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6 foot_right_recto="&chaptertitle;"
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10 toc_title="Exim's interfaces to mail filtering"
14 <title>Exim's interfaces to mail filtering</title>
15 <titleabbrev>Exim filtering</titleabbrev>
19 <author><firstname>Philip</firstname><surname>Hazel</surname></author>
20 <authorinitials>PH</authorinitials>
21 <revhistory><revision>
22 <revnumber>4.92</revnumber>
23 <date>10 Feb 2019</date>
24 <authorinitials>PH</authorinitials>
25 </revision></revhistory>
28 </year><holder>University of Cambridge</holder></copyright>
30 <chapter id="CHAPforandfilt">
31 <title>Forwarding and filtering in Exim</title>
33 This document describes the user interfaces to Exim’s in-built mail filtering
34 facilities, and is copyright © University of Cambridge 2014. It
35 corresponds to Exim version 4.92.
38 <title>Introduction</title>
40 Most Unix mail transfer agents (programs that deliver mail) permit individual
41 users to specify automatic forwarding of their mail, usually by placing a list
42 of forwarding addresses in a file called <filename>.forward</filename> in their home
43 directories. Exim extends this facility by allowing the forwarding instructions
44 to be a set of rules rather than just a list of addresses, in effect providing
45 <quote><filename>.forward</filename> with conditions</quote>. Operating the set of rules is called
46 <emphasis>filtering</emphasis>, and the file that contains them is called a <emphasis>filter file</emphasis>.
49 Exim supports two different kinds of filter file. An <emphasis>Exim filter</emphasis> contains
50 instructions in a format that is unique to Exim. A <emphasis>Sieve filter</emphasis> contains
51 instructions in the Sieve format that is defined by RFC 3028. As this is a
52 standard format, Sieve filter files may already be familiar to some users.
53 Sieve files should also be portable between different environments. However,
54 the Exim filtering facility contains more features (such as variable
55 expansion), and better integration with the host environment (such as the use
56 of external processes and pipes).
59 The choice of which kind of filter to use can be left to the end-user, provided
60 that the system administrator has configured Exim appropriately for both kinds
61 of filter. However, if interoperability is important, Sieve is the only
65 The ability to use filtering or traditional forwarding has to be enabled by the
66 system administrator, and some of the individual facilities can be separately
67 enabled or disabled. A local document should be provided to describe exactly
68 what has been enabled. In the absence of this, consult your system
72 This document describes how to use a filter file and the format of its
73 contents. It is intended for use by end-users. Both Sieve filters and Exim
74 filters are covered. However, for Sieve filters, only issues that relate to the
75 Exim implementation are discussed, since Sieve itself is described elsewhere.
78 The contents of traditional <filename>.forward</filename> files are not described here. They
79 normally contain just a list of addresses, file names, or pipe commands,
80 separated by commas or newlines, but other types of item are also available.
81 The full details can be found in the chapter on the <command>redirect</command> router in the
82 Exim specification, which also describes how the system administrator can set
83 up and control the use of filtering.
87 <title>Filter operation</title>
89 It is important to realize that, in Exim, no deliveries are actually made while
90 a filter or traditional <filename>.forward</filename> file is being processed. Running a filter
91 or processing a traditional <filename>.forward</filename> file sets up future delivery
92 operations, but does not carry them out.
95 The result of filter or <filename>.forward</filename> file processing is a list of destinations
96 to which a message should be delivered. The deliveries themselves take place
97 later, along with all other deliveries for the message. This means that it is
98 not possible to test for successful deliveries while filtering. It also means
99 that any duplicate addresses that are generated are dropped, because Exim never
100 delivers the same message to the same address more than once.
103 <section id="SECTtesting">
104 <title>Testing a new filter file</title>
106 Filter files, especially the more complicated ones, should always be tested, as
107 it is easy to make mistakes. Exim provides a facility for preliminary testing
108 of a filter file before installing it. This tests the syntax of the file and
109 its basic operation, and can also be used with traditional <filename>.forward</filename> files.
112 Because a filter can do tests on the content of messages, a test message is
113 required. Suppose you have a new filter file called <filename>myfilter</filename> and a test
114 message in a file called <filename>test-message</filename>. Assuming that Exim is installed with
115 the conventional path name <filename>/usr/sbin/sendmail</filename> (some operating systems use
116 <filename>/usr/lib/sendmail</filename>), the following command can be used:
118 <literallayout class="monospaced">
119 /usr/sbin/sendmail -bf myfilter <test-message
122 The <option>-bf</option> option tells Exim that the following item on the command line is
123 the name of a filter file that is to be tested. There is also a <option>-bF</option> option,
124 which is similar, but which is used for testing system filter files, as opposed
125 to user filter files, and which is therefore of use only to the system
129 The test message is supplied on the standard input. If there are no
130 message-dependent tests in the filter, an empty file (<filename>/dev/null</filename>) can be
131 used. A supplied message must start with header lines or the <quote>From </quote> message
132 separator line that is found in many multi-message folder files. Note that
133 blank lines at the start terminate the header lines. A warning is given if no
134 header lines are read.
137 The result of running this command, provided no errors are detected in the
138 filter file, is a list of the actions that Exim would try to take if presented
139 with the message for real. For example, for an Exim filter, the output
141 <literallayout class="monospaced">
142 Deliver message to: gulliver@lilliput.fict.example
143 Save message to: /home/lemuel/mail/archive
146 means that one copy of the message would be sent to
147 <emphasis>gulliver@lilliput.fict.example</emphasis>, and another would be added to the file
148 <filename>/home/lemuel/mail/archive</filename>, if all went well.
151 The actions themselves are not attempted while testing a filter file in this
152 way; there is no check, for example, that any forwarding addresses are valid.
153 For an Exim filter, if you want to know why a particular action is being taken,
154 add the <option>-v</option> option to the command. This causes Exim to output the results of
155 any conditional tests and to indent its output according to the depth of
156 nesting of <command>if</command> commands. Further additional output from a filter test can be
157 generated by the <command>testprint</command> command, which is described below.
160 When Exim is outputting a list of the actions it would take, if any text
161 strings are included in the output, non-printing characters therein are
162 converted to escape sequences. In particular, if any text string contains a
163 newline character, this is shown as <quote>\n</quote> in the testing output.
166 When testing a filter in this way, Exim makes up an <quote>envelope</quote> for the
167 message. The recipient is by default the user running the command, and so is
168 the sender, but the command can be run with the <option>-f</option> option to supply a
169 different sender. For example,
171 <literallayout class="monospaced">
172 /usr/sbin/sendmail -bf myfilter \
173 -f islington@never.where <test-message
176 Alternatively, if the <option>-f</option> option is not used, but the first line of the
177 supplied message is a <quote>From </quote> separator from a message folder file (not the
178 same thing as a <emphasis>From:</emphasis> header line), the sender is taken from there. If
179 <option>-f</option> is present, the contents of any <quote>From </quote> line are ignored.
182 The <quote>return path</quote> is the same as the envelope sender, unless the message
183 contains a <emphasis>Return-path:</emphasis> header, in which case it is taken from there. You
184 need not worry about any of this unless you want to test out features of a
185 filter file that rely on the sender address or the return path.
188 It is possible to change the envelope recipient by specifying further options.
189 The <option>-bfd</option> option changes the domain of the recipient address, while the
190 <option>-bfl</option> option changes the <quote>local part</quote>, that is, the part before the @
191 sign. An adviser could make use of these to test someone else’s filter file.
194 The <option>-bfp</option> and <option>-bfs</option> options specify the prefix or suffix for the local
195 part. These are relevant only when support for multiple personal mailboxes is
196 implemented; see the description in section <xref linkend="SECTmbox"/> below.
200 <title>Installing a filter file</title>
202 A filter file is normally installed under the name <filename>.forward</filename> in your home
203 directory – it is distinguished from a conventional <filename>.forward</filename> file by its
204 first line (described below). However, the file name is configurable, and some
205 system administrators may choose to use some different name or location for
210 <title>Testing an installed filter file</title>
212 Testing a filter file before installation cannot find every potential problem;
213 for example, it does not actually run commands to which messages are piped.
214 Some <quote>live</quote> tests should therefore also be done once a filter is installed.
217 If at all possible, test your filter file by sending messages from some other
218 account. If you send a message to yourself from the filtered account, and
219 delivery fails, the error message will be sent back to the same account, which
220 may cause another delivery failure. It won’t cause an infinite sequence of such
221 messages, because delivery failure messages do not themselves generate further
222 messages. However, it does mean that the failure won’t be returned to you, and
223 also that the postmaster will have to investigate the stuck message.
226 If you have to test an Exim filter from the same account, a sensible precaution
227 is to include the line
229 <literallayout class="monospaced">
230 if error_message then finish endif
233 as the first filter command, at least while testing. This causes filtering to
234 be abandoned for a delivery failure message, and since no destinations are
235 generated, the message goes on to be delivered to the original address. Unless
236 there is a good reason for not doing so, it is recommended that the above test
237 be left in all Exim filter files. (This does not apply to Sieve files.)
241 <title>Details of filtering commands</title>
243 The filtering commands for Sieve and Exim filters are completely different in
244 syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
245 chapter we describe how it is integrated into Exim. The subsequent chapter
246 covers Exim filtering commands in detail.
251 <chapter id="CHAPsievefilter">
252 <title>Sieve filter files</title>
254 The code for Sieve filtering in Exim was contributed by Michael Haardt, and
255 most of the content of this chapter is taken from the notes he provided. Since
256 Sieve is an extensible language, it is important to understand <quote>Sieve</quote> in
257 this context as <quote>the specific implementation of Sieve for Exim</quote>.
260 This chapter does not contain a description of Sieve, since that can be found
261 in RFC 3028, which should be read in conjunction with these notes.
264 The Exim Sieve implementation offers the core as defined by RFC 3028,
265 comparison tests, the subaddress parameter, the <emphasis role="bold">copy</emphasis>, <emphasis role="bold">envelope</emphasis>,
266 <emphasis role="bold">fileinto</emphasis>, <emphasis role="bold">notify</emphasis>, and <emphasis role="bold">vacation</emphasis> extensions, but not the <emphasis role="bold">reject</emphasis>
267 extension. Exim does not support message delivery notifications (MDNs), so
268 adding it just to the Sieve filter (as required for <emphasis role="bold">reject</emphasis>) makes little
272 In order for Sieve to work properly in Exim, the system administrator needs to
273 make some adjustments to the Exim configuration. These are described in the
274 chapter on the <command>redirect</command> router in the full Exim specification.
277 <title>Recognition of Sieve filters</title>
279 A filter file is interpreted as a Sieve filter if its first line is
281 <literallayout class="monospaced">
285 This is what distinguishes it from a conventional <filename>.forward</filename> file or an Exim
290 <title>Saving to specified folders</title>
292 If the system administrator has set things up as suggested in the Exim
293 specification, and you use <command>keep</command> or <command>fileinto</command> to save a mail into a
294 folder, absolute files are stored where specified, relative files are stored
295 relative to <varname>$home</varname>, and <filename>inbox</filename> goes to the standard mailbox location.
299 <title>Strings containing header names</title>
301 RFC 3028 does not specify what happens if a string denoting a header field does
302 not contain a valid header name, for example, it contains a colon. This
303 implementation generates an error instead of ignoring the header field in order
304 to ease script debugging, which fits in with the common picture of Sieve.
308 <title>Exists test with empty list of headers</title>
310 The <emphasis role="bold">exists</emphasis> test succeeds only if all the specified headers exist. RFC 3028
311 does not explicitly specify what happens on an empty list of headers. This
312 implementation evaluates that condition as true, interpreting the RFC in a
317 <title>Header test with invalid MIME encoding in header</title>
319 Some MUAs process invalid base64 encoded data, generating junk. Others ignore
320 junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
321 specify how to react in this case, other than stating that a client must not
322 forbid to process a message for that reason. RFC 2045 specifies that invalid
323 data should be ignored (apparently looking at end of line characters). It also
324 specifies that invalid data may lead to rejecting messages containing them (and
325 there it appears to talk about true encoding violations), which is a clear
326 contradiction to ignoring them.
329 RFC 3028 does not specify how to process incorrect MIME words. This
330 implementation treats them literally, as it does if the word is correct but its
331 character set cannot be converted to UTF-8.
335 <title>Address test for multiple addresses per header</title>
337 A header may contain multiple addresses. RFC 3028 does not explicitly specify
338 how to deal with them, but since the address test checks if anything matches
339 anything else, matching one address suffices to satisfy the condition. That
340 makes it impossible to test if a header contains a certain set of addresses and
341 no more, but it is more logical than letting the test fail if the header
342 contains an additional address besides the one the test checks for.
346 <title>Semantics of keep</title>
348 The <command>keep</command> command is equivalent to
350 <literallayout class="monospaced">
354 It saves the message and resets the implicit keep flag. It does not set the
355 implicit keep flag; there is no command to set it once it has been reset.
359 <title>Semantics of fileinto</title>
361 RFC 3028 does not specify whether <command>fileinto</command> should try to create a mail
362 folder if it does not exist. This implementation allows the sysadmin to
363 configure that aspect using the <command>appendfile</command> transport options
364 <option>create_directory</option>, <option>create_file</option>, and <option>file_must_exist</option>. See the
365 <command>appendfile</command> transport in the Exim specification for details.
369 <title>Semantics of redirect</title>
371 Sieve scripts are supposed to be interoperable between servers, so this
372 implementation does not allow mail to be redirected to unqualified addresses,
373 because the domain would depend on the system being used. On systems with
374 virtual mail domains, the default domain is probably not what the user expects
379 <title>String arguments</title>
381 There has been confusion if the string arguments to <command>require</command> are to be
382 matched case-sensitively or not. This implementation matches them with the
383 match type <command>:is</command> (default, see section 2.7.1 of the RFC) and the comparator
384 <command>i;ascii-casemap</command> (default, see section 2.7.3 of the RFC). The RFC defines
385 the command defaults clearly, so any different implementations violate RFC
386 3028. The same is valid for comparator names, also specified as strings.
390 <title>Number units</title>
392 There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
393 The mistake is obvious, because RFC 3028 specifies G to denote 2^30
394 (which is gibi, not tebi), and that is what this implementation uses as
395 the scaling factor for the suffix G.
399 <title>RFC compliance</title>
401 Exim requires the first line of a Sieve filter to be
403 <literallayout class="monospaced">
407 Of course the RFC does not specify that line. Do not expect examples to work
408 without adding it, though.
411 RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
412 CRLF is universally used in network protocols to mark the end of the line. This
413 implementation does not embed Sieve in a network protocol, but uses Sieve
414 scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
415 character, this implementation does, too, by default, though the system
416 administrator may choose (at Exim compile time) to use CRLF instead.
419 Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
420 implementation repeats this violation to stay consistent with Exim. This is in
421 preparation for UTF-8 data.
424 Sieve scripts cannot contain NUL characters in strings, but mail headers could
425 contain MIME encoded NUL characters, which could never be matched by Sieve
426 scripts using exact comparisons. For that reason, this implementation extends
427 the Sieve quoted string syntax with \0 to describe a NUL character, violating
428 \0 being the same as 0 in RFC 3028. Even without using \0, the following tests
429 are all true in this implementation. Implementations that use C-style strings
430 will only evaluate the first test as true.
432 <literallayout class="monospaced">
433 Subject: =?iso-8859-1?q?abc=00def
435 header :contains "Subject" ["abc"]
436 header :contains "Subject" ["def"]
437 header :matches "Subject" ["abc?def"]
440 Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
441 way that NUL characters truncating strings is allowed for Sieve
442 implementations, although not recommended. It is further allowed to use encoded
443 NUL characters in headers, but that’s not recommended either. The above example
447 RFC 3028 states that if an implementation fails to convert a character set to
448 UTF-8, two strings cannot be equal if one contains octets greater than 127.
449 Assuming that all unknown character sets are one-byte character sets with the
450 lower 128 octets being US-ASCII is not sound, so this implementation violates
451 RFC 3028 and treats such MIME words literally. That way at least something
455 The folder specified by <command>fileinto</command> must not contain the character sequence
456 <quote>..</quote> to avoid security problems. RFC 3028 does not specify the syntax of
457 folders apart from <command>keep</command> being equivalent to
459 <literallayout class="monospaced">
463 This implementation uses <filename>inbox</filename> instead.
466 Sieve script errors currently cause messages to be silently filed into
467 <filename>inbox</filename>. RFC 3028 requires that the user is notified of that condition.
468 This may be implemented in the future by adding a header line to mails that
469 are filed into <filename>inbox</filename> due to an error in the filter.
474 <chapter id="CHAPeximfilter">
475 <title>Exim filter files</title>
477 This chapter contains a full description of the contents of Exim filter files.
480 <title>Format of Exim filter files</title>
482 Apart from leading white space, the first text in an Exim filter file must be
484 <literallayout class="monospaced">
488 This is what distinguishes it from a conventional <filename>.forward</filename> file or a Sieve
489 filter file. If the file does not have this initial line (or the equivalent for
490 a Sieve filter), it is treated as a conventional <filename>.forward</filename> file, both when
491 delivering mail and when using the <option>-bf</option> testing mechanism. The white space
492 in the line is optional, and any capitalization may be used. Further text on
493 the same line is treated as a comment. For example, you could have
495 <literallayout class="monospaced">
496 # Exim filter <<== do not edit or remove this line!
499 The remainder of the file is a sequence of filtering commands, which consist of
500 keywords and data values. For example, in the command
502 <literallayout class="monospaced">
503 deliver gulliver@lilliput.fict.example
506 the keyword is <literal>deliver</literal> and the data value is
507 <literal>gulliver@lilliput.fict.example</literal>. White space or line breaks separate the
508 components of a command, except in the case of conditions for the <command>if</command>
509 command, where round brackets (parentheses) also act as separators. Complete
510 commands are separated from each other by white space or line breaks; there are
511 no special terminators. Thus, several commands may appear on one line, or one
512 command may be spread over a number of lines.
515 If the character # follows a separator anywhere in a command, everything from
516 # up to the next newline is ignored. This provides a way of including comments
521 <title>Data values in filter commands</title>
523 There are two ways in which a data value can be input:
528 If the text contains no white space, it can be typed verbatim. However, if it
529 is part of a condition, it must also be free of round brackets (parentheses),
530 as these are used for grouping in conditions.
535 Otherwise, text must be enclosed in double quotation marks. In this case, the
536 character \ (backslash) is treated as an <quote>escape character</quote> within the
537 string, causing the following character or characters to be treated specially:
540 <literal>\n</literal> is replaced by a newline
541 <literal>\r</literal> is replaced by a carriage return
542 <literal>\t</literal> is replaced by a tab
547 Backslash followed by up to three octal digits is replaced by the character
548 specified by those digits, and <literal>\x</literal> followed by up to two hexadecimal digits
549 is treated similarly. Backslash followed by any other character is replaced by
550 the second character, so that in particular, <literal>\"</literal> becomes <literal>"</literal> and <literal>\\</literal>
551 becomes <literal>\</literal>. A data item enclosed in double quotes can be continued onto the
552 next line by ending the first line with a backslash. Any leading white space at
553 the start of the continuation line is ignored.
556 In addition to the escape character processing that occurs when strings are
557 enclosed in quotes, most data values are also subject to <emphasis>string expansion</emphasis>
558 (as described in the next section), in which case the characters <literal>$</literal> and
559 <literal>\</literal> are also significant. This means that if a single backslash is actually
560 required in such a string, and the string is also quoted, <literal>\\\\</literal> has to be
564 The maximum permitted length of a data string, before expansion, is 1024
568 <section id="SECTfilterstringexpansion">
569 <title>String expansion</title>
571 Most data values are expanded before use. Expansion consists of replacing
572 substrings beginning with <literal>$</literal> with other text. The full expansion facilities
573 available in Exim are extensive. If you want to know everything that Exim can
574 do with strings, you should consult the chapter on string expansion in the Exim
578 In filter files, by far the most common use of string expansion is the
579 substitution of the contents of a variable. For example, the substring
581 <literallayout class="monospaced">
585 is replaced by the address to which replies to the message should be sent. If
586 such a variable name is followed by a letter or digit or underscore, it must be
587 enclosed in curly brackets (braces), for example,
589 <literallayout class="monospaced">
593 If a <literal>$</literal> character is actually required in an expanded string, it must be
594 escaped with a backslash, and because backslash is also an escape character in
595 quoted input strings, it must be doubled in that case. The following two
596 examples illustrate two different ways of testing for a <literal>$</literal> character in a
599 <literallayout class="monospaced">
600 if $message_body contains \$ then ...
601 if $message_body contains "\\$" then ...
604 You can prevent part of a string from being expanded by enclosing it between
605 two occurrences of <literal>\N</literal>. For example,
607 <literallayout class="monospaced">
608 if $message_body contains \N$$$$\N then ...
611 tests for a run of four dollar characters.
615 <title>Some useful general variables</title>
617 A complete list of the available variables is given in the Exim documentation.
618 This shortened list contains the ones that are most likely to be useful in
619 personal filter files:
622 <varname>$body_linecount</varname>: The number of lines in the body of the message.
625 <varname>$body_zerocount</varname>: The number of binary zero characters in the body of the
629 <varname>$home</varname>: In conventional configurations, this variable normally contains the
630 user’s home directory. The system administrator can, however, change this.
633 <varname>$local_part</varname>: The part of the email address that precedes the @ sign –
634 normally the user’s login name. If support for multiple personal mailboxes is
635 enabled (see section <xref linkend="SECTmbox"/> below) and a prefix or suffix for the local
636 part was recognized, it is removed from the string in this variable.
639 <varname>$local_part_prefix</varname>: If support for multiple personal mailboxes is enabled
640 (see section <xref linkend="SECTmbox"/> below), and a local part prefix was recognized,
641 this variable contains the prefix. Otherwise it contains an empty string.
644 <varname>$local_part_suffix</varname>: If support for multiple personal mailboxes is enabled
645 (see section <xref linkend="SECTmbox"/> below), and a local part suffix was recognized,
646 this variable contains the suffix. Otherwise it contains an empty string.
649 <varname>$message_body</varname>: The initial portion of the body of the message. By default,
650 up to 500 characters are read into this variable, but the system administrator
651 can configure this to some other value. Newlines in the body are converted into
655 <varname>$message_body_end</varname>: The final portion of the body of the message, formatted
656 and limited in the same way as <varname>$message_body</varname>.
659 <varname>$message_body_size</varname>: The size of the body of the message, in bytes.
662 <varname>$message_exim_id</varname>: The message’s local identification string, which is unique
663 for each message handled by a single host.
666 <varname>$message_headers</varname>: The header lines of the message, concatenated into a
667 single string, with newline characters between them.
670 <varname>$message_size</varname>: The size of the entire message, in bytes.
673 <varname>$original_local_part</varname>: When an address that arrived with the message is
674 being processed, this contains the same value as the variable <varname>$local_part</varname>.
675 However, if an address generated by an alias, forward, or filter file is being
676 processed, this variable contains the local part of the original address.
679 <varname>$reply_address</varname>: The contents of the <emphasis>Reply-to:</emphasis> header, if the message
680 has one; otherwise the contents of the <emphasis>From:</emphasis> header. It is the address to
681 which normal replies to the message should be sent.
684 <varname>$return_path</varname>: The return path – that is, the sender field that will be
685 transmitted as part of the message’s envelope if the message is sent to another
686 host. This is the address to which delivery errors are sent. In many cases,
687 this variable has the same value as <varname>$sender_address</varname>, but if, for example,
688 an incoming message to a mailing list has been expanded, <varname>$return_path</varname> may
689 have been changed to contain the address of the list maintainer.
692 <varname>$sender_address</varname>: The sender address that was received in the envelope of
693 the message. This is not necessarily the same as the contents of the <emphasis>From:</emphasis>
694 or <emphasis>Sender:</emphasis> header lines. For delivery error messages (<quote>bounce messages</quote>)
695 there is no sender address, and this variable is empty.
698 <varname>$tod_full</varname>: A full version of the time and date, for example: Wed, 18 Oct
699 1995 09:51:40 +0100. The timezone is always given as a numerical offset from
703 <varname>$tod_log</varname>: The time and date in the format used for writing Exim’s log files,
704 without the timezone, for example: 1995-10-12 15:32:29.
707 <varname>$tod_zone</varname>: The local timezone offset, for example: +0100.
710 <section id="SECTheadervariables">
711 <title>Header variables</title>
713 There is a special set of expansion variables containing the header lines of
714 the message being processed. These variables have names beginning with
715 <varname>$header_</varname> followed by the name of the header line, terminated by a colon.
718 <literallayout class="monospaced">
723 The whole item, including the terminating colon, is replaced by the contents of
724 the message header line. If there is more than one header line with the same
725 name, their contents are concatenated. For header lines whose data consists of
726 a list of addresses (for example, <emphasis>From:</emphasis> and <emphasis>To:</emphasis>), a comma and newline
727 is inserted between each set of data. For all other header lines, just a
731 Leading and trailing white space is removed from header line data, and if there
732 are any MIME <quote>words</quote> that are encoded as defined by RFC 2047 (because they
733 contain non-ASCII characters), they are decoded and translated, if possible, to
734 a local character set. Translation is attempted only on operating systems that
735 have the <function>iconv()</function> function. This makes the header line look the same as it
736 would when displayed by an MUA. The default character set is ISO-8859-1, but
737 this can be changed by means of the <command>headers</command> command (see below).
740 If you want to see the actual characters that make up a header line, you can
741 specify <varname>$rheader_</varname> instead of <varname>$header_</varname>. This inserts the <quote>raw</quote>
742 header line, unmodified.
745 There is also an intermediate form, requested by <varname>$bheader_</varname>, which removes
746 leading and trailing space and decodes MIME <quote>words</quote>, but does not do any
747 character translation. If an attempt to decode what looks superficially like a
748 MIME <quote>word</quote> fails, the raw string is returned. If decoding produces a binary
749 zero character, it is replaced by a question mark.
752 The capitalization of the name following <varname>$header_</varname> is not significant.
753 Because any printing character except colon may appear in the name of a
754 message’s header (this is a requirement of RFC 2822, the document that
755 describes the format of a mail message) curly brackets must <emphasis>not</emphasis> be used in
756 this case, as they will be taken as part of the header name. Two shortcuts are
757 allowed in naming header variables:
762 The initiating <varname>$header_</varname>, <varname>$rheader_</varname>, or <varname>$bheader_</varname> can be
763 abbreviated to <varname>$h_</varname>, <varname>$rh_</varname>, or <varname>$bh_</varname>, respectively.
768 The terminating colon can be omitted if the next character is white space. The
769 white space character is retained in the expanded string. However, this is not
770 recommended, because it makes it easy to forget the colon when it really is
776 If the message does not contain a header of the given name, an empty string is
777 substituted. Thus it is important to spell the names of headers correctly. Do
778 not use <varname>$header_Reply_to</varname> when you really mean <varname>$header_Reply-to</varname>.
782 <title>User variables</title>
784 There are ten user variables with names <varname>$n0</varname> – <varname>$n9</varname> that can be
785 incremented by the <command>add</command> command (see section <xref linkend="SECTadd"/>). These can be
786 used for <quote>scoring</quote> messages in various ways. If Exim is configured to run a
787 <quote>system filter</quote> on every message, the values left in these variables are
788 copied into the variables <varname>$sn0</varname> – <varname>$sn9</varname> at the end of the system filter,
789 thus making them available to users’ filter files. How these values are used is
790 entirely up to the individual installation.
794 <title>Current directory</title>
796 The contents of your filter file should not make any assumptions about the
797 current directory. It is best to use absolute paths for file names; you can
798 normally make use of the <varname>$home</varname> variable to refer to your home directory. The
799 <command>save</command> command automatically inserts <varname>$home</varname> at the start of non-absolute
803 <section id="SECTsigdel">
804 <title>Significant deliveries</title>
806 When in the course of delivery a message is processed by a filter file, what
807 happens next, that is, after the filter file has been processed, depends on
808 whether or not the filter sets up any <emphasis>significant deliveries</emphasis>. If at least
809 one significant delivery is set up, the filter is considered to have handled
810 the entire delivery arrangements for the current address, and no further
811 processing of the address takes place. If, however, no significant deliveries
812 are set up, Exim continues processing the current address as if there were no
813 filter file, and typically sets up a delivery of a copy of the message into a
814 local mailbox. In particular, this happens in the special case of a filter file
815 containing only comments.
818 The delivery commands <command>deliver</command>, <command>save</command>, and <command>pipe</command> are by default
819 significant. However, if such a command is preceded by the word <quote>unseen</quote>, its
820 delivery is not considered to be significant. In contrast, other commands such
821 as <command>mail</command> and <command>vacation</command> do not set up significant deliveries unless
822 preceded by the word <quote>seen</quote>. The following example commands set up
823 significant deliveries:
825 <literallayout class="monospaced">
826 deliver jack@beanstalk.example
827 pipe $home/bin/mymailscript
828 seen mail subject "message discarded"
832 The following example commands do not set up significant deliveries:
834 <literallayout class="monospaced">
835 unseen deliver jack@beanstalk.example
836 unseen pipe $home/bin/mymailscript
837 mail subject "message discarded"
841 <section id="SEC222">
842 <title>Filter commands</title>
844 The filter commands that are described in subsequent sections are listed
845 below, with the section in which they are described in brackets:
847 <informaltable frame="none">
848 <tgroup cols="2" colsep="0" rowsep="0">
849 <colspec colwidth="100pt" align="left"/>
850 <colspec colwidth="300pt" align="left"/>
853 <entry><command>add</command></entry>
854 <entry> increment a user variable (section <xref linkend="SECTadd"/>)</entry>
857 <entry><command>deliver</command></entry>
858 <entry> deliver to an email address (section <xref linkend="SECTdeliver"/>)</entry>
861 <entry><command>fail</command></entry>
862 <entry> force delivery failure (sysadmin use) (section <xref linkend="SECTfail"/>)</entry>
865 <entry><command>finish</command></entry>
866 <entry> end processing (section <xref linkend="SECTfinish"/>)</entry>
869 <entry><command>freeze</command></entry>
870 <entry> freeze message (sysadmin use) (section <xref linkend="SECTfreeze"/>)</entry>
873 <entry><command>headers</command></entry>
874 <entry> set the header character set (section <xref linkend="SECTheaders"/>)</entry>
877 <entry><command>if</command></entry>
878 <entry> test condition(s) (section <xref linkend="SECTif"/>)</entry>
881 <entry><command>logfile</command></entry>
882 <entry> define log file (section <xref linkend="SECTlog"/>)</entry>
885 <entry><command>logwrite</command></entry>
886 <entry> write to log file (section <xref linkend="SECTlog"/>)</entry>
889 <entry><command>mail</command></entry>
890 <entry> send a reply message (section <xref linkend="SECTmail"/>)</entry>
893 <entry><command>pipe</command></entry>
894 <entry> pipe to a command (section <xref linkend="SECTpipe"/>)</entry>
897 <entry><command>save</command></entry>
898 <entry> save to a file (section <xref linkend="SECTsave"/>)</entry>
901 <entry><command>testprint</command></entry>
902 <entry> print while testing (section <xref linkend="SECTtestprint"/>)</entry>
905 <entry><command>vacation</command></entry>
906 <entry> tailored form of <command>mail</command> (section <xref linkend="SECTmail"/>)</entry>
912 The <command>headers</command> command has additional parameters that can be used only in a
913 system filter. The <command>fail</command> and <command>freeze</command> commands are available only when
914 Exim’s filtering facilities are being used as a system filter, and are
915 therefore usable only by the system administrator and not by ordinary users.
916 They are mentioned only briefly in this document; for more information, see the
917 main Exim specification.
920 <section id="SECTadd">
921 <title>The add command</title>
923 <literal> add </literal><<emphasis>number</emphasis>><literal> to </literal><<emphasis>user variable</emphasis>>
924 <literal>e.g. add 2 to n3</literal>
927 There are 10 user variables of this type, with names <varname>$n0</varname> – <varname>$n9</varname>. Their
928 values can be obtained by the normal expansion syntax (for example <varname>$n3</varname>) in
929 other commands. At the start of filtering, these variables all contain zero.
930 Both arguments of the <command>add</command> command are expanded before use, making it
931 possible to add variables to each other. Subtraction can be obtained by adding
935 <section id="SECTdeliver">
936 <title>The deliver command</title>
938 <literal> deliver</literal> <<emphasis>mail address</emphasis>>
939 <literal>e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"</literal>
942 This command provides a forwarding operation. The delivery that it sets up is
943 significant unless the command is preceded by <quote>unseen</quote> (see section
944 <xref linkend="SECTsigdel"/>). The message is sent on to the given address, exactly as
945 happens if the address had appeared in a traditional <filename>.forward</filename> file. If you
946 want to deliver the message to a number of different addresses, you can use
947 more than one <command>deliver</command> command (each one may have only one address).
948 However, duplicate addresses are discarded.
951 To deliver a copy of the message to your normal mailbox, your login name can be
952 given as the address. Once an address has been processed by the filtering
953 mechanism, an identical generated address will not be so processed again, so
954 doing this does not cause a loop.
957 However, if you have a mail alias, you should <emphasis>not</emphasis> refer to it here. For
958 example, if the mail address <emphasis>L.Gulliver</emphasis> is aliased to <emphasis>lg303</emphasis> then all
959 references in Gulliver’s <filename>.forward</filename> file should be to <emphasis>lg303</emphasis>. A reference
960 to the alias will not work for messages that are addressed to that alias,
961 since, like <filename>.forward</filename> file processing, aliasing is performed only once on an
962 address, in order to avoid looping.
965 Following the new address, an optional second address, preceded by
966 <quote>errors_to</quote> may appear. This changes the address to which delivery errors on
967 the forwarded message will be sent. Instead of going to the message’s original
968 sender, they go to this new address. For ordinary users, the only value that is
969 permitted for this address is the user whose filter file is being processed.
970 For example, the user <emphasis>lg303</emphasis> whose mailbox is in the domain
971 <emphasis>lilliput.example</emphasis> could have a filter file that contains
973 <literallayout class="monospaced">
974 deliver jon@elsewhere.example errors_to lg303@lilliput.example
977 Clearly, using this feature makes sense only in situations where not all
978 messages are being forwarded. In particular, bounce messages must not be
979 forwarded in this way, as this is likely to create a mail loop if something
983 <section id="SECTsave">
984 <title>The save command</title>
986 <literal> save </literal><<emphasis>file name</emphasis>>
987 <literal>e.g. save $home/mail/bookfolder</literal>
990 This command specifies that a copy of the message is to be appended to the
991 given file (that is, the file is to be used as a mail folder). The delivery
992 that <command>save</command> sets up is significant unless the command is preceded by
993 <quote>unseen</quote> (see section <xref linkend="SECTsigdel"/>).
996 More than one <command>save</command> command may be obeyed; each one causes a copy of the
997 message to be written to its argument file, provided they are different
998 (duplicate <command>save</command> commands are ignored).
1001 If the file name does not start with a / character, the contents of the
1002 <varname>$home</varname> variable are prepended, unless it is empty, or the system
1003 administrator has disabled this feature. In conventional configurations, this
1004 variable is normally set in a user filter to the user’s home directory, but the
1005 system administrator may set it to some other path. In some configurations,
1006 <varname>$home</varname> may be unset, or prepending may be disabled, in which case a
1007 non-absolute path name may be generated. Such configurations convert this to an
1008 absolute path when the delivery takes place. In a system filter, <varname>$home</varname> is
1012 The user must of course have permission to write to the file, and the writing
1013 of the file takes place in a process that is running as the user, under the
1014 user’s primary group. Any secondary groups to which the user may belong are not
1015 normally taken into account, though the system administrator can configure Exim
1016 to set them up. In addition, the ability to use this command at all is
1017 controlled by the system administrator – it may be forbidden on some systems.
1020 An optional mode value may be given after the file name. The value for the mode
1021 is interpreted as an octal number, even if it does not begin with a zero. For
1024 <literallayout class="monospaced">
1025 save /some/folder 640
1028 This makes it possible for users to override the system-wide mode setting for
1029 file deliveries, which is normally 600. If an existing file does not have the
1030 correct mode, it is changed.
1033 An alternative form of delivery may be enabled on your system, in which each
1034 message is delivered into a new file in a given directory. If this is the case,
1035 this functionality can be requested by giving the directory name terminated by
1036 a slash after the <command>save</command> command, for example
1038 <literallayout class="monospaced">
1039 save separated/messages/
1042 There are several different formats for such deliveries; check with your system
1043 administrator or local documentation to find out which (if any) are available
1044 on your system. If this functionality is not enabled, the use of a path name
1045 ending in a slash causes an error.
1048 <section id="SECTpipe">
1049 <title>The pipe command</title>
1051 <literal> pipe </literal><<emphasis>command</emphasis>>
1052 <literal>e.g. pipe "$home/bin/countmail $sender_address"</literal>
1055 This command specifies that the message is to be delivered to the specified
1056 command using a pipe. The delivery that it sets up is significant unless the
1057 command is preceded by <quote>unseen</quote> (see section <xref linkend="SECTsigdel"/>). Remember,
1058 however, that no deliveries are done while the filter is being processed. All
1059 deliveries happen later on. Therefore, the result of running the pipe is not
1060 available to the filter.
1063 When the deliveries are done, a separate process is run, and a copy of the
1064 message is passed on its standard input. The process runs as the user, under
1065 the user’s primary group. Any secondary groups to which the user may belong are
1066 not normally taken into account, though the system administrator can configure
1067 Exim to set them up. More than one <command>pipe</command> command may appear; each one causes
1068 a copy of the message to be written to its argument pipe, provided they are
1069 different (duplicate <command>pipe</command> commands are ignored).
1072 When the time comes to transport the message, the command supplied to <command>pipe</command>
1073 is split up by Exim into a command name and a number of arguments. These are
1074 delimited by white space except for arguments enclosed in double quotes, in
1075 which case backslash is interpreted as an escape, or in single quotes, in which
1076 case no escaping is recognized. Note that as the whole command is normally
1077 supplied in double quotes, a second level of quoting is required for internal
1078 double quotes. For example:
1080 <literallayout class="monospaced">
1081 pipe "$home/myscript \"size is $message_size\""
1084 String expansion is performed on the separate components after the line has
1085 been split up, and the command is then run directly by Exim; it is not run
1086 under a shell. Therefore, substitution cannot change the number of arguments,
1087 nor can quotes, backslashes or other shell metacharacters in variables cause
1091 Documentation for some programs that are normally run via this kind of pipe
1092 often suggest that the command should start with
1094 <literallayout class="monospaced">
1098 This is a shell command, and should <emphasis>not</emphasis> be present in Exim filter files,
1099 since it does not normally run the command under a shell.
1102 However, there is an option that the administrator can set to cause a shell to
1103 be used. In this case, the entire command is expanded as a single string and
1104 passed to the shell for interpretation. It is recommended that this be avoided
1105 if at all possible, since it can lead to problems when inserted variables
1106 contain shell metacharacters.
1109 The default PATH set up for the command is determined by the system
1110 administrator, usually containing at least <filename>/bin</filename> and <filename>/usr/bin</filename> so that
1111 common commands are available without having to specify an absolute file name.
1112 However, it is possible for the system administrator to restrict the pipe
1113 facility so that the command name must not contain any / characters, and must
1114 be found in one of the directories in the configured PATH. It is also possible
1115 for the system administrator to lock out the use of the <command>pipe</command> command
1119 When the command is run, a number of environment variables are set up. The
1120 complete list for pipe deliveries may be found in the Exim reference manual.
1121 Those that may be useful for pipe deliveries from user filter files are:
1124 <literal>DOMAIN </literal> the domain of the address
1125 <literal>HOME </literal> your home directory
1126 <literal>LOCAL_PART </literal> see below
1127 <literal>LOCAL_PART_PREFIX </literal> see below
1128 <literal>LOCAL_PART_SUFFIX </literal> see below
1129 <literal>LOGNAME </literal> your login name
1130 <literal>MESSAGE_ID </literal> the unique id of the message
1131 <literal>PATH </literal> the command search path
1132 <literal>RECIPIENT </literal> the complete recipient address
1133 <literal>SENDER </literal> the sender of the message
1134 <literal>SHELL </literal> <literal>/bin/sh</literal>
1135 <literal>USER </literal> see below
1138 LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
1139 id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
1140 recognize prefixes or suffixes in the local parts of addresses. For example, a
1141 message addressed to <emphasis>pat-suf2@domain.example</emphasis> may cause the filter for user
1142 <emphasis>pat</emphasis> to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
1143 <literal>-suf2</literal> when the pipe command runs. The system administrator has to configure
1144 Exim specially for this feature to be available.
1147 If you run a command that is a shell script, be very careful in your use of
1148 data from the incoming message in the commands in your script. RFC 2822 is very
1149 generous in the characters that are permitted to appear in mail addresses, and
1150 in particular, an address may begin with a vertical bar or a slash. For this
1151 reason you should always use quotes round any arguments that involve data from
1152 the message, like this:
1154 <literallayout class="monospaced">
1155 /some/command '$SENDER'
1158 so that inserted shell meta-characters do not cause unwanted effects.
1161 Remember that, as was explained earlier, the pipe command is not run at the
1162 time the filter file is interpreted. The filter just defines what deliveries
1163 are required for one particular addressee of a message. The deliveries
1164 themselves happen later, once Exim has decided everything that needs to be done
1168 A consequence of this is that you cannot inspect the return code from the pipe
1169 command from within the filter. Nevertheless, the code returned by the command
1170 is important, because Exim uses it to decide whether the delivery has succeeded
1174 The command should return a zero completion code if all has gone well. Most
1175 non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1176 treated as a delivery failure, causing the message to be returned to its
1177 sender. However, there are some completion codes that are treated as temporary
1178 errors. The message remains on Exim’s spool disk, and the delivery is tried
1179 again later, though it will ultimately time out if the delivery failures go on
1180 too long. The completion codes to which this applies can be specified by the
1181 system administrator; the default values are 73 and 75.
1184 The pipe command should not normally write anything to its standard output or
1185 standard error file descriptors. If it does, whatever is written is normally
1186 returned to the sender of the message as a delivery error, though this action
1187 can be varied by the system administrator.
1190 <section id="SECTmail">
1191 <title>Mail commands</title>
1193 There are two commands that cause the creation of a new mail message, neither
1194 of which count as a significant delivery unless the command is preceded by the
1195 word <quote>seen</quote> (see section <xref linkend="SECTsigdel"/>). This is a powerful facility, but
1196 it should be used with care, because of the danger of creating infinite
1197 sequences of messages. The system administrator can forbid the use of these
1198 commands altogether.
1201 To help prevent runaway message sequences, these commands have no effect when
1202 the incoming message is a bounce (delivery error) message, and messages sent by
1203 this means are treated as if they were reporting delivery errors. Thus, they
1204 should never themselves cause a bounce message to be returned. The basic
1205 mail-sending command is
1208 <literal>mail [to </literal><<emphasis>address-list</emphasis>><literal>]</literal>
1209 <literal> [cc </literal><<emphasis>address-list</emphasis>><literal>]</literal>
1210 <literal> [bcc </literal><<emphasis>address-list</emphasis>><literal>]</literal>
1211 <literal> [from </literal><<emphasis>address</emphasis>><literal>]</literal>
1212 <literal> [reply_to </literal><<emphasis>address</emphasis>><literal>]</literal>
1213 <literal> [subject </literal><<emphasis>text</emphasis>><literal>]</literal>
1214 <literal> [extra_headers </literal><<emphasis>text</emphasis>><literal>]</literal>
1215 <literal> [text </literal><<emphasis>text</emphasis>><literal>]</literal>
1216 <literal> [[expand] file </literal><<emphasis>filename</emphasis>><literal>]</literal>
1217 <literal> [return message]</literal>
1218 <literal> [log </literal><<emphasis>log file name</emphasis>><literal>]</literal>
1219 <literal> [once </literal><<emphasis>note file name</emphasis>><literal>]</literal>
1220 <literal> [once_repeat </literal><<emphasis>time interval</emphasis>><literal>]</literal>
1221 <literal>e.g. mail text "Your message about $h_subject: has been received"</literal>
1224 Each <<emphasis>address-list</emphasis>> can contain a number of addresses, separated by commas,
1225 in the format of a <emphasis>To:</emphasis> or <emphasis>Cc:</emphasis> header line. In fact, the text you supply
1226 here is copied exactly into the appropriate header line. It may contain
1227 additional information as well as email addresses. For example:
1229 <literallayout class="monospaced">
1230 mail to "Julius Caesar <jc@rome.example>, \
1231 <ma@rome.example> (Mark A.)"
1234 Similarly, the texts supplied for <option>from</option> and <option>reply_to</option> are copied into
1235 their respective header lines.
1238 As a convenience for use in one common case, there is also a command called
1239 <command>vacation</command>. It behaves in the same way as <command>mail</command>, except that the defaults
1240 for the <option>subject</option>, <option>file</option>, <option>log</option>, <option>once</option>, and <option>once_repeat</option> options
1243 <literallayout class="monospaced">
1244 subject "On vacation"
1245 expand file .vacation.msg
1251 respectively. These are the same file names and repeat period used by the
1252 traditional Unix <command>vacation</command> command. The defaults can be overridden by
1253 explicit settings, but if a file name is given its contents are expanded only
1254 if explicitly requested.
1257 <emphasis role="bold">Warning</emphasis>: The <command>vacation</command> command should always be used conditionally,
1258 subject to at least the <command>personal</command> condition (see section <xref linkend="SECTpersonal"/>
1259 below) so as not to send automatic replies to non-personal messages from
1260 mailing lists or elsewhere. Sending an automatic response to a mailing list or
1261 a mailing list manager is an Internet Sin.
1264 For both commands, the key/value argument pairs can appear in any order. At
1265 least one of <option>text</option> or <option>file</option> must appear (except with <command>vacation</command>, where
1266 there is a default for <option>file</option>); if both are present, the text string appears
1267 first in the message. If <option>expand</option> precedes <option>file</option>, each line of the file is
1268 subject to string expansion before it is included in the message.
1271 Several lines of text can be supplied to <option>text</option> by including the escape
1272 sequence <quote>\n</quote> in the string wherever a newline is required. If the command is
1273 output during filter file testing, newlines in the text are shown as <quote>\n</quote>.
1276 Note that the keyword for creating a <emphasis>Reply-To:</emphasis> header is <option>reply_to</option>,
1277 because Exim keywords may contain underscores, but not hyphens. If the <option>from</option>
1278 keyword is present and the given address does not match the user who owns the
1279 forward file, Exim normally adds a <emphasis>Sender:</emphasis> header to the message, though it
1280 can be configured not to do this.
1283 The <option>extra_headers</option> keyword allows you to add custom header lines to the
1284 message. The text supplied must be one or more syntactically valid RFC 2822
1285 header lines. You can use <quote>\n</quote> within quoted text to specify newlines between
1286 headers, and also to define continued header lines. For example:
1288 <literallayout class="monospaced">
1289 extra_headers "h1: first\nh2: second\n continued\nh3: third"
1292 No newline should appear at the end of the final header line.
1295 If no <option>to</option> argument appears, the message is sent to the address in the
1296 <varname>$reply_address</varname> variable (see section <xref linkend="SECTfilterstringexpansion"/> above).
1297 An <emphasis>In-Reply-To:</emphasis> header is automatically included in the created message,
1298 giving a reference to the message identification of the incoming message.
1301 If <option>return message</option> is specified, the incoming message that caused the filter
1302 file to be run is added to the end of the message, subject to a maximum size
1306 If a log file is specified, a line is added to it for each message sent.
1309 If a <option>once</option> file is specified, it is used to hold a database for remembering
1310 who has received a message, and no more than one message is ever sent to any
1311 particular address, unless <option>once_repeat</option> is set. This specifies a time
1312 interval after which another copy of the message is sent. The interval is
1313 specified as a sequence of numbers, each followed by the initial letter of one
1314 of <quote>seconds</quote>, <quote>minutes</quote>, <quote>hours</quote>, <quote>days</quote>, or <quote>weeks</quote>. For example,
1316 <literallayout class="monospaced">
1320 causes a new message to be sent if at least 5 days and 4 hours have elapsed
1321 since the last one was sent. There must be no white space in a time interval.
1324 Commonly, the file name specified for <option>once</option> is used as the base name for
1325 direct-access (DBM) file operations. There are a number of different DBM
1326 libraries in existence. Some operating systems provide one as a default, but
1327 even in this case a different one may have been used when building Exim. With
1328 some DBM libraries, specifying <option>once</option> results in two files being created,
1329 with the suffixes <filename>.dir</filename> and <filename>.pag</filename> being added to the given name. With
1330 some others a single file with the suffix <filename>.db</filename> is used, or the name is used
1334 Using a DBM file for implementing the <option>once</option> feature means that the file
1335 grows as large as necessary. This is not usually a problem, but some system
1336 administrators want to put a limit on it. The facility can be configured not to
1337 use a DBM file, but instead, to use a regular file with a maximum size. The
1338 data in such a file is searched sequentially, and if the file fills up, the
1339 oldest entry is deleted to make way for a new one. This means that some
1340 correspondents may receive a second copy of the message after an unpredictable
1341 interval. Consult your local information to see if your system is configured
1345 More than one <command>mail</command> or <command>vacation</command> command may be obeyed in a single filter
1346 run; they are all honoured, even when they are to the same recipient.
1349 <section id="SECTlog">
1350 <title>Logging commands</title>
1352 A log can be kept of actions taken by a filter file. This facility is normally
1353 available in conventional configurations, but there are some situations where
1354 it might not be. Also, the system administrator may choose to disable it. Check
1355 your local information if in doubt.
1358 Logging takes place while the filter file is being interpreted. It does not
1359 queue up for later like the delivery commands. The reason for this is so that a
1360 log file need be opened only once for several write operations. There are two
1361 commands, neither of which constitutes a significant delivery. The first
1362 defines a file to which logging output is subsequently written:
1365 <literal> logfile </literal><<emphasis>file name</emphasis>>
1366 <literal>e.g. logfile $home/filter.log</literal>
1369 The file name must be fully qualified. You can use <varname>$home</varname>, as in this
1370 example, to refer to your home directory. The file name may optionally be
1371 followed by a mode for the file, which is used if the file has to be created.
1374 <literallayout class="monospaced">
1375 logfile $home/filter.log 0644
1378 The number is interpreted as octal, even if it does not begin with a zero.
1379 The default for the mode is 600. It is suggested that the <command>logfile</command> command
1380 normally appear as the first command in a filter file. Once a log file has
1381 been obeyed, the <command>logwrite</command> command can be used to write to it:
1384 <literal> logwrite "</literal><<emphasis>some text string</emphasis>><literal>"</literal>
1385 <literal>e.g. logwrite "$tod_log $message_id processed"</literal>
1388 It is possible to have more than one <command>logfile</command> command, to specify writing to
1389 different log files in different circumstances.
1390 A previously opened log is closed on a subsequent <command>logfile</command> command.
1391 Writing takes place at the end
1392 of the file, and a newline character is added to the end of each string if
1393 there isn’t one already there. Newlines can be put in the middle of the string
1394 by using the <quote>\n</quote> escape sequence. Lines from simultaneous deliveries may get
1395 interleaved in the file, as there is no interlocking, so you should plan your
1396 logging with this in mind. However, data should not get lost.
1399 <section id="SECTfinish">
1400 <title>The finish command</title>
1402 The command <command>finish</command>, which has no arguments, causes Exim to stop
1403 interpreting the filter file. This is not a significant action unless preceded
1404 by <quote>seen</quote>. A filter file containing only <quote>seen finish</quote> is a black hole.
1407 <section id="SECTtestprint">
1408 <title>The testprint command</title>
1410 It is sometimes helpful to be able to print out the values of variables when
1411 testing filter files. The command
1414 <literal> testprint </literal><<emphasis>text</emphasis>>
1415 <literal>e.g. testprint "home=$home reply_address=$reply_address"</literal>
1418 does nothing when mail is being delivered. However, when the filtering code is
1419 being tested by means of the <option>-bf</option> option (see section <xref linkend="SECTtesting"/>
1420 above), the value of the string is written to the standard output.
1423 <section id="SECTfail">
1424 <title>The fail command</title>
1426 When Exim’s filtering facilities are being used as a system filter, the
1427 <command>fail</command> command is available, to force delivery failure. Because this command
1428 is normally usable only by the system administrator, and not enabled for use by
1429 ordinary users, it is described in more detail in the main Exim specification
1430 rather than in this document.
1433 <section id="SECTfreeze">
1434 <title>The freeze command</title>
1436 When Exim’s filtering facilities are being used as a system filter, the
1437 <command>freeze</command> command is available, to freeze a message on the queue. Because this
1438 command is normally usable only by the system administrator, and not enabled
1439 for use by ordinary users, it is described in more detail in the main Exim
1440 specification rather than in this document.
1443 <section id="SECTheaders">
1444 <title>The headers command</title>
1446 The <command>headers</command> command can be used to change the target character set that is
1447 used when translating the contents of encoded header lines for insertion by the
1448 <varname>$header_</varname> mechanism (see section <xref linkend="SECTheadervariables"/> above). The
1449 default can be set in the Exim configuration; if not specified, ISO-8859-1 is
1450 used. The only currently supported format for the <command>headers</command> command in user
1451 filters is as in this example:
1453 <literallayout class="monospaced">
1454 headers charset "UTF-8"
1457 That is, <command>headers</command> is followed by the word <quote>charset</quote> and then the name of a
1458 character set. This particular example would be useful if you wanted to compare
1459 the contents of a header to a UTF-8 string.
1462 In system filter files, the <command>headers</command> command can be used to add or remove
1463 header lines from the message. These features are described in the main Exim
1467 <section id="SECTif">
1468 <title>Obeying commands conditionally</title>
1470 Most of the power of filtering comes from the ability to test conditions and
1471 obey different commands depending on the outcome. The <command>if</command> command is used to
1472 specify conditional execution, and its general form is
1475 <literal>if </literal><<emphasis>condition</emphasis>>
1476 <literal>then </literal><<emphasis>commands</emphasis>>
1477 <literal>elif </literal><<emphasis>condition</emphasis>>
1478 <literal>then </literal><<emphasis>commands</emphasis>>
1479 <literal>else </literal><<emphasis>commands</emphasis>>
1480 <literal>endif</literal>
1483 There may be any number of <command>elif</command> and <command>then</command> sections (including none) and
1484 the <command>else</command> section is also optional. Any number of commands, including nested
1485 <command>if</command> commands, may appear in any of the <<emphasis>commands</emphasis>> sections.
1488 Conditions can be combined by using the words <command>and</command> and <command>or</command>, and round
1489 brackets (parentheses) can be used to specify how several conditions are to
1490 combine. Without brackets, <command>and</command> is more binding than <command>or</command>. For example:
1492 <literallayout class="monospaced">
1494 $h_subject: contains "Make money" or
1495 $h_precedence: is "junk" or
1496 ($h_sender: matches ^\\d{8}@ and not personal) or
1497 $message_body contains "this is not spam"
1503 A condition can be preceded by <command>not</command> to negate it, and there are also some
1504 negative forms of condition that are more English-like.
1507 <section id="SEC23">
1508 <title>String testing conditions</title>
1510 There are a number of conditions that operate on text strings, using the words
1511 <quote>begins</quote>, <quote>ends</quote>, <quote>is</quote>, <quote>contains</quote> and <quote>matches</quote>. If you want to
1512 apply the same test to more than one header line, you can easily concatenate
1513 them into a single string for testing, as in this example:
1515 <literallayout class="monospaced">
1516 if "$h_to:, $h_cc:" contains me@domain.example then ...
1519 If a string-testing condition name is written in lower case, the testing
1520 of letters is done without regard to case; if it is written in upper case
1521 (for example, <quote>CONTAINS</quote>), the case of letters is taken into account.
1524 <literal> </literal><<emphasis>text1</emphasis>><literal> begins </literal><<emphasis>text2</emphasis>>
1525 <literal> </literal><<emphasis>text1</emphasis>><literal> does not begin </literal><<emphasis>text2</emphasis>>
1526 <literal>e.g. $header_from: begins "Friend@"</literal>
1529 A <quote>begins</quote> test checks for the presence of the second string at the start of
1530 the first, both strings having been expanded.
1533 <literal> </literal><<emphasis>text1</emphasis>><literal> ends </literal><<emphasis>text2</emphasis>>
1534 <literal> </literal><<emphasis>text1</emphasis>><literal> does not end </literal><<emphasis>text2</emphasis>>
1535 <literal>e.g. $header_from: ends "public.com.example"</literal>
1538 An <quote>ends</quote> test checks for the presence of the second string at the end of
1539 the first, both strings having been expanded.
1542 <literal> </literal><<emphasis>text1</emphasis>><literal> is </literal><<emphasis>text2</emphasis>>
1543 <literal> </literal><<emphasis>text1</emphasis>><literal> is not </literal><<emphasis>text2</emphasis>>
1544 <literal>e.g. $local_part_suffix is "-foo"</literal>
1547 An <quote>is</quote> test does an exact match between the strings, having first expanded
1551 <literal> </literal><<emphasis>text1</emphasis>><literal> contains </literal><<emphasis>text2</emphasis>>
1552 <literal> </literal><<emphasis>text1</emphasis>><literal> does not contain </literal><<emphasis>text2</emphasis>>
1553 <literal>e.g. $header_subject: contains "evolution"</literal>
1556 A <quote>contains</quote> test does a partial string match, having expanded both strings.
1559 <literal> </literal><<emphasis>text1</emphasis>><literal> matches </literal><<emphasis>text2</emphasis>>
1560 <literal> </literal><<emphasis>text1</emphasis>><literal> does not match </literal><<emphasis>text2</emphasis>>
1561 <literal>e.g. $sender_address matches "(bill|john)@"</literal>
1564 For a <quote>matches</quote> test, after expansion of both strings, the second one is
1565 interpreted as a regular expression. Exim uses the PCRE regular expression
1566 library, which provides regular expressions that are compatible with Perl.
1569 The match succeeds if the regular expression matches any part of the first
1570 string. If you want a regular expression to match only at the start or end of
1571 the subject string, you must encode that requirement explicitly, using the
1572 <literal>^</literal> or <literal>$</literal> metacharacters. The above example, which is not so constrained,
1573 matches all these addresses:
1575 <literallayout class="monospaced">
1578 spoonbill@example.com
1579 littlejohn@example.com
1582 To match only the first two, you could use this:
1584 <literallayout class="monospaced">
1585 if $sender_address matches "^(bill|john)@" then ...
1588 Care must be taken if you need a backslash in a regular expression, because
1589 backslashes are interpreted as escape characters both by the string expansion
1590 code and by Exim’s normal processing of strings in quotes. For example, if you
1591 want to test the sender address for a domain ending in <emphasis>.com</emphasis> the regular
1594 <literallayout class="monospaced">
1598 The backslash and dollar sign in that expression have to be escaped when used
1599 in a filter command, as otherwise they would be interpreted by the expansion
1600 code. Thus, what you actually write is
1602 <literallayout class="monospaced">
1603 if $sender_address matches \\.com\$
1606 An alternative way of handling this is to make use of the <literal>\N</literal> expansion
1607 flag for suppressing expansion:
1609 <literallayout class="monospaced">
1610 if $sender_address matches \N\.com$\N
1613 Everything between the two occurrences of <literal>\N</literal> is copied without change by
1614 the string expander (and in fact you do not need the final one, because it is
1615 at the end of the string). If the regular expression is given in quotes
1616 (mandatory only if it contains white space) you have to write either
1618 <literallayout class="monospaced">
1619 if $sender_address matches "\\\\.com\\$"
1624 <literallayout class="monospaced">
1625 if $sender_address matches "\\N\\.com$\\N"
1628 If the regular expression contains bracketed sub-expressions, numeric
1629 variable substitutions such as <varname>$1</varname> can be used in the subsequent actions
1630 after a successful match. If the match fails, the values of the numeric
1631 variables remain unchanged. Previous values are not restored after <command>endif</command>.
1632 In other words, only one set of values is ever available. If the condition
1633 contains several sub-conditions connected by <command>and</command> or <command>or</command>, it is the
1634 strings extracted from the last successful match that are available in
1635 subsequent actions. Numeric variables from any one sub-condition are also
1636 available for use in subsequent sub-conditions, because string expansion of a
1637 condition occurs just before it is tested.
1640 <section id="SEC24">
1641 <title>Numeric testing conditions</title>
1643 The following conditions are available for performing numerical tests:
1646 <literal> </literal><<emphasis>number1</emphasis>><literal> is above </literal><<emphasis>number2</emphasis>>
1647 <literal> </literal><<emphasis>number1</emphasis>><literal> is not above </literal><<emphasis>number2</emphasis>>
1648 <literal> </literal><<emphasis>number1</emphasis>><literal> is below </literal><<emphasis>number2</emphasis>>
1649 <literal> </literal><<emphasis>number1</emphasis>><literal> is not below </literal><<emphasis>number2</emphasis>>
1650 <literal>e.g. $message_size is not above 10k</literal>
1653 The <<emphasis>number</emphasis>> arguments must expand to strings of digits, optionally
1654 followed by one of the letters K or M (upper case or lower case) which cause
1655 multiplication by 1024 and 1024x1024 respectively.
1658 <section id="SEC25">
1659 <title>Testing for significant deliveries</title>
1661 You can use the <command>delivered</command> condition to test whether or not any previously
1662 obeyed filter commands have set up a significant delivery. For example:
1664 <literallayout class="monospaced">
1665 if not delivered then save mail/anomalous endif
1668 <quote>Delivered</quote> is perhaps a poor choice of name for this condition, because the
1669 message has not actually been delivered; rather, a delivery has been set up for
1673 <section id="SEC26">
1674 <title>Testing for error messages</title>
1676 The condition <command>error_message</command> is true if the incoming message is a bounce
1677 (mail delivery error) message. Putting the command
1679 <literallayout class="monospaced">
1680 if error_message then finish endif
1683 at the head of your filter file is a useful insurance against things going
1684 wrong in such a way that you cannot receive delivery error reports. <emphasis role="bold">Note</emphasis>:
1685 <command>error_message</command> is a condition, not an expansion variable, and therefore is
1686 not preceded by <literal>$</literal>.
1689 <section id="SEC27">
1690 <title>Testing a list of addresses</title>
1692 There is a facility for looping through a list of addresses and applying a
1693 condition to each of them. It takes the form
1696 <literal>foranyaddress </literal><<emphasis>string</emphasis>><literal> (</literal><<emphasis>condition</emphasis>><literal>)</literal>
1699 where <<emphasis>string</emphasis>> is interpreted as a list of RFC 2822 addresses, as in a
1700 typical header line, and <<emphasis>condition</emphasis>> is any valid filter condition or
1701 combination of conditions. The <quote>group</quote> syntax that is defined for certain
1702 header lines that contain addresses is supported.
1705 The parentheses surrounding the condition are mandatory, to delimit it from
1706 possible further sub-conditions of the enclosing <command>if</command> command. Within the
1707 condition, the expansion variable <varname>$thisaddress</varname> is set to the non-comment
1708 portion of each of the addresses in the string in turn. For example, if the
1711 <literallayout class="monospaced">
1712 B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1715 then <varname>$thisaddress</varname> would take on the values <literal>bart@sfld.example</literal> and
1716 <literal>lisa@sfld.example</literal> in turn.
1719 If there are no valid addresses in the list, the whole condition is false. If
1720 the internal condition is true for any one address, the overall condition is
1721 true and the loop ends. If the internal condition is false for all addresses in
1722 the list, the overall condition is false. This example tests for the presence
1723 of an eight-digit local part in any address in a <emphasis>To:</emphasis> header:
1725 <literallayout class="monospaced">
1726 if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1729 When the overall condition is true, the value of <varname>$thisaddress</varname> in the
1730 commands that follow <command>then</command> is the last value it took on inside the loop. At
1731 the end of the <command>if</command> command, the value of <varname>$thisaddress</varname> is reset to what it
1732 was before. It is best to avoid the use of multiple occurrences of
1733 <command>foranyaddress</command>, nested or otherwise, in a single <command>if</command> command, if the
1734 value of <varname>$thisaddress</varname> is to be used afterwards, because it isn’t always
1735 clear what the value will be. Nested <command>if</command> commands should be used instead.
1738 Header lines can be joined together if a check is to be applied to more than
1739 one of them. For example:
1741 <literallayout class="monospaced">
1742 if foranyaddress $h_to:,$h_cc: ....
1745 This scans through the addresses in both the <emphasis>To:</emphasis> and the <emphasis>Cc:</emphasis> headers.
1748 <section id="SECTpersonal">
1749 <title>Testing for personal mail</title>
1751 A common requirement is to distinguish between incoming personal mail and mail
1752 from a mailing list, or from a robot or other automatic process (for example, a
1753 bounce message). In particular, this test is normally required for <quote>vacation
1757 The <command>personal</command> condition checks that the message is not a bounce message and
1758 that the current user’s email address appears in the <emphasis>To:</emphasis> header. It also
1759 checks that the sender is not the current user or one of a number of common
1760 daemons, and that there are no header lines starting <emphasis>List-</emphasis> in the message.
1761 Finally, it checks the content of the <emphasis>Precedence:</emphasis> header line, if there is
1765 You should always use the <command>personal</command> condition when generating automatic
1766 responses. This example shows the use of <command>personal</command> in a filter file that is
1767 sending out vacation messages:
1769 <literallayout class="monospaced">
1771 mail to $reply_address
1772 subject "I am on holiday"
1773 file $home/vacation/message
1774 once $home/vacation/once
1779 It is tempting, when writing commands like the above, to quote the original
1780 subject in the reply. For example:
1782 <literallayout class="monospaced">
1783 subject "Re: $h_subject:"
1786 There is a danger in doing this, however. It may allow a third party to
1787 subscribe you to an opt-in mailing list, provided that the list accepts bounce
1788 messages as subscription confirmations. (Messages sent from filters are always
1789 sent as bounce messages.) Well-managed lists require a non-bounce message to
1790 confirm a subscription, so the danger is relatively small.
1793 If prefixes or suffixes are in use for local parts – something which depends
1794 on the configuration of Exim (see section <xref linkend="SECTmbox"/> below) – the tests
1795 for the current user are done with the full address (including the prefix and
1796 suffix, if any) as well as with the prefix and suffix removed. If the system is
1797 configured to rewrite local parts of mail addresses, for example, to rewrite
1798 <literal>dag46</literal> as <literal>Dirk.Gently</literal>, the rewritten form of the address is also used in
1802 <section id="SEC28">
1803 <title>Alias addresses for the personal condition</title>
1805 It is quite common for people who have mail accounts on a number of different
1806 systems to forward all their mail to one system, and in this case a check for
1807 personal mail should test all their various mail addresses. To allow for this,
1808 the <command>personal</command> condition keyword can be followed by
1811 <literal>alias </literal><<emphasis>address</emphasis>>
1814 any number of times, for example:
1816 <literallayout class="monospaced">
1817 if personal alias smith@else.where.example
1818 alias jones@other.place.example
1822 The alias addresses are treated as alternatives to the current user’s email
1823 address when testing the contents of header lines.
1826 <section id="SEC29">
1827 <title>Details of the personal condition</title>
1829 The basic <command>personal</command> test is roughly equivalent to the following:
1831 <literallayout class="monospaced">
1832 not error_message and
1833 $message_headers does not contain "\nList-Id:" and
1834 $message_headers does not contain "\nList-Help:" and
1835 $message_headers does not contain "\nList-Subscribe:" and
1836 $message_headers does not contain "\nList-Unsubscribe:" and
1837 $message_headers does not contain "\nList-Post:" and
1838 $message_headers does not contain "\nList-Owner:" and
1839 $message_headers does not contain "\nList-Archive:" and
1841 "${if def:h_auto-submitted:{present}{absent}}" is "absent" or
1842 $header_auto-submitted: is "no"
1844 $header_precedence: does not contain "bulk" and
1845 $header_precedence: does not contain "list" and
1846 $header_precedence: does not contain "junk" and
1847 foranyaddress $header_to:
1848 ( $thisaddress contains "$local_part$domain" ) and
1849 not foranyaddress $header_from:
1851 $thisaddress contains "$local_part@$domain" or
1852 $thisaddress contains "server@" or
1853 $thisaddress contains "daemon@" or
1854 $thisaddress contains "root@" or
1855 $thisaddress contains "listserv@" or
1856 $thisaddress contains "majordomo@" or
1857 $thisaddress contains "-request@" or
1858 $thisaddress matches "^owner-[^@]+@"
1862 The variable <varname>$local_part</varname> contains the local part of the mail address of
1863 the user whose filter file is being run – it is normally your login id. The
1864 <varname>$domain</varname> variable contains the mail domain. As explained above, if aliases
1865 or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1866 the current user are also done with alternative addresses.
1869 <section id="SEC30">
1870 <title>Testing delivery status</title>
1872 There are two conditions that are intended mainly for use in system filter
1873 files, but which are available in users’ filter files as well. The condition
1874 <command>first_delivery</command> is true if this is the first process that is attempting to
1875 deliver the message, and false otherwise. This indicator is not reset until the
1876 first delivery process successfully terminates; if there is a crash or a power
1877 failure (for example), the next delivery attempt is also a <quote>first delivery</quote>.
1880 In a user filter file <command>first_delivery</command> will be false if there was previously
1881 an error in the filter, or if a delivery for the user failed owing to, for
1882 example, a quota error, or if forwarding to a remote address was deferred for
1886 The condition <command>manually_thawed</command> is true if the message was <quote>frozen</quote> for
1887 some reason, and was subsequently released by the system administrator. It is
1888 unlikely to be of use in users’ filter files.
1891 <section id="SECTmbox">
1892 <title>Multiple personal mailboxes</title>
1893 <titleabbrev>SEC31</titleabbrev>
1895 The system administrator can configure Exim so that users can set up variants
1896 on their email addresses and handle them separately. Consult your system
1897 administrator or local documentation to see if this facility is enabled on your
1898 system, and if so, what the details are.
1901 The facility involves the use of a prefix or a suffix on an email address. For
1902 example, all mail addressed to <emphasis>lg303-</emphasis><<emphasis>something</emphasis>> would be the property
1903 of user <emphasis>lg303</emphasis>, who could determine how it was to be handled, depending on
1904 the value of <<emphasis>something</emphasis>>.
1907 There are two possible ways in which this can be set up. The first possibility
1908 is the use of multiple <filename>.forward</filename> files. In this case, mail to <emphasis>lg303-foo</emphasis>,
1909 for example, is handled by looking for a file called <filename>.forward-foo</filename> in
1910 <emphasis>lg303</emphasis>’s home directory. If such a file does not exist, delivery fails
1911 and the message is returned to its sender.
1914 The alternative approach is to pass all messages through a single <filename>.forward</filename>
1915 file, which must be a filter file so that it can distinguish between the
1916 different cases by referencing the variables <varname>$local_part_prefix</varname> or
1917 <varname>$local_part_suffix</varname>, as in the final example in section <xref linkend="SECTex"/> below.
1920 It is possible to configure Exim to support both schemes at once. In this case,
1921 a specific <filename>.forward-foo</filename> file is first sought; if it is not found, the basic
1922 <filename>.forward</filename> file is used.
1925 The <command>personal</command> test (see section <xref linkend="SECTpersonal"/>) includes prefixes and
1926 suffixes in its checking.
1929 <section id="SEC43">
1930 <title>Ignoring delivery errors</title>
1932 As was explained above, filtering just sets up addresses for delivery – no
1933 deliveries are actually done while a filter file is active. If any of the
1934 generated addresses subsequently suffers a delivery failure, an error message
1935 is generated in the normal way. However, if a filter command that sets up a
1936 delivery is preceded by the word <quote>noerror</quote>, errors for that delivery,
1937 and any deliveries consequent on it (that is, from alias, forwarding, or
1938 filter files it invokes) are ignored.
1941 <section id="SECTex">
1942 <title>Examples of Exim filter commands</title>
1946 <literallayout class="monospaced">
1948 deliver baggins@rivendell.middle-earth.example
1951 Vacation handling using traditional means, assuming that the <filename>.vacation.msg</filename>
1952 and other files have been set up in your home directory:
1954 <literallayout class="monospaced">
1956 unseen pipe "/usr/ucb/vacation \"$local_part\""
1959 Vacation handling inside Exim, having first created a file called
1960 <filename>.vacation.msg</filename> in your home directory:
1962 <literallayout class="monospaced">
1964 if personal then vacation endif
1967 File some messages by subject:
1969 <literallayout class="monospaced">
1971 if $header_subject: contains "empire" or
1972 $header_subject: contains "foundation"
1978 Save all non-urgent messages by weekday:
1980 <literallayout class="monospaced">
1982 if $header_subject: does not contain "urgent" and
1983 $tod_full matches "^(...),"
1989 Throw away all mail from one site, except from postmaster:
1991 <literallayout class="monospaced">
1993 if $reply_address contains "@spam.site.example" and
1994 $reply_address does not contain "postmaster@"
2000 Handle multiple personal mailboxes:
2002 <literallayout class="monospaced">
2004 if $local_part_suffix is "-foo"
2007 elif $local_part_suffix is "-bar"
git://git.exim.org / exim-website.git / blob