Merge branch 'debian' into hcoop_489
[hcoop/debian/exim4.git] / doc / filter.txt
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1Exim's interfaces to mail filtering
2
3Philip Hazel
4
5Copyright (c) 2014 University of Cambridge
6
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7Revision 4.89 07 Mar 2017 PH
8
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9-------------------------------------------------------------------------------
10
11TABLE OF CONTENTS
12
131. Forwarding and filtering in Exim
14
15 1.1. Introduction
16 1.2. Filter operation
17 1.3. Testing a new filter file
18 1.4. Installing a filter file
19 1.5. Testing an installed filter file
20 1.6. Details of filtering commands
21
222. Sieve filter files
23
24 2.1. Recognition of Sieve filters
25 2.2. Saving to specified folders
26 2.3. Strings containing header names
27 2.4. Exists test with empty list of headers
28 2.5. Header test with invalid MIME encoding in header
29 2.6. Address test for multiple addresses per header
30 2.7. Semantics of keep
31 2.8. Semantics of fileinto
32 2.9. Semantics of redirect
33 2.10. String arguments
34 2.11. Number units
35 2.12. RFC compliance
36
373. Exim filter files
38
39 3.1. Format of Exim filter files
40 3.2. Data values in filter commands
41 3.3. String expansion
42 3.4. Some useful general variables
43 3.5. Header variables
44 3.6. User variables
45 3.7. Current directory
46 3.8. Significant deliveries
47 3.9. Filter commands
48 3.10. The add command
49 3.11. The deliver command
50 3.12. The save command
51 3.13. The pipe command
52 3.14. Mail commands
53 3.15. Logging commands
54 3.16. The finish command
55 3.17. The testprint command
56 3.18. The fail command
57 3.19. The freeze command
58 3.20. The headers command
59 3.21. Obeying commands conditionally
60 3.22. String testing conditions
61 3.23. Numeric testing conditions
62 3.24. Testing for significant deliveries
63 3.25. Testing for error messages
64 3.26. Testing a list of addresses
65 3.27. Testing for personal mail
66 3.28. Alias addresses for the personal condition
67 3.29. Details of the personal condition
68 3.30. Testing delivery status
69 3.31. Multiple personal mailboxes
70 3.32. Ignoring delivery errors
71 3.33. Examples of Exim filter commands
72
73
74
75===============================================================================
761. FORWARDING AND FILTERING IN EXIM
77
78This document describes the user interfaces to Exim's in-built mail filtering
79facilities, and is copyright (c) University of Cambridge 2014. It corresponds
2813c06e 80to Exim version 4.89.
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81
82
831.1 Introduction
84----------------
85
86Most Unix mail transfer agents (programs that deliver mail) permit individual
87users to specify automatic forwarding of their mail, usually by placing a list
88of forwarding addresses in a file called .forward in their home directories.
89Exim extends this facility by allowing the forwarding instructions to be a set
90of rules rather than just a list of addresses, in effect providing ".forward
91with conditions". Operating the set of rules is called filtering, and the file
92that contains them is called a filter file.
93
94Exim supports two different kinds of filter file. An Exim filter contains
95instructions in a format that is unique to Exim. A Sieve filter contains
96instructions in the Sieve format that is defined by RFC 3028. As this is a
97standard format, Sieve filter files may already be familiar to some users.
98Sieve files should also be portable between different environments. However,
99the Exim filtering facility contains more features (such as variable
100expansion), and better integration with the host environment (such as the use
101of external processes and pipes).
102
103The choice of which kind of filter to use can be left to the end-user, provided
104that the system administrator has configured Exim appropriately for both kinds
105of filter. However, if interoperability is important, Sieve is the only choice.
106
107The ability to use filtering or traditional forwarding has to be enabled by the
108system administrator, and some of the individual facilities can be separately
109enabled or disabled. A local document should be provided to describe exactly
110what has been enabled. In the absence of this, consult your system
111administrator.
112
113This document describes how to use a filter file and the format of its
114contents. It is intended for use by end-users. Both Sieve filters and Exim
115filters are covered. However, for Sieve filters, only issues that relate to the
116Exim implementation are discussed, since Sieve itself is described elsewhere.
117
118The contents of traditional .forward files are not described here. They
119normally contain just a list of addresses, file names, or pipe commands,
120separated by commas or newlines, but other types of item are also available.
121The full details can be found in the chapter on the redirect router in the Exim
122specification, which also describes how the system administrator can set up and
123control the use of filtering.
124
125
1261.2 Filter operation
127--------------------
128
129It is important to realize that, in Exim, no deliveries are actually made while
130a filter or traditional .forward file is being processed. Running a filter or
131processing a traditional .forward file sets up future delivery operations, but
132does not carry them out.
133
134The result of filter or .forward file processing is a list of destinations to
135which a message should be delivered. The deliveries themselves take place
136later, along with all other deliveries for the message. This means that it is
137not possible to test for successful deliveries while filtering. It also means
138that any duplicate addresses that are generated are dropped, because Exim never
139delivers the same message to the same address more than once.
140
141
1421.3 Testing a new filter file
143-----------------------------
144
145Filter files, especially the more complicated ones, should always be tested, as
146it is easy to make mistakes. Exim provides a facility for preliminary testing
147of a filter file before installing it. This tests the syntax of the file and
148its basic operation, and can also be used with traditional .forward files.
149
150Because a filter can do tests on the content of messages, a test message is
151required. Suppose you have a new filter file called myfilter and a test message
152in a file called test-message. Assuming that Exim is installed with the
153conventional path name /usr/sbin/sendmail (some operating systems use /usr/lib/
154sendmail), the following command can be used:
155
156/usr/sbin/sendmail -bf myfilter <test-message
157
158The -bf option tells Exim that the following item on the command line is the
159name of a filter file that is to be tested. There is also a -bF option, which
160is similar, but which is used for testing system filter files, as opposed to
161user filter files, and which is therefore of use only to the system
162administrator.
163
164The test message is supplied on the standard input. If there are no
165message-dependent tests in the filter, an empty file (/dev/null) can be used. A
166supplied message must start with header lines or the "From " message separator
167line that is found in many multi-message folder files. Note that blank lines at
168the start terminate the header lines. A warning is given if no header lines are
169read.
170
171The result of running this command, provided no errors are detected in the
172filter file, is a list of the actions that Exim would try to take if presented
173with the message for real. For example, for an Exim filter, the output
174
175Deliver message to: gulliver@lilliput.fict.example
176Save message to: /home/lemuel/mail/archive
177
178means that one copy of the message would be sent to
179gulliver@lilliput.fict.example, and another would be added to the file /home/
180lemuel/mail/archive, if all went well.
181
182The actions themselves are not attempted while testing a filter file in this
183way; there is no check, for example, that any forwarding addresses are valid.
184For an Exim filter, if you want to know why a particular action is being taken,
185add the -v option to the command. This causes Exim to output the results of any
186conditional tests and to indent its output according to the depth of nesting of
187if commands. Further additional output from a filter test can be generated by
188the testprint command, which is described below.
189
190When Exim is outputting a list of the actions it would take, if any text
191strings are included in the output, non-printing characters therein are
192converted to escape sequences. In particular, if any text string contains a
193newline character, this is shown as "\n" in the testing output.
194
195When testing a filter in this way, Exim makes up an "envelope" for the message.
196The recipient is by default the user running the command, and so is the sender,
197but the command can be run with the -f option to supply a different sender. For
198example,
199
200/usr/sbin/sendmail -bf myfilter \
201 -f islington@never.where <test-message
202
203Alternatively, if the -f option is not used, but the first line of the supplied
204message is a "From " separator from a message folder file (not the same thing
205as a From: header line), the sender is taken from there. If -f is present, the
206contents of any "From " line are ignored.
207
208The "return path" is the same as the envelope sender, unless the message
209contains a Return-path: header, in which case it is taken from there. You need
210not worry about any of this unless you want to test out features of a filter
211file that rely on the sender address or the return path.
212
213It is possible to change the envelope recipient by specifying further options.
214The -bfd option changes the domain of the recipient address, while the -bfl
215option changes the "local part", that is, the part before the @ sign. An
216adviser could make use of these to test someone else's filter file.
217
218The -bfp and -bfs options specify the prefix or suffix for the local part.
219These are relevant only when support for multiple personal mailboxes is
220implemented; see the description in section 3.31 below.
221
222
2231.4 Installing a filter file
224----------------------------
225
226A filter file is normally installed under the name .forward in your home
227directory - it is distinguished from a conventional .forward file by its first
228line (described below). However, the file name is configurable, and some system
229administrators may choose to use some different name or location for filter
230files.
231
232
2331.5 Testing an installed filter file
234------------------------------------
235
236Testing a filter file before installation cannot find every potential problem;
237for example, it does not actually run commands to which messages are piped.
238Some "live" tests should therefore also be done once a filter is installed.
239
240If at all possible, test your filter file by sending messages from some other
241account. If you send a message to yourself from the filtered account, and
242delivery fails, the error message will be sent back to the same account, which
243may cause another delivery failure. It won't cause an infinite sequence of such
244messages, because delivery failure messages do not themselves generate further
245messages. However, it does mean that the failure won't be returned to you, and
246also that the postmaster will have to investigate the stuck message.
247
248If you have to test an Exim filter from the same account, a sensible precaution
249is to include the line
250
251if error_message then finish endif
252
253as the first filter command, at least while testing. This causes filtering to
254be abandoned for a delivery failure message, and since no destinations are
255generated, the message goes on to be delivered to the original address. Unless
256there is a good reason for not doing so, it is recommended that the above test
257be left in all Exim filter files. (This does not apply to Sieve files.)
258
259
2601.6 Details of filtering commands
261---------------------------------
262
263The filtering commands for Sieve and Exim filters are completely different in
264syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
265chapter we describe how it is integrated into Exim. The subsequent chapter
266covers Exim filtering commands in detail.
267
268
269
270===============================================================================
2712. SIEVE FILTER FILES
272
273The code for Sieve filtering in Exim was contributed by Michael Haardt, and
274most of the content of this chapter is taken from the notes he provided. Since
275Sieve is an extensible language, it is important to understand "Sieve" in this
276context as "the specific implementation of Sieve for Exim".
277
278This chapter does not contain a description of Sieve, since that can be found
279in RFC 3028, which should be read in conjunction with these notes.
280
281The Exim Sieve implementation offers the core as defined by RFC 3028,
282comparison tests, the subaddress parameter, the copy, envelope, fileinto,
283notify, and vacation extensions, but not the reject extension. Exim does not
284support message delivery notifications (MDNs), so adding it just to the Sieve
285filter (as required for reject) makes little sense.
286
287In order for Sieve to work properly in Exim, the system administrator needs to
288make some adjustments to the Exim configuration. These are described in the
289chapter on the redirect router in the full Exim specification.
290
291
2922.1 Recognition of Sieve filters
293--------------------------------
294
295A filter file is interpreted as a Sieve filter if its first line is
296
297# Sieve filter
298
299This is what distinguishes it from a conventional .forward file or an Exim
300filter file.
301
302
3032.2 Saving to specified folders
304-------------------------------
305
306If the system administrator has set things up as suggested in the Exim
307specification, and you use keep or fileinto to save a mail into a folder,
308absolute files are stored where specified, relative files are stored relative
309to $home, and inbox goes to the standard mailbox location.
310
311
3122.3 Strings containing header names
313-----------------------------------
314
315RFC 3028 does not specify what happens if a string denoting a header field does
316not contain a valid header name, for example, it contains a colon. This
317implementation generates an error instead of ignoring the header field in order
318to ease script debugging, which fits in with the common picture of Sieve.
319
320
3212.4 Exists test with empty list of headers
322------------------------------------------
323
324The exists test succeeds only if all the specified headers exist. RFC 3028 does
325not explicitly specify what happens on an empty list of headers. This
326implementation evaluates that condition as true, interpreting the RFC in a
327strict sense.
328
329
3302.5 Header test with invalid MIME encoding in header
331----------------------------------------------------
332
333Some MUAs process invalid base64 encoded data, generating junk. Others ignore
334junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
335specify how to react in this case, other than stating that a client must not
336forbid to process a message for that reason. RFC 2045 specifies that invalid
337data should be ignored (apparently looking at end of line characters). It also
338specifies that invalid data may lead to rejecting messages containing them (and
339there it appears to talk about true encoding violations), which is a clear
340contradiction to ignoring them.
341
342RFC 3028 does not specify how to process incorrect MIME words. This
343implementation treats them literally, as it does if the word is correct but its
344character set cannot be converted to UTF-8.
345
346
3472.6 Address test for multiple addresses per header
348--------------------------------------------------
349
350A header may contain multiple addresses. RFC 3028 does not explicitly specify
351how to deal with them, but since the address test checks if anything matches
352anything else, matching one address suffices to satisfy the condition. That
353makes it impossible to test if a header contains a certain set of addresses and
354no more, but it is more logical than letting the test fail if the header
355contains an additional address besides the one the test checks for.
356
357
3582.7 Semantics of keep
359---------------------
360
361The keep command is equivalent to
362
363fileinto "inbox";
364
365It saves the message and resets the implicit keep flag. It does not set the
366implicit keep flag; there is no command to set it once it has been reset.
367
368
3692.8 Semantics of fileinto
370-------------------------
371
372RFC 3028 does not specify whether fileinto should try to create a mail folder
373if it does not exist. This implementation allows the sysadmin to configure that
374aspect using the appendfile transport options create_directory, create_file,
375and file_must_exist. See the appendfile transport in the Exim specification for
376details.
377
378
3792.9 Semantics of redirect
380-------------------------
381
382Sieve scripts are supposed to be interoperable between servers, so this
383implementation does not allow mail to be redirected to unqualified addresses,
384because the domain would depend on the system being used. On systems with
385virtual mail domains, the default domain is probably not what the user expects
386it to be.
387
388
3892.10 String arguments
390---------------------
391
392There has been confusion if the string arguments to require are to be matched
393case-sensitively or not. This implementation matches them with the match type
394:is (default, see section 2.7.1 of the RFC) and the comparator i;ascii-casemap
395(default, see section 2.7.3 of the RFC). The RFC defines the command defaults
396clearly, so any different implementations violate RFC 3028. The same is valid
397for comparator names, also specified as strings.
398
399
4002.11 Number units
401-----------------
402
403There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte. The
404mistake is obvious, because RFC 3028 specifies G to denote 2^30 (which is gibi,
405not tebi), and that is what this implementation uses as the scaling factor for
406the suffix G.
407
408
4092.12 RFC compliance
410-------------------
411
412Exim requires the first line of a Sieve filter to be
413
414# Sieve filter
415
416Of course the RFC does not specify that line. Do not expect examples to work
417without adding it, though.
418
419RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
420CRLF is universally used in network protocols to mark the end of the line. This
421implementation does not embed Sieve in a network protocol, but uses Sieve
422scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
423character, this implementation does, too, by default, though the system
424administrator may choose (at Exim compile time) to use CRLF instead.
425
426Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
427implementation repeats this violation to stay consistent with Exim. This is in
428preparation for UTF-8 data.
429
430Sieve scripts cannot contain NUL characters in strings, but mail headers could
431contain MIME encoded NUL characters, which could never be matched by Sieve
432scripts using exact comparisons. For that reason, this implementation extends
433the Sieve quoted string syntax with \0 to describe a NUL character, violating \
4340 being the same as 0 in RFC 3028. Even without using \0, the following tests
435are all true in this implementation. Implementations that use C-style strings
436will only evaluate the first test as true.
437
438Subject: =?iso-8859-1?q?abc=00def
439
440header :contains "Subject" ["abc"]
441header :contains "Subject" ["def"]
442header :matches "Subject" ["abc?def"]
443
444Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
445way that NUL characters truncating strings is allowed for Sieve
446implementations, although not recommended. It is further allowed to use encoded
447NUL characters in headers, but that's not recommended either. The above example
448shows why.
449
450RFC 3028 states that if an implementation fails to convert a character set to
451UTF-8, two strings cannot be equal if one contains octets greater than 127.
452Assuming that all unknown character sets are one-byte character sets with the
453lower 128 octets being US-ASCII is not sound, so this implementation violates
454RFC 3028 and treats such MIME words literally. That way at least something
455could be matched.
456
457The folder specified by fileinto must not contain the character sequence ".."
458to avoid security problems. RFC 3028 does not specify the syntax of folders
459apart from keep being equivalent to
460
461fileinto "INBOX";
462
463This implementation uses inbox instead.
464
465Sieve script errors currently cause messages to be silently filed into inbox.
466RFC 3028 requires that the user is notified of that condition. This may be
467implemented in the future by adding a header line to mails that are filed into
468inbox due to an error in the filter.
469
470
471
472===============================================================================
4733. EXIM FILTER FILES
474
475This chapter contains a full description of the contents of Exim filter files.
476
477
4783.1 Format of Exim filter files
479-------------------------------
480
481Apart from leading white space, the first text in an Exim filter file must be
482
483# Exim filter
484
485This is what distinguishes it from a conventional .forward file or a Sieve
486filter file. If the file does not have this initial line (or the equivalent for
487a Sieve filter), it is treated as a conventional .forward file, both when
488delivering mail and when using the -bf testing mechanism. The white space in
489the line is optional, and any capitalization may be used. Further text on the
490same line is treated as a comment. For example, you could have
491
492# Exim filter <<== do not edit or remove this line!
493
494The remainder of the file is a sequence of filtering commands, which consist of
495keywords and data values. For example, in the command
496
497deliver gulliver@lilliput.fict.example
498
499the keyword is "deliver" and the data value is
500"gulliver@lilliput.fict.example". White space or line breaks separate the
501components of a command, except in the case of conditions for the if command,
502where round brackets (parentheses) also act as separators. Complete commands
503are separated from each other by white space or line breaks; there are no
504special terminators. Thus, several commands may appear on one line, or one
505command may be spread over a number of lines.
506
507If the character # follows a separator anywhere in a command, everything from #
508up to the next newline is ignored. This provides a way of including comments in
509a filter file.
510
511
5123.2 Data values in filter commands
513----------------------------------
514
515There are two ways in which a data value can be input:
516
517 * If the text contains no white space, it can be typed verbatim. However, if
518 it is part of a condition, it must also be free of round brackets
519 (parentheses), as these are used for grouping in conditions.
520
521 * Otherwise, text must be enclosed in double quotation marks. In this case,
522 the character \ (backslash) is treated as an "escape character" within the
523 string, causing the following character or characters to be treated
524 specially:
525
526 \n is replaced by a newline
527 \r is replaced by a carriage return
528 \t is replaced by a tab
529
530Backslash followed by up to three octal digits is replaced by the character
531specified by those digits, and "\x" followed by up to two hexadecimal digits is
532treated similarly. Backslash followed by any other character is replaced by the
533second character, so that in particular, "\"" becomes """ and "\\" becomes "\".
534A data item enclosed in double quotes can be continued onto the next line by
535ending the first line with a backslash. Any leading white space at the start of
536the continuation line is ignored.
537
538In addition to the escape character processing that occurs when strings are
539enclosed in quotes, most data values are also subject to string expansion (as
540described in the next section), in which case the characters "$" and "\" are
541also significant. This means that if a single backslash is actually required in
542such a string, and the string is also quoted, "\\\\" has to be entered.
543
544The maximum permitted length of a data string, before expansion, is 1024
545characters.
546
547
5483.3 String expansion
549--------------------
550
551Most data values are expanded before use. Expansion consists of replacing
552substrings beginning with "$" with other text. The full expansion facilities
553available in Exim are extensive. If you want to know everything that Exim can
554do with strings, you should consult the chapter on string expansion in the Exim
555documentation.
556
557In filter files, by far the most common use of string expansion is the
558substitution of the contents of a variable. For example, the substring
559
560$reply_address
561
562is replaced by the address to which replies to the message should be sent. If
563such a variable name is followed by a letter or digit or underscore, it must be
564enclosed in curly brackets (braces), for example,
565
566${reply_address}
567
568If a "$" character is actually required in an expanded string, it must be
569escaped with a backslash, and because backslash is also an escape character in
570quoted input strings, it must be doubled in that case. The following two
571examples illustrate two different ways of testing for a "$" character in a
572message:
573
574if $message_body contains \$ then ...
575if $message_body contains "\\$" then ...
576
577You can prevent part of a string from being expanded by enclosing it between
578two occurrences of "\N". For example,
579
580if $message_body contains \N$$$$\N then ...
581
582tests for a run of four dollar characters.
583
584
5853.4 Some useful general variables
586---------------------------------
587
588A complete list of the available variables is given in the Exim documentation.
589This shortened list contains the ones that are most likely to be useful in
590personal filter files:
591
592$body_linecount: The number of lines in the body of the message.
593
594$body_zerocount: The number of binary zero characters in the body of the
595message.
596
597$home: In conventional configurations, this variable normally contains the
598user's home directory. The system administrator can, however, change this.
599
600$local_part: The part of the email address that precedes the @ sign - normally
601the user's login name. If support for multiple personal mailboxes is enabled
602(see section 3.31 below) and a prefix or suffix for the local part was
603recognized, it is removed from the string in this variable.
604
605$local_part_prefix: If support for multiple personal mailboxes is enabled (see
606section 3.31 below), and a local part prefix was recognized, this variable
607contains the prefix. Otherwise it contains an empty string.
608
609$local_part_suffix: If support for multiple personal mailboxes is enabled (see
610section 3.31 below), and a local part suffix was recognized, this variable
611contains the suffix. Otherwise it contains an empty string.
612
613$message_body: The initial portion of the body of the message. By default, up
614to 500 characters are read into this variable, but the system administrator can
615configure this to some other value. Newlines in the body are converted into
616single spaces.
617
618$message_body_end: The final portion of the body of the message, formatted and
619limited in the same way as $message_body.
620
621$message_body_size: The size of the body of the message, in bytes.
622
623$message_exim_id: The message's local identification string, which is unique
624for each message handled by a single host.
625
626$message_headers: The header lines of the message, concatenated into a single
627string, with newline characters between them.
628
629$message_size: The size of the entire message, in bytes.
630
631$original_local_part: When an address that arrived with the message is being
632processed, this contains the same value as the variable $local_part. However,
633if an address generated by an alias, forward, or filter file is being
634processed, this variable contains the local part of the original address.
635
636$reply_address: The contents of the Reply-to: header, if the message has one;
637otherwise the contents of the From: header. It is the address to which normal
638replies to the message should be sent.
639
640$return_path: The return path - that is, the sender field that will be
641transmitted as part of the message's envelope if the message is sent to another
642host. This is the address to which delivery errors are sent. In many cases,
643this variable has the same value as $sender_address, but if, for example, an
644incoming message to a mailing list has been expanded, $return_path may have
645been changed to contain the address of the list maintainer.
646
647$sender_address: The sender address that was received in the envelope of the
648message. This is not necessarily the same as the contents of the From: or
649Sender: header lines. For delivery error messages ("bounce messages") there is
650no sender address, and this variable is empty.
651
652$tod_full: A full version of the time and date, for example: Wed, 18 Oct 1995
65309:51:40 +0100. The timezone is always given as a numerical offset from GMT.
654
655$tod_log: The time and date in the format used for writing Exim's log files,
656without the timezone, for example: 1995-10-12 15:32:29.
657
658$tod_zone: The local timezone offset, for example: +0100.
659
660
6613.5 Header variables
662--------------------
663
664There is a special set of expansion variables containing the header lines of
665the message being processed. These variables have names beginning with $header_
666followed by the name of the header line, terminated by a colon. For example,
667
668$header_from:
669$header_subject:
670
671The whole item, including the terminating colon, is replaced by the contents of
672the message header line. If there is more than one header line with the same
673name, their contents are concatenated. For header lines whose data consists of
674a list of addresses (for example, From: and To:), a comma and newline is
675inserted between each set of data. For all other header lines, just a newline
676is used.
677
678Leading and trailing white space is removed from header line data, and if there
679are any MIME "words" that are encoded as defined by RFC 2047 (because they
680contain non-ASCII characters), they are decoded and translated, if possible, to
681a local character set. Translation is attempted only on operating systems that
682have the iconv() function. This makes the header line look the same as it would
683when displayed by an MUA. The default character set is ISO-8859-1, but this can
684be changed by means of the headers command (see below).
685
686If you want to see the actual characters that make up a header line, you can
687specify $rheader_ instead of $header_. This inserts the "raw" header line,
688unmodified.
689
690There is also an intermediate form, requested by $bheader_, which removes
691leading and trailing space and decodes MIME "words", but does not do any
692character translation. If an attempt to decode what looks superficially like a
693MIME "word" fails, the raw string is returned. If decoding produces a binary
694zero character, it is replaced by a question mark.
695
696The capitalization of the name following $header_ is not significant. Because
697any printing character except colon may appear in the name of a message's
698header (this is a requirement of RFC 2822, the document that describes the
699format of a mail message) curly brackets must not be used in this case, as they
700will be taken as part of the header name. Two shortcuts are allowed in naming
701header variables:
702
703 * The initiating $header_, $rheader_, or $bheader_ can be abbreviated to $h_,
704 $rh_, or $bh_, respectively.
705
706 * The terminating colon can be omitted if the next character is white space.
707 The white space character is retained in the expanded string. However, this
708 is not recommended, because it makes it easy to forget the colon when it
709 really is needed.
710
711If the message does not contain a header of the given name, an empty string is
712substituted. Thus it is important to spell the names of headers correctly. Do
713not use $header_Reply_to when you really mean $header_Reply-to.
714
715
7163.6 User variables
717------------------
718
719There are ten user variables with names $n0 - $n9 that can be incremented by
720the add command (see section 3.10). These can be used for "scoring" messages in
721various ways. If Exim is configured to run a "system filter" on every message,
722the values left in these variables are copied into the variables $sn0 - $sn9 at
723the end of the system filter, thus making them available to users' filter
724files. How these values are used is entirely up to the individual installation.
725
726
7273.7 Current directory
728---------------------
729
730The contents of your filter file should not make any assumptions about the
731current directory. It is best to use absolute paths for file names; you can
732normally make use of the $home variable to refer to your home directory. The
733save command automatically inserts $home at the start of non-absolute paths.
734
735
7363.8 Significant deliveries
737--------------------------
738
739When in the course of delivery a message is processed by a filter file, what
740happens next, that is, after the filter file has been processed, depends on
741whether or not the filter sets up any significant deliveries. If at least one
742significant delivery is set up, the filter is considered to have handled the
743entire delivery arrangements for the current address, and no further processing
744of the address takes place. If, however, no significant deliveries are set up,
745Exim continues processing the current address as if there were no filter file,
746and typically sets up a delivery of a copy of the message into a local mailbox.
747In particular, this happens in the special case of a filter file containing
748only comments.
749
750The delivery commands deliver, save, and pipe are by default significant.
751However, if such a command is preceded by the word "unseen", its delivery is
752not considered to be significant. In contrast, other commands such as mail and
753vacation do not set up significant deliveries unless preceded by the word
754"seen". The following example commands set up significant deliveries:
755
756deliver jack@beanstalk.example
757pipe $home/bin/mymailscript
758seen mail subject "message discarded"
759seen finish
760
761The following example commands do not set up significant deliveries:
762
763unseen deliver jack@beanstalk.example
764unseen pipe $home/bin/mymailscript
765mail subject "message discarded"
766finish
767
768
7693.9 Filter commands
770-------------------
771
772The filter commands that are described in subsequent sections are listed below,
773with the section in which they are described in brackets:
774
775add increment a user variable (section 3.10)
776deliver deliver to an email address (section 3.11)
777fail force delivery failure (sysadmin use) (section 3.18)
778finish end processing (section 3.16)
779freeze freeze message (sysadmin use) (section 3.19)
780headers set the header character set (section 3.20)
781if test condition(s) (section 3.21)
782logfile define log file (section 3.15)
783logwrite write to log file (section 3.15)
784mail send a reply message (section 3.14)
785pipe pipe to a command (section 3.13)
786save save to a file (section 3.12)
787testprint print while testing (section 3.17)
788vacation tailored form of mail (section 3.14)
789
790The headers command has additional parameters that can be used only in a system
791filter. The fail and freeze commands are available only when Exim's filtering
792facilities are being used as a system filter, and are therefore usable only by
793the system administrator and not by ordinary users. They are mentioned only
794briefly in this document; for more information, see the main Exim
795specification.
796
797
7983.10 The add command
799--------------------
800
801 add <number> to <user variable>
802e.g. add 2 to n3
803
804There are 10 user variables of this type, with names $n0 - $n9. Their values
805can be obtained by the normal expansion syntax (for example $n3) in other
806commands. At the start of filtering, these variables all contain zero. Both
807arguments of the add command are expanded before use, making it possible to add
808variables to each other. Subtraction can be obtained by adding negative
809numbers.
810
811
8123.11 The deliver command
813------------------------
814
815 deliver <mail address>
816e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"
817
818This command provides a forwarding operation. The delivery that it sets up is
819significant unless the command is preceded by "unseen" (see section 3.8). The
820message is sent on to the given address, exactly as happens if the address had
821appeared in a traditional .forward file. If you want to deliver the message to
822a number of different addresses, you can use more than one deliver command
823(each one may have only one address). However, duplicate addresses are
824discarded.
825
826To deliver a copy of the message to your normal mailbox, your login name can be
827given as the address. Once an address has been processed by the filtering
828mechanism, an identical generated address will not be so processed again, so
829doing this does not cause a loop.
830
831However, if you have a mail alias, you should not refer to it here. For
832example, if the mail address L.Gulliver is aliased to lg303 then all references
833in Gulliver's .forward file should be to lg303. A reference to the alias will
834not work for messages that are addressed to that alias, since, like .forward
835file processing, aliasing is performed only once on an address, in order to
836avoid looping.
837
838Following the new address, an optional second address, preceded by "errors_to"
839may appear. This changes the address to which delivery errors on the forwarded
840message will be sent. Instead of going to the message's original sender, they
841go to this new address. For ordinary users, the only value that is permitted
842for this address is the user whose filter file is being processed. For example,
843the user lg303 whose mailbox is in the domain lilliput.example could have a
844filter file that contains
845
846deliver jon@elsewhere.example errors_to lg303@lilliput.example
847
848Clearly, using this feature makes sense only in situations where not all
849messages are being forwarded. In particular, bounce messages must not be
850forwarded in this way, as this is likely to create a mail loop if something
851goes wrong.
852
853
8543.12 The save command
855---------------------
856
857 save <file name>
858e.g. save $home/mail/bookfolder
859
860This command specifies that a copy of the message is to be appended to the
861given file (that is, the file is to be used as a mail folder). The delivery
862that save sets up is significant unless the command is preceded by "unseen"
863(see section 3.8).
864
865More than one save command may be obeyed; each one causes a copy of the message
866to be written to its argument file, provided they are different (duplicate save
867commands are ignored).
868
869If the file name does not start with a / character, the contents of the $home
870variable are prepended, unless it is empty, or the system administrator has
871disabled this feature. In conventional configurations, this variable is
872normally set in a user filter to the user's home directory, but the system
873administrator may set it to some other path. In some configurations, $home may
874be unset, or prepending may be disabled, in which case a non-absolute path name
875may be generated. Such configurations convert this to an absolute path when the
876delivery takes place. In a system filter, $home is never set.
877
878The user must of course have permission to write to the file, and the writing
879of the file takes place in a process that is running as the user, under the
880user's primary group. Any secondary groups to which the user may belong are not
881normally taken into account, though the system administrator can configure Exim
882to set them up. In addition, the ability to use this command at all is
883controlled by the system administrator - it may be forbidden on some systems.
884
885An optional mode value may be given after the file name. The value for the mode
886is interpreted as an octal number, even if it does not begin with a zero. For
887example:
888
889save /some/folder 640
890
891This makes it possible for users to override the system-wide mode setting for
892file deliveries, which is normally 600. If an existing file does not have the
893correct mode, it is changed.
894
895An alternative form of delivery may be enabled on your system, in which each
896message is delivered into a new file in a given directory. If this is the case,
897this functionality can be requested by giving the directory name terminated by
898a slash after the save command, for example
899
900save separated/messages/
901
902There are several different formats for such deliveries; check with your system
903administrator or local documentation to find out which (if any) are available
904on your system. If this functionality is not enabled, the use of a path name
905ending in a slash causes an error.
906
907
9083.13 The pipe command
909---------------------
910
911 pipe <command>
912e.g. pipe "$home/bin/countmail $sender_address"
913
914This command specifies that the message is to be delivered to the specified
915command using a pipe. The delivery that it sets up is significant unless the
916command is preceded by "unseen" (see section 3.8). Remember, however, that no
917deliveries are done while the filter is being processed. All deliveries happen
918later on. Therefore, the result of running the pipe is not available to the
919filter.
920
921When the deliveries are done, a separate process is run, and a copy of the
922message is passed on its standard input. The process runs as the user, under
923the user's primary group. Any secondary groups to which the user may belong are
924not normally taken into account, though the system administrator can configure
925Exim to set them up. More than one pipe command may appear; each one causes a
926copy of the message to be written to its argument pipe, provided they are
927different (duplicate pipe commands are ignored).
928
929When the time comes to transport the message, the command supplied to pipe is
930split up by Exim into a command name and a number of arguments. These are
931delimited by white space except for arguments enclosed in double quotes, in
932which case backslash is interpreted as an escape, or in single quotes, in which
933case no escaping is recognized. Note that as the whole command is normally
934supplied in double quotes, a second level of quoting is required for internal
935double quotes. For example:
936
937pipe "$home/myscript \"size is $message_size\""
938
939String expansion is performed on the separate components after the line has
940been split up, and the command is then run directly by Exim; it is not run
941under a shell. Therefore, substitution cannot change the number of arguments,
942nor can quotes, backslashes or other shell metacharacters in variables cause
943confusion.
944
945Documentation for some programs that are normally run via this kind of pipe
946often suggest that the command should start with
947
948IFS=" "
949
950This is a shell command, and should not be present in Exim filter files, since
951it does not normally run the command under a shell.
952
953However, there is an option that the administrator can set to cause a shell to
954be used. In this case, the entire command is expanded as a single string and
955passed to the shell for interpretation. It is recommended that this be avoided
956if at all possible, since it can lead to problems when inserted variables
957contain shell metacharacters.
958
959The default PATH set up for the command is determined by the system
960administrator, usually containing at least /bin and /usr/bin so that common
961commands are available without having to specify an absolute file name.
962However, it is possible for the system administrator to restrict the pipe
963facility so that the command name must not contain any / characters, and must
964be found in one of the directories in the configured PATH. It is also possible
965for the system administrator to lock out the use of the pipe command
966altogether.
967
968When the command is run, a number of environment variables are set up. The
969complete list for pipe deliveries may be found in the Exim reference manual.
970Those that may be useful for pipe deliveries from user filter files are:
971
972DOMAIN the domain of the address
973HOME your home directory
974LOCAL_PART see below
975LOCAL_PART_PREFIX see below
976LOCAL_PART_SUFFIX see below
977LOGNAME your login name
978MESSAGE_ID the unique id of the message
979PATH the command search path
980RECIPIENT the complete recipient address
981SENDER the sender of the message
982SHELL /bin/sh
983USER see below
984
985LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
986id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
987recognize prefixes or suffixes in the local parts of addresses. For example, a
988message addressed to pat-suf2@domain.example may cause the filter for user pat
989to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is "-suf2" when
990the pipe command runs. The system administrator has to configure Exim specially
991for this feature to be available.
992
993If you run a command that is a shell script, be very careful in your use of
994data from the incoming message in the commands in your script. RFC 2822 is very
995generous in the characters that are permitted to appear in mail addresses, and
996in particular, an address may begin with a vertical bar or a slash. For this
997reason you should always use quotes round any arguments that involve data from
998the message, like this:
999
1000/some/command '$SENDER'
1001
1002so that inserted shell meta-characters do not cause unwanted effects.
1003
1004Remember that, as was explained earlier, the pipe command is not run at the
1005time the filter file is interpreted. The filter just defines what deliveries
1006are required for one particular addressee of a message. The deliveries
1007themselves happen later, once Exim has decided everything that needs to be done
1008for the message.
1009
1010A consequence of this is that you cannot inspect the return code from the pipe
1011command from within the filter. Nevertheless, the code returned by the command
1012is important, because Exim uses it to decide whether the delivery has succeeded
1013or failed.
1014
1015The command should return a zero completion code if all has gone well. Most
1016non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1017treated as a delivery failure, causing the message to be returned to its
1018sender. However, there are some completion codes that are treated as temporary
1019errors. The message remains on Exim's spool disk, and the delivery is tried
1020again later, though it will ultimately time out if the delivery failures go on
1021too long. The completion codes to which this applies can be specified by the
1022system administrator; the default values are 73 and 75.
1023
1024The pipe command should not normally write anything to its standard output or
1025standard error file descriptors. If it does, whatever is written is normally
1026returned to the sender of the message as a delivery error, though this action
1027can be varied by the system administrator.
1028
1029
10303.14 Mail commands
1031------------------
1032
1033There are two commands that cause the creation of a new mail message, neither
1034of which count as a significant delivery unless the command is preceded by the
1035word "seen" (see section 3.8). This is a powerful facility, but it should be
1036used with care, because of the danger of creating infinite sequences of
1037messages. The system administrator can forbid the use of these commands
1038altogether.
1039
1040To help prevent runaway message sequences, these commands have no effect when
1041the incoming message is a bounce (delivery error) message, and messages sent by
1042this means are treated as if they were reporting delivery errors. Thus, they
1043should never themselves cause a bounce message to be returned. The basic
1044mail-sending command is
1045
1046mail [to <address-list>]
1047 [cc <address-list>]
1048 [bcc <address-list>]
1049 [from <address>]
1050 [reply_to <address>]
1051 [subject <text>]
1052 [extra_headers <text>]
1053 [text <text>]
1054 [[expand] file <filename>]
1055 [return message]
1056 [log <log file name>]
1057 [once <note file name>]
1058 [once_repeat <time interval>]
1059e.g. mail text "Your message about $h_subject: has been received"
1060
1061Each <address-list> can contain a number of addresses, separated by commas, in
1062the format of a To: or Cc: header line. In fact, the text you supply here is
1063copied exactly into the appropriate header line. It may contain additional
1064information as well as email addresses. For example:
1065
1066mail to "Julius Caesar <jc@rome.example>, \
1067 <ma@rome.example> (Mark A.)"
1068
1069Similarly, the texts supplied for from and reply_to are copied into their
1070respective header lines.
1071
1072As a convenience for use in one common case, there is also a command called
1073vacation. It behaves in the same way as mail, except that the defaults for the
1074subject, file, log, once, and once_repeat options are
1075
1076subject "On vacation"
1077expand file .vacation.msg
1078log .vacation.log
1079once .vacation
1080once_repeat 7d
1081
1082respectively. These are the same file names and repeat period used by the
1083traditional Unix vacation command. The defaults can be overridden by explicit
1084settings, but if a file name is given its contents are expanded only if
1085explicitly requested.
1086
1087Warning: The vacation command should always be used conditionally, subject to
1088at least the personal condition (see section 3.27 below) so as not to send
1089automatic replies to non-personal messages from mailing lists or elsewhere.
1090Sending an automatic response to a mailing list or a mailing list manager is an
1091Internet Sin.
1092
1093For both commands, the key/value argument pairs can appear in any order. At
1094least one of text or file must appear (except with vacation, where there is a
1095default for file); if both are present, the text string appears first in the
1096message. If expand precedes file, each line of the file is subject to string
1097expansion before it is included in the message.
1098
1099Several lines of text can be supplied to text by including the escape sequence
1100"\n" in the string wherever a newline is required. If the command is output
1101during filter file testing, newlines in the text are shown as "\n".
1102
1103Note that the keyword for creating a Reply-To: header is reply_to, because Exim
1104keywords may contain underscores, but not hyphens. If the from keyword is
1105present and the given address does not match the user who owns the forward
1106file, Exim normally adds a Sender: header to the message, though it can be
1107configured not to do this.
1108
1109The extra_headers keyword allows you to add custom header lines to the message.
1110The text supplied must be one or more syntactically valid RFC 2822 header
1111lines. You can use "\n" within quoted text to specify newlines between headers,
1112and also to define continued header lines. For example:
1113
1114extra_headers "h1: first\nh2: second\n continued\nh3: third"
1115
1116No newline should appear at the end of the final header line.
1117
1118If no to argument appears, the message is sent to the address in the
1119$reply_address variable (see section 3.3 above). An In-Reply-To: header is
1120automatically included in the created message, giving a reference to the
1121message identification of the incoming message.
1122
1123If return message is specified, the incoming message that caused the filter
1124file to be run is added to the end of the message, subject to a maximum size
1125limitation.
1126
1127If a log file is specified, a line is added to it for each message sent.
1128
1129If a once file is specified, it is used to hold a database for remembering who
1130has received a message, and no more than one message is ever sent to any
1131particular address, unless once_repeat is set. This specifies a time interval
1132after which another copy of the message is sent. The interval is specified as a
1133sequence of numbers, each followed by the initial letter of one of "seconds",
1134"minutes", "hours", "days", or "weeks". For example,
1135
1136once_repeat 5d4h
1137
1138causes a new message to be sent if at least 5 days and 4 hours have elapsed
1139since the last one was sent. There must be no white space in a time interval.
1140
1141Commonly, the file name specified for once is used as the base name for
1142direct-access (DBM) file operations. There are a number of different DBM
1143libraries in existence. Some operating systems provide one as a default, but
1144even in this case a different one may have been used when building Exim. With
1145some DBM libraries, specifying once results in two files being created, with
1146the suffixes .dir and .pag being added to the given name. With some others a
1147single file with the suffix .db is used, or the name is used unchanged.
1148
1149Using a DBM file for implementing the once feature means that the file grows as
1150large as necessary. This is not usually a problem, but some system
1151administrators want to put a limit on it. The facility can be configured not to
1152use a DBM file, but instead, to use a regular file with a maximum size. The
1153data in such a file is searched sequentially, and if the file fills up, the
1154oldest entry is deleted to make way for a new one. This means that some
1155correspondents may receive a second copy of the message after an unpredictable
1156interval. Consult your local information to see if your system is configured
1157this way.
1158
1159More than one mail or vacation command may be obeyed in a single filter run;
1160they are all honoured, even when they are to the same recipient.
1161
1162
11633.15 Logging commands
1164---------------------
1165
1166A log can be kept of actions taken by a filter file. This facility is normally
1167available in conventional configurations, but there are some situations where
1168it might not be. Also, the system administrator may choose to disable it. Check
1169your local information if in doubt.
1170
1171Logging takes place while the filter file is being interpreted. It does not
1172queue up for later like the delivery commands. The reason for this is so that a
1173log file need be opened only once for several write operations. There are two
1174commands, neither of which constitutes a significant delivery. The first
1175defines a file to which logging output is subsequently written:
1176
1177 logfile <file name>
1178e.g. logfile $home/filter.log
1179
1180The file name must be fully qualified. You can use $home, as in this example,
1181to refer to your home directory. The file name may optionally be followed by a
1182mode for the file, which is used if the file has to be created. For example,
1183
1184logfile $home/filter.log 0644
1185
1186The number is interpreted as octal, even if it does not begin with a zero. The
1187default for the mode is 600. It is suggested that the logfile command normally
1188appear as the first command in a filter file. Once a log file has been obeyed,
1189the logwrite command can be used to write to it:
1190
1191 logwrite "<some text string>"
1192e.g. logwrite "$tod_log $message_id processed"
1193
1194It is possible to have more than one logfile command, to specify writing to
1195different log files in different circumstances. Writing takes place at the end
1196of the file, and a newline character is added to the end of each string if
1197there isn't one already there. Newlines can be put in the middle of the string
1198by using the "\n" escape sequence. Lines from simultaneous deliveries may get
1199interleaved in the file, as there is no interlocking, so you should plan your
1200logging with this in mind. However, data should not get lost.
1201
1202
12033.16 The finish command
1204-----------------------
1205
1206The command finish, which has no arguments, causes Exim to stop interpreting
1207the filter file. This is not a significant action unless preceded by "seen". A
1208filter file containing only "seen finish" is a black hole.
1209
1210
12113.17 The testprint command
1212--------------------------
1213
1214It is sometimes helpful to be able to print out the values of variables when
1215testing filter files. The command
1216
1217 testprint <text>
1218e.g. testprint "home=$home reply_address=$reply_address"
1219
1220does nothing when mail is being delivered. However, when the filtering code is
1221being tested by means of the -bf option (see section 1.3 above), the value of
1222the string is written to the standard output.
1223
1224
12253.18 The fail command
1226---------------------
1227
1228When Exim's filtering facilities are being used as a system filter, the fail
1229command is available, to force delivery failure. Because this command is
1230normally usable only by the system administrator, and not enabled for use by
1231ordinary users, it is described in more detail in the main Exim specification
1232rather than in this document.
1233
1234
12353.19 The freeze command
1236-----------------------
1237
1238When Exim's filtering facilities are being used as a system filter, the freeze
1239command is available, to freeze a message on the queue. Because this command is
1240normally usable only by the system administrator, and not enabled for use by
1241ordinary users, it is described in more detail in the main Exim specification
1242rather than in this document.
1243
1244
12453.20 The headers command
1246------------------------
1247
1248The headers command can be used to change the target character set that is used
1249when translating the contents of encoded header lines for insertion by the
1250$header_ mechanism (see section 3.5 above). The default can be set in the Exim
1251configuration; if not specified, ISO-8859-1 is used. The only currently
1252supported format for the headers command in user filters is as in this example:
1253
1254headers charset "UTF-8"
1255
1256That is, headers is followed by the word "charset" and then the name of a
1257character set. This particular example would be useful if you wanted to compare
1258the contents of a header to a UTF-8 string.
1259
1260In system filter files, the headers command can be used to add or remove header
1261lines from the message. These features are described in the main Exim
1262specification.
1263
1264
12653.21 Obeying commands conditionally
1266-----------------------------------
1267
1268Most of the power of filtering comes from the ability to test conditions and
1269obey different commands depending on the outcome. The if command is used to
1270specify conditional execution, and its general form is
1271
1272if <condition>
1273then <commands>
1274elif <condition>
1275then <commands>
1276else <commands>
1277endif
1278
1279There may be any number of elif and then sections (including none) and the else
1280section is also optional. Any number of commands, including nested if commands,
1281may appear in any of the <commands> sections.
1282
1283Conditions can be combined by using the words and and or, and round brackets
1284(parentheses) can be used to specify how several conditions are to combine.
1285Without brackets, and is more binding than or. For example:
1286
1287if
1288$h_subject: contains "Make money" or
1289$h_precedence: is "junk" or
1290($h_sender: matches ^\\d{8}@ and not personal) or
1291$message_body contains "this is not spam"
1292then
1293seen finish
1294endif
1295
1296A condition can be preceded by not to negate it, and there are also some
1297negative forms of condition that are more English-like.
1298
1299
13003.22 String testing conditions
1301------------------------------
1302
1303There are a number of conditions that operate on text strings, using the words
1304"begins", "ends", "is", "contains" and "matches". If you want to apply the same
1305test to more than one header line, you can easily concatenate them into a
1306single string for testing, as in this example:
1307
1308if "$h_to:, $h_cc:" contains me@domain.example then ...
1309
1310If a string-testing condition name is written in lower case, the testing of
1311letters is done without regard to case; if it is written in upper case (for
1312example, "CONTAINS"), the case of letters is taken into account.
1313
1314 <text1> begins <text2>
1315 <text1> does not begin <text2>
1316e.g. $header_from: begins "Friend@"
1317
1318A "begins" test checks for the presence of the second string at the start of
1319the first, both strings having been expanded.
1320
1321 <text1> ends <text2>
1322 <text1> does not end <text2>
1323e.g. $header_from: ends "public.com.example"
1324
1325An "ends" test checks for the presence of the second string at the end of the
1326first, both strings having been expanded.
1327
1328 <text1> is <text2>
1329 <text1> is not <text2>
1330e.g. $local_part_suffix is "-foo"
1331
1332An "is" test does an exact match between the strings, having first expanded
1333both strings.
1334
1335 <text1> contains <text2>
1336 <text1> does not contain <text2>
1337e.g. $header_subject: contains "evolution"
1338
1339A "contains" test does a partial string match, having expanded both strings.
1340
1341 <text1> matches <text2>
1342 <text1> does not match <text2>
1343e.g. $sender_address matches "(bill|john)@"
1344
1345For a "matches" test, after expansion of both strings, the second one is
1346interpreted as a regular expression. Exim uses the PCRE regular expression
1347library, which provides regular expressions that are compatible with Perl.
1348
1349The match succeeds if the regular expression matches any part of the first
1350string. If you want a regular expression to match only at the start or end of
1351the subject string, you must encode that requirement explicitly, using the "^"
1352or "$" metacharacters. The above example, which is not so constrained, matches
1353all these addresses:
1354
1355bill@test.example
1356john@some.example
1357spoonbill@example.com
1358littlejohn@example.com
1359
1360To match only the first two, you could use this:
1361
1362if $sender_address matches "^(bill|john)@" then ...
1363
1364Care must be taken if you need a backslash in a regular expression, because
1365backslashes are interpreted as escape characters both by the string expansion
1366code and by Exim's normal processing of strings in quotes. For example, if you
1367want to test the sender address for a domain ending in .com the regular
1368expression is
1369
1370\.com$
1371
1372The backslash and dollar sign in that expression have to be escaped when used
1373in a filter command, as otherwise they would be interpreted by the expansion
1374code. Thus, what you actually write is
1375
1376if $sender_address matches \\.com\$
1377
1378An alternative way of handling this is to make use of the "\N" expansion flag
1379for suppressing expansion:
1380
1381if $sender_address matches \N\.com$\N
1382
1383Everything between the two occurrences of "\N" is copied without change by the
1384string expander (and in fact you do not need the final one, because it is at
1385the end of the string). If the regular expression is given in quotes (mandatory
1386only if it contains white space) you have to write either
1387
1388if $sender_address matches "\\\\.com\\$"
1389
1390or
1391
1392if $sender_address matches "\\N\\.com$\\N"
1393
1394If the regular expression contains bracketed sub-expressions, numeric variable
1395substitutions such as $1 can be used in the subsequent actions after a
1396successful match. If the match fails, the values of the numeric variables
1397remain unchanged. Previous values are not restored after endif. In other words,
1398only one set of values is ever available. If the condition contains several
1399sub-conditions connected by and or or, it is the strings extracted from the
1400last successful match that are available in subsequent actions. Numeric
1401variables from any one sub-condition are also available for use in subsequent
1402sub-conditions, because string expansion of a condition occurs just before it
1403is tested.
1404
1405
14063.23 Numeric testing conditions
1407-------------------------------
1408
1409The following conditions are available for performing numerical tests:
1410
1411 <number1> is above <number2>
1412 <number1> is not above <number2>
1413 <number1> is below <number2>
1414 <number1> is not below <number2>
1415e.g. $message_size is not above 10k
1416
1417The <number> arguments must expand to strings of digits, optionally followed by
1418one of the letters K or M (upper case or lower case) which cause multiplication
1419by 1024 and 1024x1024 respectively.
1420
1421
14223.24 Testing for significant deliveries
1423---------------------------------------
1424
1425You can use the delivered condition to test whether or not any previously
1426obeyed filter commands have set up a significant delivery. For example:
1427
1428if not delivered then save mail/anomalous endif
1429
1430"Delivered" is perhaps a poor choice of name for this condition, because the
1431message has not actually been delivered; rather, a delivery has been set up for
1432later processing.
1433
1434
14353.25 Testing for error messages
1436-------------------------------
1437
1438The condition error_message is true if the incoming message is a bounce (mail
1439delivery error) message. Putting the command
1440
1441if error_message then finish endif
1442
1443at the head of your filter file is a useful insurance against things going
1444wrong in such a way that you cannot receive delivery error reports. Note:
1445error_message is a condition, not an expansion variable, and therefore is not
1446preceded by "$".
1447
1448
14493.26 Testing a list of addresses
1450--------------------------------
1451
1452There is a facility for looping through a list of addresses and applying a
1453condition to each of them. It takes the form
1454
1455foranyaddress <string> (<condition>)
1456
1457where <string> is interpreted as a list of RFC 2822 addresses, as in a typical
1458header line, and <condition> is any valid filter condition or combination of
1459conditions. The "group" syntax that is defined for certain header lines that
1460contain addresses is supported.
1461
1462The parentheses surrounding the condition are mandatory, to delimit it from
1463possible further sub-conditions of the enclosing if command. Within the
1464condition, the expansion variable $thisaddress is set to the non-comment
1465portion of each of the addresses in the string in turn. For example, if the
1466string is
1467
1468B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1469
1470then $thisaddress would take on the values "bart@sfld.example" and
1471"lisa@sfld.example" in turn.
1472
1473If there are no valid addresses in the list, the whole condition is false. If
1474the internal condition is true for any one address, the overall condition is
1475true and the loop ends. If the internal condition is false for all addresses in
1476the list, the overall condition is false. This example tests for the presence
1477of an eight-digit local part in any address in a To: header:
1478
1479if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1480
1481When the overall condition is true, the value of $thisaddress in the commands
1482that follow then is the last value it took on inside the loop. At the end of
1483the if command, the value of $thisaddress is reset to what it was before. It is
1484best to avoid the use of multiple occurrences of foranyaddress, nested or
1485otherwise, in a single if command, if the value of $thisaddress is to be used
1486afterwards, because it isn't always clear what the value will be. Nested if
1487commands should be used instead.
1488
1489Header lines can be joined together if a check is to be applied to more than
1490one of them. For example:
1491
1492if foranyaddress $h_to:,$h_cc: ....
1493
1494This scans through the addresses in both the To: and the Cc: headers.
1495
1496
14973.27 Testing for personal mail
1498------------------------------
1499
1500A common requirement is to distinguish between incoming personal mail and mail
1501from a mailing list, or from a robot or other automatic process (for example, a
1502bounce message). In particular, this test is normally required for "vacation
1503messages".
1504
1505The personal condition checks that the message is not a bounce message and that
1506the current user's email address appears in the To: header. It also checks that
1507the sender is not the current user or one of a number of common daemons, and
1508that there are no header lines starting List- in the message. Finally, it
1509checks the content of the Precedence: header line, if there is one.
1510
1511You should always use the personal condition when generating automatic
1512responses. This example shows the use of personal in a filter file that is
1513sending out vacation messages:
1514
1515if personal then
1516mail to $reply_address
1517subject "I am on holiday"
1518file $home/vacation/message
1519once $home/vacation/once
1520once_repeat 10d
1521endif
1522
1523It is tempting, when writing commands like the above, to quote the original
1524subject in the reply. For example:
1525
1526subject "Re: $h_subject:"
1527
1528There is a danger in doing this, however. It may allow a third party to
1529subscribe you to an opt-in mailing list, provided that the list accepts bounce
1530messages as subscription confirmations. (Messages sent from filters are always
1531sent as bounce messages.) Well-managed lists require a non-bounce message to
1532confirm a subscription, so the danger is relatively small.
1533
1534If prefixes or suffixes are in use for local parts - something which depends on
1535the configuration of Exim (see section 3.31 below) - the tests for the current
1536user are done with the full address (including the prefix and suffix, if any)
1537as well as with the prefix and suffix removed. If the system is configured to
1538rewrite local parts of mail addresses, for example, to rewrite "dag46" as
1539"Dirk.Gently", the rewritten form of the address is also used in the tests.
1540
1541
15423.28 Alias addresses for the personal condition
1543-----------------------------------------------
1544
1545It is quite common for people who have mail accounts on a number of different
1546systems to forward all their mail to one system, and in this case a check for
1547personal mail should test all their various mail addresses. To allow for this,
1548the personal condition keyword can be followed by
1549
1550alias <address>
1551
1552any number of times, for example:
1553
1554if personal alias smith@else.where.example
1555 alias jones@other.place.example
1556then ...
1557
1558The alias addresses are treated as alternatives to the current user's email
1559address when testing the contents of header lines.
1560
1561
15623.29 Details of the personal condition
1563--------------------------------------
1564
1565The basic personal test is roughly equivalent to the following:
1566
1567not error_message and
1568$message_headers does not contain "\nList-Id:" and
1569$message_headers does not contain "\nList-Help:" and
1570$message_headers does not contain "\nList-Subscribe:" and
1571$message_headers does not contain "\nList-Unsubscribe:" and
1572$message_headers does not contain "\nList-Post:" and
1573$message_headers does not contain "\nList-Owner:" and
1574$message_headers does not contain "\nList-Archive:" and
1575(
1576"${if def:h_auto-submitted:{present}{absent}}" is "absent" or
1577$header_auto-submitted: is "no"
1578) and
1579$header_precedence: does not contain "bulk" and
1580$header_precedence: does not contain "list" and
1581$header_precedence: does not contain "junk" and
1582foranyaddress $header_to:
1583( $thisaddress contains "$local_part$domain" ) and
1584not foranyaddress $header_from:
1585(
1586$thisaddress contains "$local_part@$domain" or
1587$thisaddress contains "server@" or
1588$thisaddress contains "daemon@" or
1589$thisaddress contains "root@" or
1590$thisaddress contains "listserv@" or
1591$thisaddress contains "majordomo@" or
1592$thisaddress contains "-request@" or
1593$thisaddress matches "^owner-[^@]+@"
1594)
1595
1596The variable $local_part contains the local part of the mail address of the
1597user whose filter file is being run - it is normally your login id. The $domain
1598variable contains the mail domain. As explained above, if aliases or rewriting
1599are defined, or if prefixes or suffixes are in use, the tests for the current
1600user are also done with alternative addresses.
1601
1602
16033.30 Testing delivery status
1604----------------------------
1605
1606There are two conditions that are intended mainly for use in system filter
1607files, but which are available in users' filter files as well. The condition
1608first_delivery is true if this is the first process that is attempting to
1609deliver the message, and false otherwise. This indicator is not reset until the
1610first delivery process successfully terminates; if there is a crash or a power
1611failure (for example), the next delivery attempt is also a "first delivery".
1612
1613In a user filter file first_delivery will be false if there was previously an
1614error in the filter, or if a delivery for the user failed owing to, for
1615example, a quota error, or if forwarding to a remote address was deferred for
1616some reason.
1617
1618The condition manually_thawed is true if the message was "frozen" for some
1619reason, and was subsequently released by the system administrator. It is
1620unlikely to be of use in users' filter files.
1621
1622
16233.31 Multiple personal mailboxes
1624--------------------------------
1625
1626The system administrator can configure Exim so that users can set up variants
1627on their email addresses and handle them separately. Consult your system
1628administrator or local documentation to see if this facility is enabled on your
1629system, and if so, what the details are.
1630
1631The facility involves the use of a prefix or a suffix on an email address. For
1632example, all mail addressed to lg303-<something> would be the property of user
1633lg303, who could determine how it was to be handled, depending on the value of
1634<something>.
1635
1636There are two possible ways in which this can be set up. The first possibility
1637is the use of multiple .forward files. In this case, mail to lg303-foo, for
1638example, is handled by looking for a file called .forward-foo in lg303's home
1639directory. If such a file does not exist, delivery fails and the message is
1640returned to its sender.
1641
1642The alternative approach is to pass all messages through a single .forward
1643file, which must be a filter file so that it can distinguish between the
1644different cases by referencing the variables $local_part_prefix or
1645$local_part_suffix, as in the final example in section 3.33 below.
1646
1647It is possible to configure Exim to support both schemes at once. In this case,
1648a specific .forward-foo file is first sought; if it is not found, the basic
1649.forward file is used.
1650
1651The personal test (see section 3.27) includes prefixes and suffixes in its
1652checking.
1653
1654
16553.32 Ignoring delivery errors
1656-----------------------------
1657
1658As was explained above, filtering just sets up addresses for delivery - no
1659deliveries are actually done while a filter file is active. If any of the
1660generated addresses subsequently suffers a delivery failure, an error message
1661is generated in the normal way. However, if a filter command that sets up a
1662delivery is preceded by the word "noerror", errors for that delivery, and any
1663deliveries consequent on it (that is, from alias, forwarding, or filter files
1664it invokes) are ignored.
1665
1666
16673.33 Examples of Exim filter commands
1668-------------------------------------
1669
1670Simple forwarding:
1671
1672# Exim filter
1673deliver baggins@rivendell.middle-earth.example
1674
1675Vacation handling using traditional means, assuming that the .vacation.msg and
1676other files have been set up in your home directory:
1677
1678# Exim filter
1679unseen pipe "/usr/ucb/vacation \"$local_part\""
1680
1681Vacation handling inside Exim, having first created a file called .vacation.msg
1682in your home directory:
1683
1684# Exim filter
1685if personal then vacation endif
1686
1687File some messages by subject:
1688
1689# Exim filter
1690if $header_subject: contains "empire" or
1691$header_subject: contains "foundation"
1692then
1693save $home/mail/f+e
1694endif
1695
1696Save all non-urgent messages by weekday:
1697
1698# Exim filter
1699if $header_subject: does not contain "urgent" and
1700$tod_full matches "^(...),"
1701then
1702save $home/mail/$1
1703endif
1704
1705Throw away all mail from one site, except from postmaster:
1706
1707# Exim filter
1708if $reply_address contains "@spam.site.example" and
1709$reply_address does not contain "postmaster@"
1710then
1711seen finish
1712endif
1713
1714Handle multiple personal mailboxes:
1715
1716# Exim filter
1717if $local_part_suffix is "-foo"
1718then
1719save $home/mail/foo
1720elif $local_part_suffix is "-bar"
1721then
1722save $home/mail/bar
1723endif
1724