Revert copyright years to manual-update. Bug 1318.
[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
512010
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>
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76 <revnumber>
77.version
78 </revnumber>
79 <date>
80.fulldate
81 </date>
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82 <authorinitials>PH</authorinitials>
83</revision></revhistory>
2aee48d6 84<copyright><year>
7d837ca7 85.copyyear
2aee48d6 86 </year><holder>University of Cambridge</holder></copyright>
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87</bookinfo>
88.literal off
89
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90. /////////////////////////////////////////////////////////////////////////////
91. /////////////////////////////////////////////////////////////////////////////
92
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4aa45c31 94.chapter "Forwarding and filtering in Exim" "CHAPforandfilt"
9b371988 95This document describes the user interfaces to Exim's in-built mail filtering
7d837ca7 96facilities, and is copyright &copy; University of Cambridge &copyyear(). It
2aee48d6 97corresponds to Exim version &version().
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98
99
100
4aa45c31 101.section "Introduction" "SEC00"
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102Most Unix mail transfer agents (programs that deliver mail) permit individual
103users to specify automatic forwarding of their mail, usually by placing a list
104of forwarding addresses in a file called &_.forward_& in their home
105directories. Exim extends this facility by allowing the forwarding instructions
106to be a set of rules rather than just a list of addresses, in effect providing
107&"&_.forward_& with conditions"&. Operating the set of rules is called
108&'filtering'&, and the file that contains them is called a &'filter file'&.
109
110Exim supports two different kinds of filter file. An &'Exim filter'& contains
111instructions in a format that is unique to Exim. A &'Sieve filter'& contains
112instructions in the Sieve format that is defined by RFC 3028. As this is a
113standard format, Sieve filter files may already be familiar to some users.
114Sieve files should also be portable between different environments. However,
115the Exim filtering facility contains more features (such as variable
116expansion), and better integration with the host environment (such as the use
117of external processes and pipes).
118
119The choice of which kind of filter to use can be left to the end-user, provided
120that the system administrator has configured Exim appropriately for both kinds
121of filter. However, if interoperability is important, Sieve is the only
122choice.
123
124The ability to use filtering or traditional forwarding has to be enabled by the
125system administrator, and some of the individual facilities can be separately
126enabled or disabled. A local document should be provided to describe exactly
127what has been enabled. In the absence of this, consult your system
128administrator.
129
130This document describes how to use a filter file and the format of its
131contents. It is intended for use by end-users. Both Sieve filters and Exim
132filters are covered. However, for Sieve filters, only issues that relate to the
133Exim implementation are discussed, since Sieve itself is described elsewhere.
134
135The contents of traditional &_.forward_& files are not described here. They
136normally contain just a list of addresses, file names, or pipe commands,
137separated by commas or newlines, but other types of item are also available.
138The full details can be found in the chapter on the &(redirect)& router in the
139Exim specification, which also describes how the system administrator can set
140up and control the use of filtering.
141
142
143
4aa45c31 144.section "Filter operation" "SEC01"
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145It is important to realize that, in Exim, no deliveries are actually made while
146a filter or traditional &_.forward_& file is being processed. Running a filter
147or processing a traditional &_.forward_& file sets up future delivery
148operations, but does not carry them out.
149
150The result of filter or &_.forward_& file processing is a list of destinations
151to which a message should be delivered. The deliveries themselves take place
152later, along with all other deliveries for the message. This means that it is
153not possible to test for successful deliveries while filtering. It also means
154that any duplicate addresses that are generated are dropped, because Exim never
155delivers the same message to the same address more than once.
156
157
158
159
160.section "Testing a new filter file" "SECTtesting"
161Filter files, especially the more complicated ones, should always be tested, as
162it is easy to make mistakes. Exim provides a facility for preliminary testing
163of a filter file before installing it. This tests the syntax of the file and
164its basic operation, and can also be used with traditional &_.forward_& files.
165
166Because a filter can do tests on the content of messages, a test message is
167required. Suppose you have a new filter file called &_myfilter_& and a test
168message in a file called &_test-message_&. Assuming that Exim is installed with
169the conventional path name &_/usr/sbin/sendmail_& (some operating systems use
170&_/usr/lib/sendmail_&), the following command can be used:
171.code
172/usr/sbin/sendmail -bf myfilter <test-message
173.endd
174The &%-bf%& option tells Exim that the following item on the command line is
175the name of a filter file that is to be tested. There is also a &%-bF%& option,
176which is similar, but which is used for testing system filter files, as opposed
177to user filter files, and which is therefore of use only to the system
178administrator.
179
180The test message is supplied on the standard input. If there are no
181message-dependent tests in the filter, an empty file (&_/dev/null_&) can be
182used. A supplied message must start with header lines or the &"From&~"& message
183separator line that is found in many multi-message folder files. Note that
184blank lines at the start terminate the header lines. A warning is given if no
185header lines are read.
186
187The result of running this command, provided no errors are detected in the
188filter file, is a list of the actions that Exim would try to take if presented
189with the message for real. For example, for an Exim filter, the output
190.code
191Deliver message to: gulliver@lilliput.fict.example
192Save message to: /home/lemuel/mail/archive
193.endd
194means that one copy of the message would be sent to
195&'gulliver@lilliput.fict.example'&, and another would be added to the file
196&_/home/lemuel/mail/archive_&, if all went well.
197
198The actions themselves are not attempted while testing a filter file in this
199way; there is no check, for example, that any forwarding addresses are valid.
200For an Exim filter, if you want to know why a particular action is being taken,
201add the &%-v%& option to the command. This causes Exim to output the results of
202any conditional tests and to indent its output according to the depth of
203nesting of &(if)& commands. Further additional output from a filter test can be
204generated by the &(testprint)& command, which is described below.
205
206When Exim is outputting a list of the actions it would take, if any text
207strings are included in the output, non-printing characters therein are
208converted to escape sequences. In particular, if any text string contains a
209newline character, this is shown as &"\n"& in the testing output.
210
211When testing a filter in this way, Exim makes up an &"envelope"& for the
212message. The recipient is by default the user running the command, and so is
213the sender, but the command can be run with the &%-f%& option to supply a
214different sender. For example,
215.code
216/usr/sbin/sendmail -bf myfilter \
217 -f islington@never.where <test-message
218.endd
219Alternatively, if the &%-f%& option is not used, but the first line of the
220supplied message is a &"From&~"& separator from a message folder file (not the
221same thing as a &'From:'& header line), the sender is taken from there. If
222&%-f%& is present, the contents of any &"From&~"& line are ignored.
223
224The &"return path"& is the same as the envelope sender, unless the message
225contains a &'Return-path:'& header, in which case it is taken from there. You
226need not worry about any of this unless you want to test out features of a
227filter file that rely on the sender address or the return path.
228
229It is possible to change the envelope recipient by specifying further options.
230The &%-bfd%& option changes the domain of the recipient address, while the
231&%-bfl%& option changes the &"local part"&, that is, the part before the @
232sign. An adviser could make use of these to test someone else's filter file.
233
234The &%-bfp%& and &%-bfs%& options specify the prefix or suffix for the local
235part. These are relevant only when support for multiple personal mailboxes is
236implemented; see the description in section &<<SECTmbox>>& below.
237
238
4aa45c31 239.section "Installing a filter file" "SEC02"
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240A filter file is normally installed under the name &_.forward_& in your home
241directory &-- it is distinguished from a conventional &_.forward_& file by its
242first line (described below). However, the file name is configurable, and some
243system administrators may choose to use some different name or location for
244filter files.
245
246
4aa45c31 247.section "Testing an installed filter file" "SEC03"
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248Testing a filter file before installation cannot find every potential problem;
249for example, it does not actually run commands to which messages are piped.
250Some &"live"& tests should therefore also be done once a filter is installed.
251
252If at all possible, test your filter file by sending messages from some other
253account. If you send a message to yourself from the filtered account, and
254delivery fails, the error message will be sent back to the same account, which
255may cause another delivery failure. It won't cause an infinite sequence of such
256messages, because delivery failure messages do not themselves generate further
257messages. However, it does mean that the failure won't be returned to you, and
258also that the postmaster will have to investigate the stuck message.
259
260If you have to test an Exim filter from the same account, a sensible precaution
261is to include the line
262.code
263if error_message then finish endif
264.endd
265as the first filter command, at least while testing. This causes filtering to
266be abandoned for a delivery failure message, and since no destinations are
267generated, the message goes on to be delivered to the original address. Unless
268there is a good reason for not doing so, it is recommended that the above test
269be left in all Exim filter files. (This does not apply to Sieve files.)
270
271
272
4aa45c31 273.section "Details of filtering commands" "SEC04"
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274The filtering commands for Sieve and Exim filters are completely different in
275syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
276chapter we describe how it is integrated into Exim. The subsequent chapter
277covers Exim filtering commands in detail.
278
279
280
281.chapter "Sieve filter files" "CHAPsievefilter"
282The code for Sieve filtering in Exim was contributed by Michael Haardt, and
283most of the content of this chapter is taken from the notes he provided. Since
284Sieve is an extensible language, it is important to understand &"Sieve"& in
285this context as &"the specific implementation of Sieve for Exim"&.
286
287This chapter does not contain a description of Sieve, since that can be found
288in RFC 3028, which should be read in conjunction with these notes.
289
290The Exim Sieve implementation offers the core as defined by RFC 3028,
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291comparison tests, the subaddress parameter, the &*copy*&, &*envelope*&,
292&*fileinto*&, &*notify*&, and &*vacation*& extensions, but not the &*reject*&
293extension. Exim does not support message delivery notifications (MDNs), so
294adding it just to the Sieve filter (as required for &*reject*&) makes little
295sense.
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296
297In order for Sieve to work properly in Exim, the system administrator needs to
298make some adjustments to the Exim configuration. These are described in the
299chapter on the &(redirect)& router in the full Exim specification.
300
301
4aa45c31 302.section "Recognition of Sieve filters" "SEC05"
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303A filter file is interpreted as a Sieve filter if its first line is
304.code
305# Sieve filter
306.endd
307This is what distinguishes it from a conventional &_.forward_& file or an Exim
308filter file.
309
310
311
4aa45c31 312.section "Saving to specified folders" "SEC06"
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313If the system administrator has set things up as suggested in the Exim
314specification, and you use &(keep)& or &(fileinto)& to save a mail into a
315folder, absolute files are stored where specified, relative files are stored
316relative to &$home$&, and &_inbox_& goes to the standard mailbox location.
317
318
319
4aa45c31 320.section "Strings containing header names" "SEC07"
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321RFC 3028 does not specify what happens if a string denoting a header field does
322not contain a valid header name, for example, it contains a colon. This
323implementation generates an error instead of ignoring the header field in order
324to ease script debugging, which fits in with the common picture of Sieve.
325
326
327
4aa45c31 328.section "Exists test with empty list of headers" "SEC08"
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329The &*exists*& test succeeds only if all the specified headers exist. RFC 3028
330does not explicitly specify what happens on an empty list of headers. This
331implementation evaluates that condition as true, interpreting the RFC in a
332strict sense.
333
334
335
4aa45c31 336.section "Header test with invalid MIME encoding in header" "SEC09"
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337Some MUAs process invalid base64 encoded data, generating junk. Others ignore
338junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
339specify how to react in this case, other than stating that a client must not
340forbid to process a message for that reason. RFC 2045 specifies that invalid
341data should be ignored (apparently looking at end of line characters). It also
342specifies that invalid data may lead to rejecting messages containing them (and
343there it appears to talk about true encoding violations), which is a clear
344contradiction to ignoring them.
345
346RFC 3028 does not specify how to process incorrect MIME words. This
347implementation treats them literally, as it does if the word is correct but its
348character set cannot be converted to UTF-8.
349
350
351
4aa45c31 352.section "Address test for multiple addresses per header" "SEC10"
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353A header may contain multiple addresses. RFC 3028 does not explicitly specify
354how to deal with them, but since the address test checks if anything matches
355anything else, matching one address suffices to satisfy the condition. That
356makes it impossible to test if a header contains a certain set of addresses and
357no more, but it is more logical than letting the test fail if the header
358contains an additional address besides the one the test checks for.
359
360
361
4aa45c31 362.section "Semantics of keep" "SEC11"
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363The &(keep)& command is equivalent to
364.code
365fileinto "inbox";
366.endd
367It saves the message and resets the implicit keep flag. It does not set the
368implicit keep flag; there is no command to set it once it has been reset.
369
370
371
4aa45c31 372.section "Semantics of fileinto" "SEC12"
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373RFC 3028 does not specify whether &(fileinto)& should try to create a mail
374folder if it does not exist. This implementation allows the sysadmin to
375configure that aspect using the &(appendfile)& transport options
376&%create_directory%&, &%create_file%&, and &%file_must_exist%&. See the
377&(appendfile)& transport in the Exim specification for details.
378
379
380
4aa45c31 381.section "Semantics of redirect" "SEC13"
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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
389
4aa45c31 390.section "String arguments" "SEC14"
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391There has been confusion if the string arguments to &(require)& are to be
392matched case-sensitively or not. This implementation matches them with the
393match type &(:is)& (default, see section 2.7.1 of the RFC) and the comparator
394&(i;ascii-casemap)& (default, see section 2.7.3 of the RFC). The RFC defines
395the command defaults clearly, so any different implementations violate RFC
3963028. The same is valid for comparator names, also specified as strings.
397
398
399
4aa45c31 400.section "Number units" "SEC15"
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401There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
402The mistake is obvious, because RFC 3028 specifies G to denote 2^30
403(which is gibi, not tebi), and that is what this implementation uses as
404the scaling factor for the suffix G.
405
406
407
4aa45c31 408.section "RFC compliance" "SEC16"
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409Exim requires the first line of a Sieve filter to be
410.code
411# Sieve filter
412.endd
413Of course the RFC does not specify that line. Do not expect examples to work
414without adding it, though.
415
416RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
417CRLF is universally used in network protocols to mark the end of the line. This
418implementation does not embed Sieve in a network protocol, but uses Sieve
419scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
420character, this implementation does, too, by default, though the system
421administrator may choose (at Exim compile time) to use CRLF instead.
422
423Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
424implementation repeats this violation to stay consistent with Exim. This is in
425preparation for UTF-8 data.
426
427Sieve scripts cannot contain NUL characters in strings, but mail headers could
428contain MIME encoded NUL characters, which could never be matched by Sieve
429scripts using exact comparisons. For that reason, this implementation extends
430the Sieve quoted string syntax with \0 to describe a NUL character, violating
431\0 being the same as 0 in RFC 3028. Even without using \0, the following tests
432are all true in this implementation. Implementations that use C-style strings
433will only evaluate the first test as true.
434.code
435Subject: =?iso-8859-1?q?abc=00def
436
437header :contains "Subject" ["abc"]
438header :contains "Subject" ["def"]
439header :matches "Subject" ["abc?def"]
440.endd
441Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
442way that NUL characters truncating strings is allowed for Sieve
443implementations, although not recommended. It is further allowed to use encoded
444NUL characters in headers, but that's not recommended either. The above example
445shows why.
446
447RFC 3028 states that if an implementation fails to convert a character set to
448UTF-8, two strings cannot be equal if one contains octets greater than 127.
449Assuming that all unknown character sets are one-byte character sets with the
450lower 128 octets being US-ASCII is not sound, so this implementation violates
451RFC 3028 and treats such MIME words literally. That way at least something
452could be matched.
453
454The folder specified by &(fileinto)& must not contain the character sequence
455&".."& to avoid security problems. RFC 3028 does not specify the syntax of
456folders apart from &(keep)& being equivalent to
457.code
458fileinto "INBOX";
459.endd
460This implementation uses &_inbox_& instead.
461
462Sieve script errors currently cause messages to be silently filed into
463&_inbox_&. RFC 3028 requires that the user is notified of that condition.
464This may be implemented in the future by adding a header line to mails that
465are filed into &_inbox_& due to an error in the filter.
466
467
468
469.chapter "Exim filter files" "CHAPeximfilter"
470This chapter contains a full description of the contents of Exim filter files.
471
472
4aa45c31 473.section "Format of Exim filter files" "SEC17"
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474Apart from leading white space, the first text in an Exim filter file must be
475.code
476# Exim filter
477.endd
478This is what distinguishes it from a conventional &_.forward_& file or a Sieve
479filter file. If the file does not have this initial line (or the equivalent for
480a Sieve filter), it is treated as a conventional &_.forward_& file, both when
481delivering mail and when using the &%-bf%& testing mechanism. The white space
482in the line is optional, and any capitalization may be used. Further text on
483the same line is treated as a comment. For example, you could have
484.code
485# Exim filter <<== do not edit or remove this line!
486.endd
487The remainder of the file is a sequence of filtering commands, which consist of
488keywords and data values. For example, in the command
489.code
490deliver gulliver@lilliput.fict.example
491.endd
492the keyword is &`deliver`& and the data value is
493&`gulliver@lilliput.fict.example`&. White space or line breaks separate the
494components of a command, except in the case of conditions for the &(if)&
495command, where round brackets (parentheses) also act as separators. Complete
496commands are separated from each other by white space or line breaks; there are
497no special terminators. Thus, several commands may appear on one line, or one
498command may be spread over a number of lines.
499
500If the character # follows a separator anywhere in a command, everything from
501# up to the next newline is ignored. This provides a way of including comments
502in a filter file.
503
504
4aa45c31 505.section "Data values in filter commands" "SEC18"
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506There are two ways in which a data value can be input:
507
508.ilist
509If the text contains no white space, it can be typed verbatim. However, if it
510is part of a condition, it must also be free of round brackets (parentheses),
511as these are used for grouping in conditions.
512.next
513Otherwise, text must be enclosed in double quotation marks. In this case, the
514character \ (backslash) is treated as an &"escape character"& within the
515string, causing the following character or characters to be treated specially:
516.display
517&`\n`& is replaced by a newline
518&`\r`& is replaced by a carriage return
519&`\t`& is replaced by a tab
520.endd
521.endlist
522
523Backslash followed by up to three octal digits is replaced by the character
524specified by those digits, and &`\x`& followed by up to two hexadecimal digits
525is treated similarly. Backslash followed by any other character is replaced by
526the second character, so that in particular, &`\"`& becomes &`"`& and &`\\`&
527becomes &`\`&. A data item enclosed in double quotes can be continued onto the
528next line by ending the first line with a backslash. Any leading white space at
529the start of the continuation line is ignored.
530
531In addition to the escape character processing that occurs when strings are
532enclosed in quotes, most data values are also subject to &'string expansion'&
533(as described in the next section), in which case the characters &`$`& and
534&`\`& are also significant. This means that if a single backslash is actually
535required in such a string, and the string is also quoted, &`\\\\`& has to be
536entered.
537
538The maximum permitted length of a data string, before expansion, is 1024
539characters.
540
541
542.section "String expansion" "SECTfilterstringexpansion"
543Most data values are expanded before use. Expansion consists of replacing
544substrings beginning with &`$`& with other text. The full expansion facilities
545available in Exim are extensive. If you want to know everything that Exim can
546do with strings, you should consult the chapter on string expansion in the Exim
547documentation.
548
549In filter files, by far the most common use of string expansion is the
550substitution of the contents of a variable. For example, the substring
551.code
552$reply_address
553.endd
554is replaced by the address to which replies to the message should be sent. If
555such a variable name is followed by a letter or digit or underscore, it must be
556enclosed in curly brackets (braces), for example,
557.code
558${reply_address}
559.endd
560If a &`$`& character is actually required in an expanded string, it must be
561escaped with a backslash, and because backslash is also an escape character in
562quoted input strings, it must be doubled in that case. The following two
563examples illustrate two different ways of testing for a &`$`& character in a
564message:
565.code
566if $message_body contains \$ then ...
567if $message_body contains "\\$" then ...
568.endd
569You can prevent part of a string from being expanded by enclosing it between
570two occurrences of &`\N`&. For example,
571.code
572if $message_body contains \N$$$$\N then ...
573.endd
574tests for a run of four dollar characters.
575
576
4aa45c31 577.section "Some useful general variables" "SEC19"
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578A complete list of the available variables is given in the Exim documentation.
579This shortened list contains the ones that are most likely to be useful in
580personal filter files:
581
582&$body_linecount$&: The number of lines in the body of the message.
583
584&$body_zerocount$&: The number of binary zero characters in the body of the
585message.
586
587&$home$&: In conventional configurations, this variable normally contains the
588user's home directory. The system administrator can, however, change this.
589
590&$local_part$&: The part of the email address that precedes the @ sign &--
591normally the user's login name. If support for multiple personal mailboxes is
592enabled (see section &<<SECTmbox>>& below) and a prefix or suffix for the local
593part was recognized, it is removed from the string in this variable.
594
595&$local_part_prefix$&: If support for multiple personal mailboxes is enabled
596(see section &<<SECTmbox>>& below), and a local part prefix was recognized,
597this variable contains the prefix. Otherwise it contains an empty string.
598
599&$local_part_suffix$&: If support for multiple personal mailboxes is enabled
600(see section &<<SECTmbox>>& below), and a local part suffix was recognized,
601this variable contains the suffix. Otherwise it contains an empty string.
602
603&$message_body$&: The initial portion of the body of the message. By default,
604up to 500 characters are read into this variable, but the system administrator
605can configure this to some other value. Newlines in the body are converted into
606single spaces.
607
608&$message_body_end$&: The final portion of the body of the message, formatted
609and limited in the same way as &$message_body$&.
610
611&$message_body_size$&: The size of the body of the message, in bytes.
612
613&$message_exim_id$&: The message's local identification string, which is unique
614for each message handled by a single host.
615
616&$message_headers$&: The header lines of the message, concatenated into a
617single string, with newline characters between them.
618
619&$message_size$&: The size of the entire message, in bytes.
620
621&$original_local_part$&: When an address that arrived with the message is
622being processed, this contains the same value as the variable &$local_part$&.
623However, if an address generated by an alias, forward, or filter file is being
624processed, this variable contains the local part of the original address.
625
626&$reply_address$&: The contents of the &'Reply-to:'& header, if the message
627has one; otherwise the contents of the &'From:'& header. It is the address to
628which normal replies to the message should be sent.
629
630&$return_path$&: The return path &-- that is, the sender field that will be
631transmitted as part of the message's envelope if the message is sent to another
632host. This is the address to which delivery errors are sent. In many cases,
633this variable has the same value as &$sender_address$&, but if, for example,
634an incoming message to a mailing list has been expanded, &$return_path$& may
635have been changed to contain the address of the list maintainer.
636
637&$sender_address$&: The sender address that was received in the envelope of
638the message. This is not necessarily the same as the contents of the &'From:'&
639or &'Sender:'& header lines. For delivery error messages (&"bounce messages"&)
640there is no sender address, and this variable is empty.
641
642&$tod_full$&: A full version of the time and date, for example: Wed, 18 Oct
6431995 09:51:40 +0100. The timezone is always given as a numerical offset from
644GMT.
645
646&$tod_log$&: The time and date in the format used for writing Exim's log files,
647without the timezone, for example: 1995-10-12 15:32:29.
648
649&$tod_zone$&: The local timezone offset, for example: +0100.
650
651
652
653.section "Header variables" "SECTheadervariables"
654There is a special set of expansion variables containing the header lines of
655the message being processed. These variables have names beginning with
656&$header_$& followed by the name of the header line, terminated by a colon.
657For example,
658.code
659$header_from:
660$header_subject:
661.endd
662The whole item, including the terminating colon, is replaced by the contents of
663the message header line. If there is more than one header line with the same
664name, their contents are concatenated. For header lines whose data consists of
665a list of addresses (for example, &'From:'& and &'To:'&), a comma and newline
666is inserted between each set of data. For all other header lines, just a
667newline is used.
668
669Leading and trailing white space is removed from header line data, and if there
670are any MIME &"words"& that are encoded as defined by RFC 2047 (because they
671contain non-ASCII characters), they are decoded and translated, if possible, to
672a local character set. Translation is attempted only on operating systems that
673have the &[iconv()]& function. This makes the header line look the same as it
674would when displayed by an MUA. The default character set is ISO-8859-1, but
675this can be changed by means of the &(headers)& command (see below).
676
677If you want to see the actual characters that make up a header line, you can
678specify &$rheader_$& instead of &$header_$&. This inserts the &"raw"&
679header line, unmodified.
680
681There is also an intermediate form, requested by &$bheader_$&, which removes
682leading and trailing space and decodes MIME &"words"&, but does not do any
683character translation. If an attempt to decode what looks superficially like a
684MIME &"word"& fails, the raw string is returned. If decoding produces a binary
685zero character, it is replaced by a question mark.
686
687The capitalization of the name following &$header_$& is not significant.
688Because any printing character except colon may appear in the name of a
689message's header (this is a requirement of RFC 2822, the document that
690describes the format of a mail message) curly brackets must &'not'& be used in
691this case, as they will be taken as part of the header name. Two shortcuts are
692allowed in naming header variables:
693
694.ilist
695The initiating &$header_$&, &$rheader_$&, or &$bheader_$& can be
696abbreviated to &$h_$&, &$rh_$&, or &$bh_$&, respectively.
697.next
698The terminating colon can be omitted if the next character is white space. The
699white space character is retained in the expanded string. However, this is not
700recommended, because it makes it easy to forget the colon when it really is
701needed.
702.endlist
703
704If the message does not contain a header of the given name, an empty string is
705substituted. Thus it is important to spell the names of headers correctly. Do
706not use &$header_Reply_to$& when you really mean &$header_Reply-to$&.
707
708
4aa45c31 709.section "User variables" "SEC20"
9b371988
PH
710There are ten user variables with names &$n0$& &-- &$n9$& that can be
711incremented by the &(add)& command (see section &<<SECTadd>>&). These can be
712used for &"scoring"& messages in various ways. If Exim is configured to run a
713&"system filter"& on every message, the values left in these variables are
714copied into the variables &$sn0$& &-- &$sn9$& at the end of the system filter,
715thus making them available to users' filter files. How these values are used is
716entirely up to the individual installation.
717
718
4aa45c31 719.section "Current directory" "SEC21"
9b371988
PH
720The contents of your filter file should not make any assumptions about the
721current directory. It is best to use absolute paths for file names; you can
722normally make use of the &$home$& variable to refer to your home directory. The
723&(save)& command automatically inserts &$home$& at the start of non-absolute
724paths.
725
726
727
728
729.section "Significant deliveries" "SECTsigdel"
730When in the course of delivery a message is processed by a filter file, what
731happens next, that is, after the filter file has been processed, depends on
732whether or not the filter sets up any &'significant deliveries'&. If at least
733one significant delivery is set up, the filter is considered to have handled
734the entire delivery arrangements for the current address, and no further
735processing of the address takes place. If, however, no significant deliveries
736are set up, Exim continues processing the current address as if there were no
737filter file, and typically sets up a delivery of a copy of the message into a
738local mailbox. In particular, this happens in the special case of a filter file
739containing only comments.
740
741The delivery commands &(deliver)&, &(save)&, and &(pipe)& are by default
742significant. However, if such a command is preceded by the word &"unseen"&, its
743delivery is not considered to be significant. In contrast, other commands such
744as &(mail)& and &(vacation)& do not set up significant deliveries unless
745preceded by the word &"seen"&. The following example commands set up
746significant deliveries:
747.code
748deliver jack@beanstalk.example
749pipe $home/bin/mymailscript
750seen mail subject "message discarded"
751seen finish
752.endd
753The following example commands do not set up significant deliveries:
754.code
755unseen deliver jack@beanstalk.example
756unseen pipe $home/bin/mymailscript
757mail subject "message discarded"
758finish
759.endd
760
761
762
4aa45c31 763.section "Filter commands" "SEC222"
9b371988
PH
764The filter commands that are described in subsequent sections are listed
765below, with the section in which they are described in brackets:
766
767.table2
768.row &(add)& "&~&~increment a user variable (section &<<SECTadd>>&)"
769.row &(deliver)& "&~&~deliver to an email address (section &<<SECTdeliver>>&)"
770.row &(fail)& "&~&~force delivery failure (sysadmin use) (section &<<SECTfail>>&)"
771.row &(finish)& "&~&~end processing (section &<<SECTfinish>>&)"
772.row &(freeze)& "&~&~freeze message (sysadmin use) (section &<<SECTfreeze>>&)"
773.row &(headers)& "&~&~set the header character set (section &<<SECTheaders>>&)"
774.row &(if)& "&~&~test condition(s) (section &<<SECTif>>&)"
775.row &(logfile)& "&~&~define log file (section &<<SECTlog>>&)"
776.row &(logwrite)& "&~&~write to log file (section &<<SECTlog>>&)"
777.row &(mail)& "&~&~send a reply message (section &<<SECTmail>>&)"
778.row &(pipe)& "&~&~pipe to a command (section &<<SECTpipe>>&)"
779.row &(save)& "&~&~save to a file (section &<<SECTsave>>&)"
780.row &(testprint)& "&~&~print while testing (section &<<SECTtestprint>>&)"
781.row &(vacation)& "&~&~tailored form of &(mail)& (section &<<SECTmail>>&)"
782.endtable
783
784The &(headers)& command has additional parameters that can be used only in a
785system filter. The &(fail)& and &(freeze)& commands are available only when
786Exim's filtering facilities are being used as a system filter, and are
787therefore usable only by the system administrator and not by ordinary users.
788They are mentioned only briefly in this document; for more information, see the
789main Exim specification.
790
791
792
793.section "The add command" "SECTadd"
794.display
795&` add `&<&'number'&>&` to `&<&'user variable'&>
796&`e.g. add 2 to n3`&
797.endd
798
799There are 10 user variables of this type, with names &$n0$& &-- &$n9$&. Their
800values can be obtained by the normal expansion syntax (for example &$n3$&) in
801other commands. At the start of filtering, these variables all contain zero.
802Both arguments of the &(add)& command are expanded before use, making it
803possible to add variables to each other. Subtraction can be obtained by adding
804negative numbers.
805
806
807
808.section "The deliver command" "SECTdeliver"
809.display
810&` deliver`& <&'mail address'&>
811&`e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"`&
812.endd
813
814This command provides a forwarding operation. The delivery that it sets up is
815significant unless the command is preceded by &"unseen"& (see section
816&<<SECTsigdel>>&). The message is sent on to the given address, exactly as
817happens if the address had appeared in a traditional &_.forward_& file. If you
818want to deliver the message to a number of different addresses, you can use
819more than one &(deliver)& command (each one may have only one address).
820However, duplicate addresses are discarded.
821
822To deliver a copy of the message to your normal mailbox, your login name can be
823given as the address. Once an address has been processed by the filtering
824mechanism, an identical generated address will not be so processed again, so
825doing this does not cause a loop.
826
827However, if you have a mail alias, you should &'not'& refer to it here. For
828example, if the mail address &'L.Gulliver'& is aliased to &'lg303'& then all
829references in Gulliver's &_.forward_& file should be to &'lg303'&. A reference
830to the alias will not work for messages that are addressed to that alias,
831since, like &_.forward_& file processing, aliasing is performed only once on an
832address, in order to avoid looping.
833
834Following the new address, an optional second address, preceded by
835&"errors_to"& may appear. This changes the address to which delivery errors on
836the forwarded message will be sent. Instead of going to the message's original
837sender, they go to this new address. For ordinary users, the only value that is
838permitted for this address is the user whose filter file is being processed.
839For example, the user &'lg303'& whose mailbox is in the domain
840&'lilliput.example'& could have a filter file that contains
841.code
842deliver jon@elsewhere.example errors_to lg303@lilliput.example
843.endd
844Clearly, using this feature makes sense only in situations where not all
845messages are being forwarded. In particular, bounce messages must not be
846forwarded in this way, as this is likely to create a mail loop if something
847goes wrong.
848
849
850
851.section "The save command" "SECTsave"
852.display
853&` save `&<&'file name'&>
854&`e.g. save $home/mail/bookfolder`&
855.endd
856
857This command specifies that a copy of the message is to be appended to the
858given file (that is, the file is to be used as a mail folder). The delivery
859that &(save)& sets up is significant unless the command is preceded by
860&"unseen"& (see section &<<SECTsigdel>>&).
861
862More than one &(save)& command may be obeyed; each one causes a copy of the
863message to be written to its argument file, provided they are different
864(duplicate &(save)& commands are ignored).
865
866If the file name does not start with a / character, the contents of the
f89d2485
PH
867&$home$& variable are prepended, unless it is empty, or the system
868administrator has disabled this feature. In conventional configurations, this
553c0e3a
PH
869variable is normally set in a user filter to the user's home directory, but the
870system administrator may set it to some other path. In some configurations,
f89d2485 871&$home$& may be unset, or prepending may be disabled, in which case a
553c0e3a
PH
872non-absolute path name may be generated. Such configurations convert this to an
873absolute path when the delivery takes place. In a system filter, &$home$& is
874never set.
9b371988
PH
875
876The user must of course have permission to write to the file, and the writing
877of the file takes place in a process that is running as the user, under the
878user's primary group. Any secondary groups to which the user may belong are not
879normally taken into account, though the system administrator can configure Exim
880to set them up. In addition, the ability to use this command at all is
881controlled by the system administrator &-- it may be forbidden on some systems.
882
883An optional mode value may be given after the file name. The value for the mode
884is interpreted as an octal number, even if it does not begin with a zero. For
885example:
886.code
887save /some/folder 640
888.endd
889This makes it possible for users to override the system-wide mode setting for
890file deliveries, which is normally 600. If an existing file does not have the
891correct mode, it is changed.
892
893An alternative form of delivery may be enabled on your system, in which each
894message is delivered into a new file in a given directory. If this is the case,
895this functionality can be requested by giving the directory name terminated by
896a slash after the &(save)& command, for example
897.code
898save separated/messages/
899.endd
900There are several different formats for such deliveries; check with your system
901administrator or local documentation to find out which (if any) are available
902on your system. If this functionality is not enabled, the use of a path name
903ending in a slash causes an error.
904
905
906
907.section "The pipe command" "SECTpipe"
908.display
909&` pipe `&<&'command'&>
910&`e.g. pipe "$home/bin/countmail $sender_address"`&
911.endd
912
913This command specifies that the message is to be delivered to the specified
914command using a pipe. The delivery that it sets up is significant unless the
915command is preceded by &"unseen"& (see section &<<SECTsigdel>>&). Remember,
916however, that no deliveries are done while the filter is being processed. All
917deliveries happen later on. Therefore, the result of running the pipe is not
918available to the filter.
919
920When the deliveries are done, a separate process is run, and a copy of the
921message is passed on its standard input. The process runs as the user, under
922the user's primary group. Any secondary groups to which the user may belong are
923not normally taken into account, though the system administrator can configure
924Exim to set them up. More than one &(pipe)& command may appear; each one causes
925a copy of the message to be written to its argument pipe, provided they are
926different (duplicate &(pipe)& commands are ignored).
927
928When the time comes to transport the message, the command supplied to &(pipe)&
929is split up by Exim into a command name and a number of arguments. These are
930delimited by white space except for arguments enclosed in double quotes, in
931which case backslash is interpreted as an escape, or in single quotes, in which
932case no escaping is recognized. Note that as the whole command is normally
933supplied in double quotes, a second level of quoting is required for internal
934double quotes. For example:
935.code
936pipe "$home/myscript \"size is $message_size\""
937.endd
938String expansion is performed on the separate components after the line has
939been split up, and the command is then run directly by Exim; it is not run
940under a shell. Therefore, substitution cannot change the number of arguments,
941nor can quotes, backslashes or other shell metacharacters in variables cause
942confusion.
943
944Documentation for some programs that are normally run via this kind of pipe
945often suggest that the command should start with
946.code
947IFS=" "
948.endd
949This is a shell command, and should &'not'& be present in Exim filter files,
950since it does not normally run the command under a shell.
951
952However, there is an option that the administrator can set to cause a shell to
953be used. In this case, the entire command is expanded as a single string and
954passed to the shell for interpretation. It is recommended that this be avoided
955if at all possible, since it can lead to problems when inserted variables
956contain shell metacharacters.
957
958The default PATH set up for the command is determined by the system
959administrator, usually containing at least &_/bin_& and &_/usr/bin_& so that
960common commands are available without having to specify an absolute file name.
961However, it is possible for the system administrator to restrict the pipe
962facility so that the command name must not contain any / characters, and must
963be found in one of the directories in the configured PATH. It is also possible
964for the system administrator to lock out the use of the &(pipe)& command
965altogether.
966
967When the command is run, a number of environment variables are set up. The
968complete list for pipe deliveries may be found in the Exim reference manual.
969Those that may be useful for pipe deliveries from user filter files are:
970
971.display
972&`DOMAIN `& the domain of the address
973&`HOME `& your home directory
974&`LOCAL_PART `& see below
975&`LOCAL_PART_PREFIX `& see below
976&`LOCAL_PART_SUFFIX `& see below
977&`LOGNAME `& your login name
978&`MESSAGE_ID `& the unique id of the message
979&`PATH `& the command search path
980&`RECIPIENT `& the complete recipient address
981&`SENDER `& the sender of the message
982&`SHELL `& &`/bin/sh`&
983&`USER `& see below
984.endd
985
986LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
987id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
988recognize prefixes or suffixes in the local parts of addresses. For example, a
989message addressed to &'pat-suf2@domain.example'& may cause the filter for user
990&'pat'& to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
991&`-suf2`& when the pipe command runs. The system administrator has to configure
992Exim specially for this feature to be available.
993
994If you run a command that is a shell script, be very careful in your use of
995data from the incoming message in the commands in your script. RFC 2822 is very
996generous in the characters that are permitted to appear in mail addresses, and
997in particular, an address may begin with a vertical bar or a slash. For this
998reason you should always use quotes round any arguments that involve data from
999the message, like this:
1000.code
1001/some/command '$SENDER'
1002.endd
1003so that inserted shell meta-characters do not cause unwanted effects.
1004
1005Remember that, as was explained earlier, the pipe command is not run at the
1006time the filter file is interpreted. The filter just defines what deliveries
1007are required for one particular addressee of a message. The deliveries
1008themselves happen later, once Exim has decided everything that needs to be done
1009for the message.
1010
1011A consequence of this is that you cannot inspect the return code from the pipe
1012command from within the filter. Nevertheless, the code returned by the command
1013is important, because Exim uses it to decide whether the delivery has succeeded
1014or failed.
1015
1016The command should return a zero completion code if all has gone well. Most
1017non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1018treated as a delivery failure, causing the message to be returned to its
1019sender. However, there are some completion codes that are treated as temporary
1020errors. The message remains on Exim's spool disk, and the delivery is tried
1021again later, though it will ultimately time out if the delivery failures go on
1022too long. The completion codes to which this applies can be specified by the
1023system administrator; the default values are 73 and 75.
1024
1025The pipe command should not normally write anything to its standard output or
1026standard error file descriptors. If it does, whatever is written is normally
1027returned to the sender of the message as a delivery error, though this action
1028can be varied by the system administrator.
1029
1030
1031
1032.section "Mail commands" "SECTmail"
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 &<<SECTsigdel>>&). This is a powerful facility, but
1036it should be used with care, because of the danger of creating infinite
1037sequences of messages. The system administrator can forbid the use of these
1038commands altogether.
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.display
1046&`mail [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'&>&`]`&
9b371988
PH
1059&`e.g. mail text "Your message about $h_subject: has been received"`&
1060.endd
1061Each <&'address-list'&> can contain a number of addresses, separated by commas,
1062in the format of a &'To:'& or &'Cc:'& header line. In fact, the text you supply
1063here is copied exactly into the appropriate header line. It may contain
1064additional information as well as email addresses. For example:
1065.code
1066mail to "Julius Caesar <jc@rome.example>, \
1067 <ma@rome.example> (Mark A.)"
1068.endd
1069Similarly, the texts supplied for &%from%& and &%reply_to%& are copied into
1070their respective header lines.
1071
1072As a convenience for use in one common case, there is also a command called
1073&(vacation)&. It behaves in the same way as &(mail)&, except that the defaults
1074for the &%subject%&, &%file%&, &%log%&, &%once%&, and &%once_repeat%& options
1075are
1076.code
1077subject "On vacation"
1078expand file .vacation.msg
1079log .vacation.log
1080once .vacation
1081once_repeat 7d
1082.endd
1083respectively. These are the same file names and repeat period used by the
1084traditional Unix &(vacation)& command. The defaults can be overridden by
1085explicit settings, but if a file name is given its contents are expanded only
1086if explicitly requested.
1087
1088&*Warning*&: The &(vacation)& command should always be used conditionally,
1089subject to at least the &(personal)& condition (see section &<<SECTpersonal>>&
1090below) so as not to send automatic replies to non-personal messages from
1091mailing lists or elsewhere. Sending an automatic response to a mailing list or
1092a mailing list manager is an Internet Sin.
1093
1094For both commands, the key/value argument pairs can appear in any order. At
1095least one of &%text%& or &%file%& must appear (except with &(vacation)&, where
1096there is a default for &%file%&); if both are present, the text string appears
1097first in the message. If &%expand%& precedes &%file%&, each line of the file is
1098subject to string expansion before it is included in the message.
1099
1100Several lines of text can be supplied to &%text%& by including the escape
1101sequence &"\n"& in the string wherever a newline is required. If the command is
1102output during filter file testing, newlines in the text are shown as &"\n"&.
1103
1104Note that the keyword for creating a &'Reply-To:'& header is &%reply_to%&,
1105because Exim keywords may contain underscores, but not hyphens. If the &%from%&
1106keyword is present and the given address does not match the user who owns the
1107forward file, Exim normally adds a &'Sender:'& header to the message, though it
1108can be configured not to do this.
1109
1110The &%extra_headers%& keyword allows you to add custom header lines to the
1111message. The text supplied must be one or more syntactically valid RFC 2822
1112header lines. You can use &"\n"& within quoted text to specify newlines between
1113headers, and also to define continued header lines. For example:
1114.code
1115extra_headers "h1: first\nh2: second\n continued\nh3: third"
1116.endd
1117No newline should appear at the end of the final header line.
1118
1119If no &%to%& argument appears, the message is sent to the address in the
1120&$reply_address$& variable (see section &<<SECTfilterstringexpansion>>& above).
1121An &'In-Reply-To:'& header is automatically included in the created message,
1122giving a reference to the message identification of the incoming message.
1123
1124If &%return message%& is specified, the incoming message that caused the filter
1125file to be run is added to the end of the message, subject to a maximum size
1126limitation.
1127
1128If a log file is specified, a line is added to it for each message sent.
1129
1130If a &%once%& file is specified, it is used to hold a database for remembering
1131who has received a message, and no more than one message is ever sent to any
1132particular address, unless &%once_repeat%& is set. This specifies a time
1133interval after which another copy of the message is sent. The interval is
1134specified as a sequence of numbers, each followed by the initial letter of one
1135of &"seconds"&, &"minutes"&, &"hours"&, &"days"&, or &"weeks"&. For example,
1136.code
1137once_repeat 5d4h
1138.endd
1139causes a new message to be sent if at least 5 days and 4 hours have elapsed
1140since the last one was sent. There must be no white space in a time interval.
1141
1142Commonly, the file name specified for &%once%& is used as the base name for
1143direct-access (DBM) file operations. There are a number of different DBM
1144libraries in existence. Some operating systems provide one as a default, but
1145even in this case a different one may have been used when building Exim. With
1146some DBM libraries, specifying &%once%& results in two files being created,
1147with the suffixes &_.dir_& and &_.pag_& being added to the given name. With
1148some others a single file with the suffix &_.db_& is used, or the name is used
1149unchanged.
1150
1151Using a DBM file for implementing the &%once%& feature means that the file
1152grows as large as necessary. This is not usually a problem, but some system
1153administrators want to put a limit on it. The facility can be configured not to
1154use a DBM file, but instead, to use a regular file with a maximum size. The
1155data in such a file is searched sequentially, and if the file fills up, the
1156oldest entry is deleted to make way for a new one. This means that some
1157correspondents may receive a second copy of the message after an unpredictable
1158interval. Consult your local information to see if your system is configured
1159this way.
1160
1161More than one &(mail)& or &(vacation)& command may be obeyed in a single filter
1162run; they are all honoured, even when they are to the same recipient.
1163
1164
1165
1166.section "Logging commands" "SECTlog"
1167A log can be kept of actions taken by a filter file. This facility is normally
1168available in conventional configurations, but there are some situations where
1169it might not be. Also, the system administrator may choose to disable it. Check
1170your local information if in doubt.
1171
1172Logging takes place while the filter file is being interpreted. It does not
1173queue up for later like the delivery commands. The reason for this is so that a
1174log file need be opened only once for several write operations. There are two
1175commands, neither of which constitutes a significant delivery. The first
1176defines a file to which logging output is subsequently written:
1177.display
1178&` logfile `&<&'file name'&>
1179&`e.g. logfile $home/filter.log`&
1180.endd
1181The file name must be fully qualified. You can use &$home$&, as in this
1182example, to refer to your home directory. The file name may optionally be
1183followed by a mode for the file, which is used if the file has to be created.
1184For example,
1185.code
1186logfile $home/filter.log 0644
1187.endd
1188The number is interpreted as octal, even if it does not begin with a zero.
1189The default for the mode is 600. It is suggested that the &(logfile)& command
1190normally appear as the first command in a filter file. Once a log file has
1191been obeyed, the &(logwrite)& command can be used to write to it:
1192.display
1193&` logwrite "`&<&'some text string'&>&`"`&
1194&`e.g. logwrite "$tod_log $message_id processed"`&
1195.endd
1196It is possible to have more than one &(logfile)& command, to specify writing to
1197different log files in different circumstances. Writing takes place at the end
1198of the file, and a newline character is added to the end of each string if
1199there isn't one already there. Newlines can be put in the middle of the string
1200by using the &"\n"& escape sequence. Lines from simultaneous deliveries may get
1201interleaved in the file, as there is no interlocking, so you should plan your
1202logging with this in mind. However, data should not get lost.
1203
1204
1205
1206.section "The finish command" "SECTfinish"
1207The command &(finish)&, which has no arguments, causes Exim to stop
1208interpreting the filter file. This is not a significant action unless preceded
1209by &"seen"&. A filter file containing only &"seen finish"& is a black hole.
1210
1211
1212.section "The testprint command" "SECTtestprint"
1213It is sometimes helpful to be able to print out the values of variables when
1214testing filter files. The command
1215.display
1216&` testprint `&<&'text'&>
1217&`e.g. testprint "home=$home reply_address=$reply_address"`&
1218.endd
1219does nothing when mail is being delivered. However, when the filtering code is
1220being tested by means of the &%-bf%& option (see section &<<SECTtesting>>&
1221above), the value of the string is written to the standard output.
1222
1223
1224.section "The fail command" "SECTfail"
1225When Exim's filtering facilities are being used as a system filter, the
1226&(fail)& command is available, to force delivery failure. Because this command
1227is normally usable only by the system administrator, and not enabled for use by
1228ordinary users, it is described in more detail in the main Exim specification
1229rather than in this document.
1230
1231
1232.section "The freeze command" "SECTfreeze"
1233When Exim's filtering facilities are being used as a system filter, the
1234&(freeze)& command is available, to freeze a message on the queue. Because this
1235command is normally usable only by the system administrator, and not enabled
1236for use by ordinary users, it is described in more detail in the main Exim
1237specification rather than in this document.
1238
1239
1240
1241.section "The headers command" "SECTheaders"
1242The &(headers)& command can be used to change the target character set that is
1243used when translating the contents of encoded header lines for insertion by the
1244&$header_$& mechanism (see section &<<SECTheadervariables>>& above). The
1245default can be set in the Exim configuration; if not specified, ISO-8859-1 is
1246used. The only currently supported format for the &(headers)& command in user
1247filters is as in this example:
1248.code
1249headers charset "UTF-8"
1250.endd
1251That is, &(headers)& is followed by the word &"charset"& and then the name of a
1252character set. This particular example would be useful if you wanted to compare
1253the contents of a header to a UTF-8 string.
1254
1255In system filter files, the &(headers)& command can be used to add or remove
1256header lines from the message. These features are described in the main Exim
1257specification.
1258
1259
1260
1261.section "Obeying commands conditionally" "SECTif"
1262Most of the power of filtering comes from the ability to test conditions and
1263obey different commands depending on the outcome. The &(if)& command is used to
1264specify conditional execution, and its general form is
1265.display
1266&`if `&<&'condition'&>
1267&`then `&<&'commands'&>
1268&`elif `&<&'condition'&>
1269&`then `&<&'commands'&>
1270&`else `&<&'commands'&>
1271&`endif`&
1272.endd
1273There may be any number of &(elif)& and &(then)& sections (including none) and
1274the &(else)& section is also optional. Any number of commands, including nested
1275&(if)& commands, may appear in any of the <&'commands'&> sections.
1276
1277Conditions can be combined by using the words &(and)& and &(or)&, and round
1278brackets (parentheses) can be used to specify how several conditions are to
1279combine. Without brackets, &(and)& is more binding than &(or)&. For example:
1280.code
1281if
1282$h_subject: contains "Make money" or
1283$h_precedence: is "junk" or
1284($h_sender: matches ^\\d{8}@ and not personal) or
1285$message_body contains "this is not spam"
1286then
1287seen finish
1288endif
1289.endd
1290A condition can be preceded by &(not)& to negate it, and there are also some
1291negative forms of condition that are more English-like.
1292
1293
1294
4aa45c31 1295.section "String testing conditions" "SEC23"
9b371988
PH
1296There are a number of conditions that operate on text strings, using the words
1297&"begins"&, &"ends"&, &"is"&, &"contains"& and &"matches"&. If you want to
1298apply the same test to more than one header line, you can easily concatenate
1299them into a single string for testing, as in this example:
1300.code
1301if "$h_to:, $h_cc:" contains me@domain.example then ...
1302.endd
1303If a string-testing condition name is written in lower case, the testing
1304of letters is done without regard to case; if it is written in upper case
1305(for example, &"CONTAINS"&), the case of letters is taken into account.
1306
1307.display
1308&` `&<&'text1'&>&` begins `&<&'text2'&>
1309&` `&<&'text1'&>&` does not begin `&<&'text2'&>
1310&`e.g. $header_from: begins "Friend@"`&
1311.endd
1312
1313A &"begins"& test checks for the presence of the second string at the start of
1314the first, both strings having been expanded.
1315
1316.display
1317&` `&<&'text1'&>&` ends `&<&'text2'&>
1318&` `&<&'text1'&>&` does not end `&<&'text2'&>
1319&`e.g. $header_from: ends "public.com.example"`&
1320.endd
1321
1322An &"ends"& test checks for the presence of the second string at the end of
1323the first, both strings having been expanded.
1324
1325.display
1326&` `&<&'text1'&>&` is `&<&'text2'&>
1327&` `&<&'text1'&>&` is not `&<&'text2'&>
1328&`e.g. $local_part_suffix is "-foo"`&
1329.endd
1330
1331An &"is"& test does an exact match between the strings, having first expanded
1332both strings.
1333
1334.display
1335&` `&<&'text1'&>&` contains `&<&'text2'&>
1336&` `&<&'text1'&>&` does not contain `&<&'text2'&>
1337&`e.g. $header_subject: contains "evolution"`&
1338.endd
1339
1340A &"contains"& test does a partial string match, having expanded both strings.
1341
1342.display
1343&` `&<&'text1'&>&` matches `&<&'text2'&>
1344&` `&<&'text1'&>&` does not match `&<&'text2'&>
1345&`e.g. $sender_address matches "(bill|john)@"`&
1346.endd
1347
1348For a &"matches"& test, after expansion of both strings, the second one is
1349interpreted as a regular expression. Exim uses the PCRE regular expression
1350library, which provides regular expressions that are compatible with Perl.
1351
1352The match succeeds if the regular expression matches any part of the first
1353string. If you want a regular expression to match only at the start or end of
1354the subject string, you must encode that requirement explicitly, using the
1355&`^`& or &`$`& metacharacters. The above example, which is not so constrained,
1356matches all these addresses:
1357.code
1358bill@test.example
1359john@some.example
1360spoonbill@example.com
1361littlejohn@example.com
1362.endd
1363To match only the first two, you could use this:
1364.code
1365if $sender_address matches "^(bill|john)@" then ...
1366.endd
1367Care must be taken if you need a backslash in a regular expression, because
1368backslashes are interpreted as escape characters both by the string expansion
1369code and by Exim's normal processing of strings in quotes. For example, if you
1370want to test the sender address for a domain ending in &'.com'& the regular
1371expression is
1372.code
1373\.com$
1374.endd
1375The backslash and dollar sign in that expression have to be escaped when used
1376in a filter command, as otherwise they would be interpreted by the expansion
1377code. Thus, what you actually write is
1378.code
1379if $sender_address matches \\.com\$
1380.endd
1381An alternative way of handling this is to make use of the &`\N`& expansion
1382flag for suppressing expansion:
1383.code
1384if $sender_address matches \N\.com$\N
1385.endd
1386Everything between the two occurrences of &`\N`& is copied without change by
1387the string expander (and in fact you do not need the final one, because it is
1388at the end of the string). If the regular expression is given in quotes
1389(mandatory only if it contains white space) you have to write either
1390.code
1391if $sender_address matches "\\\\.com\\$"
1392.endd
1393or
1394.code
1395if $sender_address matches "\\N\\.com$\\N"
1396.endd
1397
1398If the regular expression contains bracketed sub-expressions, numeric
1399variable substitutions such as &$1$& can be used in the subsequent actions
1400after a successful match. If the match fails, the values of the numeric
1401variables remain unchanged. Previous values are not restored after &(endif)&.
1402In other words, only one set of values is ever available. If the condition
1403contains several sub-conditions connected by &(and)& or &(or)&, it is the
1404strings extracted from the last successful match that are available in
1405subsequent actions. Numeric variables from any one sub-condition are also
1406available for use in subsequent sub-conditions, because string expansion of a
1407condition occurs just before it is tested.
1408
1409
4aa45c31 1410.section "Numeric testing conditions" "SEC24"
9b371988
PH
1411The following conditions are available for performing numerical tests:
1412
1413.display
1414&` `&<&'number1'&>&` is above `&<&'number2'&>
1415&` `&<&'number1'&>&` is not above `&<&'number2'&>
1416&` `&<&'number1'&>&` is below `&<&'number2'&>
1417&` `&<&'number1'&>&` is not below `&<&'number2'&>
1418&`e.g. $message_size is not above 10k`&
1419.endd
1420
1421The <&'number'&> arguments must expand to strings of digits, optionally
1422followed by one of the letters K or M (upper case or lower case) which cause
1423multiplication by 1024 and 1024x1024 respectively.
1424
1425
4aa45c31 1426.section "Testing for significant deliveries" "SEC25"
9b371988
PH
1427You can use the &(delivered)& condition to test whether or not any previously
1428obeyed filter commands have set up a significant delivery. For example:
1429.code
1430if not delivered then save mail/anomalous endif
1431.endd
1432&"Delivered"& is perhaps a poor choice of name for this condition, because the
1433message has not actually been delivered; rather, a delivery has been set up for
1434later processing.
1435
1436
4aa45c31 1437.section "Testing for error messages" "SEC26"
9b371988
PH
1438The condition &(error_message)& is true if the incoming message is a bounce
1439(mail delivery error) message. Putting the command
1440.code
1441if error_message then finish endif
1442.endd
1443at the head of your filter file is a useful insurance against things going
1444wrong in such a way that you cannot receive delivery error reports. &*Note*&:
1445&(error_message)& is a condition, not an expansion variable, and therefore is
1446not preceded by &`$`&.
1447
1448
4aa45c31 1449.section "Testing a list of addresses" "SEC27"
9b371988
PH
1450There is a facility for looping through a list of addresses and applying a
1451condition to each of them. It takes the form
1452.display
1453&`foranyaddress `&<&'string'&>&` (`&<&'condition'&>&`)`&
1454.endd
1455where <&'string'&> is interpreted as a list of RFC 2822 addresses, as in a
1456typical header line, and <&'condition'&> is any valid filter condition or
1457combination of conditions. The &"group"& syntax that is defined for certain
1458header lines that contain addresses is supported.
1459
1460The parentheses surrounding the condition are mandatory, to delimit it from
1461possible further sub-conditions of the enclosing &(if)& command. Within the
1462condition, the expansion variable &$thisaddress$& is set to the non-comment
1463portion of each of the addresses in the string in turn. For example, if the
1464string is
1465.code
1466B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1467.endd
1468then &$thisaddress$& would take on the values &`bart@sfld.example`& and
1469&`lisa@sfld.example`& in turn.
1470
1471If there are no valid addresses in the list, the whole condition is false. If
1472the internal condition is true for any one address, the overall condition is
1473true and the loop ends. If the internal condition is false for all addresses in
1474the list, the overall condition is false. This example tests for the presence
1475of an eight-digit local part in any address in a &'To:'& header:
1476.code
1477if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1478.endd
1479When the overall condition is true, the value of &$thisaddress$& in the
1480commands that follow &(then)& is the last value it took on inside the loop. At
1481the end of the &(if)& command, the value of &$thisaddress$& is reset to what it
1482was before. It is best to avoid the use of multiple occurrences of
1483&(foranyaddress)&, nested or otherwise, in a single &(if)& command, if the
1484value of &$thisaddress$& is to be used afterwards, because it isn't always
1485clear what the value will be. Nested &(if)& commands should be used instead.
1486
1487Header lines can be joined together if a check is to be applied to more than
1488one of them. For example:
1489.code
1490if foranyaddress $h_to:,$h_cc: ....
1491.endd
1492This scans through the addresses in both the &'To:'& and the &'Cc:'& headers.
1493
1494
1495.section "Testing for personal mail" "SECTpersonal"
1496A common requirement is to distinguish between incoming personal mail and mail
1497from a mailing list, or from a robot or other automatic process (for example, a
1498bounce message). In particular, this test is normally required for &"vacation
1499messages"&.
1500
1501The &(personal)& condition checks that the message is not a bounce message and
1502that the current user's email address appears in the &'To:'& header. It also
1503checks that the sender is not the current user or one of a number of common
1504daemons, and that there are no header lines starting &'List-'& in the message.
1505Finally, it checks the content of the &'Precedence:'& header line, if there is
1506one.
1507
1508You should always use the &(personal)& condition when generating automatic
1509responses. This example shows the use of &(personal)& in a filter file that is
1510sending out vacation messages:
1511.code
1512if personal then
1513mail to $reply_address
1514subject "I am on holiday"
1515file $home/vacation/message
1516once $home/vacation/once
1517once_repeat 10d
1518endif
1519.endd
1520It is tempting, when writing commands like the above, to quote the original
1521subject in the reply. For example:
1522.code
1523subject "Re: $h_subject:"
1524.endd
1525There is a danger in doing this, however. It may allow a third party to
1526subscribe you to an opt-in mailing list, provided that the list accepts bounce
1527messages as subscription confirmations. (Messages sent from filters are always
1528sent as bounce messages.) Well-managed lists require a non-bounce message to
1529confirm a subscription, so the danger is relatively small.
1530
1531If prefixes or suffixes are in use for local parts &-- something which depends
1532on the configuration of Exim (see section &<<SECTmbox>>& below) &-- the tests
1533for the current user are done with the full address (including the prefix and
1534suffix, if any) as well as with the prefix and suffix removed. If the system is
1535configured to rewrite local parts of mail addresses, for example, to rewrite
1536&`dag46`& as &`Dirk.Gently`&, the rewritten form of the address is also used in
1537the tests.
1538
1539
1540
4aa45c31 1541.section "Alias addresses for the personal condition" "SEC28"
9b371988
PH
1542It is quite common for people who have mail accounts on a number of different
1543systems to forward all their mail to one system, and in this case a check for
1544personal mail should test all their various mail addresses. To allow for this,
1545the &(personal)& condition keyword can be followed by
1546.display
1547&`alias `&<&'address'&>
1548.endd
1549any number of times, for example:
1550.code
1551if personal alias smith@else.where.example
1552 alias jones@other.place.example
1553then ...
1554.endd
1555The alias addresses are treated as alternatives to the current user's email
1556address when testing the contents of header lines.
1557
1558
4aa45c31 1559.section "Details of the personal condition" "SEC29"
9b371988
PH
1560The basic &(personal)& test is roughly equivalent to the following:
1561.code
1562not error_message and
1563$message_headers does not contain "\nList-Id:" and
1564$message_headers does not contain "\nList-Help:" and
1565$message_headers does not contain "\nList-Subscribe:" and
1566$message_headers does not contain "\nList-Unsubscribe:" and
1567$message_headers does not contain "\nList-Post:" and
1568$message_headers does not contain "\nList-Owner:" and
1569$message_headers does not contain "\nList-Archive:" and
1570(
8f3414a1 1571"${if def:h_auto-submitted:{present}{absent}}" is "absent" or
9b371988
PH
1572$header_auto-submitted: is "no"
1573) and
1574$header_precedence: does not contain "bulk" and
1575$header_precedence: does not contain "list" and
1576$header_precedence: does not contain "junk" and
1577foranyaddress $header_to:
1578( $thisaddress contains "$local_part$domain" ) and
1579not foranyaddress $header_from:
1580(
c0712871
PH
1581$thisaddress contains "$local_part@$domain" or
1582$thisaddress contains "server@" or
1583$thisaddress contains "daemon@" or
1584$thisaddress contains "root@" or
1585$thisaddress contains "listserv@" or
1586$thisaddress contains "majordomo@" or
1587$thisaddress contains "-request@" or
1588$thisaddress matches "^owner-[^@]+@"
9b371988
PH
1589)
1590.endd
1591The variable &$local_part$& contains the local part of the mail address of
1592the user whose filter file is being run &-- it is normally your login id. The
1593&$domain$& variable contains the mail domain. As explained above, if aliases
1594or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1595the current user are also done with alternative addresses.
1596
1597
1598
1599
4aa45c31 1600.section "Testing delivery status" "SEC30"
9b371988
PH
1601There are two conditions that are intended mainly for use in system filter
1602files, but which are available in users' filter files as well. The condition
1603&(first_delivery)& is true if this is the first process that is attempting to
1604deliver the message, and false otherwise. This indicator is not reset until the
1605first delivery process successfully terminates; if there is a crash or a power
1606failure (for example), the next delivery attempt is also a &"first delivery"&.
1607
1608In a user filter file &(first_delivery)& will be false if there was previously
1609an error in the filter, or if a delivery for the user failed owing to, for
1610example, a quota error, or if forwarding to a remote address was deferred for
1611some reason.
1612
1613The condition &(manually_thawed)& is true if the message was &"frozen"& for
1614some reason, and was subsequently released by the system administrator. It is
1615unlikely to be of use in users' filter files.
1616
1617
4aa45c31 1618.section "Multiple personal mailboxes" "SECTmbox" "SEC31"
9b371988
PH
1619The system administrator can configure Exim so that users can set up variants
1620on their email addresses and handle them separately. Consult your system
1621administrator or local documentation to see if this facility is enabled on your
1622system, and if so, what the details are.
1623
1624The facility involves the use of a prefix or a suffix on an email address. For
1625example, all mail addressed to &'lg303-'&<&'something'&> would be the property
1626of user &'lg303'&, who could determine how it was to be handled, depending on
1627the value of <&'something'&>.
1628
1629There are two possible ways in which this can be set up. The first possibility
1630is the use of multiple &_.forward_& files. In this case, mail to &'lg303-foo'&,
1631for example, is handled by looking for a file called &_.forward-foo_& in
1632&'lg303'&'s home directory. If such a file does not exist, delivery fails
1633and the message is returned to its sender.
1634
1635The alternative approach is to pass all messages through a single &_.forward_&
1636file, which must be a filter file so that it can distinguish between the
1637different cases by referencing the variables &$local_part_prefix$& or
1638&$local_part_suffix$&, as in the final example in section &<<SECTex>>& below.
1639
1640It is possible to configure Exim to support both schemes at once. In this case,
1641a specific &_.forward-foo_& file is first sought; if it is not found, the basic
1642&_.forward_& file is used.
1643
1644The &(personal)& test (see section &<<SECTpersonal>>&) includes prefixes and
1645suffixes in its checking.
1646
1647
1648
4aa45c31 1649.section "Ignoring delivery errors" "SEC43"
9b371988
PH
1650As was explained above, filtering just sets up addresses for delivery &-- no
1651deliveries are actually done while a filter file is active. If any of the
1652generated addresses subsequently suffers a delivery failure, an error message
1653is generated in the normal way. However, if a filter command that sets up a
1654delivery is preceded by the word &"noerror"&, errors for that delivery,
1655and any deliveries consequent on it (that is, from alias, forwarding, or
1656filter files it invokes) are ignored.
1657
1658
1659
1660.section "Examples of Exim filter commands" "SECTex"
1661Simple forwarding:
1662
1663.code
1664# Exim filter
1665deliver baggins@rivendell.middle-earth.example
1666.endd
1667
1668Vacation handling using traditional means, assuming that the &_.vacation.msg_&
1669and other files have been set up in your home directory:
1670
1671.code
1672# Exim filter
1673unseen pipe "/usr/ucb/vacation \"$local_part\""
1674.endd
1675
1676Vacation handling inside Exim, having first created a file called
1677&_.vacation.msg_& in your home directory:
1678
1679.code
1680# Exim filter
1681if personal then vacation endif
1682.endd
1683
1684File some messages by subject:
1685
1686.code
1687# Exim filter
1688if $header_subject: contains "empire" or
1689$header_subject: contains "foundation"
1690then
1691save $home/mail/f+e
1692endif
1693.endd
1694
1695Save all non-urgent messages by weekday:
1696
1697.code
1698# Exim filter
1699if $header_subject: does not contain "urgent" and
1700$tod_full matches "^(...),"
1701then
1702save $home/mail/$1
1703endif
1704.endd
1705
1706Throw away all mail from one site, except from postmaster:
1707
1708.code
1709# Exim filter
1710if $reply_address contains "@spam.site.example" and
1711$reply_address does not contain "postmaster@"
1712then
1713seen finish
1714endif
1715.endd
1716
1717Handle multiple personal mailboxes:
1718
1719.code
1720# Exim filter
1721if $local_part_suffix is "-foo"
1722then
1723save $home/mail/foo
1724elif $local_part_suffix is "-bar"
1725then
1726save $home/mail/bar
1727endif
1728.endd
1729