. Otherwise it outputs the version number and build date, the DBM library that is being used, and information about which drivers and other optional code modules are included in the binary. Some simple routing tests can be done by using the address testing option. For example, .display exim -bt <> .endd should verify that it recognizes a local mailbox, and .display exim -bt <> .endd a remote one. Then try getting it to deliver mail, both locally and remotely. This can be done by passing messages directly to Exim, without going through a user agent. For example: .display exim -v postmaster@@your.domain.example From: user@@your.domain.example To: postmaster@@your.domain.example Subject: Testing Exim This is a test message. ^D .endd The \-v-\ option causes Exim to output some verification of what it is doing. In this case you should see copies of three log lines, one for the message's arrival, one for its delivery, and one containing `Completed'. .index delivery||problems with If you encounter problems, look at Exim's log files (\*mainlog*\ and \*paniclog*\) 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 <> .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 <> .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-\<