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diff --git a/doc/doc-docbook/filter.ascd b/doc/doc-docbook/filter.ascd new file mode 100644 index 000000000..8fd9c7e3c --- /dev/null +++ b/doc/doc-docbook/filter.ascd @@ -0,0 +1,1759 @@ +/// +$Cambridge: exim/doc/doc-docbook/filter.ascd,v 1.1 2005/06/16 10:32:31 ph10 Exp $ + +This file contains the Asciidoc source for the document that describes Exim's +filtering facilities from a user's point of view. See the file AdMarkup.txt for +an explanation of the markup that is used. It is more or less standard +Asciidoc, but with a few changes and additions. +/// + + +/// +This preliminary stuff creates a <bookinfo> entry in the XML. This is removed +when creating the PostScript/PDF output, because we do not want a full-blown +title page created for those versions. The stylesheet fudges up a title line to +replace the text "Table of contents". However, for the other forms of output, +the <bookinfo> element is retained and used. +/// + +Exim's interfaces to mail filtering +=================================== +:author: Philip Hazel +:copyright: University of Cambridge +:cpyear: 2005 +:date: 13 May 2005 +:doctitleabbrev: Exim filtering +:revision: 4.50 + + +////////////////////////////////////////////////////////////////////////////// +***WARNING*** Do not put anything, not even a titleabbrev setting, before +the first chapter (luckily it does not need one) because if you do, AsciiDoc +creates an empty <preface> element, which we do not want. +////////////////////////////////////////////////////////////////////////////// + + +Forwarding and filtering in Exim +-------------------------------- + +This document describes the user interfaces to Exim's in-built mail filtering +facilities, and is copyright (C) University of Cambridge 2005. It corresponds +to Exim version 4.50. + + + +Introduction +~~~~~~~~~~~~ +Most Unix mail transfer agents (programs that deliver mail) permit individual +users to specify automatic forwarding of their mail, usually by placing a list +of forwarding addresses in a file called '.forward' in their home directories. +Exim extends this facility by allowing the forwarding instructions to be a set +of rules rather than just a list of addresses, in effect providing ``'.forward' +with conditions''. Operating the set of rules is called 'filtering', and the +file that contains them is called a 'filter file'. + +Exim supports two different kinds of filter file. An 'Exim filter' contains +instructions in a format that is unique to Exim. A 'Sieve filter' contains +instructions in the Sieve format that is defined by RFC 3028. As this is a +standard format, Sieve filter files may already be familiar to some users. +Sieve files should also be portable between different environments. However, +the Exim filtering facility contains more features (such as variable +expansion), and better integration with the host environment (such as the use +of external processes and pipes). + +The choice of which kind of filter to use can be left to the end-user, provided +that the system administrator has configured Exim appropriately for both kinds +of filter. However, if interoperability is important, Sieve is the only +choice. + +The ability to use filtering or traditional forwarding has to be enabled by the +system administrator, and some of the individual facilities can be separately +enabled or disabled. A local document should be provided to describe exactly +what has been enabled. In the absence of this, consult your system +administrator. + +This document describes how to use a filter file and the format of its +contents. It is intended for use by end-users. Both Sieve filters and Exim +filters are covered. However, for Sieve filters, only issues that relate to the +Exim implementation are discussed, since Sieve itself is described elsewhere. + +The contents of traditional '.forward' files are not described here. They +normally contain just a list of addresses, file names, or pipe commands, +separated by commas or newlines, but other types of item are also available. +The full details can be found in the chapter on the ^redirect^ router in the +Exim specification, which also describes how the system administrator can set +up and control the use of filtering. + + + +Filter operation +~~~~~~~~~~~~~~~~ +It is important to realize that, in Exim, no deliveries are actually made while +a filter or traditional '.forward' file is being processed. Running a filter +or processing a traditional '.forward' file sets up future delivery +operations, but does not carry them out. + +The result of filter or '.forward' file processing is a list of destinations +to which a message should be delivered. The deliveries themselves take place +later, along with all other deliveries for the message. This means that it is +not possible to test for successful deliveries while filtering. It also means +that any duplicate addresses that are generated are dropped, because Exim never +delivers the same message to the same address more than once. + + + + +[[SECTtesting]] +Testing a new filter file +~~~~~~~~~~~~~~~~~~~~~~~~~ +Filter files, especially the more complicated ones, should always be tested, as +it is easy to make mistakes. Exim provides a facility for preliminary testing +of a filter file before installing it. This tests the syntax of the file and +its basic operation, and can also be used with traditional '.forward' files. + +Because a filter can do tests on the content of messages, a test message is +required. Suppose you have a new filter file called 'myfilter' and a test +message called 'test-message'. Assuming that Exim is installed with the +conventional path name '/usr/sbin/sendmail' (some operating systems use +'/usr/lib/sendmail'), the following command can be used: + + /usr/sbin/sendmail -bf myfilter <test-message + +The %-bf% option tells Exim that the following item on the command line is the +name of a filter file that is to be tested. There is also a %-bF% option, +which is similar, but which is used for testing system filter files, as opposed +to user filter files, and which is therefore of use only to the system +administrator. + +The test message is supplied on the standard input. If there are no +message-dependent tests in the filter, an empty file ('/dev/null') can be +used. A supplied message must start with header lines or the ``From'' message +separator line which is found in many multi-message folder files. Note that +blank lines at the start terminate the header lines. A warning is given if no +header lines are read. + +The result of running this command, provided no errors are detected in the +filter file, is a list of the actions that Exim would try to take if presented +with the message for real. +For example, for an Exim filter, the output + + Deliver message to: gulliver@lilliput.fict.example + Save message to: /home/lemuel/mail/archive + +means that one copy of the message would be sent to +'gulliver@lilliput.fict.example', and another would be added to the file +_/home/lemuel/mail/archive_, if all went well. + +The actions themselves are not attempted while testing a filter file in this +way; there is no check, for example, that any forwarding addresses are valid. +For an Exim filter, +if you want to know why a particular action is being taken, add the %-v% +option to the command. This causes Exim to output the results of any +conditional tests and to indent its output according to the depth of nesting of +^if^ commands. Further additional output from a filter test can be generated +by the ^testprint^ command, which is described below. + +When Exim is outputting a list of the actions it would take, if any text +strings are included in the output, non-printing characters therein are +converted to escape sequences. In particular, if any text string contains a +newline character, this is shown as ``\n'' in the testing output. + +When testing a filter in this way, Exim makes up an ``envelope'' for the message. +The recipient is by default the user running the command, and so is the sender, +but the command can be run with the %-f% option to supply a different sender. +For example, + +... +/usr/sbin/sendmail -bf myfilter \ + -f islington@never.where <test-message +... + +Alternatively, if the %-f% option is not used, but the first line of the +supplied message is a ``From'' separator from a message folder file (not the same +thing as a 'From:' header line), the sender is taken from there. If %-f% is +present, the contents of any ``From'' line are ignored. + +The ``return path'' is the same as the envelope sender, unless the message +contains a 'Return-path:' header, in which case it is taken from there. You +need not worry about any of this unless you want to test out features of a +filter file that rely on the sender address or the return path. + +It is possible to change the envelope recipient by specifying further options. +The %-bfd% option changes the domain of the recipient address, while the +%-bfl% option changes the ``local part'', that is, the part before the @ sign. +An adviser could make use of these to test someone else's filter file. + +The %-bfp% and %-bfs% options specify the prefix or suffix for the local part. +These are relevant only when support for multiple personal mailboxes is +implemented; see the description in section <<SECTmbox>> below. + + +Installing a filter file +~~~~~~~~~~~~~~~~~~~~~~~~ +A filter file is normally installed under the name '.forward' in your home +directory -- it is distinguished from a conventional '.forward' file by its +first line (described below). However, the file name is configurable, and some +system administrators may choose to use some different name or location for +filter files. + + +Testing an installed filter file +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Testing a filter file before installation cannot find every potential problem; +for example, it does not actually run commands to which messages are piped. +Some ``live'' tests should therefore also be done once a filter is installed. + +If at all possible, test your filter file by sending messages from some other +account. If you send a message to yourself from the filtered account, and +delivery fails, the error message will be sent back to the same account, which +may cause another delivery failure. It won't cause an infinite sequence of such +messages, because delivery failure messages do not themselves generate further +messages. However, it does mean that the failure won't be returned to you, and +also that the postmaster will have to investigate the stuck message. + +If you have to test an Exim filter from the same account, a sensible precaution +is to include the line + + if error_message then finish endif + +as the first filter command, at least while testing. This causes filtering to +be abandoned for a delivery failure message, and since no destinations are +generated, the message goes on to be delivered to the original address. Unless +there is a good reason for not doing so, it is recommended that the above test +be left in all Exim filter files. +(This does not apply to Sieve files.) + + + +Details of filtering commands +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The filtering commands for Sieve and Exim filters are completely different in +syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next +chapter we describe how it is integrated into Exim. The subsequent chapter +covers Exim filtering commands in detail. + + + +[[CHAPsievefilter]] +Sieve filter files +------------------ +The code for Sieve filtering in Exim was contributed by Michael Haardt, and +most of the content of this chapter is taken from the notes he provided. Since +Sieve is a extensible language, it is important to understand ``Sieve'' in this +context as ``the specific implementation of Sieve for Exim''. + +This chapter does not contain a description of Sieve, since that can be found +in RFC 3028, which should be read in conjunction with these notes. + +The Exim Sieve implementation offers the core as defined by RFC 3028, +comparison tests, the *copy*, *envelope*, *fileinto*, and *vacation* +extensions, but not the *reject* extension. Exim does not support message +delivery notifications (MDNs), so adding it just to the Sieve filter (as +required for *reject*) makes little sense. + +In order for Sieve to work properly in Exim, the system administrator needs to +make some adjustments to the Exim configuration. These are described in the +chapter on the ^redirect^ router in the full Exim specification. + + +Recognition of Sieve filters +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A filter file is interpreted as a Sieve filter if its first line is + + # Sieve filter + +This is what distinguishes it from a conventional '.forward' file or an Exim +filter file. + + + +Saving to specified folders +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If the system administrator has set things up as suggested in the Exim +specification, and you use *keep* or *fileinto* to save a mail into a +folder, absolute files are stored where specified, relative files are stored +relative to $home$, and *inbox* goes to the standard mailbox location. + + + +Strings containing header names +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +RFC 3028 does not specify what happens if a string denoting a header field does +not contain a valid header name, for example, it contains a colon. This +implementation generates an error instead of ignoring the header field in order +to ease script debugging, which fits in the common picture of Sieve. + + + +Exists test with empty list of headers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The *exists* test succeeds only if all specified headers exist. RFC 3028 +does not explicitly specify what happens on an empty list of headers. This +implementation evaluates that condition as true, interpreting the RFC in a +strict sense. + + + +Header test with invalid MIME encoding in header +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Some MUAs process invalid base64 encoded data, generating junk. +Others ignore junk after seeing an equal sign in base64 encoded data. +RFC 2047 does not specify how to react in this case, other than stating +that a client must not forbid to process a message for that reason. +RFC 2045 specifies that invalid data should be ignored (apparently +looking at end of line characters). It also specifies that invalid data +may lead to rejecting messages containing them (and there it appears to +talk about true encoding violations), which is a clear contradiction to +ignoring them. + +RFC 3028 does not specify how to process incorrect MIME words. +This implementation treats them literally, as it does if the word is +correct but its character set cannot be converted to UTF-8. + + + +Address test for multiple addresses per header +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A header may contain multiple addresses. RFC 3028 does not explicitly +specify how to deal with them, but since the address test checks if +anything matches anything else, matching one address suffices to +satisfy the condition. That makes it impossible to test if a header +contains a certain set of addresses and no more, but it is more logical +than letting the test fail if the header contains an additional address +besides the one the test checks for. + + + +Semantics of keep +~~~~~~~~~~~~~~~~~ +The *keep* command is equivalent to + + fileinto "inbox"; + +It saves the message and resets the implicit keep flag. It does not set the +implicit keep flag; there is no command to set it once it has been reset. + + + +Semantics of fileinto +~~~~~~~~~~~~~~~~~~~~~ +RFC 3028 does not specify whether %fileinto% should try to create a mail folder +if it does not exist. This implementation allows the sysadmin to configure that +aspect using the ^appendfile^ transport options %create_directory%, +%create_file%, and %file_must_exist%. See the ^appendfile^ transport in +the Exim specification for details. + + + +Semantics of redirect +~~~~~~~~~~~~~~~~~~~~~ +Sieve scripts are supposed to be interoperable between servers, so this +implementation does not allow mail to be redirected to unqualified addresses, +because the domain would depend on the system being used. On systems with +virtual mail domains, the default domain is probably not what the user expects +it to be. + + + +String arguments +~~~~~~~~~~~~~~~~ +There has been confusion if the string arguments to *require* are to be +matched case-sensitively or not. This implementation matches them with +the match type ^:is^ (default, see section 2.7.1) and the comparator +^i;ascii-casemap^ (default, see section 2.7.3). The RFC defines the +command defaults clearly, so any different implementations violate RFC +3028. The same is valid for comparator names, also specified as strings. + + + +Number units +~~~~~~~~~~~~ +There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte. +The mistake is obvious, because RFC 3028 specifies G to denote 2^30 +(which is gibi, not tebi), and that is what this implementation uses as +scaling factor for the suffix G. + + + +RFC compliance +~~~~~~~~~~~~~~ +Exim requires the first line of a Sieve filter to be + + # Sieve filter + +Of course the RFC does not specify that line. Do not expect examples to work +without adding it, though. + +RFC 3028 requires the use of CRLF to terminate a line. +The rationale was that CRLF is universally used in network protocols +to mark the end of the line. This implementation does not embed Sieve +in a network protocol, but uses Sieve scripts as part of the Exim MTA. +Since all parts of Exim use LF as newline character, this implementation +does, too, by default, though the system administrator may choose (at Exim +compile time) to use CRLF instead. + +Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so +this implementation repeats this violation to stay consistent with Exim. +This is in preparation to UTF-8 data. + +Sieve scripts cannot contain NUL characters in strings, but mail +headers could contain MIME encoded NUL characters, which could never +be matched by Sieve scripts using exact comparisons. For that reason, +this implementation extends the Sieve quoted string syntax with \0 +to describe a NUL character, violating \0 being the same as 0 in +RFC 3028. Even without using \0, the following tests are all true in +this implementation. Implementations that use C-style strings will only +evaluate the first test as true. + + Subject: =?iso-8859-1?q?abc=00def + + header :contains "Subject" ["abc"] + header :contains "Subject" ["def"] + header :matches "Subject" ["abc?def"] + +Note that by considering Sieve to be a MUA, RFC 2047 can be interpreted +in a way that NUL characters truncating strings is allowed for Sieve +implementations, although not recommended. It is further allowed to use +encoded NUL characters in headers, but that's not recommended either. +The above example shows why. + +RFC 3028 states that if an implementation fails to convert a character +set to UTF-8, two strings cannot be equal if one contains octets greater +than 127. Assuming that all unknown character sets are one-byte character +sets with the lower 128 octets being US-ASCII is not sound, so this +implementation violates RFC 3028 and treats such MIME words literally. +That way at least something could be matched. + +The folder specified by *fileinto* must not contain the character +sequence ``..'' to avoid security problems. RFC 3028 does not specify the +syntax of folders apart from *keep* being equivalent to + + fileinto "INBOX"; + +This implementation uses _inbox_ instead. + +Sieve script errors currently cause messages to be silently filed into +_inbox_. RFC 3028 requires that the user is notified of that condition. +This may be implemented in future by adding a header line to mails that +are filed into _inbox_ due to an error in the filter. + + + +[[CHAPeximfilter]] +Exim filter files +----------------- +This chapter contains a full description of the contents of Exim filter files. + + +Format of Exim filter files +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Apart from leading white space, the first text in an Exim filter file must be + + # Exim filter + +This is what distinguishes it from a conventional '.forward' file or a Sieve +filter file. If the file does not have this initial line (or the equivalent for +a Sieve filter), it is treated as a conventional '.forward' file, both when +delivering mail and when using the %-bf% testing mechanism. The white space in +the line is optional, and any capitalization may be used. Further text on the +same line is treated as a comment. For example, you could have + + # Exim filter <<== do not edit or remove this line! + +The remainder of the file is a sequence of filtering commands, which consist of +keywords and data values. For example, in the command + + deliver gulliver@lilliput.fict.example + +the keyword is `deliver` and the data value is +`gulliver@lilliput.fict.example`. White space or line breaks separate the +components of a command, except in the case of conditions for the ^if^ command, +where round brackets (parentheses) also act as separators. Complete commands +are separated from each other by white space or line breaks; there are no +special terminators. Thus, several commands may appear on one line, or one +command may be spread over a number of lines. + +If the character # follows a separator anywhere in a command, everything from +# up to the next newline is ignored. This provides a way of including comments +in a filter file. + + +Data values in filter commands +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +There are two ways in which a data value can be input: + +- If the text contains no white space then it can be typed verbatim. However, if +it is part of a condition, it must also be free of round brackets +(parentheses), as these are used for grouping in conditions. + +- Otherwise, it must be enclosed in double quotation marks. In this case, the +character \ (backslash) is treated as an ``escape character'' within the string, +causing the following character or characters to be treated specially: + +&&&& +`\n` is replaced by a newline +`\r` is replaced by a carriage return +`\t` is replaced by a tab +&&&& + +Backslash followed by up to three octal digits is replaced by the character +specified by those digits, and \x followed by up to two hexadecimal digits is +treated similarly. Backslash followed by any other character is replaced +by the second character, so that in particular, \\" becomes " and \\ becomes +\. A data item enclosed in double quotes can be continued onto the next line +by ending the first line with a backslash. Any leading white space at the start +of the continuation line is ignored. + +In addition to the escape character processing that occurs when strings are +enclosed in quotes, most data values are also subject to 'string expansion' +(as described in the next section), in which case the characters `\$` and `\` +are also significant. This means that if a single backslash is actually +required in such a string, and the string is also quoted, \\\\ has to be +entered. + +The maximum permitted length of a data string, before expansion, is 1024 +characters. + + +++++++++++++ +<?hard-pagebreak?> +++++++++++++ + +[[SECTfilterstringexpansion]] +String expansion +~~~~~~~~~~~~~~~~ +Most data values are expanded before use. Expansion consists of replacing +substrings beginning with `\$` with other text. The full expansion facilities +available in Exim are extensive. If you want to know everything that Exim can +do with strings, you should consult the chapter on string expansion in the Exim +documentation. + +In filter files, by far the most common use of string expansion is the +substitution of the contents of a variable. For example, the substring + + $reply_address + +is replaced by the address to which replies to the message should be sent. If +such a variable name is followed by a letter or digit or underscore, it must be +enclosed in curly brackets (braces), for example, + + ${reply_address} + +If a `\$` character is actually required in an expanded string, it must be +escaped with a backslash, and because backslash is also an escape character in +quoted input strings, it must be doubled in that case. The following two +examples illustrate two different ways of testing for a `\$` character in a +message: + + if $message_body contains \$ then ... + if $message_body contains "\\$" then ... + +You can prevent part of a string from being expanded by enclosing it between +two occurrences of `\N`. For example, + + if $message_body contains \N$$$$\N then ... + +tests for a run of four dollar characters. + + +Some useful general variables +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A complete list of the available variables is given in the Exim documentation. +This shortened list contains the ones that are most likely to be useful in +personal filter files: + +$body_linecount$: The number of lines in the body of the message. + +$body_zerocount$: The number of binary zero characters in the body of the +message. + + +$home$: In conventional configurations, this variable normally contains the +user's home directory. The system administrator can, however, change this. + +$local_part$: The part of the email address that precedes the @ sign -- +normally the user's login name. If support for multiple personal mailboxes is +enabled (see section <<SECTmbox>> below) and a prefix or suffix for the local +part was recognized, it is removed from the string in this variable. + +$local_part_prefix$: If support for multiple personal mailboxes is enabled +(see section <<SECTmbox>> below), and a local part prefix was recognized, +this variable contains the prefix. Otherwise it contains an empty string. + +$local_part_suffix$: If support for multiple personal mailboxes is enabled +(see section <<SECTmbox>> below), and a local part suffix was recognized, +this variable contains the suffix. Otherwise it contains an empty string. + +$message_body$: The initial portion of the body of the message. By default, +up to 500 characters are read into this variable, but the system administrator +can configure this to some other value. Newlines in the body are converted into +single spaces. + +$message_body_end$: The final portion of the body of the message, formatted +and limited in the same way as $message_body$. + +$message_body_size$: The size of the body of the message, in bytes. + +$message_headers$: The header lines of the message, concatenated into a +single string, with newline characters between them. + +$message_id$: The message's local identification string, which is unique for +each message handled by a single host. + +$message_size$: The size of the entire message, in bytes. + +$original_local_part$: When an address that arrived with the message is +being processed, this contains the same value as the variable $local_part$. +However, if an address generated by an alias, forward, or filter file is being +processed, this variable contains the local part of the original address. + +$reply_address$: The contents of the 'Reply-to:' header, if the message +has one; otherwise the contents of the 'From:' header. It is the address to +which normal replies to the message should be sent. + +$return_path$: The return path -- that is, the sender field that will be +transmitted as part of the message's envelope if the message is sent to another +host. This is the address to which delivery errors are sent. In many cases, +this variable has the same value as $sender_address$, but if, for example, +an incoming message to a mailing list has been expanded, $return_path$ may +have been changed to contain the address of the list maintainer. + +$sender_address$: The sender address that was received in the envelope of +the message. This is not necessarily the same as the contents of the 'From:' +or 'Sender:' header lines. For delivery error messages (``bounce messages'') +there is no sender address, and this variable is empty. + +$tod_full$: A full version of the time and date, for example: Wed, 18 Oct +1995 09:51:40 +0100. The timezone is always given as a numerical offset from +GMT. + +$tod_log$: The time and date in the format used for writing Exim's log files, +without the timezone, for example: 1995-10-12 15:32:29. + +$tod_zone$: The local timezone offset, for example: +0100. + + + +[[SECTheadervariables]] +Header variables +~~~~~~~~~~~~~~~~ +There is a special set of expansion variables containing the header lines of +the message being processed. These variables have names beginning with +$header_$ followed by the name of the header line, terminated by a colon. +For example, + + $header_from: + $header_subject: + +The whole item, including the terminating colon, is replaced by the contents of +the message header line. If there is more than one header line with the same +name, their contents are concatenated. For header lines whose data consists of +a list of addresses (for example, 'From:' and 'To:'), a comma and newline is +inserted between each set of data. For all other header lines, just a newline +is used. + +Leading and trailing white space is removed from header line data, and if there +are any MIME ``words'' that are encoded as defined by RFC 2047 (because they +contain non-ASCII characters), they are decoded and translated, if possible, to +a local character set. Translation is attempted only on operating systems that +have the ^^iconv()^^ function. This makes the header line look the same as it +would when displayed by an MUA. The default character set is ISO-8859-1, but +this can be changed by means of the ^headers^ command (see below). + +If you want to see the actual characters that make up a header line, you can +specify $rheader_$ instead of $header_$. This inserts the ``raw'' +header line, unmodified. + +There is also an intermediate form, requested by $bheader_$, which removes +leading and trailing space and decodes MIME ``words'', but does not do any +character translation. If an attempt to decode what looks superficially like a +MIME ``word'' fails, the raw string is returned. If decoding produces a binary +zero character, it is replaced by a question mark. + +The capitalization of the name following $header_$ is not significant. +Because any printing character except colon may appear in the name of a +message's header (this is a requirement of RFC 2822, the document that +describes the format of a mail message) curly brackets must 'not' be used in +this case, as they will be taken as part of the header name. Two shortcuts are +allowed in naming header variables: + +- The initiating $header_$, $rheader_$, or $bheader_$ can be +abbreviated to $h_$, $rh_$, or $bh_$, respectively. + +- The terminating colon can be omitted if the next character is white space. The +white space character is retained in the expanded string. However, this is not +recommended, because it makes it easy to forget the colon when it really is +needed. + +If the message does not contain a header of the given name, an empty string is +substituted. Thus it is important to spell the names of headers correctly. Do +not use $header_Reply_to$ when you really mean $header_Reply-to$. + + +User variables +~~~~~~~~~~~~~~ +There are ten user variables with names $n0$ -- $n9$ that can be +incremented by the ^add^ command (see section <<SECTadd>>). These can be used +for ``scoring'' messages in various ways. If Exim is configured to run a +``system filter'' on every message, the values left in these variables are +copied into the variables $sn0$ -- $sn9$ at the end of the system filter, thus +making them available to users' filter files. How these values are used is +entirely up to the individual installation. + + +Current directory +~~~~~~~~~~~~~~~~~ +The contents of your filter file should not make any assumptions about the +current directory. It is best to use absolute paths for file names; you +can normally make use of the $home$ variable to refer to your home directory. +The ^save^ command automatically inserts $home$ at the start of non-absolute +paths. + + + + +[[SECTsigdel]] +Significant deliveries +~~~~~~~~~~~~~~~~~~~~~~ +When in the course of delivery a message is processed by a filter file, what +happens next, that is, after the filter file has been processed, depends on +whether or not the filter sets up any 'significant deliveries'. If at least +one significant delivery is set up, the filter is considered to have handled +the entire delivery arrangements for the current address, and no further +processing of the address takes place. If, however, no significant deliveries +are set up, Exim continues processing the current address as if there were no +filter file, and typically sets up a delivery of a copy of the message into a +local mailbox. In particular, this happens in the special case of a filter file +containing only comments. + +The delivery commands ^deliver^, ^save^, and ^pipe^ are by default +significant. However, if such a command is preceded by the word ^unseen^, its +delivery is not considered to be significant. In contrast, other commands such +as ^mail^ and ^vacation^ do not set up significant deliveries unless +preceded by the word ^seen^. + +The following example commands set up significant deliveries: + + deliver jack@beanstalk.example + pipe $home/bin/mymailscript + seen mail subject "message discarded" + seen finish + +The following example commands do not set up significant deliveries: + + unseen deliver jack@beanstalk.example + unseen pipe $home/bin/mymailscript + mail subject "message discarded" + finish + + + + +Filter commands +~~~~~~~~~~~~~~~ +The filter commands that are described in subsequent sections are listed +below, with the section in which they are described in brackets: + +[frame="none"] +`-------------`----------------------------------------------- +^add^ ~~increment a user variable (section <<SECTadd>>) +^deliver^ ~~deliver to an email address (section <<SECTdeliver>>) +^fail^ ~~force delivery failure (sysadmin use) (section <<SECTfail>>) +^finish^ ~~end processing (section <<SECTfinish>>) +^freeze^ ~~freeze message (sysadmin use) (section <<SECTfreeze>>) +^headers^ ~~set the header character set (section <<SECTheaders>>) +^if^ ~~test condition(s) (section <<SECTif>>) +^logfile^ ~~define log file (section <<SECTlog>>) +^logwrite^ ~~write to log file (section <<SECTlog>>) +^mail^ ~~send a reply message (section <<SECTmail>>) +^pipe^ ~~pipe to a command (section <<SECTpipe>>) +^save^ ~~save to a file (section <<SECTsave>>) +^testprint^ ~~print while testing (section <<SECTtestprint>>) +^vacation^ ~~tailored form of ^mail^ (section <<SECTmail>>) +-------------------------------------------------------------- + +The ^headers^ command has additional parameters that can be used only in a +system filter. The ^fail^ and ^freeze^ commands are available only when +Exim's filtering facilities are being used as a system filter, and are +therefore usable only by the system administrator and not by ordinary users. +They are mentioned only briefly in this document; for more information, see the +main Exim specification. + + + +[[SECTadd]] +The add command +~~~~~~~~~~~~~~~ +&&& +` add `<'number'>` to `<'user variable'> +`e.g. add 2 to n3` +&&& + +There are 10 user variables of this type, with names $n0$ -- $n9$. Their +values can be obtained by the normal expansion syntax (for example $n3$) in +other commands. At the start of filtering, these variables all contain zero. +Both arguments of the ^add^ command are expanded before use, making it +possible to add variables to each other. Subtraction can be obtained by adding +negative numbers. + + + +[[SECTdeliver]] +The deliver command +~~~~~~~~~~~~~~~~~~~ + +&&& +` deliver` <'mail address'> +`e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"` +&&& + +This command provides a forwarding operation. The delivery that it sets up is +significant unless the command is preceded by ^unseen^ (see section +<<SECTsigdel>>). The message is sent on to the given address, exactly as +happens if the address had appeared in a traditional '.forward' file. If you +want to deliver the message to a number of different addresses, you can use +more than one ^deliver^ command (each one may have only one address). However, +duplicate addresses are discarded. + +To deliver a copy of the message to your normal mailbox, your login name can be +given as the address. Once an address has been processed by the filtering +mechanism, an identical generated address will not be so processed again, so +doing this does not cause a loop. + +However, if you have a mail alias, you should 'not' refer to it here. For +example, if the mail address 'L.Gulliver' is aliased to 'lg303' then all +references in Gulliver's '.forward' file should be to 'lg303'. A reference +to the alias will not work for messages that are addressed to that alias, +since, like '.forward' file processing, aliasing is performed only once on an +address, in order to avoid looping. + +Following the new address, an optional second address, preceded by +^errors_to^ may appear. This changes the address to which delivery errors on +the forwarded message will be sent. Instead of going to the message's original +sender, they go to this new address. For ordinary users, the only value that is +permitted for this address is the user whose filter file is being processed. +For example, the user 'lg303' whose mailbox is in the domain +'lilliput.example' could have a filter file that contains + + deliver jon@elsewhere.example errors_to lg303@lilliput.example + +Clearly, using this feature makes sense only in situations where not all +messages are being forwarded. In particular, bounce messages must not be +forwarded in this way, as this is likely to create a mail loop if something +goes wrong. + + + +[[SECTsave]] +The save command +~~~~~~~~~~~~~~~~ +&&& +` save `<'file name'> +`e.g. save $home/mail/bookfolder` +&&& + +This command specifies that a copy of the message is to be appended to the +given file (that is, the file is to be used as a mail folder). The delivery +that ^save^ sets up is significant unless the command is preceded by +^unseen^ (see section <<SECTsigdel>>). + +More than one ^save^ command may be obeyed; each one causes a copy of the +message to be written to its argument file, provided they are different +(duplicate ^save^ commands are ignored). + +If the file name does not start with a / character, the contents of the +$home$ variable are prepended, unless it is empty. In conventional +configurations, this variable is normally set in a user filter to the user's +home directory, but the system administrator may set it to some other path. In +some configurations, $home$ may be unset, in which case a non-absolute path +name may be generated. Such configurations convert this to an absolute path +when the delivery takes place. In a system filter, $home$ is never set. + +The user must of course have permission to write to the file, and the writing +of the file takes place in a process that is running as the user, under the +user's primary group. Any secondary groups to which the user may belong are not +normally taken into account, though the system administrator can configure Exim +to set them up. In addition, the ability to use this command at all is +controlled by the system administrator -- it may be forbidden on some systems. + +An optional mode value may be given after the file name. The value for the mode +is interpreted as an octal number, even if it does not begin with a zero. For +example: + + save /some/folder 640 + +This makes it possible for users to override the system-wide mode setting for +file deliveries, which is normally 600. If an existing file does not have the +correct mode, it is changed. + +An alternative form of delivery may be enabled on your system, in which each +message is delivered into a new file in a given directory. If this is the case, +this functionality can be requested by giving the directory name terminated by +a slash after the ^save^ command, for example + + save separated/messages/ + +There are several different formats for such deliveries; check with your system +administrator or local documentation to find out which (if any) are available +on your system. If this functionality is not enabled, the use of a path name +ending in a slash causes an error. + + + +[[SECTpipe]] +The pipe command +~~~~~~~~~~~~~~~~ +&&& +` pipe `<'command'> +`e.g. pipe "$home/bin/countmail $sender_address"` +&&& + +This command specifies that the message is to be delivered to the specified +command using a pipe. The delivery that it sets up is significant unless the +command is preceded by ^unseen^ (see section <<SECTsigdel>>). Remember, +however, that no deliveries are done while the filter is being processed. All +deliveries happen later on. Therefore, the result of running the pipe is not +available to the filter. + +When the deliveries are done, a separate process is run, and a copy of the +message is passed on its standard input. The process runs as the user, under +the user's primary group. Any secondary groups to which the user may belong are +not normally taken into account, though the system administrator can configure +Exim to set them up. More than one ^pipe^ command may appear; each one causes +a copy of the message to be written to its argument pipe, provided they are +different (duplicate ^pipe^ commands are ignored). + +When the time comes to transport the message, +the command supplied to ^pipe^ is split up by Exim into a command name and a +number of arguments. These are delimited by white space except for arguments +enclosed in double quotes, in which case backslash is interpreted as an escape, +or in single quotes, in which case no escaping is recognized. Note that as the +whole command is normally supplied in double quotes, a second level of quoting +is required for internal double quotes. For example: + + pipe "$home/myscript \"size is $message_size\"" + +String expansion is performed on the separate components after the line has +been split up, and the command is then run directly by Exim; it is not run +under a shell. Therefore, substitution cannot change the number of arguments, +nor can quotes, backslashes or other shell metacharacters in variables cause +confusion. + +Documentation for some programs that are normally run via this kind of pipe +often suggest that the command should start with + + IFS=" " + +This is a shell command, and should 'not' be present in Exim filter files, +since it does not normally run the command under a shell. + +However, there is an option that the administrator can set to cause a shell to +be used. In this case, the entire command is expanded as a single string and +passed to the shell for interpretation. It is recommended that this be avoided +if at all possible, since it can lead to problems when inserted variables +contain shell metacharacters. + +The default PATH set up for the command is determined by the system +administrator, usually containing at least _/usr/bin_ so that common commands +are available without having to specify an absolute file name. However, it is +possible for the system administrator to restrict the pipe facility so that the +command name must not contain any / characters, and must be found in one of the +directories in the configured PATH. It is also possible for the system +administrator to lock out the use of the ^pipe^ command altogether. + +When the command is run, a number of environment variables are set up. The +complete list for pipe deliveries may be found in the Exim reference manual. +Those that may be useful for pipe deliveries from user filter files are: + +&&& +`DOMAIN ` the domain of the address +`HOME ` your home directory +`LOCAL_PART ` see below +`LOCAL_PART_PREFIX ` see below +`LOCAL_PART_SUFFIX ` see below +`LOGNAME ` your login name +`MESSAGE_ID ` the unique id of the message +`PATH ` the command search path +`RECIPIENT ` the complete recipient address +`SENDER ` the sender of the message +`SHELL ` `/bin/sh` +`USER ` see below +&&& + +LOCAL_PART, LOGNAME, and USER are all set to the same value, +namely, your login id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may +be set if Exim is configured to recognize prefixes or suffixes in the local +parts of addresses. For example, a message addressed to +'pat-suf2@domain.example' may cause the filter for user 'pat' to be run. If +this sets up a pipe delivery, LOCAL_PART_SUFFIX is `-suf2` when the +pipe command runs. The system administrator has to configure Exim specially for +this feature to be available. + +If you run a command that is a shell script, be very careful in your use of +data from the incoming message in the commands in your script. RFC 2822 is very +generous in the characters that are permitted to appear in mail addresses, and +in particular, an address may begin with a vertical bar or a slash. For this +reason you should always use quotes round any arguments that involve data from +the message, like this: + + /some/command '$SENDER' + +so that inserted shell meta-characters do not cause unwanted effects. + +Remember that, as was explained earlier, the pipe command is not run at the +time the filter file is interpreted. The filter just defines what deliveries +are required for one particular addressee of a message. The deliveries +themselves happen later, once Exim has decided everything that needs to be done +for the message. + +A consequence of this is that you cannot inspect the return code from the pipe +command from within the filter. Nevertheless, the code returned by the command +is important, because Exim uses it to decide whether the delivery has succeeded +or failed. + +The command should return a zero completion code if all has gone well. Most +non-zero codes are treated by Exim as indicating a failure of the pipe. This is +treated as a delivery failure, causing the message to be returned to its +sender. However, there are some completion codes that are treated as temporary +errors. The message remains on Exim's spool disk, and the delivery is tried +again later, though it will ultimately time out if the delivery failures go on +too long. The completion codes to which this applies can be specified by the +system administrator; the default values are 73 and 75. + +The pipe command should not normally write anything to its standard output or +standard error file descriptors. If it does, whatever is written is normally +returned to the sender of the message as a delivery error, though this action +can be varied by the system administrator. + + + +[[SECTmail]] +Mail commands +~~~~~~~~~~~~~ +There are two commands that cause the creation of a new mail message, neither +of which count as a significant delivery unless the command is preceded by the +word ^seen^ (see section <<SECTsigdel>>). This is a powerful facility, but it +should be used with care, because of the danger of creating infinite sequences +of messages. The system administrator can forbid the use of these commands +altogether. + +To help prevent runaway message sequences, these commands have no effect when +the incoming message is a bounce (delivery error) message, and messages sent by +this means are treated as if they were reporting delivery errors. Thus, they +should never themselves cause a bounce message to be returned. The basic +mail-sending command is + +&&& +`mail [to `<'address-list'>`]` +` [cc `<'address-list'>`]` +` [bcc `<'address-list'>`]` +` [from `<'address'>`]` +` [reply_to `<'address'>`]` +` [subject `<'text'>`]` +` [extra_headers `<'text'>`]` +` [text `<'text'>`]` +` [[expand] file `<'filename'>`]` +` [return message]` +` [log `<'log file name'>`]` +` [once `<'note file name'>`]` +` [once_repeat `<'time interval'>`]` + +`e.g. mail text "Your message about $h_subject: has been received"` +&&& + +Each <'address-list'> can contain a number of addresses, separated by commas, +in the format of a 'To:' or 'Cc:' header line. In fact, the text you supply +here is copied exactly into the appropriate header line. It may contain +additional information as well as email addresses. For example: + +... +mail to "Julius Caesar <jc@rome.example>, \ + <ma@rome.example> (Mark A.)" +... + +Similarly, the texts supplied for ^from^ and ^reply_to^ are copied into +their respective header lines. + +As a convenience for use in one common case, there is also a command called +^vacation^. It behaves in the same way as ^mail^, except that the defaults for +the %subject%, %file%, %log%, %once%, and %once_repeat% options are + + subject "On vacation" + expand file .vacation.msg + log .vacation.log + once .vacation + once_repeat 7d + +respectively. These are the same file names and repeat period used by the +traditional Unix ^vacation^ command. The defaults can be overridden by +explicit settings, but if a file name is given its contents are expanded only +if explicitly requested. + +*Warning*: The ^vacation^ command should always be used conditionally, +subject to at least the ^personal^ condition (see section <<SECTpersonal>> +below) so as not to send automatic replies to non-personal messages from +mailing lists or elsewhere. Sending an automatic response to a mailing list or +a mailing list manager is an Internet Sin. + +For both commands, the key/value argument pairs can appear in any order. At +least one of ^text^ or ^file^ must appear (except with ^vacation^, where +there is a default for ^file^); if both are present, the text string appears +first in the message. If ^expand^ precedes ^file^, each line of the file is +subject to string expansion before it is included in the message. + +Several lines of text can be supplied to ^text^ by including the escape +sequence ``\n'' in the string wherever a newline is required. If the command is +output during filter file testing, newlines in the text are shown as ``\n''. + +Note that the keyword for creating a 'Reply-To:' header is ^reply_to^, +because Exim keywords may contain underscores, but not hyphens. If the ^from^ +keyword is present and the given address does not match the user who owns the +forward file, Exim normally adds a 'Sender:' header to the message, +though it can be configured not to do this. + +The %extra_headers% keyword allows you to add custom header lines to the +message. The text supplied must be one or more syntactically valid RFC 2882 +header lines. You can use ``\n'' within quoted text to specify newlines between +headers, and also to define continued header lines. For example: + + extra_headers "h1: first\nh2: second\n continued\nh3: third" + +No newline should appear at the end of the final header line. + +If no ^to^ argument appears, the message is sent to the address in the +$reply_address$ variable (see section <<SECTfilterstringexpansion>> above). +An 'In-Reply-To:' header is automatically included in the created message, +giving a reference to the message identification of the incoming message. + +If ^return message^ is specified, the incoming message that caused the filter +file to be run is added to the end of the message, subject to a maximum size +limitation. + +If a log file is specified, a line is added to it for each message sent. + +If a ^once^ file is specified, it is used to hold a database for remembering +who has received a message, and no more than one message is ever sent to any +particular address, unless ^once_repeat^ is set. This specifies a time +interval after which another copy of the message is sent. The interval is +specified as a sequence of numbers, each followed by the initial letter of one +of ``seconds'', ``minutes'', ``hours'', ``days'', or ``weeks''. For example, + + once_repeat 5d4h + +causes a new message to be sent if 5 days and 4 hours have elapsed since the +last one was sent. There must be no white space in a time interval. + +Commonly, the file name specified for ^once^ is used as the base name for +direct-access (DBM) file operations. There are a number of different DBM +libraries in existence. Some operating systems provide one as a default, but +even in this case a different one may have been used when building Exim. With +some DBM libraries, specifying ^once^ results in two files being created, +with the suffixes _.dir_ and _.pag_ being added to the given name. With +some others a single file with the suffix _.db_ is used, or the name is used +unchanged. + +Using a DBM file for implementing the ^once^ feature means that the file +grows as large as necessary. This is not usually a problem, but some system +administrators want to put a limit on it. The facility can be configured not to +use a DBM file, but instead, to use a regular file with a maximum size. The +data in such a file is searched sequentially, and if the file fills up, the +oldest entry is deleted to make way for a new one. This means that some +correspondents may receive a second copy of the message after an unpredictable +interval. Consult your local information to see if your system is configured +this way. + +More than one ^mail^ or ^vacation^ command may be obeyed in a single filter +run; they are all honoured, even when they are to the same recipient. + + + +[[SECTlog]] +Logging commands +~~~~~~~~~~~~~~~~ +A log can be kept of actions taken by a filter file. This facility is normally +available in conventional configurations, but there are some situations where +it might not be. Also, the system administrator may choose to disable it. Check +your local information if in doubt. + +Logging takes place while the filter file is being interpreted. It does not +queue up for later like the delivery commands. The reason for this is so that a +log file need be opened only once for several write operations. There are two +commands, neither of which constitutes a significant delivery. The first +defines a file to which logging output is subsequently written: + +&&& +` logfile `<'file name'> +`e.g. logfile $home/filter.log` +&&& + +The file name must be fully qualified. You can use $home$, as in this +example, to refer to your home directory. The file name may optionally be +followed by a mode for the file, which is used if the file has to be created. +For example, + + logfile $home/filter.log 0644 + +The number is interpreted as octal, even if it does not begin with a zero. +The default for the mode is 600. It is suggested that the ^logfile^ command +normally appear as the first command in a filter file. Once ^logfile^ has +been obeyed, the ^logwrite^ command can be used to write to the log file: + +&&& +` logwrite "`<'some text string'>`"` +`e.g. logwrite "$tod_log $message_id processed"` +&&& + +It is possible to have more than one ^logfile^ command, to specify writing to +different log files in different circumstances. Writing takes place at the end +of the file, and a newline character is added to the end of each string if +there isn't one already there. Newlines can be put in the middle of the string +by using the ``\n'' escape sequence. Lines from simultaneous deliveries may get +interleaved in the file, as there is no interlocking, so you should plan your +logging with this in mind. However, data should not get lost. + + + +[[SECTfinish]] +The finish command +~~~~~~~~~~~~~~~~~~ +The command ^finish^, which has no arguments, causes Exim to stop +interpreting the filter file. This is not a significant action unless preceded +by ^seen^. A filter file containing only ^seen finish^ is a black hole. + + +[[SECTtestprint]] +The testprint command +~~~~~~~~~~~~~~~~~~~~~ +It is sometimes helpful to be able to print out the values of variables when +testing filter files. The command + +&&& +` testprint `<'text'> +`e.g. testprint "home=$home reply_address=$reply_address"` +&&& + +does nothing when mail is being delivered. However, when the filtering code is +being tested by means of the %-bf% option (see section <<SECTtesting>> above), +the value of the string is written to the standard output. + + +++++++++++++ +<?hard-pagebreak?> +++++++++++++ +[[SECTfail]] +The fail command +~~~~~~~~~~~~~~~~ +When Exim's filtering facilities are being used as a system filter, the +^fail^ command is available, to force delivery failure. Because this command +is normally usable only by the system administrator, and not enabled for use by +ordinary users, it is described in more detail in the main Exim specification +rather than in this document. + + +[[SECTfreeze]] +The freeze command +~~~~~~~~~~~~~~~~~~ +When Exim's filtering facilities are being used as a system filter, the +^freeze^ command is available, to freeze a message on the queue. Because this +command is normally usable only by the system administrator, and not enabled +for use by ordinary users, it is described in more detail in the main Exim +specification rather than in this document. + + + +[[SECTheaders]] +The headers command +~~~~~~~~~~~~~~~~~~~ +The ^headers^ command can be used to change the target character set that is +used when translating the contents of encoded header lines for insertion by the +$header_$ mechanism (see section <<SECTheadervariables>> above). The default +can be set in the Exim configuration; if not specified, ISO-8859-1 is used. The +only currently supported format for the ^headers^ command in user filters is as +in this example: + + headers charset "UTF-8" + +That is, ^headers^ is followed by the word ^charset^ and then the name of a +character set. This particular example would be useful if you wanted to compare +the contents of a header to a UTF-8 string. + +In system filter files, the ^headers^ command can be used to add or remove +header lines from the message. These features are described in the main Exim +specification. + + + +[[SECTif]] +Obeying commands conditionally +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Most of the power of filtering comes from the ability to test conditions and +obey different commands depending on the outcome. The ^if^ command is used to +specify conditional execution, and its general form is + +&&& +`if `<'condition'> +`then `<'commands'> +`elif `<'condition'> +`then `<'commands'> +`else `<'commands'> +`endif` +&&& + +There may be any number of ^elif^ and ^then^ sections (including none) and +the ^else^ section is also optional. Any number of commands, including nested +^if^ commands, may appear in any of the <'commands'> sections. + +Conditions can be combined by using the words ^and^ and ^or^, and round +brackets (parentheses) can be used to specify how several conditions are to +combine. Without brackets, ^and^ is more binding than ^or^. +For example, + + if + $h_subject: contains "Make money" or + $h_precedence: is "junk" or + ($h_sender: matches ^\\d{8}@ and not personal) or + $message_body contains "this is not spam" + then + seen finish + endif + +A condition can be preceded by ^not^ to negate it, and there are also some +negative forms of condition that are more English-like. + + + +++++++++++++ +<?hard-pagebreak?> +++++++++++++ +String testing conditions +~~~~~~~~~~~~~~~~~~~~~~~~~ +There are a number of conditions that operate on text strings, using the words +``begins'', ``ends'', ``is'', ``contains'' and ``matches''. If you want to apply the same +test to more than one header line, you can easily concatenate them into a +single string for testing, as in this example: + + if "$h_to:, $h_cc:" contains me@domain.example then ... + +If a string-testing condition name is written in lower case, the testing +of letters is done without regard to case; if it is written in upper case +(for example, ``CONTAINS''), the case of letters is taken into account. + +&&& +` `<'text1'>` begins `<'text2'> +` `<'text1'>` does not begin `<'text2'> +`e.g. $header_from: begins "Friend@"` +&&& + +A ``begins'' test checks for the presence of the second string at the start of +the first, both strings having been expanded. + +&&& +` `<'text1'>` ends `<'text2'> +` `<'text1'>` does not end `<'text2'> +`e.g. $header_from: ends "public.com.example"` +&&& + +An ``ends'' test checks for the presence of the second string at the end of +the first, both strings having been expanded. + +&&& +` `<'text1'>` is `<'text2'> +` `<'text1'>` is not `<'text2'> +`e.g. $local_part_suffix is "-foo"` +&&& + +An ``is'' test does an exact match between the strings, having first expanded +both strings. + +&&& +` `<'text1'>` contains `<'text2'> +` `<'text1'>` does not contain `<'text2'> +`e.g. $header_subject: contains "evolution"` +&&& + +A ``contains'' test does a partial string match, having expanded both strings. + +&&& +` `<'text1'>` matches `<'text2'> +` `<'text1'>` does not match `<'text2'> +`e.g. $sender_address matches "(bill|john)@"` +&&& + +For a ``matches'' test, after expansion of both strings, the second one is +interpreted as a regular expression. Exim uses the PCRE regular expression +library, which provides regular expressions that are compatible with Perl. + +The match succeeds if the regular expression matches any part of the first +string. If you want a regular expression to match only at the start or end of +the subject string, you must encode that requirement explicitly, using the `^` +or `$` metacharacters. The above example, which is not so constrained, matches +all these addresses: + + bill@test.example + john@some.example + spoonbill@example.com + littlejohn@example.com + +To match only the first two, you could use this: + + if $sender_address matches "^(bill|john)@" then ... + +Care must be taken if you need a backslash in a regular expression, because +backslashes are interpreted as escape characters both by the string expansion +code and by Exim's normal processing of strings in quotes. For example, if you +want to test the sender address for a domain ending in '.com' the regular +expression is + + \.com$ + +The backslash and dollar sign in that expression have to be escaped when used +in a filter command, as otherwise they would be interpreted by the expansion +code. Thus, what you actually write is + + if $sender_address matches \\.com\$ + +An alternative way of handling this is to make use of the `\N` expansion +flag for suppressing expansion: + + if $sender_address matches \N\.com$\N + +Everything between the two occurrences of `\N` is copied without change by +the string expander (and in fact you do not need the final one, because it is +at the end of the string). If the regular expression is given in quotes +(mandatory only if it contains white space) you have to write either + + if $sender_address matches "\\\\.com\\$" + +or + + if $sender_address matches "\\N\\.com$\\N" + + +If the regular expression contains bracketed sub-expressions, numeric +variable substitutions such as $1$ can be used in the subsequent actions +after a successful match. If the match fails, the values of the numeric +variables remain unchanged. Previous values are not restored after ^endif^. +In other words, only one set of values is ever available. If the condition +contains several sub-conditions connected by ^and^ or ^or^, it is the +strings extracted from the last successful match that are available in +subsequent actions. Numeric variables from any one sub-condition are also +available for use in subsequent sub-conditions, because string expansion of a +condition occurs just before it is tested. + + +Numeric testing conditions +~~~~~~~~~~~~~~~~~~~~~~~~~~ +The following conditions are available for performing numerical tests: + +&&& +` `<'number1'>` is above `<'number2'> +` `<'number1'>` is not above `<'number2'> +` `<'number1'>` is below `<'number2'> +` `<'number1'>` is not below `<'number2'> +`e.g. $message_size is not above 10k` +&&& + +The <'number'> arguments must expand to strings of digits, optionally followed +by one of the letters K or M (upper case or lower case) which cause +multiplication by 1024 and 1024x1024 respectively. + + +Testing for significant deliveries +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +You can use the ^delivered^ condition to test whether or not any previously +obeyed filter commands have set up a significant delivery. For example: + + if not delivered then save mail/anomalous endif + +``Delivered'' is perhaps a poor choice of name for this condition, because the +message has not actually been delivered; rather, a delivery has been set up for +later processing. + + +Testing for error messages +~~~~~~~~~~~~~~~~~~~~~~~~~~ +The condition ^error_message^ is true if the incoming message is a bounce +(mail delivery error) message. Putting the command + + if error_message then finish endif + +at the head of your filter file is a useful insurance against things going +wrong in such a way that you cannot receive delivery error reports. *Note*: +^error_message^ is a condition, not an expansion variable, and therefore is +not preceded by `$`. + + +Testing a list of addresses +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +There is a facility for looping through a list of addresses and applying a +condition to each of them. It takes the form + +&&& +`foranyaddress `<'string'>` (`<'condition'>`)` +&&& + +where <'string'> is interpreted as a list of RFC 2822 addresses, as in a +typical header line, and <'condition'> is any valid filter condition or +combination of conditions. The ``group'' syntax that is defined for certain +header lines that contain addresses is supported. + +The parentheses surrounding the condition are mandatory, to delimit it from +possible further sub-conditions of the enclosing ^if^ command. Within the +condition, the expansion variable $thisaddress$ is set to the non-comment +portion of each of the addresses in the string in turn. For example, if the +string is + + B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister) + +then $thisaddress$ would take on the values `bart@sfld.example` and +`lisa@sfld.example` in turn. + +If there are no valid addresses in the list, the whole condition is false. If +the internal condition is true for any one address, the overall condition is +true and the loop ends. If the internal condition is false for all addresses in +the list, the overall condition is false. This example tests for the presence +of an eight-digit local part in any address in a 'To:' header: + + if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ... + +When the overall condition is true, the value of $thisaddress$ in the +commands that follow ^then^ is the last value it took on inside the loop. At +the end of the ^if^ command, the value of $thisaddress$ is reset to what it +was before. It is best to avoid the use of multiple occurrences of +^foranyaddress^, nested or otherwise, in a single ^if^ command, if the +value of $thisaddress$ is to be used afterwards, because it isn't always +clear what the value will be. Nested ^if^ commands should be used instead. + +Header lines can be joined together if a check is to be applied to more than +one of them. For example: + + if foranyaddress $h_to:,$h_cc: .... + +scans through the addresses in both the 'To:' and the 'Cc:' headers. + + +[[SECTpersonal]] +Testing for personal mail +~~~~~~~~~~~~~~~~~~~~~~~~~ +A common requirement is to distinguish between incoming personal mail and mail +from a mailing list, or from a robot or other automatic process (for example, a +bounce message). In particular, this test is normally required for ``vacation +messages''. + +The ^personal^ condition checks that the message is not a bounce message and +that the current user's email address appears in the 'To:' header. It also +checks that the sender is not the current user or one of a number of common +daemons, and that there are no header lines starting 'List-' in the message. +Finally, it checks the content of the 'Precedence:' header line, if there is +one. + +You should always use the ^personal^ condition when generating automatic +responses. This example shows the use of ^personal^ in a filter file that is +sending out vacation messages: + + if personal then + mail to $reply_address + subject "I am on holiday" + file $home/vacation/message + once $home/vacation/once + once_repeat 10d + endif + +It is tempting, when writing commands like the above, to quote the original +subject in the reply. For example: + + subject "Re: $h_subject:" + +There is a danger in doing this, however. It may allow a third party to +subscribe you to an opt-in mailing list, provided that the list accepts bounce +messages as subscription confirmations. (Messages sent from filters are always +sent as bounce messages.) Well-managed lists require a non-bounce message to +confirm a subscription, so the danger is relatively small. + +If prefixes or suffixes are in use for local parts -- something which depends +on the configuration of Exim (see section <<SECTmbox>> below) -- the tests for +the current user are done with the full address (including the prefix and +suffix, if any) as well as with the prefix and suffix removed. If the system is +configured to rewrite local parts of mail addresses, for example, to rewrite +`dag46` as `Dirk.Gently`, the rewritten form of the address is also used in +the tests. + + + +Alias addresses for the personal condition +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It is quite common for people who have mail accounts on a number of different +systems to forward all their mail to one system, and in this case a check for +personal mail should test all their various mail addresses. To allow for this, +the ^personal^ condition keyword can be followed by + +&&& +`alias `<'address'> +&&& + +any number of times, for example + + if personal alias smith@else.where.example + alias jones@other.place.example + then ... + +The alias addresses are treated as alternatives to the current user's email +address when testing the contents of header lines. + + +Details of the personal condition +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The basic ^personal^ test is roughly equivalent to the following: + + not error_message and + $message_headers does not contain "\nList-" and + $header_auto-submitted: does not contain "auto-" and + $header_precedence: does not contain "bulk" and + $header_precedence: does not contain "list" and + $header_precedence: does not contain "junk" and + foranyaddress $header_to: + ( $thisaddress contains "$local_part$domain" ) and + not foranyaddress $header_from: + ( + $thisaddress contains "$local_partdomain" or + $thisaddress contains "server" or + $thisaddress contains "daemon" or + $thisaddress contains "root" or + $thisaddress contains "listserv" or + $thisaddress contains "majordomo" or + $thisaddress contains "-request" or + $thisaddress matches "^owner-[^]+" + ) + +The variable $local_part$ contains the local part of the mail address of +the user whose filter file is being run -- it is normally your login id. The +$domain$ variable contains the mail domain. As explained above, if aliases +or rewriting are defined, or if prefixes or suffixes are in use, the tests for +the current user are also done with alternative addresses. + + + + +Testing delivery status +~~~~~~~~~~~~~~~~~~~~~~~ +There are two conditions that are intended mainly for use in system filter +files, but which are available in users' filter files as well. The condition +^first_delivery^ is true if this is the first process that is attempting to +deliver the message, and false otherwise. This indicator is not reset until the +first delivery process successfully terminates; if there is a crash or a power +failure (for example), the next delivery attempt is also a ``first delivery''. + +In a user filter file ^first_delivery^ will be false if there was previously an +error in the filter, or if a delivery for the user failed owing to, for +example, a quota error, or if forwarding to a remote address was deferred for +some reason. + +The condition ^manually_thawed^ is true if the message was ``frozen'' for some +reason, and was subsequently released by the system administrator. It is +unlikely to be of use in users' filter files. + + +[[SECTmbox]] +Multiple personal mailboxes +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The system administrator can configure Exim so that users can set up variants +on their email addresses and handle them separately. Consult your system +administrator or local documentation to see if this facility is enabled on your +system, and if so, what the details are. + +The facility involves the use of a prefix or a suffix on an email address. For +example, all mail addressed to 'lg303-'<'something'> would be the property of +user 'lg303', who could determine how it was to be handled, depending on the +value of <'something'>. + +There are two possible ways in which this can be set up. The first possibility +is the use of multiple '.forward' files. In this case, mail to 'lg303-foo', +for example, is handled by looking for a file called _.forward-foo_ in +'lg303'{ap}s home directory. If such a file does not exist, delivery fails and the +message is returned to its sender. + +The alternative approach is to pass all messages through a single _.forward_ +file, which must be a filter file so that it can distinguish between the +different cases by referencing the variables $local_part_prefix$ or +$local_part_suffix$, as in the final example in section <<SECTex>> below. + +It is possible to configure Exim to support both schemes at once. In this case, +a specific _.forward-foo_ file is first sought; if it is not found, the basic +_.forward_ file is used. + +The ^personal^ test (see section <<SECTpersonal>>) includes prefixes and +suffixes in its checking. + + + +Ignoring delivery errors +~~~~~~~~~~~~~~~~~~~~~~~~ +As was explained above, filtering just sets up addresses for delivery -- no +deliveries are actually done while a filter file is active. If any of the +generated addresses subsequently suffers a delivery failure, an error message +is generated in the normal way. However, if a filter command that sets up a +delivery is preceded by the word ^noerror^, errors for that delivery, +'and any deliveries consequent on it' (that is, from alias, forwarding, or +filter files it invokes) are ignored. + + + +[[SECTex]] +Examples of Exim filter commands +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Simple forwarding: + + # Exim filter + deliver baggins@rivendell.middle-earth.example + +Vacation handling using traditional means, assuming that the _.vacation.msg_ +and other files have been set up in your home directory: + + # Exim filter + unseen pipe "/usr/ucb/vacation \"$local_part\"" + +Vacation handling inside Exim, having first created a file called +_.vacation.msg_ in your home directory: + + # Exim filter + if personal then vacation endif + +File some messages by subject: + + # Exim filter + if $header_subject: contains "empire" or + $header_subject: contains "foundation" + then + save $home/mail/f+e + endif + +Save all non-urgent messages by weekday: + + # Exim filter + if $header_subject: does not contain "urgent" and + $tod_full matches "^(...)," + then + save $home/mail/$1 + endif + +Throw away all mail from one site, except from postmaster: + + # Exim filter + if $reply_address contains "@spam.site.example" and + $reply_address does not contain "postmaster@" + then + seen finish + endif + +Handle multiple personal mailboxes + + # Exim filter + if $local_part_suffix is "-foo" + then + save $home/mail/foo + elif $local_part_suffix is "-bar" + then + save $home/mail/bar + endif + + |