Ensure version numbers all updated
[exim.git] / doc / doc-docbook / filter.xfpt
CommitLineData
2f1c4d4c 1. $Cambridge: exim/doc/doc-docbook/filter.xfpt,v 1.10 2009/11/23 13:24:13 nm4 Exp $
9b371988
PH
2
3. /////////////////////////////////////////////////////////////////////////////
4. This is the primary source of the document that describes Exim's filtering
5. facilities. It is an xfpt document that is converted into DocBook XML for
6. subsequent conversion into printing and online formats. The markup used
7. herein is "standard" xfpt markup, with some extras. The markup is summarized
8. in a file called Markup.txt.
9. /////////////////////////////////////////////////////////////////////////////
10
11.include stdflags
12.include stdmacs
13.docbook
f89d2485
PH
14
15. /////////////////////////////////////////////////////////////////////////////
16. These lines are processing instructions for the Simple DocBook Processor that
17. Philip Hazel has developed as a less cumbersome way of making PostScript and
18. PDFs than using xmlto and fop. They will be ignored by all other XML
19. processors.
20. /////////////////////////////////////////////////////////////////////////////
21
22.literal xml
23<?sdop
24 foot_right_recto="&chaptertitle;"
25 foot_right_verso="&chaptertitle;"
26 table_warn_soft_overflow="no"
27 toc_chapter_blanks="yes,yes"
28 toc_title="Exim's interfaces to mail filtering"
29?>
30.literal off
31
9b371988
PH
32.book
33
34. ===========================================================================
35. Additional xfpt markup used by this document, over and above the default
36. provided in the xfpt library.
37
38. Override the &$ flag to automatically insert a $ with the variable name
39
40.flag &$ $& "<varname>$" "</varname>"
41
42. A macro for the common 2-column tables
43
44.macro table2 100pt 300pt
45.itable none 0 0 2 $1 left $2 left
46.endmacro
47. ===========================================================================
48
49
f89d2485
PH
50. /////////////////////////////////////////////////////////////////////////////
51. /////////////////////////////////////////////////////////////////////////////
52
9b371988
PH
53. This preliminary stuff creates a <bookinfo> entry in the XML. This is removed
54. when creating the PostScript/PDF output, because we do not want a full-blown
f89d2485
PH
55. title page created for those versions. When fop is being used to create
56. PS/PDF, the stylesheet fudges up a title line to replace the text "Table of
57. contents". When SDoP is being used, a processing instruction does this job.
58. For the other forms of output, the <bookinfo> element is retained and used.
9b371988
PH
59
60.literal xml
61<bookinfo>
62<title>Exim's interfaces to mail filtering</title>
63<titleabbrev>Exim filtering</titleabbrev>
2f1c4d4c 64<date>23 November 2009</date>
9b371988
PH
65<author><firstname>Philip</firstname><surname>Hazel</surname></author>
66<authorinitials>PH</authorinitials>
67<revhistory><revision>
2f1c4d4c
NM
68 <revnumber>4.71</revnumber>
69 <date>23 November 2009</date>
9b371988
PH
70 <authorinitials>PH</authorinitials>
71</revision></revhistory>
2f1c4d4c 72<copyright><year>2009</year><holder>University of Cambridge</holder></copyright>
9b371988
PH
73</bookinfo>
74.literal off
75
f89d2485
PH
76. /////////////////////////////////////////////////////////////////////////////
77. /////////////////////////////////////////////////////////////////////////////
78
9b371988 79
4aa45c31 80.chapter "Forwarding and filtering in Exim" "CHAPforandfilt"
9b371988 81This document describes the user interfaces to Exim's in-built mail filtering
f89d2485 82facilities, and is copyright &copy; University of Cambridge 2007. It
2f1c4d4c 83corresponds to Exim version 4.71.
9b371988
PH
84
85
86
4aa45c31 87.section "Introduction" "SEC00"
9b371988
PH
88Most Unix mail transfer agents (programs that deliver mail) permit individual
89users to specify automatic forwarding of their mail, usually by placing a list
90of forwarding addresses in a file called &_.forward_& in their home
91directories. Exim extends this facility by allowing the forwarding instructions
92to be a set of rules rather than just a list of addresses, in effect providing
93&"&_.forward_& with conditions"&. Operating the set of rules is called
94&'filtering'&, and the file that contains them is called a &'filter file'&.
95
96Exim supports two different kinds of filter file. An &'Exim filter'& contains
97instructions in a format that is unique to Exim. A &'Sieve filter'& contains
98instructions in the Sieve format that is defined by RFC 3028. As this is a
99standard format, Sieve filter files may already be familiar to some users.
100Sieve files should also be portable between different environments. However,
101the Exim filtering facility contains more features (such as variable
102expansion), and better integration with the host environment (such as the use
103of external processes and pipes).
104
105The choice of which kind of filter to use can be left to the end-user, provided
106that the system administrator has configured Exim appropriately for both kinds
107of filter. However, if interoperability is important, Sieve is the only
108choice.
109
110The ability to use filtering or traditional forwarding has to be enabled by the
111system administrator, and some of the individual facilities can be separately
112enabled or disabled. A local document should be provided to describe exactly
113what has been enabled. In the absence of this, consult your system
114administrator.
115
116This document describes how to use a filter file and the format of its
117contents. It is intended for use by end-users. Both Sieve filters and Exim
118filters are covered. However, for Sieve filters, only issues that relate to the
119Exim implementation are discussed, since Sieve itself is described elsewhere.
120
121The contents of traditional &_.forward_& files are not described here. They
122normally contain just a list of addresses, file names, or pipe commands,
123separated by commas or newlines, but other types of item are also available.
124The full details can be found in the chapter on the &(redirect)& router in the
125Exim specification, which also describes how the system administrator can set
126up and control the use of filtering.
127
128
129
4aa45c31 130.section "Filter operation" "SEC01"
9b371988
PH
131It is important to realize that, in Exim, no deliveries are actually made while
132a filter or traditional &_.forward_& file is being processed. Running a filter
133or processing a traditional &_.forward_& file sets up future delivery
134operations, but does not carry them out.
135
136The result of filter or &_.forward_& file processing is a list of destinations
137to which a message should be delivered. The deliveries themselves take place
138later, along with all other deliveries for the message. This means that it is
139not possible to test for successful deliveries while filtering. It also means
140that any duplicate addresses that are generated are dropped, because Exim never
141delivers the same message to the same address more than once.
142
143
144
145
146.section "Testing a new filter file" "SECTtesting"
147Filter files, especially the more complicated ones, should always be tested, as
148it is easy to make mistakes. Exim provides a facility for preliminary testing
149of a filter file before installing it. This tests the syntax of the file and
150its basic operation, and can also be used with traditional &_.forward_& files.
151
152Because a filter can do tests on the content of messages, a test message is
153required. Suppose you have a new filter file called &_myfilter_& and a test
154message in a file called &_test-message_&. Assuming that Exim is installed with
155the conventional path name &_/usr/sbin/sendmail_& (some operating systems use
156&_/usr/lib/sendmail_&), the following command can be used:
157.code
158/usr/sbin/sendmail -bf myfilter <test-message
159.endd
160The &%-bf%& option tells Exim that the following item on the command line is
161the name of a filter file that is to be tested. There is also a &%-bF%& option,
162which is similar, but which is used for testing system filter files, as opposed
163to user filter files, and which is therefore of use only to the system
164administrator.
165
166The test message is supplied on the standard input. If there are no
167message-dependent tests in the filter, an empty file (&_/dev/null_&) can be
168used. A supplied message must start with header lines or the &"From&~"& message
169separator line that is found in many multi-message folder files. Note that
170blank lines at the start terminate the header lines. A warning is given if no
171header lines are read.
172
173The result of running this command, provided no errors are detected in the
174filter file, is a list of the actions that Exim would try to take if presented
175with the message for real. For example, for an Exim filter, the output
176.code
177Deliver message to: gulliver@lilliput.fict.example
178Save message to: /home/lemuel/mail/archive
179.endd
180means that one copy of the message would be sent to
181&'gulliver@lilliput.fict.example'&, and another would be added to the file
182&_/home/lemuel/mail/archive_&, if all went well.
183
184The actions themselves are not attempted while testing a filter file in this
185way; there is no check, for example, that any forwarding addresses are valid.
186For an Exim filter, if you want to know why a particular action is being taken,
187add the &%-v%& option to the command. This causes Exim to output the results of
188any conditional tests and to indent its output according to the depth of
189nesting of &(if)& commands. Further additional output from a filter test can be
190generated by the &(testprint)& command, which is described below.
191
192When Exim is outputting a list of the actions it would take, if any text
193strings are included in the output, non-printing characters therein are
194converted to escape sequences. In particular, if any text string contains a
195newline character, this is shown as &"\n"& in the testing output.
196
197When testing a filter in this way, Exim makes up an &"envelope"& for the
198message. The recipient is by default the user running the command, and so is
199the sender, but the command can be run with the &%-f%& option to supply a
200different sender. For example,
201.code
202/usr/sbin/sendmail -bf myfilter \
203 -f islington@never.where <test-message
204.endd
205Alternatively, if the &%-f%& option is not used, but the first line of the
206supplied message is a &"From&~"& separator from a message folder file (not the
207same thing as a &'From:'& header line), the sender is taken from there. If
208&%-f%& is present, the contents of any &"From&~"& line are ignored.
209
210The &"return path"& is the same as the envelope sender, unless the message
211contains a &'Return-path:'& header, in which case it is taken from there. You
212need not worry about any of this unless you want to test out features of a
213filter file that rely on the sender address or the return path.
214
215It is possible to change the envelope recipient by specifying further options.
216The &%-bfd%& option changes the domain of the recipient address, while the
217&%-bfl%& option changes the &"local part"&, that is, the part before the @
218sign. An adviser could make use of these to test someone else's filter file.
219
220The &%-bfp%& and &%-bfs%& options specify the prefix or suffix for the local
221part. These are relevant only when support for multiple personal mailboxes is
222implemented; see the description in section &<<SECTmbox>>& below.
223
224
4aa45c31 225.section "Installing a filter file" "SEC02"
9b371988
PH
226A filter file is normally installed under the name &_.forward_& in your home
227directory &-- it is distinguished from a conventional &_.forward_& file by its
228first line (described below). However, the file name is configurable, and some
229system administrators may choose to use some different name or location for
230filter files.
231
232
4aa45c31 233.section "Testing an installed filter file" "SEC03"
9b371988
PH
234Testing a filter file before installation cannot find every potential problem;
235for example, it does not actually run commands to which messages are piped.
236Some &"live"& tests should therefore also be done once a filter is installed.
237
238If at all possible, test your filter file by sending messages from some other
239account. If you send a message to yourself from the filtered account, and
240delivery fails, the error message will be sent back to the same account, which
241may cause another delivery failure. It won't cause an infinite sequence of such
242messages, because delivery failure messages do not themselves generate further
243messages. However, it does mean that the failure won't be returned to you, and
244also that the postmaster will have to investigate the stuck message.
245
246If you have to test an Exim filter from the same account, a sensible precaution
247is to include the line
248.code
249if error_message then finish endif
250.endd
251as the first filter command, at least while testing. This causes filtering to
252be abandoned for a delivery failure message, and since no destinations are
253generated, the message goes on to be delivered to the original address. Unless
254there is a good reason for not doing so, it is recommended that the above test
255be left in all Exim filter files. (This does not apply to Sieve files.)
256
257
258
4aa45c31 259.section "Details of filtering commands" "SEC04"
9b371988
PH
260The filtering commands for Sieve and Exim filters are completely different in
261syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
262chapter we describe how it is integrated into Exim. The subsequent chapter
263covers Exim filtering commands in detail.
264
265
266
267.chapter "Sieve filter files" "CHAPsievefilter"
268The code for Sieve filtering in Exim was contributed by Michael Haardt, and
269most of the content of this chapter is taken from the notes he provided. Since
270Sieve is an extensible language, it is important to understand &"Sieve"& in
271this context as &"the specific implementation of Sieve for Exim"&.
272
273This chapter does not contain a description of Sieve, since that can be found
274in RFC 3028, which should be read in conjunction with these notes.
275
276The Exim Sieve implementation offers the core as defined by RFC 3028,
f89d2485
PH
277comparison tests, the subaddress parameter, the &*copy*&, &*envelope*&,
278&*fileinto*&, &*notify*&, and &*vacation*& extensions, but not the &*reject*&
279extension. Exim does not support message delivery notifications (MDNs), so
280adding it just to the Sieve filter (as required for &*reject*&) makes little
281sense.
9b371988
PH
282
283In order for Sieve to work properly in Exim, the system administrator needs to
284make some adjustments to the Exim configuration. These are described in the
285chapter on the &(redirect)& router in the full Exim specification.
286
287
4aa45c31 288.section "Recognition of Sieve filters" "SEC05"
9b371988
PH
289A filter file is interpreted as a Sieve filter if its first line is
290.code
291# Sieve filter
292.endd
293This is what distinguishes it from a conventional &_.forward_& file or an Exim
294filter file.
295
296
297
4aa45c31 298.section "Saving to specified folders" "SEC06"
9b371988
PH
299If the system administrator has set things up as suggested in the Exim
300specification, and you use &(keep)& or &(fileinto)& to save a mail into a
301folder, absolute files are stored where specified, relative files are stored
302relative to &$home$&, and &_inbox_& goes to the standard mailbox location.
303
304
305
4aa45c31 306.section "Strings containing header names" "SEC07"
9b371988
PH
307RFC 3028 does not specify what happens if a string denoting a header field does
308not contain a valid header name, for example, it contains a colon. This
309implementation generates an error instead of ignoring the header field in order
310to ease script debugging, which fits in with the common picture of Sieve.
311
312
313
4aa45c31 314.section "Exists test with empty list of headers" "SEC08"
9b371988
PH
315The &*exists*& test succeeds only if all the specified headers exist. RFC 3028
316does not explicitly specify what happens on an empty list of headers. This
317implementation evaluates that condition as true, interpreting the RFC in a
318strict sense.
319
320
321
4aa45c31 322.section "Header test with invalid MIME encoding in header" "SEC09"
9b371988
PH
323Some MUAs process invalid base64 encoded data, generating junk. Others ignore
324junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
325specify how to react in this case, other than stating that a client must not
326forbid to process a message for that reason. RFC 2045 specifies that invalid
327data should be ignored (apparently looking at end of line characters). It also
328specifies that invalid data may lead to rejecting messages containing them (and
329there it appears to talk about true encoding violations), which is a clear
330contradiction to ignoring them.
331
332RFC 3028 does not specify how to process incorrect MIME words. This
333implementation treats them literally, as it does if the word is correct but its
334character set cannot be converted to UTF-8.
335
336
337
4aa45c31 338.section "Address test for multiple addresses per header" "SEC10"
9b371988
PH
339A header may contain multiple addresses. RFC 3028 does not explicitly specify
340how to deal with them, but since the address test checks if anything matches
341anything else, matching one address suffices to satisfy the condition. That
342makes it impossible to test if a header contains a certain set of addresses and
343no more, but it is more logical than letting the test fail if the header
344contains an additional address besides the one the test checks for.
345
346
347
4aa45c31 348.section "Semantics of keep" "SEC11"
9b371988
PH
349The &(keep)& command is equivalent to
350.code
351fileinto "inbox";
352.endd
353It saves the message and resets the implicit keep flag. It does not set the
354implicit keep flag; there is no command to set it once it has been reset.
355
356
357
4aa45c31 358.section "Semantics of fileinto" "SEC12"
9b371988
PH
359RFC 3028 does not specify whether &(fileinto)& should try to create a mail
360folder if it does not exist. This implementation allows the sysadmin to
361configure that aspect using the &(appendfile)& transport options
362&%create_directory%&, &%create_file%&, and &%file_must_exist%&. See the
363&(appendfile)& transport in the Exim specification for details.
364
365
366
4aa45c31 367.section "Semantics of redirect" "SEC13"
9b371988
PH
368Sieve scripts are supposed to be interoperable between servers, so this
369implementation does not allow mail to be redirected to unqualified addresses,
370because the domain would depend on the system being used. On systems with
371virtual mail domains, the default domain is probably not what the user expects
372it to be.
373
374
375
4aa45c31 376.section "String arguments" "SEC14"
9b371988
PH
377There has been confusion if the string arguments to &(require)& are to be
378matched case-sensitively or not. This implementation matches them with the
379match type &(:is)& (default, see section 2.7.1 of the RFC) and the comparator
380&(i;ascii-casemap)& (default, see section 2.7.3 of the RFC). The RFC defines
381the command defaults clearly, so any different implementations violate RFC
3823028. The same is valid for comparator names, also specified as strings.
383
384
385
4aa45c31 386.section "Number units" "SEC15"
9b371988
PH
387There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
388The mistake is obvious, because RFC 3028 specifies G to denote 2^30
389(which is gibi, not tebi), and that is what this implementation uses as
390the scaling factor for the suffix G.
391
392
393
4aa45c31 394.section "RFC compliance" "SEC16"
9b371988
PH
395Exim requires the first line of a Sieve filter to be
396.code
397# Sieve filter
398.endd
399Of course the RFC does not specify that line. Do not expect examples to work
400without adding it, though.
401
402RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
403CRLF is universally used in network protocols to mark the end of the line. This
404implementation does not embed Sieve in a network protocol, but uses Sieve
405scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
406character, this implementation does, too, by default, though the system
407administrator may choose (at Exim compile time) to use CRLF instead.
408
409Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
410implementation repeats this violation to stay consistent with Exim. This is in
411preparation for UTF-8 data.
412
413Sieve scripts cannot contain NUL characters in strings, but mail headers could
414contain MIME encoded NUL characters, which could never be matched by Sieve
415scripts using exact comparisons. For that reason, this implementation extends
416the Sieve quoted string syntax with \0 to describe a NUL character, violating
417\0 being the same as 0 in RFC 3028. Even without using \0, the following tests
418are all true in this implementation. Implementations that use C-style strings
419will only evaluate the first test as true.
420.code
421Subject: =?iso-8859-1?q?abc=00def
422
423header :contains "Subject" ["abc"]
424header :contains "Subject" ["def"]
425header :matches "Subject" ["abc?def"]
426.endd
427Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
428way that NUL characters truncating strings is allowed for Sieve
429implementations, although not recommended. It is further allowed to use encoded
430NUL characters in headers, but that's not recommended either. The above example
431shows why.
432
433RFC 3028 states that if an implementation fails to convert a character set to
434UTF-8, two strings cannot be equal if one contains octets greater than 127.
435Assuming that all unknown character sets are one-byte character sets with the
436lower 128 octets being US-ASCII is not sound, so this implementation violates
437RFC 3028 and treats such MIME words literally. That way at least something
438could be matched.
439
440The folder specified by &(fileinto)& must not contain the character sequence
441&".."& to avoid security problems. RFC 3028 does not specify the syntax of
442folders apart from &(keep)& being equivalent to
443.code
444fileinto "INBOX";
445.endd
446This implementation uses &_inbox_& instead.
447
448Sieve script errors currently cause messages to be silently filed into
449&_inbox_&. RFC 3028 requires that the user is notified of that condition.
450This may be implemented in the future by adding a header line to mails that
451are filed into &_inbox_& due to an error in the filter.
452
453
454
455.chapter "Exim filter files" "CHAPeximfilter"
456This chapter contains a full description of the contents of Exim filter files.
457
458
4aa45c31 459.section "Format of Exim filter files" "SEC17"
9b371988
PH
460Apart from leading white space, the first text in an Exim filter file must be
461.code
462# Exim filter
463.endd
464This is what distinguishes it from a conventional &_.forward_& file or a Sieve
465filter file. If the file does not have this initial line (or the equivalent for
466a Sieve filter), it is treated as a conventional &_.forward_& file, both when
467delivering mail and when using the &%-bf%& testing mechanism. The white space
468in the line is optional, and any capitalization may be used. Further text on
469the same line is treated as a comment. For example, you could have
470.code
471# Exim filter <<== do not edit or remove this line!
472.endd
473The remainder of the file is a sequence of filtering commands, which consist of
474keywords and data values. For example, in the command
475.code
476deliver gulliver@lilliput.fict.example
477.endd
478the keyword is &`deliver`& and the data value is
479&`gulliver@lilliput.fict.example`&. White space or line breaks separate the
480components of a command, except in the case of conditions for the &(if)&
481command, where round brackets (parentheses) also act as separators. Complete
482commands are separated from each other by white space or line breaks; there are
483no special terminators. Thus, several commands may appear on one line, or one
484command may be spread over a number of lines.
485
486If the character # follows a separator anywhere in a command, everything from
487# up to the next newline is ignored. This provides a way of including comments
488in a filter file.
489
490
4aa45c31 491.section "Data values in filter commands" "SEC18"
9b371988
PH
492There are two ways in which a data value can be input:
493
494.ilist
495If the text contains no white space, it can be typed verbatim. However, if it
496is part of a condition, it must also be free of round brackets (parentheses),
497as these are used for grouping in conditions.
498.next
499Otherwise, text must be enclosed in double quotation marks. In this case, the
500character \ (backslash) is treated as an &"escape character"& within the
501string, causing the following character or characters to be treated specially:
502.display
503&`\n`& is replaced by a newline
504&`\r`& is replaced by a carriage return
505&`\t`& is replaced by a tab
506.endd
507.endlist
508
509Backslash followed by up to three octal digits is replaced by the character
510specified by those digits, and &`\x`& followed by up to two hexadecimal digits
511is treated similarly. Backslash followed by any other character is replaced by
512the second character, so that in particular, &`\"`& becomes &`"`& and &`\\`&
513becomes &`\`&. A data item enclosed in double quotes can be continued onto the
514next line by ending the first line with a backslash. Any leading white space at
515the start of the continuation line is ignored.
516
517In addition to the escape character processing that occurs when strings are
518enclosed in quotes, most data values are also subject to &'string expansion'&
519(as described in the next section), in which case the characters &`$`& and
520&`\`& are also significant. This means that if a single backslash is actually
521required in such a string, and the string is also quoted, &`\\\\`& has to be
522entered.
523
524The maximum permitted length of a data string, before expansion, is 1024
525characters.
526
527
528.section "String expansion" "SECTfilterstringexpansion"
529Most data values are expanded before use. Expansion consists of replacing
530substrings beginning with &`$`& with other text. The full expansion facilities
531available in Exim are extensive. If you want to know everything that Exim can
532do with strings, you should consult the chapter on string expansion in the Exim
533documentation.
534
535In filter files, by far the most common use of string expansion is the
536substitution of the contents of a variable. For example, the substring
537.code
538$reply_address
539.endd
540is replaced by the address to which replies to the message should be sent. If
541such a variable name is followed by a letter or digit or underscore, it must be
542enclosed in curly brackets (braces), for example,
543.code
544${reply_address}
545.endd
546If a &`$`& character is actually required in an expanded string, it must be
547escaped with a backslash, and because backslash is also an escape character in
548quoted input strings, it must be doubled in that case. The following two
549examples illustrate two different ways of testing for a &`$`& character in a
550message:
551.code
552if $message_body contains \$ then ...
553if $message_body contains "\\$" then ...
554.endd
555You can prevent part of a string from being expanded by enclosing it between
556two occurrences of &`\N`&. For example,
557.code
558if $message_body contains \N$$$$\N then ...
559.endd
560tests for a run of four dollar characters.
561
562
4aa45c31 563.section "Some useful general variables" "SEC19"
9b371988
PH
564A complete list of the available variables is given in the Exim documentation.
565This shortened list contains the ones that are most likely to be useful in
566personal filter files:
567
568&$body_linecount$&: The number of lines in the body of the message.
569
570&$body_zerocount$&: The number of binary zero characters in the body of the
571message.
572
573&$home$&: In conventional configurations, this variable normally contains the
574user's home directory. The system administrator can, however, change this.
575
576&$local_part$&: The part of the email address that precedes the @ sign &--
577normally the user's login name. If support for multiple personal mailboxes is
578enabled (see section &<<SECTmbox>>& below) and a prefix or suffix for the local
579part was recognized, it is removed from the string in this variable.
580
581&$local_part_prefix$&: If support for multiple personal mailboxes is enabled
582(see section &<<SECTmbox>>& below), and a local part prefix was recognized,
583this variable contains the prefix. Otherwise it contains an empty string.
584
585&$local_part_suffix$&: If support for multiple personal mailboxes is enabled
586(see section &<<SECTmbox>>& below), and a local part suffix was recognized,
587this variable contains the suffix. Otherwise it contains an empty string.
588
589&$message_body$&: The initial portion of the body of the message. By default,
590up to 500 characters are read into this variable, but the system administrator
591can configure this to some other value. Newlines in the body are converted into
592single spaces.
593
594&$message_body_end$&: The final portion of the body of the message, formatted
595and limited in the same way as &$message_body$&.
596
597&$message_body_size$&: The size of the body of the message, in bytes.
598
599&$message_exim_id$&: The message's local identification string, which is unique
600for each message handled by a single host.
601
602&$message_headers$&: The header lines of the message, concatenated into a
603single string, with newline characters between them.
604
605&$message_size$&: The size of the entire message, in bytes.
606
607&$original_local_part$&: When an address that arrived with the message is
608being processed, this contains the same value as the variable &$local_part$&.
609However, if an address generated by an alias, forward, or filter file is being
610processed, this variable contains the local part of the original address.
611
612&$reply_address$&: The contents of the &'Reply-to:'& header, if the message
613has one; otherwise the contents of the &'From:'& header. It is the address to
614which normal replies to the message should be sent.
615
616&$return_path$&: The return path &-- that is, the sender field that will be
617transmitted as part of the message's envelope if the message is sent to another
618host. This is the address to which delivery errors are sent. In many cases,
619this variable has the same value as &$sender_address$&, but if, for example,
620an incoming message to a mailing list has been expanded, &$return_path$& may
621have been changed to contain the address of the list maintainer.
622
623&$sender_address$&: The sender address that was received in the envelope of
624the message. This is not necessarily the same as the contents of the &'From:'&
625or &'Sender:'& header lines. For delivery error messages (&"bounce messages"&)
626there is no sender address, and this variable is empty.
627
628&$tod_full$&: A full version of the time and date, for example: Wed, 18 Oct
6291995 09:51:40 +0100. The timezone is always given as a numerical offset from
630GMT.
631
632&$tod_log$&: The time and date in the format used for writing Exim's log files,
633without the timezone, for example: 1995-10-12 15:32:29.
634
635&$tod_zone$&: The local timezone offset, for example: +0100.
636
637
638
639.section "Header variables" "SECTheadervariables"
640There is a special set of expansion variables containing the header lines of
641the message being processed. These variables have names beginning with
642&$header_$& followed by the name of the header line, terminated by a colon.
643For example,
644.code
645$header_from:
646$header_subject:
647.endd
648The whole item, including the terminating colon, is replaced by the contents of
649the message header line. If there is more than one header line with the same
650name, their contents are concatenated. For header lines whose data consists of
651a list of addresses (for example, &'From:'& and &'To:'&), a comma and newline
652is inserted between each set of data. For all other header lines, just a
653newline is used.
654
655Leading and trailing white space is removed from header line data, and if there
656are any MIME &"words"& that are encoded as defined by RFC 2047 (because they
657contain non-ASCII characters), they are decoded and translated, if possible, to
658a local character set. Translation is attempted only on operating systems that
659have the &[iconv()]& function. This makes the header line look the same as it
660would when displayed by an MUA. The default character set is ISO-8859-1, but
661this can be changed by means of the &(headers)& command (see below).
662
663If you want to see the actual characters that make up a header line, you can
664specify &$rheader_$& instead of &$header_$&. This inserts the &"raw"&
665header line, unmodified.
666
667There is also an intermediate form, requested by &$bheader_$&, which removes
668leading and trailing space and decodes MIME &"words"&, but does not do any
669character translation. If an attempt to decode what looks superficially like a
670MIME &"word"& fails, the raw string is returned. If decoding produces a binary
671zero character, it is replaced by a question mark.
672
673The capitalization of the name following &$header_$& is not significant.
674Because any printing character except colon may appear in the name of a
675message's header (this is a requirement of RFC 2822, the document that
676describes the format of a mail message) curly brackets must &'not'& be used in
677this case, as they will be taken as part of the header name. Two shortcuts are
678allowed in naming header variables:
679
680.ilist
681The initiating &$header_$&, &$rheader_$&, or &$bheader_$& can be
682abbreviated to &$h_$&, &$rh_$&, or &$bh_$&, respectively.
683.next
684The terminating colon can be omitted if the next character is white space. The
685white space character is retained in the expanded string. However, this is not
686recommended, because it makes it easy to forget the colon when it really is
687needed.
688.endlist
689
690If the message does not contain a header of the given name, an empty string is
691substituted. Thus it is important to spell the names of headers correctly. Do
692not use &$header_Reply_to$& when you really mean &$header_Reply-to$&.
693
694
4aa45c31 695.section "User variables" "SEC20"
9b371988
PH
696There are ten user variables with names &$n0$& &-- &$n9$& that can be
697incremented by the &(add)& command (see section &<<SECTadd>>&). These can be
698used for &"scoring"& messages in various ways. If Exim is configured to run a
699&"system filter"& on every message, the values left in these variables are
700copied into the variables &$sn0$& &-- &$sn9$& at the end of the system filter,
701thus making them available to users' filter files. How these values are used is
702entirely up to the individual installation.
703
704
4aa45c31 705.section "Current directory" "SEC21"
9b371988
PH
706The contents of your filter file should not make any assumptions about the
707current directory. It is best to use absolute paths for file names; you can
708normally make use of the &$home$& variable to refer to your home directory. The
709&(save)& command automatically inserts &$home$& at the start of non-absolute
710paths.
711
712
713
714
715.section "Significant deliveries" "SECTsigdel"
716When in the course of delivery a message is processed by a filter file, what
717happens next, that is, after the filter file has been processed, depends on
718whether or not the filter sets up any &'significant deliveries'&. If at least
719one significant delivery is set up, the filter is considered to have handled
720the entire delivery arrangements for the current address, and no further
721processing of the address takes place. If, however, no significant deliveries
722are set up, Exim continues processing the current address as if there were no
723filter file, and typically sets up a delivery of a copy of the message into a
724local mailbox. In particular, this happens in the special case of a filter file
725containing only comments.
726
727The delivery commands &(deliver)&, &(save)&, and &(pipe)& are by default
728significant. However, if such a command is preceded by the word &"unseen"&, its
729delivery is not considered to be significant. In contrast, other commands such
730as &(mail)& and &(vacation)& do not set up significant deliveries unless
731preceded by the word &"seen"&. The following example commands set up
732significant deliveries:
733.code
734deliver jack@beanstalk.example
735pipe $home/bin/mymailscript
736seen mail subject "message discarded"
737seen finish
738.endd
739The following example commands do not set up significant deliveries:
740.code
741unseen deliver jack@beanstalk.example
742unseen pipe $home/bin/mymailscript
743mail subject "message discarded"
744finish
745.endd
746
747
748
4aa45c31 749.section "Filter commands" "SEC222"
9b371988
PH
750The filter commands that are described in subsequent sections are listed
751below, with the section in which they are described in brackets:
752
753.table2
754.row &(add)& "&~&~increment a user variable (section &<<SECTadd>>&)"
755.row &(deliver)& "&~&~deliver to an email address (section &<<SECTdeliver>>&)"
756.row &(fail)& "&~&~force delivery failure (sysadmin use) (section &<<SECTfail>>&)"
757.row &(finish)& "&~&~end processing (section &<<SECTfinish>>&)"
758.row &(freeze)& "&~&~freeze message (sysadmin use) (section &<<SECTfreeze>>&)"
759.row &(headers)& "&~&~set the header character set (section &<<SECTheaders>>&)"
760.row &(if)& "&~&~test condition(s) (section &<<SECTif>>&)"
761.row &(logfile)& "&~&~define log file (section &<<SECTlog>>&)"
762.row &(logwrite)& "&~&~write to log file (section &<<SECTlog>>&)"
763.row &(mail)& "&~&~send a reply message (section &<<SECTmail>>&)"
764.row &(pipe)& "&~&~pipe to a command (section &<<SECTpipe>>&)"
765.row &(save)& "&~&~save to a file (section &<<SECTsave>>&)"
766.row &(testprint)& "&~&~print while testing (section &<<SECTtestprint>>&)"
767.row &(vacation)& "&~&~tailored form of &(mail)& (section &<<SECTmail>>&)"
768.endtable
769
770The &(headers)& command has additional parameters that can be used only in a
771system filter. The &(fail)& and &(freeze)& commands are available only when
772Exim's filtering facilities are being used as a system filter, and are
773therefore usable only by the system administrator and not by ordinary users.
774They are mentioned only briefly in this document; for more information, see the
775main Exim specification.
776
777
778
779.section "The add command" "SECTadd"
780.display
781&` add `&<&'number'&>&` to `&<&'user variable'&>
782&`e.g. add 2 to n3`&
783.endd
784
785There are 10 user variables of this type, with names &$n0$& &-- &$n9$&. Their
786values can be obtained by the normal expansion syntax (for example &$n3$&) in
787other commands. At the start of filtering, these variables all contain zero.
788Both arguments of the &(add)& command are expanded before use, making it
789possible to add variables to each other. Subtraction can be obtained by adding
790negative numbers.
791
792
793
794.section "The deliver command" "SECTdeliver"
795.display
796&` deliver`& <&'mail address'&>
797&`e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"`&
798.endd
799
800This command provides a forwarding operation. The delivery that it sets up is
801significant unless the command is preceded by &"unseen"& (see section
802&<<SECTsigdel>>&). The message is sent on to the given address, exactly as
803happens if the address had appeared in a traditional &_.forward_& file. If you
804want to deliver the message to a number of different addresses, you can use
805more than one &(deliver)& command (each one may have only one address).
806However, duplicate addresses are discarded.
807
808To deliver a copy of the message to your normal mailbox, your login name can be
809given as the address. Once an address has been processed by the filtering
810mechanism, an identical generated address will not be so processed again, so
811doing this does not cause a loop.
812
813However, if you have a mail alias, you should &'not'& refer to it here. For
814example, if the mail address &'L.Gulliver'& is aliased to &'lg303'& then all
815references in Gulliver's &_.forward_& file should be to &'lg303'&. A reference
816to the alias will not work for messages that are addressed to that alias,
817since, like &_.forward_& file processing, aliasing is performed only once on an
818address, in order to avoid looping.
819
820Following the new address, an optional second address, preceded by
821&"errors_to"& may appear. This changes the address to which delivery errors on
822the forwarded message will be sent. Instead of going to the message's original
823sender, they go to this new address. For ordinary users, the only value that is
824permitted for this address is the user whose filter file is being processed.
825For example, the user &'lg303'& whose mailbox is in the domain
826&'lilliput.example'& could have a filter file that contains
827.code
828deliver jon@elsewhere.example errors_to lg303@lilliput.example
829.endd
830Clearly, using this feature makes sense only in situations where not all
831messages are being forwarded. In particular, bounce messages must not be
832forwarded in this way, as this is likely to create a mail loop if something
833goes wrong.
834
835
836
837.section "The save command" "SECTsave"
838.display
839&` save `&<&'file name'&>
840&`e.g. save $home/mail/bookfolder`&
841.endd
842
843This command specifies that a copy of the message is to be appended to the
844given file (that is, the file is to be used as a mail folder). The delivery
845that &(save)& sets up is significant unless the command is preceded by
846&"unseen"& (see section &<<SECTsigdel>>&).
847
848More than one &(save)& command may be obeyed; each one causes a copy of the
849message to be written to its argument file, provided they are different
850(duplicate &(save)& commands are ignored).
851
852If the file name does not start with a / character, the contents of the
f89d2485
PH
853&$home$& variable are prepended, unless it is empty, or the system
854administrator has disabled this feature. In conventional configurations, this
553c0e3a
PH
855variable is normally set in a user filter to the user's home directory, but the
856system administrator may set it to some other path. In some configurations,
f89d2485 857&$home$& may be unset, or prepending may be disabled, in which case a
553c0e3a
PH
858non-absolute path name may be generated. Such configurations convert this to an
859absolute path when the delivery takes place. In a system filter, &$home$& is
860never set.
9b371988
PH
861
862The user must of course have permission to write to the file, and the writing
863of the file takes place in a process that is running as the user, under the
864user's primary group. Any secondary groups to which the user may belong are not
865normally taken into account, though the system administrator can configure Exim
866to set them up. In addition, the ability to use this command at all is
867controlled by the system administrator &-- it may be forbidden on some systems.
868
869An optional mode value may be given after the file name. The value for the mode
870is interpreted as an octal number, even if it does not begin with a zero. For
871example:
872.code
873save /some/folder 640
874.endd
875This makes it possible for users to override the system-wide mode setting for
876file deliveries, which is normally 600. If an existing file does not have the
877correct mode, it is changed.
878
879An alternative form of delivery may be enabled on your system, in which each
880message is delivered into a new file in a given directory. If this is the case,
881this functionality can be requested by giving the directory name terminated by
882a slash after the &(save)& command, for example
883.code
884save separated/messages/
885.endd
886There are several different formats for such deliveries; check with your system
887administrator or local documentation to find out which (if any) are available
888on your system. If this functionality is not enabled, the use of a path name
889ending in a slash causes an error.
890
891
892
893.section "The pipe command" "SECTpipe"
894.display
895&` pipe `&<&'command'&>
896&`e.g. pipe "$home/bin/countmail $sender_address"`&
897.endd
898
899This command specifies that the message is to be delivered to the specified
900command using a pipe. The delivery that it sets up is significant unless the
901command is preceded by &"unseen"& (see section &<<SECTsigdel>>&). Remember,
902however, that no deliveries are done while the filter is being processed. All
903deliveries happen later on. Therefore, the result of running the pipe is not
904available to the filter.
905
906When the deliveries are done, a separate process is run, and a copy of the
907message is passed on its standard input. The process runs as the user, under
908the user's primary group. Any secondary groups to which the user may belong are
909not normally taken into account, though the system administrator can configure
910Exim to set them up. More than one &(pipe)& command may appear; each one causes
911a copy of the message to be written to its argument pipe, provided they are
912different (duplicate &(pipe)& commands are ignored).
913
914When the time comes to transport the message, the command supplied to &(pipe)&
915is split up by Exim into a command name and a number of arguments. These are
916delimited by white space except for arguments enclosed in double quotes, in
917which case backslash is interpreted as an escape, or in single quotes, in which
918case no escaping is recognized. Note that as the whole command is normally
919supplied in double quotes, a second level of quoting is required for internal
920double quotes. For example:
921.code
922pipe "$home/myscript \"size is $message_size\""
923.endd
924String expansion is performed on the separate components after the line has
925been split up, and the command is then run directly by Exim; it is not run
926under a shell. Therefore, substitution cannot change the number of arguments,
927nor can quotes, backslashes or other shell metacharacters in variables cause
928confusion.
929
930Documentation for some programs that are normally run via this kind of pipe
931often suggest that the command should start with
932.code
933IFS=" "
934.endd
935This is a shell command, and should &'not'& be present in Exim filter files,
936since it does not normally run the command under a shell.
937
938However, there is an option that the administrator can set to cause a shell to
939be used. In this case, the entire command is expanded as a single string and
940passed to the shell for interpretation. It is recommended that this be avoided
941if at all possible, since it can lead to problems when inserted variables
942contain shell metacharacters.
943
944The default PATH set up for the command is determined by the system
945administrator, usually containing at least &_/bin_& and &_/usr/bin_& so that
946common commands are available without having to specify an absolute file name.
947However, it is possible for the system administrator to restrict the pipe
948facility so that the command name must not contain any / characters, and must
949be found in one of the directories in the configured PATH. It is also possible
950for the system administrator to lock out the use of the &(pipe)& command
951altogether.
952
953When the command is run, a number of environment variables are set up. The
954complete list for pipe deliveries may be found in the Exim reference manual.
955Those that may be useful for pipe deliveries from user filter files are:
956
957.display
958&`DOMAIN `& the domain of the address
959&`HOME `& your home directory
960&`LOCAL_PART `& see below
961&`LOCAL_PART_PREFIX `& see below
962&`LOCAL_PART_SUFFIX `& see below
963&`LOGNAME `& your login name
964&`MESSAGE_ID `& the unique id of the message
965&`PATH `& the command search path
966&`RECIPIENT `& the complete recipient address
967&`SENDER `& the sender of the message
968&`SHELL `& &`/bin/sh`&
969&`USER `& see below
970.endd
971
972LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
973id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
974recognize prefixes or suffixes in the local parts of addresses. For example, a
975message addressed to &'pat-suf2@domain.example'& may cause the filter for user
976&'pat'& to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
977&`-suf2`& when the pipe command runs. The system administrator has to configure
978Exim specially for this feature to be available.
979
980If you run a command that is a shell script, be very careful in your use of
981data from the incoming message in the commands in your script. RFC 2822 is very
982generous in the characters that are permitted to appear in mail addresses, and
983in particular, an address may begin with a vertical bar or a slash. For this
984reason you should always use quotes round any arguments that involve data from
985the message, like this:
986.code
987/some/command '$SENDER'
988.endd
989so that inserted shell meta-characters do not cause unwanted effects.
990
991Remember that, as was explained earlier, the pipe command is not run at the
992time the filter file is interpreted. The filter just defines what deliveries
993are required for one particular addressee of a message. The deliveries
994themselves happen later, once Exim has decided everything that needs to be done
995for the message.
996
997A consequence of this is that you cannot inspect the return code from the pipe
998command from within the filter. Nevertheless, the code returned by the command
999is important, because Exim uses it to decide whether the delivery has succeeded
1000or failed.
1001
1002The command should return a zero completion code if all has gone well. Most
1003non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1004treated as a delivery failure, causing the message to be returned to its
1005sender. However, there are some completion codes that are treated as temporary
1006errors. The message remains on Exim's spool disk, and the delivery is tried
1007again later, though it will ultimately time out if the delivery failures go on
1008too long. The completion codes to which this applies can be specified by the
1009system administrator; the default values are 73 and 75.
1010
1011The pipe command should not normally write anything to its standard output or
1012standard error file descriptors. If it does, whatever is written is normally
1013returned to the sender of the message as a delivery error, though this action
1014can be varied by the system administrator.
1015
1016
1017
1018.section "Mail commands" "SECTmail"
1019There are two commands that cause the creation of a new mail message, neither
1020of which count as a significant delivery unless the command is preceded by the
1021word &"seen"& (see section &<<SECTsigdel>>&). This is a powerful facility, but
1022it should be used with care, because of the danger of creating infinite
1023sequences of messages. The system administrator can forbid the use of these
1024commands altogether.
1025
1026To help prevent runaway message sequences, these commands have no effect when
1027the incoming message is a bounce (delivery error) message, and messages sent by
1028this means are treated as if they were reporting delivery errors. Thus, they
1029should never themselves cause a bounce message to be returned. The basic
1030mail-sending command is
1031.display
1032&`mail [to `&<&'address-list'&>&`]`&
1033&` [cc `&<&'address-list'&>&`]`&
1034&` [bcc `&<&'address-list'&>&`]`&
1035&` [from `&<&'address'&>&`]`&
1036&` [reply_to `&<&'address'&>&`]`&
1037&` [subject `&<&'text'&>&`]`&
1038&` [extra_headers `&<&'text'&>&`]`&
1039&` [text `&<&'text'&>&`]`&
1040&` [[expand] file `&<&'filename'&>&`]`&
1041&` [return message]`&
1042&` [log `&<&'log file name'&>&`]`&
1043&` [once `&<&'note file name'&>&`]`&
1044&` [once_repeat `&<&'time interval'&>&`]`&
9b371988
PH
1045&`e.g. mail text "Your message about $h_subject: has been received"`&
1046.endd
1047Each <&'address-list'&> can contain a number of addresses, separated by commas,
1048in the format of a &'To:'& or &'Cc:'& header line. In fact, the text you supply
1049here is copied exactly into the appropriate header line. It may contain
1050additional information as well as email addresses. For example:
1051.code
1052mail to "Julius Caesar <jc@rome.example>, \
1053 <ma@rome.example> (Mark A.)"
1054.endd
1055Similarly, the texts supplied for &%from%& and &%reply_to%& are copied into
1056their respective header lines.
1057
1058As a convenience for use in one common case, there is also a command called
1059&(vacation)&. It behaves in the same way as &(mail)&, except that the defaults
1060for the &%subject%&, &%file%&, &%log%&, &%once%&, and &%once_repeat%& options
1061are
1062.code
1063subject "On vacation"
1064expand file .vacation.msg
1065log .vacation.log
1066once .vacation
1067once_repeat 7d
1068.endd
1069respectively. These are the same file names and repeat period used by the
1070traditional Unix &(vacation)& command. The defaults can be overridden by
1071explicit settings, but if a file name is given its contents are expanded only
1072if explicitly requested.
1073
1074&*Warning*&: The &(vacation)& command should always be used conditionally,
1075subject to at least the &(personal)& condition (see section &<<SECTpersonal>>&
1076below) so as not to send automatic replies to non-personal messages from
1077mailing lists or elsewhere. Sending an automatic response to a mailing list or
1078a mailing list manager is an Internet Sin.
1079
1080For both commands, the key/value argument pairs can appear in any order. At
1081least one of &%text%& or &%file%& must appear (except with &(vacation)&, where
1082there is a default for &%file%&); if both are present, the text string appears
1083first in the message. If &%expand%& precedes &%file%&, each line of the file is
1084subject to string expansion before it is included in the message.
1085
1086Several lines of text can be supplied to &%text%& by including the escape
1087sequence &"\n"& in the string wherever a newline is required. If the command is
1088output during filter file testing, newlines in the text are shown as &"\n"&.
1089
1090Note that the keyword for creating a &'Reply-To:'& header is &%reply_to%&,
1091because Exim keywords may contain underscores, but not hyphens. If the &%from%&
1092keyword is present and the given address does not match the user who owns the
1093forward file, Exim normally adds a &'Sender:'& header to the message, though it
1094can be configured not to do this.
1095
1096The &%extra_headers%& keyword allows you to add custom header lines to the
1097message. The text supplied must be one or more syntactically valid RFC 2822
1098header lines. You can use &"\n"& within quoted text to specify newlines between
1099headers, and also to define continued header lines. For example:
1100.code
1101extra_headers "h1: first\nh2: second\n continued\nh3: third"
1102.endd
1103No newline should appear at the end of the final header line.
1104
1105If no &%to%& argument appears, the message is sent to the address in the
1106&$reply_address$& variable (see section &<<SECTfilterstringexpansion>>& above).
1107An &'In-Reply-To:'& header is automatically included in the created message,
1108giving a reference to the message identification of the incoming message.
1109
1110If &%return message%& is specified, the incoming message that caused the filter
1111file to be run is added to the end of the message, subject to a maximum size
1112limitation.
1113
1114If a log file is specified, a line is added to it for each message sent.
1115
1116If a &%once%& file is specified, it is used to hold a database for remembering
1117who has received a message, and no more than one message is ever sent to any
1118particular address, unless &%once_repeat%& is set. This specifies a time
1119interval after which another copy of the message is sent. The interval is
1120specified as a sequence of numbers, each followed by the initial letter of one
1121of &"seconds"&, &"minutes"&, &"hours"&, &"days"&, or &"weeks"&. For example,
1122.code
1123once_repeat 5d4h
1124.endd
1125causes a new message to be sent if at least 5 days and 4 hours have elapsed
1126since the last one was sent. There must be no white space in a time interval.
1127
1128Commonly, the file name specified for &%once%& is used as the base name for
1129direct-access (DBM) file operations. There are a number of different DBM
1130libraries in existence. Some operating systems provide one as a default, but
1131even in this case a different one may have been used when building Exim. With
1132some DBM libraries, specifying &%once%& results in two files being created,
1133with the suffixes &_.dir_& and &_.pag_& being added to the given name. With
1134some others a single file with the suffix &_.db_& is used, or the name is used
1135unchanged.
1136
1137Using a DBM file for implementing the &%once%& feature means that the file
1138grows as large as necessary. This is not usually a problem, but some system
1139administrators want to put a limit on it. The facility can be configured not to
1140use a DBM file, but instead, to use a regular file with a maximum size. The
1141data in such a file is searched sequentially, and if the file fills up, the
1142oldest entry is deleted to make way for a new one. This means that some
1143correspondents may receive a second copy of the message after an unpredictable
1144interval. Consult your local information to see if your system is configured
1145this way.
1146
1147More than one &(mail)& or &(vacation)& command may be obeyed in a single filter
1148run; they are all honoured, even when they are to the same recipient.
1149
1150
1151
1152.section "Logging commands" "SECTlog"
1153A log can be kept of actions taken by a filter file. This facility is normally
1154available in conventional configurations, but there are some situations where
1155it might not be. Also, the system administrator may choose to disable it. Check
1156your local information if in doubt.
1157
1158Logging takes place while the filter file is being interpreted. It does not
1159queue up for later like the delivery commands. The reason for this is so that a
1160log file need be opened only once for several write operations. There are two
1161commands, neither of which constitutes a significant delivery. The first
1162defines a file to which logging output is subsequently written:
1163.display
1164&` logfile `&<&'file name'&>
1165&`e.g. logfile $home/filter.log`&
1166.endd
1167The file name must be fully qualified. You can use &$home$&, as in this
1168example, to refer to your home directory. The file name may optionally be
1169followed by a mode for the file, which is used if the file has to be created.
1170For example,
1171.code
1172logfile $home/filter.log 0644
1173.endd
1174The number is interpreted as octal, even if it does not begin with a zero.
1175The default for the mode is 600. It is suggested that the &(logfile)& command
1176normally appear as the first command in a filter file. Once a log file has
1177been obeyed, the &(logwrite)& command can be used to write to it:
1178.display
1179&` logwrite "`&<&'some text string'&>&`"`&
1180&`e.g. logwrite "$tod_log $message_id processed"`&
1181.endd
1182It is possible to have more than one &(logfile)& command, to specify writing to
1183different log files in different circumstances. Writing takes place at the end
1184of the file, and a newline character is added to the end of each string if
1185there isn't one already there. Newlines can be put in the middle of the string
1186by using the &"\n"& escape sequence. Lines from simultaneous deliveries may get
1187interleaved in the file, as there is no interlocking, so you should plan your
1188logging with this in mind. However, data should not get lost.
1189
1190
1191
1192.section "The finish command" "SECTfinish"
1193The command &(finish)&, which has no arguments, causes Exim to stop
1194interpreting the filter file. This is not a significant action unless preceded
1195by &"seen"&. A filter file containing only &"seen finish"& is a black hole.
1196
1197
1198.section "The testprint command" "SECTtestprint"
1199It is sometimes helpful to be able to print out the values of variables when
1200testing filter files. The command
1201.display
1202&` testprint `&<&'text'&>
1203&`e.g. testprint "home=$home reply_address=$reply_address"`&
1204.endd
1205does nothing when mail is being delivered. However, when the filtering code is
1206being tested by means of the &%-bf%& option (see section &<<SECTtesting>>&
1207above), the value of the string is written to the standard output.
1208
1209
1210.section "The fail command" "SECTfail"
1211When Exim's filtering facilities are being used as a system filter, the
1212&(fail)& command is available, to force delivery failure. Because this command
1213is normally usable only by the system administrator, and not enabled for use by
1214ordinary users, it is described in more detail in the main Exim specification
1215rather than in this document.
1216
1217
1218.section "The freeze command" "SECTfreeze"
1219When Exim's filtering facilities are being used as a system filter, the
1220&(freeze)& command is available, to freeze a message on the queue. Because this
1221command is normally usable only by the system administrator, and not enabled
1222for use by ordinary users, it is described in more detail in the main Exim
1223specification rather than in this document.
1224
1225
1226
1227.section "The headers command" "SECTheaders"
1228The &(headers)& command can be used to change the target character set that is
1229used when translating the contents of encoded header lines for insertion by the
1230&$header_$& mechanism (see section &<<SECTheadervariables>>& above). The
1231default can be set in the Exim configuration; if not specified, ISO-8859-1 is
1232used. The only currently supported format for the &(headers)& command in user
1233filters is as in this example:
1234.code
1235headers charset "UTF-8"
1236.endd
1237That is, &(headers)& is followed by the word &"charset"& and then the name of a
1238character set. This particular example would be useful if you wanted to compare
1239the contents of a header to a UTF-8 string.
1240
1241In system filter files, the &(headers)& command can be used to add or remove
1242header lines from the message. These features are described in the main Exim
1243specification.
1244
1245
1246
1247.section "Obeying commands conditionally" "SECTif"
1248Most of the power of filtering comes from the ability to test conditions and
1249obey different commands depending on the outcome. The &(if)& command is used to
1250specify conditional execution, and its general form is
1251.display
1252&`if `&<&'condition'&>
1253&`then `&<&'commands'&>
1254&`elif `&<&'condition'&>
1255&`then `&<&'commands'&>
1256&`else `&<&'commands'&>
1257&`endif`&
1258.endd
1259There may be any number of &(elif)& and &(then)& sections (including none) and
1260the &(else)& section is also optional. Any number of commands, including nested
1261&(if)& commands, may appear in any of the <&'commands'&> sections.
1262
1263Conditions can be combined by using the words &(and)& and &(or)&, and round
1264brackets (parentheses) can be used to specify how several conditions are to
1265combine. Without brackets, &(and)& is more binding than &(or)&. For example:
1266.code
1267if
1268$h_subject: contains "Make money" or
1269$h_precedence: is "junk" or
1270($h_sender: matches ^\\d{8}@ and not personal) or
1271$message_body contains "this is not spam"
1272then
1273seen finish
1274endif
1275.endd
1276A condition can be preceded by &(not)& to negate it, and there are also some
1277negative forms of condition that are more English-like.
1278
1279
1280
4aa45c31 1281.section "String testing conditions" "SEC23"
9b371988
PH
1282There are a number of conditions that operate on text strings, using the words
1283&"begins"&, &"ends"&, &"is"&, &"contains"& and &"matches"&. If you want to
1284apply the same test to more than one header line, you can easily concatenate
1285them into a single string for testing, as in this example:
1286.code
1287if "$h_to:, $h_cc:" contains me@domain.example then ...
1288.endd
1289If a string-testing condition name is written in lower case, the testing
1290of letters is done without regard to case; if it is written in upper case
1291(for example, &"CONTAINS"&), the case of letters is taken into account.
1292
1293.display
1294&` `&<&'text1'&>&` begins `&<&'text2'&>
1295&` `&<&'text1'&>&` does not begin `&<&'text2'&>
1296&`e.g. $header_from: begins "Friend@"`&
1297.endd
1298
1299A &"begins"& test checks for the presence of the second string at the start of
1300the first, both strings having been expanded.
1301
1302.display
1303&` `&<&'text1'&>&` ends `&<&'text2'&>
1304&` `&<&'text1'&>&` does not end `&<&'text2'&>
1305&`e.g. $header_from: ends "public.com.example"`&
1306.endd
1307
1308An &"ends"& test checks for the presence of the second string at the end of
1309the first, both strings having been expanded.
1310
1311.display
1312&` `&<&'text1'&>&` is `&<&'text2'&>
1313&` `&<&'text1'&>&` is not `&<&'text2'&>
1314&`e.g. $local_part_suffix is "-foo"`&
1315.endd
1316
1317An &"is"& test does an exact match between the strings, having first expanded
1318both strings.
1319
1320.display
1321&` `&<&'text1'&>&` contains `&<&'text2'&>
1322&` `&<&'text1'&>&` does not contain `&<&'text2'&>
1323&`e.g. $header_subject: contains "evolution"`&
1324.endd
1325
1326A &"contains"& test does a partial string match, having expanded both strings.
1327
1328.display
1329&` `&<&'text1'&>&` matches `&<&'text2'&>
1330&` `&<&'text1'&>&` does not match `&<&'text2'&>
1331&`e.g. $sender_address matches "(bill|john)@"`&
1332.endd
1333
1334For a &"matches"& test, after expansion of both strings, the second one is
1335interpreted as a regular expression. Exim uses the PCRE regular expression
1336library, which provides regular expressions that are compatible with Perl.
1337
1338The match succeeds if the regular expression matches any part of the first
1339string. If you want a regular expression to match only at the start or end of
1340the subject string, you must encode that requirement explicitly, using the
1341&`^`& or &`$`& metacharacters. The above example, which is not so constrained,
1342matches all these addresses:
1343.code
1344bill@test.example
1345john@some.example
1346spoonbill@example.com
1347littlejohn@example.com
1348.endd
1349To match only the first two, you could use this:
1350.code
1351if $sender_address matches "^(bill|john)@" then ...
1352.endd
1353Care must be taken if you need a backslash in a regular expression, because
1354backslashes are interpreted as escape characters both by the string expansion
1355code and by Exim's normal processing of strings in quotes. For example, if you
1356want to test the sender address for a domain ending in &'.com'& the regular
1357expression is
1358.code
1359\.com$
1360.endd
1361The backslash and dollar sign in that expression have to be escaped when used
1362in a filter command, as otherwise they would be interpreted by the expansion
1363code. Thus, what you actually write is
1364.code
1365if $sender_address matches \\.com\$
1366.endd
1367An alternative way of handling this is to make use of the &`\N`& expansion
1368flag for suppressing expansion:
1369.code
1370if $sender_address matches \N\.com$\N
1371.endd
1372Everything between the two occurrences of &`\N`& is copied without change by
1373the string expander (and in fact you do not need the final one, because it is
1374at the end of the string). If the regular expression is given in quotes
1375(mandatory only if it contains white space) you have to write either
1376.code
1377if $sender_address matches "\\\\.com\\$"
1378.endd
1379or
1380.code
1381if $sender_address matches "\\N\\.com$\\N"
1382.endd
1383
1384If the regular expression contains bracketed sub-expressions, numeric
1385variable substitutions such as &$1$& can be used in the subsequent actions
1386after a successful match. If the match fails, the values of the numeric
1387variables remain unchanged. Previous values are not restored after &(endif)&.
1388In other words, only one set of values is ever available. If the condition
1389contains several sub-conditions connected by &(and)& or &(or)&, it is the
1390strings extracted from the last successful match that are available in
1391subsequent actions. Numeric variables from any one sub-condition are also
1392available for use in subsequent sub-conditions, because string expansion of a
1393condition occurs just before it is tested.
1394
1395
4aa45c31 1396.section "Numeric testing conditions" "SEC24"
9b371988
PH
1397The following conditions are available for performing numerical tests:
1398
1399.display
1400&` `&<&'number1'&>&` is above `&<&'number2'&>
1401&` `&<&'number1'&>&` is not above `&<&'number2'&>
1402&` `&<&'number1'&>&` is below `&<&'number2'&>
1403&` `&<&'number1'&>&` is not below `&<&'number2'&>
1404&`e.g. $message_size is not above 10k`&
1405.endd
1406
1407The <&'number'&> arguments must expand to strings of digits, optionally
1408followed by one of the letters K or M (upper case or lower case) which cause
1409multiplication by 1024 and 1024x1024 respectively.
1410
1411
4aa45c31 1412.section "Testing for significant deliveries" "SEC25"
9b371988
PH
1413You can use the &(delivered)& condition to test whether or not any previously
1414obeyed filter commands have set up a significant delivery. For example:
1415.code
1416if not delivered then save mail/anomalous endif
1417.endd
1418&"Delivered"& is perhaps a poor choice of name for this condition, because the
1419message has not actually been delivered; rather, a delivery has been set up for
1420later processing.
1421
1422
4aa45c31 1423.section "Testing for error messages" "SEC26"
9b371988
PH
1424The condition &(error_message)& is true if the incoming message is a bounce
1425(mail delivery error) message. Putting the command
1426.code
1427if error_message then finish endif
1428.endd
1429at the head of your filter file is a useful insurance against things going
1430wrong in such a way that you cannot receive delivery error reports. &*Note*&:
1431&(error_message)& is a condition, not an expansion variable, and therefore is
1432not preceded by &`$`&.
1433
1434
4aa45c31 1435.section "Testing a list of addresses" "SEC27"
9b371988
PH
1436There is a facility for looping through a list of addresses and applying a
1437condition to each of them. It takes the form
1438.display
1439&`foranyaddress `&<&'string'&>&` (`&<&'condition'&>&`)`&
1440.endd
1441where <&'string'&> is interpreted as a list of RFC 2822 addresses, as in a
1442typical header line, and <&'condition'&> is any valid filter condition or
1443combination of conditions. The &"group"& syntax that is defined for certain
1444header lines that contain addresses is supported.
1445
1446The parentheses surrounding the condition are mandatory, to delimit it from
1447possible further sub-conditions of the enclosing &(if)& command. Within the
1448condition, the expansion variable &$thisaddress$& is set to the non-comment
1449portion of each of the addresses in the string in turn. For example, if the
1450string is
1451.code
1452B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1453.endd
1454then &$thisaddress$& would take on the values &`bart@sfld.example`& and
1455&`lisa@sfld.example`& in turn.
1456
1457If there are no valid addresses in the list, the whole condition is false. If
1458the internal condition is true for any one address, the overall condition is
1459true and the loop ends. If the internal condition is false for all addresses in
1460the list, the overall condition is false. This example tests for the presence
1461of an eight-digit local part in any address in a &'To:'& header:
1462.code
1463if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1464.endd
1465When the overall condition is true, the value of &$thisaddress$& in the
1466commands that follow &(then)& is the last value it took on inside the loop. At
1467the end of the &(if)& command, the value of &$thisaddress$& is reset to what it
1468was before. It is best to avoid the use of multiple occurrences of
1469&(foranyaddress)&, nested or otherwise, in a single &(if)& command, if the
1470value of &$thisaddress$& is to be used afterwards, because it isn't always
1471clear what the value will be. Nested &(if)& commands should be used instead.
1472
1473Header lines can be joined together if a check is to be applied to more than
1474one of them. For example:
1475.code
1476if foranyaddress $h_to:,$h_cc: ....
1477.endd
1478This scans through the addresses in both the &'To:'& and the &'Cc:'& headers.
1479
1480
1481.section "Testing for personal mail" "SECTpersonal"
1482A common requirement is to distinguish between incoming personal mail and mail
1483from a mailing list, or from a robot or other automatic process (for example, a
1484bounce message). In particular, this test is normally required for &"vacation
1485messages"&.
1486
1487The &(personal)& condition checks that the message is not a bounce message and
1488that the current user's email address appears in the &'To:'& header. It also
1489checks that the sender is not the current user or one of a number of common
1490daemons, and that there are no header lines starting &'List-'& in the message.
1491Finally, it checks the content of the &'Precedence:'& header line, if there is
1492one.
1493
1494You should always use the &(personal)& condition when generating automatic
1495responses. This example shows the use of &(personal)& in a filter file that is
1496sending out vacation messages:
1497.code
1498if personal then
1499mail to $reply_address
1500subject "I am on holiday"
1501file $home/vacation/message
1502once $home/vacation/once
1503once_repeat 10d
1504endif
1505.endd
1506It is tempting, when writing commands like the above, to quote the original
1507subject in the reply. For example:
1508.code
1509subject "Re: $h_subject:"
1510.endd
1511There is a danger in doing this, however. It may allow a third party to
1512subscribe you to an opt-in mailing list, provided that the list accepts bounce
1513messages as subscription confirmations. (Messages sent from filters are always
1514sent as bounce messages.) Well-managed lists require a non-bounce message to
1515confirm a subscription, so the danger is relatively small.
1516
1517If prefixes or suffixes are in use for local parts &-- something which depends
1518on the configuration of Exim (see section &<<SECTmbox>>& below) &-- the tests
1519for the current user are done with the full address (including the prefix and
1520suffix, if any) as well as with the prefix and suffix removed. If the system is
1521configured to rewrite local parts of mail addresses, for example, to rewrite
1522&`dag46`& as &`Dirk.Gently`&, the rewritten form of the address is also used in
1523the tests.
1524
1525
1526
4aa45c31 1527.section "Alias addresses for the personal condition" "SEC28"
9b371988
PH
1528It is quite common for people who have mail accounts on a number of different
1529systems to forward all their mail to one system, and in this case a check for
1530personal mail should test all their various mail addresses. To allow for this,
1531the &(personal)& condition keyword can be followed by
1532.display
1533&`alias `&<&'address'&>
1534.endd
1535any number of times, for example:
1536.code
1537if personal alias smith@else.where.example
1538 alias jones@other.place.example
1539then ...
1540.endd
1541The alias addresses are treated as alternatives to the current user's email
1542address when testing the contents of header lines.
1543
1544
4aa45c31 1545.section "Details of the personal condition" "SEC29"
9b371988
PH
1546The basic &(personal)& test is roughly equivalent to the following:
1547.code
1548not error_message and
1549$message_headers does not contain "\nList-Id:" and
1550$message_headers does not contain "\nList-Help:" and
1551$message_headers does not contain "\nList-Subscribe:" and
1552$message_headers does not contain "\nList-Unsubscribe:" and
1553$message_headers does not contain "\nList-Post:" and
1554$message_headers does not contain "\nList-Owner:" and
1555$message_headers does not contain "\nList-Archive:" and
1556(
8f3414a1 1557"${if def:h_auto-submitted:{present}{absent}}" is "absent" or
9b371988
PH
1558$header_auto-submitted: is "no"
1559) and
1560$header_precedence: does not contain "bulk" and
1561$header_precedence: does not contain "list" and
1562$header_precedence: does not contain "junk" and
1563foranyaddress $header_to:
1564( $thisaddress contains "$local_part$domain" ) and
1565not foranyaddress $header_from:
1566(
c0712871
PH
1567$thisaddress contains "$local_part@$domain" or
1568$thisaddress contains "server@" or
1569$thisaddress contains "daemon@" or
1570$thisaddress contains "root@" or
1571$thisaddress contains "listserv@" or
1572$thisaddress contains "majordomo@" or
1573$thisaddress contains "-request@" or
1574$thisaddress matches "^owner-[^@]+@"
9b371988
PH
1575)
1576.endd
1577The variable &$local_part$& contains the local part of the mail address of
1578the user whose filter file is being run &-- it is normally your login id. The
1579&$domain$& variable contains the mail domain. As explained above, if aliases
1580or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1581the current user are also done with alternative addresses.
1582
1583
1584
1585
4aa45c31 1586.section "Testing delivery status" "SEC30"
9b371988
PH
1587There are two conditions that are intended mainly for use in system filter
1588files, but which are available in users' filter files as well. The condition
1589&(first_delivery)& is true if this is the first process that is attempting to
1590deliver the message, and false otherwise. This indicator is not reset until the
1591first delivery process successfully terminates; if there is a crash or a power
1592failure (for example), the next delivery attempt is also a &"first delivery"&.
1593
1594In a user filter file &(first_delivery)& will be false if there was previously
1595an error in the filter, or if a delivery for the user failed owing to, for
1596example, a quota error, or if forwarding to a remote address was deferred for
1597some reason.
1598
1599The condition &(manually_thawed)& is true if the message was &"frozen"& for
1600some reason, and was subsequently released by the system administrator. It is
1601unlikely to be of use in users' filter files.
1602
1603
4aa45c31 1604.section "Multiple personal mailboxes" "SECTmbox" "SEC31"
9b371988
PH
1605The system administrator can configure Exim so that users can set up variants
1606on their email addresses and handle them separately. Consult your system
1607administrator or local documentation to see if this facility is enabled on your
1608system, and if so, what the details are.
1609
1610The facility involves the use of a prefix or a suffix on an email address. For
1611example, all mail addressed to &'lg303-'&<&'something'&> would be the property
1612of user &'lg303'&, who could determine how it was to be handled, depending on
1613the value of <&'something'&>.
1614
1615There are two possible ways in which this can be set up. The first possibility
1616is the use of multiple &_.forward_& files. In this case, mail to &'lg303-foo'&,
1617for example, is handled by looking for a file called &_.forward-foo_& in
1618&'lg303'&'s home directory. If such a file does not exist, delivery fails
1619and the message is returned to its sender.
1620
1621The alternative approach is to pass all messages through a single &_.forward_&
1622file, which must be a filter file so that it can distinguish between the
1623different cases by referencing the variables &$local_part_prefix$& or
1624&$local_part_suffix$&, as in the final example in section &<<SECTex>>& below.
1625
1626It is possible to configure Exim to support both schemes at once. In this case,
1627a specific &_.forward-foo_& file is first sought; if it is not found, the basic
1628&_.forward_& file is used.
1629
1630The &(personal)& test (see section &<<SECTpersonal>>&) includes prefixes and
1631suffixes in its checking.
1632
1633
1634
4aa45c31 1635.section "Ignoring delivery errors" "SEC43"
9b371988
PH
1636As was explained above, filtering just sets up addresses for delivery &-- no
1637deliveries are actually done while a filter file is active. If any of the
1638generated addresses subsequently suffers a delivery failure, an error message
1639is generated in the normal way. However, if a filter command that sets up a
1640delivery is preceded by the word &"noerror"&, errors for that delivery,
1641and any deliveries consequent on it (that is, from alias, forwarding, or
1642filter files it invokes) are ignored.
1643
1644
1645
1646.section "Examples of Exim filter commands" "SECTex"
1647Simple forwarding:
1648
1649.code
1650# Exim filter
1651deliver baggins@rivendell.middle-earth.example
1652.endd
1653
1654Vacation handling using traditional means, assuming that the &_.vacation.msg_&
1655and other files have been set up in your home directory:
1656
1657.code
1658# Exim filter
1659unseen pipe "/usr/ucb/vacation \"$local_part\""
1660.endd
1661
1662Vacation handling inside Exim, having first created a file called
1663&_.vacation.msg_& in your home directory:
1664
1665.code
1666# Exim filter
1667if personal then vacation endif
1668.endd
1669
1670File some messages by subject:
1671
1672.code
1673# Exim filter
1674if $header_subject: contains "empire" or
1675$header_subject: contains "foundation"
1676then
1677save $home/mail/f+e
1678endif
1679.endd
1680
1681Save all non-urgent messages by weekday:
1682
1683.code
1684# Exim filter
1685if $header_subject: does not contain "urgent" and
1686$tod_full matches "^(...),"
1687then
1688save $home/mail/$1
1689endif
1690.endd
1691
1692Throw away all mail from one site, except from postmaster:
1693
1694.code
1695# Exim filter
1696if $reply_address contains "@spam.site.example" and
1697$reply_address does not contain "postmaster@"
1698then
1699seen finish
1700endif
1701.endd
1702
1703Handle multiple personal mailboxes:
1704
1705.code
1706# Exim filter
1707if $local_part_suffix is "-foo"
1708then
1709save $home/mail/foo
1710elif $local_part_suffix is "-bar"
1711then
1712save $home/mail/bar
1713endif
1714.endd
1715