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[exim.git] / doc / doc-docbook / filter.xfpt
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1. /////////////////////////////////////////////////////////////////////////////
2. This is the primary source of the document that describes Exim's filtering
3. facilities. It is an xfpt document that is converted into DocBook XML for
4. subsequent conversion into printing and online formats. The markup used
5. herein is "standard" xfpt markup, with some extras. The markup is summarized
6. in a file called Markup.txt.
7. /////////////////////////////////////////////////////////////////////////////
8
9.include stdflags
10.include stdmacs
2aee48d6 11.include ./local_params
9b371988 12.docbook
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13
14. /////////////////////////////////////////////////////////////////////////////
15. These lines are processing instructions for the Simple DocBook Processor that
16. Philip Hazel has developed as a less cumbersome way of making PostScript and
17. PDFs than using xmlto and fop. They will be ignored by all other XML
18. processors.
19. /////////////////////////////////////////////////////////////////////////////
20
21.literal xml
22<?sdop
23 foot_right_recto="&chaptertitle;"
24 foot_right_verso="&chaptertitle;"
2ff4a98a 25 table_warn_overflow="overprint"
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26 toc_chapter_blanks="yes,yes"
27 toc_title="Exim's interfaces to mail filtering"
28?>
29.literal off
30
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31.book
32
33. ===========================================================================
34. Additional xfpt markup used by this document, over and above the default
35. provided in the xfpt library.
36
37. Override the &$ flag to automatically insert a $ with the variable name
38
39.flag &$ $& "<varname>$" "</varname>"
40
41. A macro for the common 2-column tables
42
43.macro table2 100pt 300pt
44.itable none 0 0 2 $1 left $2 left
45.endmacro
46. ===========================================================================
47
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48. Copyright year. Update this (only) when changing content.
49
50.macro copyyear
1e1ddfac 512018
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52.endmacro
53
54. ===========================================================================
9b371988 55
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56. /////////////////////////////////////////////////////////////////////////////
57. /////////////////////////////////////////////////////////////////////////////
58
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59. This preliminary stuff creates a <bookinfo> entry in the XML. This is removed
60. when creating the PostScript/PDF output, because we do not want a full-blown
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61. title page created for those versions. When fop is being used to create
62. PS/PDF, the stylesheet fudges up a title line to replace the text "Table of
63. contents". When SDoP is being used, a processing instruction does this job.
64. For the other forms of output, the <bookinfo> element is retained and used.
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65
66.literal xml
67<bookinfo>
68<title>Exim's interfaces to mail filtering</title>
69<titleabbrev>Exim filtering</titleabbrev>
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70<date>
71.fulldate
72</date>
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73<author><firstname>Philip</firstname><surname>Hazel</surname></author>
74<authorinitials>PH</authorinitials>
75<revhistory><revision>
7cafba52 76.versiondatexml
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77 <authorinitials>PH</authorinitials>
78</revision></revhistory>
2aee48d6 79<copyright><year>
7d837ca7 80.copyyear
2aee48d6 81 </year><holder>University of Cambridge</holder></copyright>
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82</bookinfo>
83.literal off
84
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85. /////////////////////////////////////////////////////////////////////////////
86. /////////////////////////////////////////////////////////////////////////////
87
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4aa45c31 89.chapter "Forwarding and filtering in Exim" "CHAPforandfilt"
9b371988 90This document describes the user interfaces to Exim's in-built mail filtering
7d837ca7 91facilities, and is copyright &copy; University of Cambridge &copyyear(). It
2aee48d6 92corresponds to Exim version &version().
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93
94
95
4aa45c31 96.section "Introduction" "SEC00"
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97Most Unix mail transfer agents (programs that deliver mail) permit individual
98users to specify automatic forwarding of their mail, usually by placing a list
99of forwarding addresses in a file called &_.forward_& in their home
100directories. Exim extends this facility by allowing the forwarding instructions
101to be a set of rules rather than just a list of addresses, in effect providing
102&"&_.forward_& with conditions"&. Operating the set of rules is called
103&'filtering'&, and the file that contains them is called a &'filter file'&.
104
105Exim supports two different kinds of filter file. An &'Exim filter'& contains
106instructions in a format that is unique to Exim. A &'Sieve filter'& contains
107instructions in the Sieve format that is defined by RFC 3028. As this is a
108standard format, Sieve filter files may already be familiar to some users.
109Sieve files should also be portable between different environments. However,
110the Exim filtering facility contains more features (such as variable
111expansion), and better integration with the host environment (such as the use
112of external processes and pipes).
113
114The choice of which kind of filter to use can be left to the end-user, provided
115that the system administrator has configured Exim appropriately for both kinds
116of filter. However, if interoperability is important, Sieve is the only
117choice.
118
119The ability to use filtering or traditional forwarding has to be enabled by the
120system administrator, and some of the individual facilities can be separately
121enabled or disabled. A local document should be provided to describe exactly
122what has been enabled. In the absence of this, consult your system
123administrator.
124
125This document describes how to use a filter file and the format of its
126contents. It is intended for use by end-users. Both Sieve filters and Exim
127filters are covered. However, for Sieve filters, only issues that relate to the
128Exim implementation are discussed, since Sieve itself is described elsewhere.
129
130The contents of traditional &_.forward_& files are not described here. They
131normally contain just a list of addresses, file names, or pipe commands,
132separated by commas or newlines, but other types of item are also available.
133The full details can be found in the chapter on the &(redirect)& router in the
134Exim specification, which also describes how the system administrator can set
135up and control the use of filtering.
136
137
138
4aa45c31 139.section "Filter operation" "SEC01"
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140It is important to realize that, in Exim, no deliveries are actually made while
141a filter or traditional &_.forward_& file is being processed. Running a filter
142or processing a traditional &_.forward_& file sets up future delivery
143operations, but does not carry them out.
144
145The result of filter or &_.forward_& file processing is a list of destinations
146to which a message should be delivered. The deliveries themselves take place
147later, along with all other deliveries for the message. This means that it is
148not possible to test for successful deliveries while filtering. It also means
149that any duplicate addresses that are generated are dropped, because Exim never
150delivers the same message to the same address more than once.
151
152
153
154
155.section "Testing a new filter file" "SECTtesting"
156Filter files, especially the more complicated ones, should always be tested, as
157it is easy to make mistakes. Exim provides a facility for preliminary testing
158of a filter file before installing it. This tests the syntax of the file and
159its basic operation, and can also be used with traditional &_.forward_& files.
160
161Because a filter can do tests on the content of messages, a test message is
162required. Suppose you have a new filter file called &_myfilter_& and a test
163message in a file called &_test-message_&. Assuming that Exim is installed with
164the conventional path name &_/usr/sbin/sendmail_& (some operating systems use
165&_/usr/lib/sendmail_&), the following command can be used:
166.code
167/usr/sbin/sendmail -bf myfilter <test-message
168.endd
169The &%-bf%& option tells Exim that the following item on the command line is
170the name of a filter file that is to be tested. There is also a &%-bF%& option,
171which is similar, but which is used for testing system filter files, as opposed
172to user filter files, and which is therefore of use only to the system
173administrator.
174
175The test message is supplied on the standard input. If there are no
176message-dependent tests in the filter, an empty file (&_/dev/null_&) can be
177used. A supplied message must start with header lines or the &"From&~"& message
178separator line that is found in many multi-message folder files. Note that
179blank lines at the start terminate the header lines. A warning is given if no
180header lines are read.
181
182The result of running this command, provided no errors are detected in the
183filter file, is a list of the actions that Exim would try to take if presented
184with the message for real. For example, for an Exim filter, the output
185.code
186Deliver message to: gulliver@lilliput.fict.example
187Save message to: /home/lemuel/mail/archive
188.endd
189means that one copy of the message would be sent to
190&'gulliver@lilliput.fict.example'&, and another would be added to the file
191&_/home/lemuel/mail/archive_&, if all went well.
192
193The actions themselves are not attempted while testing a filter file in this
194way; there is no check, for example, that any forwarding addresses are valid.
195For an Exim filter, if you want to know why a particular action is being taken,
196add the &%-v%& option to the command. This causes Exim to output the results of
197any conditional tests and to indent its output according to the depth of
198nesting of &(if)& commands. Further additional output from a filter test can be
199generated by the &(testprint)& command, which is described below.
200
201When Exim is outputting a list of the actions it would take, if any text
202strings are included in the output, non-printing characters therein are
203converted to escape sequences. In particular, if any text string contains a
204newline character, this is shown as &"\n"& in the testing output.
205
206When testing a filter in this way, Exim makes up an &"envelope"& for the
207message. The recipient is by default the user running the command, and so is
208the sender, but the command can be run with the &%-f%& option to supply a
209different sender. For example,
210.code
211/usr/sbin/sendmail -bf myfilter \
212 -f islington@never.where <test-message
213.endd
214Alternatively, if the &%-f%& option is not used, but the first line of the
215supplied message is a &"From&~"& separator from a message folder file (not the
216same thing as a &'From:'& header line), the sender is taken from there. If
217&%-f%& is present, the contents of any &"From&~"& line are ignored.
218
219The &"return path"& is the same as the envelope sender, unless the message
220contains a &'Return-path:'& header, in which case it is taken from there. You
221need not worry about any of this unless you want to test out features of a
222filter file that rely on the sender address or the return path.
223
224It is possible to change the envelope recipient by specifying further options.
225The &%-bfd%& option changes the domain of the recipient address, while the
226&%-bfl%& option changes the &"local part"&, that is, the part before the @
227sign. An adviser could make use of these to test someone else's filter file.
228
229The &%-bfp%& and &%-bfs%& options specify the prefix or suffix for the local
230part. These are relevant only when support for multiple personal mailboxes is
231implemented; see the description in section &<<SECTmbox>>& below.
232
233
4aa45c31 234.section "Installing a filter file" "SEC02"
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235A filter file is normally installed under the name &_.forward_& in your home
236directory &-- it is distinguished from a conventional &_.forward_& file by its
237first line (described below). However, the file name is configurable, and some
238system administrators may choose to use some different name or location for
239filter files.
240
241
4aa45c31 242.section "Testing an installed filter file" "SEC03"
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243Testing a filter file before installation cannot find every potential problem;
244for example, it does not actually run commands to which messages are piped.
245Some &"live"& tests should therefore also be done once a filter is installed.
246
247If at all possible, test your filter file by sending messages from some other
248account. If you send a message to yourself from the filtered account, and
249delivery fails, the error message will be sent back to the same account, which
250may cause another delivery failure. It won't cause an infinite sequence of such
251messages, because delivery failure messages do not themselves generate further
252messages. However, it does mean that the failure won't be returned to you, and
253also that the postmaster will have to investigate the stuck message.
254
255If you have to test an Exim filter from the same account, a sensible precaution
256is to include the line
257.code
258if error_message then finish endif
259.endd
260as the first filter command, at least while testing. This causes filtering to
261be abandoned for a delivery failure message, and since no destinations are
262generated, the message goes on to be delivered to the original address. Unless
263there is a good reason for not doing so, it is recommended that the above test
264be left in all Exim filter files. (This does not apply to Sieve files.)
265
266
267
4aa45c31 268.section "Details of filtering commands" "SEC04"
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269The filtering commands for Sieve and Exim filters are completely different in
270syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
271chapter we describe how it is integrated into Exim. The subsequent chapter
272covers Exim filtering commands in detail.
273
274
275
276.chapter "Sieve filter files" "CHAPsievefilter"
277The code for Sieve filtering in Exim was contributed by Michael Haardt, and
278most of the content of this chapter is taken from the notes he provided. Since
279Sieve is an extensible language, it is important to understand &"Sieve"& in
280this context as &"the specific implementation of Sieve for Exim"&.
281
282This chapter does not contain a description of Sieve, since that can be found
283in RFC 3028, which should be read in conjunction with these notes.
284
285The Exim Sieve implementation offers the core as defined by RFC 3028,
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286comparison tests, the subaddress parameter, the &*copy*&, &*envelope*&,
287&*fileinto*&, &*notify*&, and &*vacation*& extensions, but not the &*reject*&
288extension. Exim does not support message delivery notifications (MDNs), so
289adding it just to the Sieve filter (as required for &*reject*&) makes little
290sense.
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291
292In order for Sieve to work properly in Exim, the system administrator needs to
293make some adjustments to the Exim configuration. These are described in the
294chapter on the &(redirect)& router in the full Exim specification.
295
296
4aa45c31 297.section "Recognition of Sieve filters" "SEC05"
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298A filter file is interpreted as a Sieve filter if its first line is
299.code
300# Sieve filter
301.endd
302This is what distinguishes it from a conventional &_.forward_& file or an Exim
303filter file.
304
305
306
4aa45c31 307.section "Saving to specified folders" "SEC06"
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308If the system administrator has set things up as suggested in the Exim
309specification, and you use &(keep)& or &(fileinto)& to save a mail into a
310folder, absolute files are stored where specified, relative files are stored
311relative to &$home$&, and &_inbox_& goes to the standard mailbox location.
312
313
314
4aa45c31 315.section "Strings containing header names" "SEC07"
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316RFC 3028 does not specify what happens if a string denoting a header field does
317not contain a valid header name, for example, it contains a colon. This
318implementation generates an error instead of ignoring the header field in order
319to ease script debugging, which fits in with the common picture of Sieve.
320
321
322
4aa45c31 323.section "Exists test with empty list of headers" "SEC08"
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324The &*exists*& test succeeds only if all the specified headers exist. RFC 3028
325does not 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
330
4aa45c31 331.section "Header test with invalid MIME encoding in header" "SEC09"
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332Some MUAs process invalid base64 encoded data, generating junk. Others ignore
333junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
334specify how to react in this case, other than stating that a client must not
335forbid to process a message for that reason. RFC 2045 specifies that invalid
336data should be ignored (apparently looking at end of line characters). It also
337specifies that invalid data may lead to rejecting messages containing them (and
338there it appears to talk about true encoding violations), which is a clear
339contradiction to ignoring them.
340
341RFC 3028 does not specify how to process incorrect MIME words. This
342implementation treats them literally, as it does if the word is correct but its
343character set cannot be converted to UTF-8.
344
345
346
4aa45c31 347.section "Address test for multiple addresses per header" "SEC10"
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348A header may contain multiple addresses. RFC 3028 does not explicitly specify
349how to deal with them, but since the address test checks if anything matches
350anything else, matching one address suffices to satisfy the condition. That
351makes it impossible to test if a header contains a certain set of addresses and
352no more, but it is more logical than letting the test fail if the header
353contains an additional address besides the one the test checks for.
354
355
356
4aa45c31 357.section "Semantics of keep" "SEC11"
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358The &(keep)& command is equivalent to
359.code
360fileinto "inbox";
361.endd
362It saves the message and resets the implicit keep flag. It does not set the
363implicit keep flag; there is no command to set it once it has been reset.
364
365
366
4aa45c31 367.section "Semantics of fileinto" "SEC12"
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368RFC 3028 does not specify whether &(fileinto)& should try to create a mail
369folder if it does not exist. This implementation allows the sysadmin to
370configure that aspect using the &(appendfile)& transport options
371&%create_directory%&, &%create_file%&, and &%file_must_exist%&. See the
372&(appendfile)& transport in the Exim specification for details.
373
374
375
4aa45c31 376.section "Semantics of redirect" "SEC13"
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377Sieve scripts are supposed to be interoperable between servers, so this
378implementation does not allow mail to be redirected to unqualified addresses,
379because the domain would depend on the system being used. On systems with
380virtual mail domains, the default domain is probably not what the user expects
381it to be.
382
383
384
4aa45c31 385.section "String arguments" "SEC14"
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386There has been confusion if the string arguments to &(require)& are to be
387matched case-sensitively or not. This implementation matches them with the
388match type &(:is)& (default, see section 2.7.1 of the RFC) and the comparator
389&(i;ascii-casemap)& (default, see section 2.7.3 of the RFC). The RFC defines
390the command defaults clearly, so any different implementations violate RFC
3913028. The same is valid for comparator names, also specified as strings.
392
393
394
4aa45c31 395.section "Number units" "SEC15"
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396There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
397The mistake is obvious, because RFC 3028 specifies G to denote 2^30
398(which is gibi, not tebi), and that is what this implementation uses as
399the scaling factor for the suffix G.
400
401
402
4aa45c31 403.section "RFC compliance" "SEC16"
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404Exim requires the first line of a Sieve filter to be
405.code
406# Sieve filter
407.endd
408Of course the RFC does not specify that line. Do not expect examples to work
409without adding it, though.
410
411RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
412CRLF is universally used in network protocols to mark the end of the line. This
413implementation does not embed Sieve in a network protocol, but uses Sieve
414scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
415character, this implementation does, too, by default, though the system
416administrator may choose (at Exim compile time) to use CRLF instead.
417
418Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
419implementation repeats this violation to stay consistent with Exim. This is in
420preparation for UTF-8 data.
421
422Sieve scripts cannot contain NUL characters in strings, but mail headers could
423contain MIME encoded NUL characters, which could never be matched by Sieve
424scripts using exact comparisons. For that reason, this implementation extends
425the Sieve quoted string syntax with \0 to describe a NUL character, violating
426\0 being the same as 0 in RFC 3028. Even without using \0, the following tests
427are all true in this implementation. Implementations that use C-style strings
428will only evaluate the first test as true.
429.code
430Subject: =?iso-8859-1?q?abc=00def
431
432header :contains "Subject" ["abc"]
433header :contains "Subject" ["def"]
434header :matches "Subject" ["abc?def"]
435.endd
436Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
437way that NUL characters truncating strings is allowed for Sieve
438implementations, although not recommended. It is further allowed to use encoded
439NUL characters in headers, but that's not recommended either. The above example
440shows why.
441
442RFC 3028 states that if an implementation fails to convert a character set to
443UTF-8, two strings cannot be equal if one contains octets greater than 127.
444Assuming that all unknown character sets are one-byte character sets with the
445lower 128 octets being US-ASCII is not sound, so this implementation violates
446RFC 3028 and treats such MIME words literally. That way at least something
447could be matched.
448
449The folder specified by &(fileinto)& must not contain the character sequence
450&".."& to avoid security problems. RFC 3028 does not specify the syntax of
451folders apart from &(keep)& being equivalent to
452.code
453fileinto "INBOX";
454.endd
455This implementation uses &_inbox_& instead.
456
457Sieve script errors currently cause messages to be silently filed into
458&_inbox_&. RFC 3028 requires that the user is notified of that condition.
459This may be implemented in the future by adding a header line to mails that
460are filed into &_inbox_& due to an error in the filter.
461
462
463
464.chapter "Exim filter files" "CHAPeximfilter"
465This chapter contains a full description of the contents of Exim filter files.
466
467
4aa45c31 468.section "Format of Exim filter files" "SEC17"
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469Apart from leading white space, the first text in an Exim filter file must be
470.code
471# Exim filter
472.endd
473This is what distinguishes it from a conventional &_.forward_& file or a Sieve
474filter file. If the file does not have this initial line (or the equivalent for
475a Sieve filter), it is treated as a conventional &_.forward_& file, both when
476delivering mail and when using the &%-bf%& testing mechanism. The white space
477in the line is optional, and any capitalization may be used. Further text on
478the same line is treated as a comment. For example, you could have
479.code
480# Exim filter <<== do not edit or remove this line!
481.endd
482The remainder of the file is a sequence of filtering commands, which consist of
483keywords and data values. For example, in the command
484.code
485deliver gulliver@lilliput.fict.example
486.endd
487the keyword is &`deliver`& and the data value is
488&`gulliver@lilliput.fict.example`&. White space or line breaks separate the
489components of a command, except in the case of conditions for the &(if)&
490command, where round brackets (parentheses) also act as separators. Complete
491commands are separated from each other by white space or line breaks; there are
492no special terminators. Thus, several commands may appear on one line, or one
493command may be spread over a number of lines.
494
495If the character # follows a separator anywhere in a command, everything from
496# up to the next newline is ignored. This provides a way of including comments
497in a filter file.
498
499
4aa45c31 500.section "Data values in filter commands" "SEC18"
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501There are two ways in which a data value can be input:
502
503.ilist
504If the text contains no white space, it can be typed verbatim. However, if it
505is part of a condition, it must also be free of round brackets (parentheses),
506as these are used for grouping in conditions.
507.next
508Otherwise, text must be enclosed in double quotation marks. In this case, the
509character \ (backslash) is treated as an &"escape character"& within the
510string, causing the following character or characters to be treated specially:
511.display
512&`\n`& is replaced by a newline
513&`\r`& is replaced by a carriage return
514&`\t`& is replaced by a tab
515.endd
516.endlist
517
518Backslash followed by up to three octal digits is replaced by the character
519specified by those digits, and &`\x`& followed by up to two hexadecimal digits
520is treated similarly. Backslash followed by any other character is replaced by
521the second character, so that in particular, &`\"`& becomes &`"`& and &`\\`&
522becomes &`\`&. A data item enclosed in double quotes can be continued onto the
523next line by ending the first line with a backslash. Any leading white space at
524the start of the continuation line is ignored.
525
526In addition to the escape character processing that occurs when strings are
527enclosed in quotes, most data values are also subject to &'string expansion'&
528(as described in the next section), in which case the characters &`$`& and
529&`\`& are also significant. This means that if a single backslash is actually
530required in such a string, and the string is also quoted, &`\\\\`& has to be
531entered.
532
533The maximum permitted length of a data string, before expansion, is 1024
534characters.
535
536
537.section "String expansion" "SECTfilterstringexpansion"
538Most data values are expanded before use. Expansion consists of replacing
539substrings beginning with &`$`& with other text. The full expansion facilities
540available in Exim are extensive. If you want to know everything that Exim can
541do with strings, you should consult the chapter on string expansion in the Exim
542documentation.
543
544In filter files, by far the most common use of string expansion is the
545substitution of the contents of a variable. For example, the substring
546.code
547$reply_address
548.endd
549is replaced by the address to which replies to the message should be sent. If
550such a variable name is followed by a letter or digit or underscore, it must be
551enclosed in curly brackets (braces), for example,
552.code
553${reply_address}
554.endd
555If a &`$`& character is actually required in an expanded string, it must be
556escaped with a backslash, and because backslash is also an escape character in
557quoted input strings, it must be doubled in that case. The following two
558examples illustrate two different ways of testing for a &`$`& character in a
559message:
560.code
561if $message_body contains \$ then ...
562if $message_body contains "\\$" then ...
563.endd
564You can prevent part of a string from being expanded by enclosing it between
565two occurrences of &`\N`&. For example,
566.code
567if $message_body contains \N$$$$\N then ...
568.endd
569tests for a run of four dollar characters.
570
571
4aa45c31 572.section "Some useful general variables" "SEC19"
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573A complete list of the available variables is given in the Exim documentation.
574This shortened list contains the ones that are most likely to be useful in
575personal filter files:
576
577&$body_linecount$&: The number of lines in the body of the message.
578
579&$body_zerocount$&: The number of binary zero characters in the body of the
580message.
581
582&$home$&: In conventional configurations, this variable normally contains the
583user's home directory. The system administrator can, however, change this.
584
585&$local_part$&: The part of the email address that precedes the @ sign &--
586normally the user's login name. If support for multiple personal mailboxes is
587enabled (see section &<<SECTmbox>>& below) and a prefix or suffix for the local
588part was recognized, it is removed from the string in this variable.
589
590&$local_part_prefix$&: If support for multiple personal mailboxes is enabled
591(see section &<<SECTmbox>>& below), and a local part prefix was recognized,
592this variable contains the prefix. Otherwise it contains an empty string.
593
594&$local_part_suffix$&: If support for multiple personal mailboxes is enabled
595(see section &<<SECTmbox>>& below), and a local part suffix was recognized,
596this variable contains the suffix. Otherwise it contains an empty string.
597
598&$message_body$&: The initial portion of the body of the message. By default,
599up to 500 characters are read into this variable, but the system administrator
600can configure this to some other value. Newlines in the body are converted into
601single spaces.
602
603&$message_body_end$&: The final portion of the body of the message, formatted
604and limited in the same way as &$message_body$&.
605
606&$message_body_size$&: The size of the body of the message, in bytes.
607
608&$message_exim_id$&: The message's local identification string, which is unique
609for each message handled by a single host.
610
611&$message_headers$&: The header lines of the message, concatenated into a
612single string, with newline characters between them.
613
614&$message_size$&: The size of the entire message, in bytes.
615
616&$original_local_part$&: When an address that arrived with the message is
617being processed, this contains the same value as the variable &$local_part$&.
618However, if an address generated by an alias, forward, or filter file is being
619processed, this variable contains the local part of the original address.
620
621&$reply_address$&: The contents of the &'Reply-to:'& header, if the message
622has one; otherwise the contents of the &'From:'& header. It is the address to
623which normal replies to the message should be sent.
624
625&$return_path$&: The return path &-- that is, the sender field that will be
626transmitted as part of the message's envelope if the message is sent to another
627host. This is the address to which delivery errors are sent. In many cases,
628this variable has the same value as &$sender_address$&, but if, for example,
629an incoming message to a mailing list has been expanded, &$return_path$& may
630have been changed to contain the address of the list maintainer.
631
632&$sender_address$&: The sender address that was received in the envelope of
633the message. This is not necessarily the same as the contents of the &'From:'&
634or &'Sender:'& header lines. For delivery error messages (&"bounce messages"&)
635there is no sender address, and this variable is empty.
636
637&$tod_full$&: A full version of the time and date, for example: Wed, 18 Oct
6381995 09:51:40 +0100. The timezone is always given as a numerical offset from
639GMT.
640
641&$tod_log$&: The time and date in the format used for writing Exim's log files,
642without the timezone, for example: 1995-10-12 15:32:29.
643
644&$tod_zone$&: The local timezone offset, for example: +0100.
645
646
647
648.section "Header variables" "SECTheadervariables"
649There is a special set of expansion variables containing the header lines of
650the message being processed. These variables have names beginning with
651&$header_$& followed by the name of the header line, terminated by a colon.
652For example,
653.code
654$header_from:
655$header_subject:
656.endd
657The whole item, including the terminating colon, is replaced by the contents of
658the message header line. If there is more than one header line with the same
659name, their contents are concatenated. For header lines whose data consists of
660a list of addresses (for example, &'From:'& and &'To:'&), a comma and newline
661is inserted between each set of data. For all other header lines, just a
662newline is used.
663
664Leading and trailing white space is removed from header line data, and if there
665are any MIME &"words"& that are encoded as defined by RFC 2047 (because they
666contain non-ASCII characters), they are decoded and translated, if possible, to
667a local character set. Translation is attempted only on operating systems that
668have the &[iconv()]& function. This makes the header line look the same as it
669would when displayed by an MUA. The default character set is ISO-8859-1, but
670this can be changed by means of the &(headers)& command (see below).
671
672If you want to see the actual characters that make up a header line, you can
673specify &$rheader_$& instead of &$header_$&. This inserts the &"raw"&
674header line, unmodified.
675
676There is also an intermediate form, requested by &$bheader_$&, which removes
677leading and trailing space and decodes MIME &"words"&, but does not do any
678character translation. If an attempt to decode what looks superficially like a
679MIME &"word"& fails, the raw string is returned. If decoding produces a binary
680zero character, it is replaced by a question mark.
681
682The capitalization of the name following &$header_$& is not significant.
683Because any printing character except colon may appear in the name of a
684message's header (this is a requirement of RFC 2822, the document that
685describes the format of a mail message) curly brackets must &'not'& be used in
686this case, as they will be taken as part of the header name. Two shortcuts are
687allowed in naming header variables:
688
689.ilist
690The initiating &$header_$&, &$rheader_$&, or &$bheader_$& can be
691abbreviated to &$h_$&, &$rh_$&, or &$bh_$&, respectively.
692.next
693The terminating colon can be omitted if the next character is white space. The
694white space character is retained in the expanded string. However, this is not
695recommended, because it makes it easy to forget the colon when it really is
696needed.
697.endlist
698
699If the message does not contain a header of the given name, an empty string is
700substituted. Thus it is important to spell the names of headers correctly. Do
701not use &$header_Reply_to$& when you really mean &$header_Reply-to$&.
702
703
4aa45c31 704.section "User variables" "SEC20"
9b371988
PH
705There are ten user variables with names &$n0$& &-- &$n9$& that can be
706incremented by the &(add)& command (see section &<<SECTadd>>&). These can be
707used for &"scoring"& messages in various ways. If Exim is configured to run a
708&"system filter"& on every message, the values left in these variables are
709copied into the variables &$sn0$& &-- &$sn9$& at the end of the system filter,
710thus making them available to users' filter files. How these values are used is
711entirely up to the individual installation.
712
713
4aa45c31 714.section "Current directory" "SEC21"
9b371988
PH
715The contents of your filter file should not make any assumptions about the
716current directory. It is best to use absolute paths for file names; you can
717normally make use of the &$home$& variable to refer to your home directory. The
718&(save)& command automatically inserts &$home$& at the start of non-absolute
719paths.
720
721
722
723
724.section "Significant deliveries" "SECTsigdel"
725When in the course of delivery a message is processed by a filter file, what
726happens next, that is, after the filter file has been processed, depends on
727whether or not the filter sets up any &'significant deliveries'&. If at least
728one significant delivery is set up, the filter is considered to have handled
729the entire delivery arrangements for the current address, and no further
730processing of the address takes place. If, however, no significant deliveries
731are set up, Exim continues processing the current address as if there were no
732filter file, and typically sets up a delivery of a copy of the message into a
733local mailbox. In particular, this happens in the special case of a filter file
734containing only comments.
735
736The delivery commands &(deliver)&, &(save)&, and &(pipe)& are by default
737significant. However, if such a command is preceded by the word &"unseen"&, its
738delivery is not considered to be significant. In contrast, other commands such
739as &(mail)& and &(vacation)& do not set up significant deliveries unless
740preceded by the word &"seen"&. The following example commands set up
741significant deliveries:
742.code
743deliver jack@beanstalk.example
744pipe $home/bin/mymailscript
745seen mail subject "message discarded"
746seen finish
747.endd
748The following example commands do not set up significant deliveries:
749.code
750unseen deliver jack@beanstalk.example
751unseen pipe $home/bin/mymailscript
752mail subject "message discarded"
753finish
754.endd
755
756
757
4aa45c31 758.section "Filter commands" "SEC222"
9b371988
PH
759The filter commands that are described in subsequent sections are listed
760below, with the section in which they are described in brackets:
761
762.table2
763.row &(add)& "&~&~increment a user variable (section &<<SECTadd>>&)"
764.row &(deliver)& "&~&~deliver to an email address (section &<<SECTdeliver>>&)"
765.row &(fail)& "&~&~force delivery failure (sysadmin use) (section &<<SECTfail>>&)"
766.row &(finish)& "&~&~end processing (section &<<SECTfinish>>&)"
767.row &(freeze)& "&~&~freeze message (sysadmin use) (section &<<SECTfreeze>>&)"
768.row &(headers)& "&~&~set the header character set (section &<<SECTheaders>>&)"
769.row &(if)& "&~&~test condition(s) (section &<<SECTif>>&)"
770.row &(logfile)& "&~&~define log file (section &<<SECTlog>>&)"
771.row &(logwrite)& "&~&~write to log file (section &<<SECTlog>>&)"
772.row &(mail)& "&~&~send a reply message (section &<<SECTmail>>&)"
773.row &(pipe)& "&~&~pipe to a command (section &<<SECTpipe>>&)"
774.row &(save)& "&~&~save to a file (section &<<SECTsave>>&)"
775.row &(testprint)& "&~&~print while testing (section &<<SECTtestprint>>&)"
776.row &(vacation)& "&~&~tailored form of &(mail)& (section &<<SECTmail>>&)"
777.endtable
778
779The &(headers)& command has additional parameters that can be used only in a
780system filter. The &(fail)& and &(freeze)& commands are available only when
781Exim's filtering facilities are being used as a system filter, and are
782therefore usable only by the system administrator and not by ordinary users.
783They are mentioned only briefly in this document; for more information, see the
784main Exim specification.
785
786
787
788.section "The add command" "SECTadd"
789.display
790&` add `&<&'number'&>&` to `&<&'user variable'&>
791&`e.g. add 2 to n3`&
792.endd
793
794There are 10 user variables of this type, with names &$n0$& &-- &$n9$&. Their
795values can be obtained by the normal expansion syntax (for example &$n3$&) in
796other commands. At the start of filtering, these variables all contain zero.
797Both arguments of the &(add)& command are expanded before use, making it
798possible to add variables to each other. Subtraction can be obtained by adding
799negative numbers.
800
801
802
803.section "The deliver command" "SECTdeliver"
804.display
805&` deliver`& <&'mail address'&>
806&`e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"`&
807.endd
808
809This command provides a forwarding operation. The delivery that it sets up is
810significant unless the command is preceded by &"unseen"& (see section
811&<<SECTsigdel>>&). The message is sent on to the given address, exactly as
812happens if the address had appeared in a traditional &_.forward_& file. If you
813want to deliver the message to a number of different addresses, you can use
814more than one &(deliver)& command (each one may have only one address).
815However, duplicate addresses are discarded.
816
817To deliver a copy of the message to your normal mailbox, your login name can be
818given as the address. Once an address has been processed by the filtering
819mechanism, an identical generated address will not be so processed again, so
820doing this does not cause a loop.
821
822However, if you have a mail alias, you should &'not'& refer to it here. For
823example, if the mail address &'L.Gulliver'& is aliased to &'lg303'& then all
824references in Gulliver's &_.forward_& file should be to &'lg303'&. A reference
825to the alias will not work for messages that are addressed to that alias,
826since, like &_.forward_& file processing, aliasing is performed only once on an
827address, in order to avoid looping.
828
829Following the new address, an optional second address, preceded by
830&"errors_to"& may appear. This changes the address to which delivery errors on
831the forwarded message will be sent. Instead of going to the message's original
832sender, they go to this new address. For ordinary users, the only value that is
833permitted for this address is the user whose filter file is being processed.
834For example, the user &'lg303'& whose mailbox is in the domain
835&'lilliput.example'& could have a filter file that contains
836.code
837deliver jon@elsewhere.example errors_to lg303@lilliput.example
838.endd
839Clearly, using this feature makes sense only in situations where not all
840messages are being forwarded. In particular, bounce messages must not be
841forwarded in this way, as this is likely to create a mail loop if something
842goes wrong.
843
844
845
846.section "The save command" "SECTsave"
847.display
848&` save `&<&'file name'&>
849&`e.g. save $home/mail/bookfolder`&
850.endd
851
852This command specifies that a copy of the message is to be appended to the
853given file (that is, the file is to be used as a mail folder). The delivery
854that &(save)& sets up is significant unless the command is preceded by
855&"unseen"& (see section &<<SECTsigdel>>&).
856
857More than one &(save)& command may be obeyed; each one causes a copy of the
858message to be written to its argument file, provided they are different
859(duplicate &(save)& commands are ignored).
860
861If the file name does not start with a / character, the contents of the
f89d2485
PH
862&$home$& variable are prepended, unless it is empty, or the system
863administrator has disabled this feature. In conventional configurations, this
553c0e3a
PH
864variable is normally set in a user filter to the user's home directory, but the
865system administrator may set it to some other path. In some configurations,
f89d2485 866&$home$& may be unset, or prepending may be disabled, in which case a
553c0e3a
PH
867non-absolute path name may be generated. Such configurations convert this to an
868absolute path when the delivery takes place. In a system filter, &$home$& is
869never set.
9b371988
PH
870
871The user must of course have permission to write to the file, and the writing
872of the file takes place in a process that is running as the user, under the
873user's primary group. Any secondary groups to which the user may belong are not
874normally taken into account, though the system administrator can configure Exim
875to set them up. In addition, the ability to use this command at all is
876controlled by the system administrator &-- it may be forbidden on some systems.
877
878An optional mode value may be given after the file name. The value for the mode
879is interpreted as an octal number, even if it does not begin with a zero. For
880example:
881.code
882save /some/folder 640
883.endd
884This makes it possible for users to override the system-wide mode setting for
885file deliveries, which is normally 600. If an existing file does not have the
886correct mode, it is changed.
887
888An alternative form of delivery may be enabled on your system, in which each
889message is delivered into a new file in a given directory. If this is the case,
890this functionality can be requested by giving the directory name terminated by
891a slash after the &(save)& command, for example
892.code
893save separated/messages/
894.endd
895There are several different formats for such deliveries; check with your system
896administrator or local documentation to find out which (if any) are available
897on your system. If this functionality is not enabled, the use of a path name
898ending in a slash causes an error.
899
900
901
902.section "The pipe command" "SECTpipe"
903.display
904&` pipe `&<&'command'&>
905&`e.g. pipe "$home/bin/countmail $sender_address"`&
906.endd
907
908This command specifies that the message is to be delivered to the specified
909command using a pipe. The delivery that it sets up is significant unless the
910command is preceded by &"unseen"& (see section &<<SECTsigdel>>&). Remember,
911however, that no deliveries are done while the filter is being processed. All
912deliveries happen later on. Therefore, the result of running the pipe is not
913available to the filter.
914
915When the deliveries are done, a separate process is run, and a copy of the
916message is passed on its standard input. The process runs as the user, under
917the user's primary group. Any secondary groups to which the user may belong are
918not normally taken into account, though the system administrator can configure
919Exim to set them up. More than one &(pipe)& command may appear; each one causes
920a copy of the message to be written to its argument pipe, provided they are
921different (duplicate &(pipe)& commands are ignored).
922
923When the time comes to transport the message, the command supplied to &(pipe)&
924is split up by Exim into a command name and a number of arguments. These are
925delimited by white space except for arguments enclosed in double quotes, in
926which case backslash is interpreted as an escape, or in single quotes, in which
927case no escaping is recognized. Note that as the whole command is normally
928supplied in double quotes, a second level of quoting is required for internal
929double quotes. For example:
930.code
931pipe "$home/myscript \"size is $message_size\""
932.endd
933String expansion is performed on the separate components after the line has
934been split up, and the command is then run directly by Exim; it is not run
935under a shell. Therefore, substitution cannot change the number of arguments,
936nor can quotes, backslashes or other shell metacharacters in variables cause
937confusion.
938
939Documentation for some programs that are normally run via this kind of pipe
940often suggest that the command should start with
941.code
942IFS=" "
943.endd
944This is a shell command, and should &'not'& be present in Exim filter files,
945since it does not normally run the command under a shell.
946
947However, there is an option that the administrator can set to cause a shell to
948be used. In this case, the entire command is expanded as a single string and
949passed to the shell for interpretation. It is recommended that this be avoided
950if at all possible, since it can lead to problems when inserted variables
951contain shell metacharacters.
952
953The default PATH set up for the command is determined by the system
954administrator, usually containing at least &_/bin_& and &_/usr/bin_& so that
955common commands are available without having to specify an absolute file name.
956However, it is possible for the system administrator to restrict the pipe
957facility so that the command name must not contain any / characters, and must
958be found in one of the directories in the configured PATH. It is also possible
959for the system administrator to lock out the use of the &(pipe)& command
960altogether.
961
962When the command is run, a number of environment variables are set up. The
963complete list for pipe deliveries may be found in the Exim reference manual.
964Those that may be useful for pipe deliveries from user filter files are:
965
966.display
967&`DOMAIN `& the domain of the address
968&`HOME `& your home directory
969&`LOCAL_PART `& see below
970&`LOCAL_PART_PREFIX `& see below
971&`LOCAL_PART_SUFFIX `& see below
972&`LOGNAME `& your login name
973&`MESSAGE_ID `& the unique id of the message
974&`PATH `& the command search path
975&`RECIPIENT `& the complete recipient address
976&`SENDER `& the sender of the message
977&`SHELL `& &`/bin/sh`&
978&`USER `& see below
979.endd
980
981LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
982id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
983recognize prefixes or suffixes in the local parts of addresses. For example, a
984message addressed to &'pat-suf2@domain.example'& may cause the filter for user
985&'pat'& to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
986&`-suf2`& when the pipe command runs. The system administrator has to configure
987Exim specially for this feature to be available.
988
989If you run a command that is a shell script, be very careful in your use of
990data from the incoming message in the commands in your script. RFC 2822 is very
991generous in the characters that are permitted to appear in mail addresses, and
992in particular, an address may begin with a vertical bar or a slash. For this
993reason you should always use quotes round any arguments that involve data from
994the message, like this:
995.code
996/some/command '$SENDER'
997.endd
998so that inserted shell meta-characters do not cause unwanted effects.
999
1000Remember that, as was explained earlier, the pipe command is not run at the
1001time the filter file is interpreted. The filter just defines what deliveries
1002are required for one particular addressee of a message. The deliveries
1003themselves happen later, once Exim has decided everything that needs to be done
1004for the message.
1005
1006A consequence of this is that you cannot inspect the return code from the pipe
1007command from within the filter. Nevertheless, the code returned by the command
1008is important, because Exim uses it to decide whether the delivery has succeeded
1009or failed.
1010
1011The command should return a zero completion code if all has gone well. Most
1012non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1013treated as a delivery failure, causing the message to be returned to its
1014sender. However, there are some completion codes that are treated as temporary
1015errors. The message remains on Exim's spool disk, and the delivery is tried
1016again later, though it will ultimately time out if the delivery failures go on
1017too long. The completion codes to which this applies can be specified by the
1018system administrator; the default values are 73 and 75.
1019
1020The pipe command should not normally write anything to its standard output or
1021standard error file descriptors. If it does, whatever is written is normally
1022returned to the sender of the message as a delivery error, though this action
1023can be varied by the system administrator.
1024
1025
1026
1027.section "Mail commands" "SECTmail"
1028There are two commands that cause the creation of a new mail message, neither
1029of which count as a significant delivery unless the command is preceded by the
1030word &"seen"& (see section &<<SECTsigdel>>&). This is a powerful facility, but
1031it should be used with care, because of the danger of creating infinite
1032sequences of messages. The system administrator can forbid the use of these
1033commands altogether.
1034
1035To help prevent runaway message sequences, these commands have no effect when
1036the incoming message is a bounce (delivery error) message, and messages sent by
1037this means are treated as if they were reporting delivery errors. Thus, they
1038should never themselves cause a bounce message to be returned. The basic
1039mail-sending command is
1040.display
1041&`mail [to `&<&'address-list'&>&`]`&
1042&` [cc `&<&'address-list'&>&`]`&
1043&` [bcc `&<&'address-list'&>&`]`&
1044&` [from `&<&'address'&>&`]`&
1045&` [reply_to `&<&'address'&>&`]`&
1046&` [subject `&<&'text'&>&`]`&
1047&` [extra_headers `&<&'text'&>&`]`&
1048&` [text `&<&'text'&>&`]`&
1049&` [[expand] file `&<&'filename'&>&`]`&
1050&` [return message]`&
1051&` [log `&<&'log file name'&>&`]`&
1052&` [once `&<&'note file name'&>&`]`&
1053&` [once_repeat `&<&'time interval'&>&`]`&
9b371988
PH
1054&`e.g. mail text "Your message about $h_subject: has been received"`&
1055.endd
1056Each <&'address-list'&> can contain a number of addresses, separated by commas,
1057in the format of a &'To:'& or &'Cc:'& header line. In fact, the text you supply
1058here is copied exactly into the appropriate header line. It may contain
1059additional information as well as email addresses. For example:
1060.code
1061mail to "Julius Caesar <jc@rome.example>, \
1062 <ma@rome.example> (Mark A.)"
1063.endd
1064Similarly, the texts supplied for &%from%& and &%reply_to%& are copied into
1065their respective header lines.
1066
1067As a convenience for use in one common case, there is also a command called
1068&(vacation)&. It behaves in the same way as &(mail)&, except that the defaults
1069for the &%subject%&, &%file%&, &%log%&, &%once%&, and &%once_repeat%& options
1070are
1071.code
1072subject "On vacation"
1073expand file .vacation.msg
1074log .vacation.log
1075once .vacation
1076once_repeat 7d
1077.endd
1078respectively. These are the same file names and repeat period used by the
1079traditional Unix &(vacation)& command. The defaults can be overridden by
1080explicit settings, but if a file name is given its contents are expanded only
1081if explicitly requested.
1082
1083&*Warning*&: The &(vacation)& command should always be used conditionally,
1084subject to at least the &(personal)& condition (see section &<<SECTpersonal>>&
1085below) so as not to send automatic replies to non-personal messages from
1086mailing lists or elsewhere. Sending an automatic response to a mailing list or
1087a mailing list manager is an Internet Sin.
1088
1089For both commands, the key/value argument pairs can appear in any order. At
1090least one of &%text%& or &%file%& must appear (except with &(vacation)&, where
1091there is a default for &%file%&); if both are present, the text string appears
1092first in the message. If &%expand%& precedes &%file%&, each line of the file is
1093subject to string expansion before it is included in the message.
1094
1095Several lines of text can be supplied to &%text%& by including the escape
1096sequence &"\n"& in the string wherever a newline is required. If the command is
1097output during filter file testing, newlines in the text are shown as &"\n"&.
1098
1099Note that the keyword for creating a &'Reply-To:'& header is &%reply_to%&,
1100because Exim keywords may contain underscores, but not hyphens. If the &%from%&
1101keyword is present and the given address does not match the user who owns the
1102forward file, Exim normally adds a &'Sender:'& header to the message, though it
1103can be configured not to do this.
1104
1105The &%extra_headers%& keyword allows you to add custom header lines to the
1106message. The text supplied must be one or more syntactically valid RFC 2822
1107header lines. You can use &"\n"& within quoted text to specify newlines between
1108headers, and also to define continued header lines. For example:
1109.code
1110extra_headers "h1: first\nh2: second\n continued\nh3: third"
1111.endd
1112No newline should appear at the end of the final header line.
1113
1114If no &%to%& argument appears, the message is sent to the address in the
1115&$reply_address$& variable (see section &<<SECTfilterstringexpansion>>& above).
1116An &'In-Reply-To:'& header is automatically included in the created message,
1117giving a reference to the message identification of the incoming message.
1118
1119If &%return message%& is specified, the incoming message that caused the filter
1120file to be run is added to the end of the message, subject to a maximum size
1121limitation.
1122
1123If a log file is specified, a line is added to it for each message sent.
1124
1125If a &%once%& file is specified, it is used to hold a database for remembering
1126who has received a message, and no more than one message is ever sent to any
1127particular address, unless &%once_repeat%& is set. This specifies a time
1128interval after which another copy of the message is sent. The interval is
1129specified as a sequence of numbers, each followed by the initial letter of one
1130of &"seconds"&, &"minutes"&, &"hours"&, &"days"&, or &"weeks"&. For example,
1131.code
1132once_repeat 5d4h
1133.endd
1134causes a new message to be sent if at least 5 days and 4 hours have elapsed
1135since the last one was sent. There must be no white space in a time interval.
1136
1137Commonly, the file name specified for &%once%& is used as the base name for
1138direct-access (DBM) file operations. There are a number of different DBM
1139libraries in existence. Some operating systems provide one as a default, but
1140even in this case a different one may have been used when building Exim. With
1141some DBM libraries, specifying &%once%& results in two files being created,
1142with the suffixes &_.dir_& and &_.pag_& being added to the given name. With
1143some others a single file with the suffix &_.db_& is used, or the name is used
1144unchanged.
1145
1146Using a DBM file for implementing the &%once%& feature means that the file
1147grows as large as necessary. This is not usually a problem, but some system
1148administrators want to put a limit on it. The facility can be configured not to
1149use a DBM file, but instead, to use a regular file with a maximum size. The
1150data in such a file is searched sequentially, and if the file fills up, the
1151oldest entry is deleted to make way for a new one. This means that some
1152correspondents may receive a second copy of the message after an unpredictable
1153interval. Consult your local information to see if your system is configured
1154this way.
1155
1156More than one &(mail)& or &(vacation)& command may be obeyed in a single filter
1157run; they are all honoured, even when they are to the same recipient.
1158
1159
1160
1161.section "Logging commands" "SECTlog"
1162A log can be kept of actions taken by a filter file. This facility is normally
1163available in conventional configurations, but there are some situations where
1164it might not be. Also, the system administrator may choose to disable it. Check
1165your local information if in doubt.
1166
1167Logging takes place while the filter file is being interpreted. It does not
1168queue up for later like the delivery commands. The reason for this is so that a
1169log file need be opened only once for several write operations. There are two
1170commands, neither of which constitutes a significant delivery. The first
1171defines a file to which logging output is subsequently written:
1172.display
1173&` logfile `&<&'file name'&>
1174&`e.g. logfile $home/filter.log`&
1175.endd
1176The file name must be fully qualified. You can use &$home$&, as in this
1177example, to refer to your home directory. The file name may optionally be
1178followed by a mode for the file, which is used if the file has to be created.
1179For example,
1180.code
1181logfile $home/filter.log 0644
1182.endd
1183The number is interpreted as octal, even if it does not begin with a zero.
1184The default for the mode is 600. It is suggested that the &(logfile)& command
1185normally appear as the first command in a filter file. Once a log file has
1186been obeyed, the &(logwrite)& command can be used to write to it:
1187.display
1188&` logwrite "`&<&'some text string'&>&`"`&
1189&`e.g. logwrite "$tod_log $message_id processed"`&
1190.endd
1191It is possible to have more than one &(logfile)& command, to specify writing to
5ffbf3a3
JH
1192different log files in different circumstances.
1193A previously opened log is closed on a subsequent &(logfile)& command.
1194Writing takes place at the end
9b371988
PH
1195of the file, and a newline character is added to the end of each string if
1196there isn't one already there. Newlines can be put in the middle of the string
1197by using the &"\n"& escape sequence. Lines from simultaneous deliveries may get
1198interleaved in the file, as there is no interlocking, so you should plan your
1199logging with this in mind. However, data should not get lost.
1200
1201
1202
1203.section "The finish command" "SECTfinish"
1204The command &(finish)&, which has no arguments, causes Exim to stop
1205interpreting the filter file. This is not a significant action unless preceded
1206by &"seen"&. A filter file containing only &"seen finish"& is a black hole.
1207
1208
1209.section "The testprint command" "SECTtestprint"
1210It is sometimes helpful to be able to print out the values of variables when
1211testing filter files. The command
1212.display
1213&` testprint `&<&'text'&>
1214&`e.g. testprint "home=$home reply_address=$reply_address"`&
1215.endd
1216does nothing when mail is being delivered. However, when the filtering code is
1217being tested by means of the &%-bf%& option (see section &<<SECTtesting>>&
1218above), the value of the string is written to the standard output.
1219
1220
1221.section "The fail command" "SECTfail"
1222When Exim's filtering facilities are being used as a system filter, the
1223&(fail)& command is available, to force delivery failure. Because this command
1224is normally usable only by the system administrator, and not enabled for use by
1225ordinary users, it is described in more detail in the main Exim specification
1226rather than in this document.
1227
1228
1229.section "The freeze command" "SECTfreeze"
1230When Exim's filtering facilities are being used as a system filter, the
1231&(freeze)& command is available, to freeze a message on the queue. Because this
1232command is normally usable only by the system administrator, and not enabled
1233for use by ordinary users, it is described in more detail in the main Exim
1234specification rather than in this document.
1235
1236
1237
1238.section "The headers command" "SECTheaders"
1239The &(headers)& command can be used to change the target character set that is
1240used when translating the contents of encoded header lines for insertion by the
1241&$header_$& mechanism (see section &<<SECTheadervariables>>& above). The
1242default can be set in the Exim configuration; if not specified, ISO-8859-1 is
1243used. The only currently supported format for the &(headers)& command in user
1244filters is as in this example:
1245.code
1246headers charset "UTF-8"
1247.endd
1248That is, &(headers)& is followed by the word &"charset"& and then the name of a
1249character set. This particular example would be useful if you wanted to compare
1250the contents of a header to a UTF-8 string.
1251
1252In system filter files, the &(headers)& command can be used to add or remove
1253header lines from the message. These features are described in the main Exim
1254specification.
1255
1256
1257
1258.section "Obeying commands conditionally" "SECTif"
1259Most of the power of filtering comes from the ability to test conditions and
1260obey different commands depending on the outcome. The &(if)& command is used to
1261specify conditional execution, and its general form is
1262.display
1263&`if `&<&'condition'&>
1264&`then `&<&'commands'&>
1265&`elif `&<&'condition'&>
1266&`then `&<&'commands'&>
1267&`else `&<&'commands'&>
1268&`endif`&
1269.endd
1270There may be any number of &(elif)& and &(then)& sections (including none) and
1271the &(else)& section is also optional. Any number of commands, including nested
1272&(if)& commands, may appear in any of the <&'commands'&> sections.
1273
1274Conditions can be combined by using the words &(and)& and &(or)&, and round
1275brackets (parentheses) can be used to specify how several conditions are to
1276combine. Without brackets, &(and)& is more binding than &(or)&. For example:
1277.code
1278if
1279$h_subject: contains "Make money" or
1280$h_precedence: is "junk" or
1281($h_sender: matches ^\\d{8}@ and not personal) or
1282$message_body contains "this is not spam"
1283then
1284seen finish
1285endif
1286.endd
1287A condition can be preceded by &(not)& to negate it, and there are also some
1288negative forms of condition that are more English-like.
1289
1290
1291
4aa45c31 1292.section "String testing conditions" "SEC23"
9b371988
PH
1293There are a number of conditions that operate on text strings, using the words
1294&"begins"&, &"ends"&, &"is"&, &"contains"& and &"matches"&. If you want to
1295apply the same test to more than one header line, you can easily concatenate
1296them into a single string for testing, as in this example:
1297.code
1298if "$h_to:, $h_cc:" contains me@domain.example then ...
1299.endd
1300If a string-testing condition name is written in lower case, the testing
1301of letters is done without regard to case; if it is written in upper case
1302(for example, &"CONTAINS"&), the case of letters is taken into account.
1303
1304.display
1305&` `&<&'text1'&>&` begins `&<&'text2'&>
1306&` `&<&'text1'&>&` does not begin `&<&'text2'&>
1307&`e.g. $header_from: begins "Friend@"`&
1308.endd
1309
1310A &"begins"& test checks for the presence of the second string at the start of
1311the first, both strings having been expanded.
1312
1313.display
1314&` `&<&'text1'&>&` ends `&<&'text2'&>
1315&` `&<&'text1'&>&` does not end `&<&'text2'&>
1316&`e.g. $header_from: ends "public.com.example"`&
1317.endd
1318
1319An &"ends"& test checks for the presence of the second string at the end of
1320the first, both strings having been expanded.
1321
1322.display
1323&` `&<&'text1'&>&` is `&<&'text2'&>
1324&` `&<&'text1'&>&` is not `&<&'text2'&>
1325&`e.g. $local_part_suffix is "-foo"`&
1326.endd
1327
1328An &"is"& test does an exact match between the strings, having first expanded
1329both strings.
1330
1331.display
1332&` `&<&'text1'&>&` contains `&<&'text2'&>
1333&` `&<&'text1'&>&` does not contain `&<&'text2'&>
1334&`e.g. $header_subject: contains "evolution"`&
1335.endd
1336
1337A &"contains"& test does a partial string match, having expanded both strings.
1338
1339.display
1340&` `&<&'text1'&>&` matches `&<&'text2'&>
1341&` `&<&'text1'&>&` does not match `&<&'text2'&>
1342&`e.g. $sender_address matches "(bill|john)@"`&
1343.endd
1344
1345For a &"matches"& test, after expansion of both strings, the second one is
1346interpreted as a regular expression. Exim uses the PCRE regular expression
1347library, which provides regular expressions that are compatible with Perl.
1348
1349The match succeeds if the regular expression matches any part of the first
1350string. If you want a regular expression to match only at the start or end of
1351the subject string, you must encode that requirement explicitly, using the
1352&`^`& or &`$`& metacharacters. The above example, which is not so constrained,
1353matches all these addresses:
1354.code
1355bill@test.example
1356john@some.example
1357spoonbill@example.com
1358littlejohn@example.com
1359.endd
1360To match only the first two, you could use this:
1361.code
1362if $sender_address matches "^(bill|john)@" then ...
1363.endd
1364Care must be taken if you need a backslash in a regular expression, because
1365backslashes are interpreted as escape characters both by the string expansion
1366code and by Exim's normal processing of strings in quotes. For example, if you
1367want to test the sender address for a domain ending in &'.com'& the regular
1368expression is
1369.code
1370\.com$
1371.endd
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.code
1376if $sender_address matches \\.com\$
1377.endd
1378An alternative way of handling this is to make use of the &`\N`& expansion
1379flag for suppressing expansion:
1380.code
1381if $sender_address matches \N\.com$\N
1382.endd
1383Everything between the two occurrences of &`\N`& is copied without change by
1384the string expander (and in fact you do not need the final one, because it is
1385at the end of the string). If the regular expression is given in quotes
1386(mandatory only if it contains white space) you have to write either
1387.code
1388if $sender_address matches "\\\\.com\\$"
1389.endd
1390or
1391.code
1392if $sender_address matches "\\N\\.com$\\N"
1393.endd
1394
1395If the regular expression contains bracketed sub-expressions, numeric
1396variable substitutions such as &$1$& can be used in the subsequent actions
1397after a successful match. If the match fails, the values of the numeric
1398variables remain unchanged. Previous values are not restored after &(endif)&.
1399In other words, only one set of values is ever available. If the condition
1400contains several sub-conditions connected by &(and)& or &(or)&, it is the
1401strings extracted from the last successful match that are available in
1402subsequent actions. Numeric variables from any one sub-condition are also
1403available for use in subsequent sub-conditions, because string expansion of a
1404condition occurs just before it is tested.
1405
1406
4aa45c31 1407.section "Numeric testing conditions" "SEC24"
9b371988
PH
1408The following conditions are available for performing numerical tests:
1409
1410.display
1411&` `&<&'number1'&>&` is above `&<&'number2'&>
1412&` `&<&'number1'&>&` is not above `&<&'number2'&>
1413&` `&<&'number1'&>&` is below `&<&'number2'&>
1414&` `&<&'number1'&>&` is not below `&<&'number2'&>
1415&`e.g. $message_size is not above 10k`&
1416.endd
1417
1418The <&'number'&> arguments must expand to strings of digits, optionally
1419followed by one of the letters K or M (upper case or lower case) which cause
1420multiplication by 1024 and 1024x1024 respectively.
1421
1422
4aa45c31 1423.section "Testing for significant deliveries" "SEC25"
9b371988
PH
1424You can use the &(delivered)& condition to test whether or not any previously
1425obeyed filter commands have set up a significant delivery. For example:
1426.code
1427if not delivered then save mail/anomalous endif
1428.endd
1429&"Delivered"& is perhaps a poor choice of name for this condition, because the
1430message has not actually been delivered; rather, a delivery has been set up for
1431later processing.
1432
1433
4aa45c31 1434.section "Testing for error messages" "SEC26"
9b371988
PH
1435The condition &(error_message)& is true if the incoming message is a bounce
1436(mail delivery error) message. Putting the command
1437.code
1438if error_message then finish endif
1439.endd
1440at the head of your filter file is a useful insurance against things going
1441wrong in such a way that you cannot receive delivery error reports. &*Note*&:
1442&(error_message)& is a condition, not an expansion variable, and therefore is
1443not preceded by &`$`&.
1444
1445
4aa45c31 1446.section "Testing a list of addresses" "SEC27"
9b371988
PH
1447There is a facility for looping through a list of addresses and applying a
1448condition to each of them. It takes the form
1449.display
1450&`foranyaddress `&<&'string'&>&` (`&<&'condition'&>&`)`&
1451.endd
1452where <&'string'&> is interpreted as a list of RFC 2822 addresses, as in a
1453typical header line, and <&'condition'&> is any valid filter condition or
1454combination of conditions. The &"group"& syntax that is defined for certain
1455header lines that contain addresses is supported.
1456
1457The parentheses surrounding the condition are mandatory, to delimit it from
1458possible further sub-conditions of the enclosing &(if)& command. Within the
1459condition, the expansion variable &$thisaddress$& is set to the non-comment
1460portion of each of the addresses in the string in turn. For example, if the
1461string is
1462.code
1463B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1464.endd
1465then &$thisaddress$& would take on the values &`bart@sfld.example`& and
1466&`lisa@sfld.example`& in turn.
1467
1468If there are no valid addresses in the list, the whole condition is false. If
1469the internal condition is true for any one address, the overall condition is
1470true and the loop ends. If the internal condition is false for all addresses in
1471the list, the overall condition is false. This example tests for the presence
1472of an eight-digit local part in any address in a &'To:'& header:
1473.code
1474if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1475.endd
1476When the overall condition is true, the value of &$thisaddress$& in the
1477commands that follow &(then)& is the last value it took on inside the loop. At
1478the end of the &(if)& command, the value of &$thisaddress$& is reset to what it
1479was before. It is best to avoid the use of multiple occurrences of
1480&(foranyaddress)&, nested or otherwise, in a single &(if)& command, if the
1481value of &$thisaddress$& is to be used afterwards, because it isn't always
1482clear what the value will be. Nested &(if)& commands should be used instead.
1483
1484Header lines can be joined together if a check is to be applied to more than
1485one of them. For example:
1486.code
1487if foranyaddress $h_to:,$h_cc: ....
1488.endd
1489This scans through the addresses in both the &'To:'& and the &'Cc:'& headers.
1490
1491
1492.section "Testing for personal mail" "SECTpersonal"
1493A common requirement is to distinguish between incoming personal mail and mail
1494from a mailing list, or from a robot or other automatic process (for example, a
1495bounce message). In particular, this test is normally required for &"vacation
1496messages"&.
1497
1498The &(personal)& condition checks that the message is not a bounce message and
1499that the current user's email address appears in the &'To:'& header. It also
1500checks that the sender is not the current user or one of a number of common
1501daemons, and that there are no header lines starting &'List-'& in the message.
1502Finally, it checks the content of the &'Precedence:'& header line, if there is
1503one.
1504
1505You should always use the &(personal)& condition when generating automatic
1506responses. This example shows the use of &(personal)& in a filter file that is
1507sending out vacation messages:
1508.code
1509if personal then
1510mail to $reply_address
1511subject "I am on holiday"
1512file $home/vacation/message
1513once $home/vacation/once
1514once_repeat 10d
1515endif
1516.endd
1517It is tempting, when writing commands like the above, to quote the original
1518subject in the reply. For example:
1519.code
1520subject "Re: $h_subject:"
1521.endd
1522There is a danger in doing this, however. It may allow a third party to
1523subscribe you to an opt-in mailing list, provided that the list accepts bounce
1524messages as subscription confirmations. (Messages sent from filters are always
1525sent as bounce messages.) Well-managed lists require a non-bounce message to
1526confirm a subscription, so the danger is relatively small.
1527
1528If prefixes or suffixes are in use for local parts &-- something which depends
1529on the configuration of Exim (see section &<<SECTmbox>>& below) &-- the tests
1530for the current user are done with the full address (including the prefix and
1531suffix, if any) as well as with the prefix and suffix removed. If the system is
1532configured to rewrite local parts of mail addresses, for example, to rewrite
1533&`dag46`& as &`Dirk.Gently`&, the rewritten form of the address is also used in
1534the tests.
1535
1536
1537
4aa45c31 1538.section "Alias addresses for the personal condition" "SEC28"
9b371988
PH
1539It is quite common for people who have mail accounts on a number of different
1540systems to forward all their mail to one system, and in this case a check for
1541personal mail should test all their various mail addresses. To allow for this,
1542the &(personal)& condition keyword can be followed by
1543.display
1544&`alias `&<&'address'&>
1545.endd
1546any number of times, for example:
1547.code
1548if personal alias smith@else.where.example
1549 alias jones@other.place.example
1550then ...
1551.endd
1552The alias addresses are treated as alternatives to the current user's email
1553address when testing the contents of header lines.
1554
1555
4aa45c31 1556.section "Details of the personal condition" "SEC29"
9b371988
PH
1557The basic &(personal)& test is roughly equivalent to the following:
1558.code
1559not error_message and
1560$message_headers does not contain "\nList-Id:" and
1561$message_headers does not contain "\nList-Help:" and
1562$message_headers does not contain "\nList-Subscribe:" and
1563$message_headers does not contain "\nList-Unsubscribe:" and
1564$message_headers does not contain "\nList-Post:" and
1565$message_headers does not contain "\nList-Owner:" and
1566$message_headers does not contain "\nList-Archive:" and
1567(
8f3414a1 1568"${if def:h_auto-submitted:{present}{absent}}" is "absent" or
9b371988
PH
1569$header_auto-submitted: is "no"
1570) and
1571$header_precedence: does not contain "bulk" and
1572$header_precedence: does not contain "list" and
1573$header_precedence: does not contain "junk" and
1574foranyaddress $header_to:
1575( $thisaddress contains "$local_part$domain" ) and
1576not foranyaddress $header_from:
1577(
c0712871
PH
1578$thisaddress contains "$local_part@$domain" or
1579$thisaddress contains "server@" or
1580$thisaddress contains "daemon@" or
1581$thisaddress contains "root@" or
1582$thisaddress contains "listserv@" or
1583$thisaddress contains "majordomo@" or
1584$thisaddress contains "-request@" or
1585$thisaddress matches "^owner-[^@]+@"
9b371988
PH
1586)
1587.endd
1588The variable &$local_part$& contains the local part of the mail address of
1589the user whose filter file is being run &-- it is normally your login id. The
1590&$domain$& variable contains the mail domain. As explained above, if aliases
1591or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1592the current user are also done with alternative addresses.
1593
1594
1595
1596
4aa45c31 1597.section "Testing delivery status" "SEC30"
9b371988
PH
1598There are two conditions that are intended mainly for use in system filter
1599files, but which are available in users' filter files as well. The condition
1600&(first_delivery)& is true if this is the first process that is attempting to
1601deliver the message, and false otherwise. This indicator is not reset until the
1602first delivery process successfully terminates; if there is a crash or a power
1603failure (for example), the next delivery attempt is also a &"first delivery"&.
1604
1605In a user filter file &(first_delivery)& will be false if there was previously
1606an error in the filter, or if a delivery for the user failed owing to, for
1607example, a quota error, or if forwarding to a remote address was deferred for
1608some reason.
1609
1610The condition &(manually_thawed)& is true if the message was &"frozen"& for
1611some reason, and was subsequently released by the system administrator. It is
1612unlikely to be of use in users' filter files.
1613
1614
4aa45c31 1615.section "Multiple personal mailboxes" "SECTmbox" "SEC31"
9b371988
PH
1616The system administrator can configure Exim so that users can set up variants
1617on their email addresses and handle them separately. Consult your system
1618administrator or local documentation to see if this facility is enabled on your
1619system, and if so, what the details are.
1620
1621The facility involves the use of a prefix or a suffix on an email address. For
1622example, all mail addressed to &'lg303-'&<&'something'&> would be the property
1623of user &'lg303'&, who could determine how it was to be handled, depending on
1624the value of <&'something'&>.
1625
1626There are two possible ways in which this can be set up. The first possibility
1627is the use of multiple &_.forward_& files. In this case, mail to &'lg303-foo'&,
1628for example, is handled by looking for a file called &_.forward-foo_& in
1629&'lg303'&'s home directory. If such a file does not exist, delivery fails
1630and the message is returned to its sender.
1631
1632The alternative approach is to pass all messages through a single &_.forward_&
1633file, which must be a filter file so that it can distinguish between the
1634different cases by referencing the variables &$local_part_prefix$& or
1635&$local_part_suffix$&, as in the final example in section &<<SECTex>>& below.
1636
1637It is possible to configure Exim to support both schemes at once. In this case,
1638a specific &_.forward-foo_& file is first sought; if it is not found, the basic
1639&_.forward_& file is used.
1640
1641The &(personal)& test (see section &<<SECTpersonal>>&) includes prefixes and
1642suffixes in its checking.
1643
1644
1645
4aa45c31 1646.section "Ignoring delivery errors" "SEC43"
9b371988
PH
1647As was explained above, filtering just sets up addresses for delivery &-- no
1648deliveries are actually done while a filter file is active. If any of the
1649generated addresses subsequently suffers a delivery failure, an error message
1650is generated in the normal way. However, if a filter command that sets up a
1651delivery is preceded by the word &"noerror"&, errors for that delivery,
1652and any deliveries consequent on it (that is, from alias, forwarding, or
1653filter files it invokes) are ignored.
1654
1655
1656
1657.section "Examples of Exim filter commands" "SECTex"
1658Simple forwarding:
1659
1660.code
1661# Exim filter
1662deliver baggins@rivendell.middle-earth.example
1663.endd
1664
1665Vacation handling using traditional means, assuming that the &_.vacation.msg_&
1666and other files have been set up in your home directory:
1667
1668.code
1669# Exim filter
1670unseen pipe "/usr/ucb/vacation \"$local_part\""
1671.endd
1672
1673Vacation handling inside Exim, having first created a file called
1674&_.vacation.msg_& in your home directory:
1675
1676.code
1677# Exim filter
1678if personal then vacation endif
1679.endd
1680
1681File some messages by subject:
1682
1683.code
1684# Exim filter
1685if $header_subject: contains "empire" or
1686$header_subject: contains "foundation"
1687then
1688save $home/mail/f+e
1689endif
1690.endd
1691
1692Save all non-urgent messages by weekday:
1693
1694.code
1695# Exim filter
1696if $header_subject: does not contain "urgent" and
1697$tod_full matches "^(...),"
1698then
1699save $home/mail/$1
1700endif
1701.endd
1702
1703Throw away all mail from one site, except from postmaster:
1704
1705.code
1706# Exim filter
1707if $reply_address contains "@spam.site.example" and
1708$reply_address does not contain "postmaster@"
1709then
1710seen finish
1711endif
1712.endd
1713
1714Handle multiple personal mailboxes:
1715
1716.code
1717# Exim filter
1718if $local_part_suffix is "-foo"
1719then
1720save $home/mail/foo
1721elif $local_part_suffix is "-bar"
1722then
1723save $home/mail/bar
1724endif
1725.endd
1726