Update release date, prep for 4.77 final cut
[exim.git] / doc / doc-docbook / filter.xfpt
CommitLineData
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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
11.docbook
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12
13. /////////////////////////////////////////////////////////////////////////////
14. These lines are processing instructions for the Simple DocBook Processor that
15. Philip Hazel has developed as a less cumbersome way of making PostScript and
16. PDFs than using xmlto and fop. They will be ignored by all other XML
17. processors.
18. /////////////////////////////////////////////////////////////////////////////
19
20.literal xml
21<?sdop
22 foot_right_recto="&chaptertitle;"
23 foot_right_verso="&chaptertitle;"
24 table_warn_soft_overflow="no"
25 toc_chapter_blanks="yes,yes"
26 toc_title="Exim's interfaces to mail filtering"
27?>
28.literal off
29
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30.book
31
32. ===========================================================================
33. Additional xfpt markup used by this document, over and above the default
34. provided in the xfpt library.
35
36. Override the &$ flag to automatically insert a $ with the variable name
37
38.flag &$ $& "<varname>$" "</varname>"
39
40. A macro for the common 2-column tables
41
42.macro table2 100pt 300pt
43.itable none 0 0 2 $1 left $2 left
44.endmacro
45. ===========================================================================
46
47
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48. /////////////////////////////////////////////////////////////////////////////
49. /////////////////////////////////////////////////////////////////////////////
50
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51. This preliminary stuff creates a <bookinfo> entry in the XML. This is removed
52. when creating the PostScript/PDF output, because we do not want a full-blown
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53. title page created for those versions. When fop is being used to create
54. PS/PDF, the stylesheet fudges up a title line to replace the text "Table of
55. contents". When SDoP is being used, a processing instruction does this job.
56. For the other forms of output, the <bookinfo> element is retained and used.
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57
58.literal xml
59<bookinfo>
60<title>Exim's interfaces to mail filtering</title>
61<titleabbrev>Exim filtering</titleabbrev>
2f1c4d4c 62<date>23 November 2009</date>
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63<author><firstname>Philip</firstname><surname>Hazel</surname></author>
64<authorinitials>PH</authorinitials>
65<revhistory><revision>
0c7e1801 66 <revnumber>4.77</revnumber>
92a14cf5 67 <date>10 Oct 2011</date>
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68 <authorinitials>PH</authorinitials>
69</revision></revhistory>
aa9c3669 70<copyright><year>2010</year><holder>University of Cambridge</holder></copyright>
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71</bookinfo>
72.literal off
73
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74. /////////////////////////////////////////////////////////////////////////////
75. /////////////////////////////////////////////////////////////////////////////
76
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4aa45c31 78.chapter "Forwarding and filtering in Exim" "CHAPforandfilt"
9b371988 79This document describes the user interfaces to Exim's in-built mail filtering
f89d2485 80facilities, and is copyright &copy; University of Cambridge 2007. It
0c7e1801 81corresponds to Exim version 4.77.
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82
83
84
4aa45c31 85.section "Introduction" "SEC00"
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86Most Unix mail transfer agents (programs that deliver mail) permit individual
87users to specify automatic forwarding of their mail, usually by placing a list
88of forwarding addresses in a file called &_.forward_& in their home
89directories. Exim extends this facility by allowing the forwarding instructions
90to be a set of rules rather than just a list of addresses, in effect providing
91&"&_.forward_& with conditions"&. Operating the set of rules is called
92&'filtering'&, and the file that contains them is called a &'filter file'&.
93
94Exim supports two different kinds of filter file. An &'Exim filter'& contains
95instructions in a format that is unique to Exim. A &'Sieve filter'& contains
96instructions in the Sieve format that is defined by RFC 3028. As this is a
97standard format, Sieve filter files may already be familiar to some users.
98Sieve files should also be portable between different environments. However,
99the Exim filtering facility contains more features (such as variable
100expansion), and better integration with the host environment (such as the use
101of external processes and pipes).
102
103The choice of which kind of filter to use can be left to the end-user, provided
104that the system administrator has configured Exim appropriately for both kinds
105of filter. However, if interoperability is important, Sieve is the only
106choice.
107
108The ability to use filtering or traditional forwarding has to be enabled by the
109system administrator, and some of the individual facilities can be separately
110enabled or disabled. A local document should be provided to describe exactly
111what has been enabled. In the absence of this, consult your system
112administrator.
113
114This document describes how to use a filter file and the format of its
115contents. It is intended for use by end-users. Both Sieve filters and Exim
116filters are covered. However, for Sieve filters, only issues that relate to the
117Exim implementation are discussed, since Sieve itself is described elsewhere.
118
119The contents of traditional &_.forward_& files are not described here. They
120normally contain just a list of addresses, file names, or pipe commands,
121separated by commas or newlines, but other types of item are also available.
122The full details can be found in the chapter on the &(redirect)& router in the
123Exim specification, which also describes how the system administrator can set
124up and control the use of filtering.
125
126
127
4aa45c31 128.section "Filter operation" "SEC01"
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129It is important to realize that, in Exim, no deliveries are actually made while
130a filter or traditional &_.forward_& file is being processed. Running a filter
131or processing a traditional &_.forward_& file sets up future delivery
132operations, but does not carry them out.
133
134The result of filter or &_.forward_& file processing is a list of destinations
135to which a message should be delivered. The deliveries themselves take place
136later, along with all other deliveries for the message. This means that it is
137not possible to test for successful deliveries while filtering. It also means
138that any duplicate addresses that are generated are dropped, because Exim never
139delivers the same message to the same address more than once.
140
141
142
143
144.section "Testing a new filter file" "SECTtesting"
145Filter files, especially the more complicated ones, should always be tested, as
146it is easy to make mistakes. Exim provides a facility for preliminary testing
147of a filter file before installing it. This tests the syntax of the file and
148its basic operation, and can also be used with traditional &_.forward_& files.
149
150Because a filter can do tests on the content of messages, a test message is
151required. Suppose you have a new filter file called &_myfilter_& and a test
152message in a file called &_test-message_&. Assuming that Exim is installed with
153the conventional path name &_/usr/sbin/sendmail_& (some operating systems use
154&_/usr/lib/sendmail_&), the following command can be used:
155.code
156/usr/sbin/sendmail -bf myfilter <test-message
157.endd
158The &%-bf%& option tells Exim that the following item on the command line is
159the name of a filter file that is to be tested. There is also a &%-bF%& option,
160which is similar, but which is used for testing system filter files, as opposed
161to user filter files, and which is therefore of use only to the system
162administrator.
163
164The test message is supplied on the standard input. If there are no
165message-dependent tests in the filter, an empty file (&_/dev/null_&) can be
166used. A supplied message must start with header lines or the &"From&~"& message
167separator line that is found in many multi-message folder files. Note that
168blank lines at the start terminate the header lines. A warning is given if no
169header lines are read.
170
171The result of running this command, provided no errors are detected in the
172filter file, is a list of the actions that Exim would try to take if presented
173with the message for real. For example, for an Exim filter, the output
174.code
175Deliver message to: gulliver@lilliput.fict.example
176Save message to: /home/lemuel/mail/archive
177.endd
178means that one copy of the message would be sent to
179&'gulliver@lilliput.fict.example'&, and another would be added to the file
180&_/home/lemuel/mail/archive_&, if all went well.
181
182The actions themselves are not attempted while testing a filter file in this
183way; there is no check, for example, that any forwarding addresses are valid.
184For an Exim filter, if you want to know why a particular action is being taken,
185add the &%-v%& option to the command. This causes Exim to output the results of
186any conditional tests and to indent its output according to the depth of
187nesting of &(if)& commands. Further additional output from a filter test can be
188generated by the &(testprint)& command, which is described below.
189
190When Exim is outputting a list of the actions it would take, if any text
191strings are included in the output, non-printing characters therein are
192converted to escape sequences. In particular, if any text string contains a
193newline character, this is shown as &"\n"& in the testing output.
194
195When testing a filter in this way, Exim makes up an &"envelope"& for the
196message. The recipient is by default the user running the command, and so is
197the sender, but the command can be run with the &%-f%& option to supply a
198different sender. For example,
199.code
200/usr/sbin/sendmail -bf myfilter \
201 -f islington@never.where <test-message
202.endd
203Alternatively, if the &%-f%& option is not used, but the first line of the
204supplied message is a &"From&~"& separator from a message folder file (not the
205same thing as a &'From:'& header line), the sender is taken from there. If
206&%-f%& is present, the contents of any &"From&~"& line are ignored.
207
208The &"return path"& is the same as the envelope sender, unless the message
209contains a &'Return-path:'& header, in which case it is taken from there. You
210need not worry about any of this unless you want to test out features of a
211filter file that rely on the sender address or the return path.
212
213It is possible to change the envelope recipient by specifying further options.
214The &%-bfd%& option changes the domain of the recipient address, while the
215&%-bfl%& option changes the &"local part"&, that is, the part before the @
216sign. An adviser could make use of these to test someone else's filter file.
217
218The &%-bfp%& and &%-bfs%& options specify the prefix or suffix for the local
219part. These are relevant only when support for multiple personal mailboxes is
220implemented; see the description in section &<<SECTmbox>>& below.
221
222
4aa45c31 223.section "Installing a filter file" "SEC02"
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224A filter file is normally installed under the name &_.forward_& in your home
225directory &-- it is distinguished from a conventional &_.forward_& file by its
226first line (described below). However, the file name is configurable, and some
227system administrators may choose to use some different name or location for
228filter files.
229
230
4aa45c31 231.section "Testing an installed filter file" "SEC03"
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232Testing a filter file before installation cannot find every potential problem;
233for example, it does not actually run commands to which messages are piped.
234Some &"live"& tests should therefore also be done once a filter is installed.
235
236If at all possible, test your filter file by sending messages from some other
237account. If you send a message to yourself from the filtered account, and
238delivery fails, the error message will be sent back to the same account, which
239may cause another delivery failure. It won't cause an infinite sequence of such
240messages, because delivery failure messages do not themselves generate further
241messages. However, it does mean that the failure won't be returned to you, and
242also that the postmaster will have to investigate the stuck message.
243
244If you have to test an Exim filter from the same account, a sensible precaution
245is to include the line
246.code
247if error_message then finish endif
248.endd
249as the first filter command, at least while testing. This causes filtering to
250be abandoned for a delivery failure message, and since no destinations are
251generated, the message goes on to be delivered to the original address. Unless
252there is a good reason for not doing so, it is recommended that the above test
253be left in all Exim filter files. (This does not apply to Sieve files.)
254
255
256
4aa45c31 257.section "Details of filtering commands" "SEC04"
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258The filtering commands for Sieve and Exim filters are completely different in
259syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
260chapter we describe how it is integrated into Exim. The subsequent chapter
261covers Exim filtering commands in detail.
262
263
264
265.chapter "Sieve filter files" "CHAPsievefilter"
266The code for Sieve filtering in Exim was contributed by Michael Haardt, and
267most of the content of this chapter is taken from the notes he provided. Since
268Sieve is an extensible language, it is important to understand &"Sieve"& in
269this context as &"the specific implementation of Sieve for Exim"&.
270
271This chapter does not contain a description of Sieve, since that can be found
272in RFC 3028, which should be read in conjunction with these notes.
273
274The Exim Sieve implementation offers the core as defined by RFC 3028,
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275comparison tests, the subaddress parameter, the &*copy*&, &*envelope*&,
276&*fileinto*&, &*notify*&, and &*vacation*& extensions, but not the &*reject*&
277extension. Exim does not support message delivery notifications (MDNs), so
278adding it just to the Sieve filter (as required for &*reject*&) makes little
279sense.
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280
281In order for Sieve to work properly in Exim, the system administrator needs to
282make some adjustments to the Exim configuration. These are described in the
283chapter on the &(redirect)& router in the full Exim specification.
284
285
4aa45c31 286.section "Recognition of Sieve filters" "SEC05"
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287A filter file is interpreted as a Sieve filter if its first line is
288.code
289# Sieve filter
290.endd
291This is what distinguishes it from a conventional &_.forward_& file or an Exim
292filter file.
293
294
295
4aa45c31 296.section "Saving to specified folders" "SEC06"
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297If the system administrator has set things up as suggested in the Exim
298specification, and you use &(keep)& or &(fileinto)& to save a mail into a
299folder, absolute files are stored where specified, relative files are stored
300relative to &$home$&, and &_inbox_& goes to the standard mailbox location.
301
302
303
4aa45c31 304.section "Strings containing header names" "SEC07"
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305RFC 3028 does not specify what happens if a string denoting a header field does
306not contain a valid header name, for example, it contains a colon. This
307implementation generates an error instead of ignoring the header field in order
308to ease script debugging, which fits in with the common picture of Sieve.
309
310
311
4aa45c31 312.section "Exists test with empty list of headers" "SEC08"
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313The &*exists*& test succeeds only if all the specified headers exist. RFC 3028
314does not explicitly specify what happens on an empty list of headers. This
315implementation evaluates that condition as true, interpreting the RFC in a
316strict sense.
317
318
319
4aa45c31 320.section "Header test with invalid MIME encoding in header" "SEC09"
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321Some MUAs process invalid base64 encoded data, generating junk. Others ignore
322junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
323specify how to react in this case, other than stating that a client must not
324forbid to process a message for that reason. RFC 2045 specifies that invalid
325data should be ignored (apparently looking at end of line characters). It also
326specifies that invalid data may lead to rejecting messages containing them (and
327there it appears to talk about true encoding violations), which is a clear
328contradiction to ignoring them.
329
330RFC 3028 does not specify how to process incorrect MIME words. This
331implementation treats them literally, as it does if the word is correct but its
332character set cannot be converted to UTF-8.
333
334
335
4aa45c31 336.section "Address test for multiple addresses per header" "SEC10"
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337A header may contain multiple addresses. RFC 3028 does not explicitly specify
338how to deal with them, but since the address test checks if anything matches
339anything else, matching one address suffices to satisfy the condition. That
340makes it impossible to test if a header contains a certain set of addresses and
341no more, but it is more logical than letting the test fail if the header
342contains an additional address besides the one the test checks for.
343
344
345
4aa45c31 346.section "Semantics of keep" "SEC11"
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347The &(keep)& command is equivalent to
348.code
349fileinto "inbox";
350.endd
351It saves the message and resets the implicit keep flag. It does not set the
352implicit keep flag; there is no command to set it once it has been reset.
353
354
355
4aa45c31 356.section "Semantics of fileinto" "SEC12"
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357RFC 3028 does not specify whether &(fileinto)& should try to create a mail
358folder if it does not exist. This implementation allows the sysadmin to
359configure that aspect using the &(appendfile)& transport options
360&%create_directory%&, &%create_file%&, and &%file_must_exist%&. See the
361&(appendfile)& transport in the Exim specification for details.
362
363
364
4aa45c31 365.section "Semantics of redirect" "SEC13"
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366Sieve scripts are supposed to be interoperable between servers, so this
367implementation does not allow mail to be redirected to unqualified addresses,
368because the domain would depend on the system being used. On systems with
369virtual mail domains, the default domain is probably not what the user expects
370it to be.
371
372
373
4aa45c31 374.section "String arguments" "SEC14"
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375There has been confusion if the string arguments to &(require)& are to be
376matched case-sensitively or not. This implementation matches them with the
377match type &(:is)& (default, see section 2.7.1 of the RFC) and the comparator
378&(i;ascii-casemap)& (default, see section 2.7.3 of the RFC). The RFC defines
379the command defaults clearly, so any different implementations violate RFC
3803028. The same is valid for comparator names, also specified as strings.
381
382
383
4aa45c31 384.section "Number units" "SEC15"
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385There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
386The mistake is obvious, because RFC 3028 specifies G to denote 2^30
387(which is gibi, not tebi), and that is what this implementation uses as
388the scaling factor for the suffix G.
389
390
391
4aa45c31 392.section "RFC compliance" "SEC16"
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393Exim requires the first line of a Sieve filter to be
394.code
395# Sieve filter
396.endd
397Of course the RFC does not specify that line. Do not expect examples to work
398without adding it, though.
399
400RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
401CRLF is universally used in network protocols to mark the end of the line. This
402implementation does not embed Sieve in a network protocol, but uses Sieve
403scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
404character, this implementation does, too, by default, though the system
405administrator may choose (at Exim compile time) to use CRLF instead.
406
407Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
408implementation repeats this violation to stay consistent with Exim. This is in
409preparation for UTF-8 data.
410
411Sieve scripts cannot contain NUL characters in strings, but mail headers could
412contain MIME encoded NUL characters, which could never be matched by Sieve
413scripts using exact comparisons. For that reason, this implementation extends
414the Sieve quoted string syntax with \0 to describe a NUL character, violating
415\0 being the same as 0 in RFC 3028. Even without using \0, the following tests
416are all true in this implementation. Implementations that use C-style strings
417will only evaluate the first test as true.
418.code
419Subject: =?iso-8859-1?q?abc=00def
420
421header :contains "Subject" ["abc"]
422header :contains "Subject" ["def"]
423header :matches "Subject" ["abc?def"]
424.endd
425Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
426way that NUL characters truncating strings is allowed for Sieve
427implementations, although not recommended. It is further allowed to use encoded
428NUL characters in headers, but that's not recommended either. The above example
429shows why.
430
431RFC 3028 states that if an implementation fails to convert a character set to
432UTF-8, two strings cannot be equal if one contains octets greater than 127.
433Assuming that all unknown character sets are one-byte character sets with the
434lower 128 octets being US-ASCII is not sound, so this implementation violates
435RFC 3028 and treats such MIME words literally. That way at least something
436could be matched.
437
438The folder specified by &(fileinto)& must not contain the character sequence
439&".."& to avoid security problems. RFC 3028 does not specify the syntax of
440folders apart from &(keep)& being equivalent to
441.code
442fileinto "INBOX";
443.endd
444This implementation uses &_inbox_& instead.
445
446Sieve script errors currently cause messages to be silently filed into
447&_inbox_&. RFC 3028 requires that the user is notified of that condition.
448This may be implemented in the future by adding a header line to mails that
449are filed into &_inbox_& due to an error in the filter.
450
451
452
453.chapter "Exim filter files" "CHAPeximfilter"
454This chapter contains a full description of the contents of Exim filter files.
455
456
4aa45c31 457.section "Format of Exim filter files" "SEC17"
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458Apart from leading white space, the first text in an Exim filter file must be
459.code
460# Exim filter
461.endd
462This is what distinguishes it from a conventional &_.forward_& file or a Sieve
463filter file. If the file does not have this initial line (or the equivalent for
464a Sieve filter), it is treated as a conventional &_.forward_& file, both when
465delivering mail and when using the &%-bf%& testing mechanism. The white space
466in the line is optional, and any capitalization may be used. Further text on
467the same line is treated as a comment. For example, you could have
468.code
469# Exim filter <<== do not edit or remove this line!
470.endd
471The remainder of the file is a sequence of filtering commands, which consist of
472keywords and data values. For example, in the command
473.code
474deliver gulliver@lilliput.fict.example
475.endd
476the keyword is &`deliver`& and the data value is
477&`gulliver@lilliput.fict.example`&. White space or line breaks separate the
478components of a command, except in the case of conditions for the &(if)&
479command, where round brackets (parentheses) also act as separators. Complete
480commands are separated from each other by white space or line breaks; there are
481no special terminators. Thus, several commands may appear on one line, or one
482command may be spread over a number of lines.
483
484If the character # follows a separator anywhere in a command, everything from
485# up to the next newline is ignored. This provides a way of including comments
486in a filter file.
487
488
4aa45c31 489.section "Data values in filter commands" "SEC18"
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490There are two ways in which a data value can be input:
491
492.ilist
493If the text contains no white space, it can be typed verbatim. However, if it
494is part of a condition, it must also be free of round brackets (parentheses),
495as these are used for grouping in conditions.
496.next
497Otherwise, text must be enclosed in double quotation marks. In this case, the
498character \ (backslash) is treated as an &"escape character"& within the
499string, causing the following character or characters to be treated specially:
500.display
501&`\n`& is replaced by a newline
502&`\r`& is replaced by a carriage return
503&`\t`& is replaced by a tab
504.endd
505.endlist
506
507Backslash followed by up to three octal digits is replaced by the character
508specified by those digits, and &`\x`& followed by up to two hexadecimal digits
509is treated similarly. Backslash followed by any other character is replaced by
510the second character, so that in particular, &`\"`& becomes &`"`& and &`\\`&
511becomes &`\`&. A data item enclosed in double quotes can be continued onto the
512next line by ending the first line with a backslash. Any leading white space at
513the start of the continuation line is ignored.
514
515In addition to the escape character processing that occurs when strings are
516enclosed in quotes, most data values are also subject to &'string expansion'&
517(as described in the next section), in which case the characters &`$`& and
518&`\`& are also significant. This means that if a single backslash is actually
519required in such a string, and the string is also quoted, &`\\\\`& has to be
520entered.
521
522The maximum permitted length of a data string, before expansion, is 1024
523characters.
524
525
526.section "String expansion" "SECTfilterstringexpansion"
527Most data values are expanded before use. Expansion consists of replacing
528substrings beginning with &`$`& with other text. The full expansion facilities
529available in Exim are extensive. If you want to know everything that Exim can
530do with strings, you should consult the chapter on string expansion in the Exim
531documentation.
532
533In filter files, by far the most common use of string expansion is the
534substitution of the contents of a variable. For example, the substring
535.code
536$reply_address
537.endd
538is replaced by the address to which replies to the message should be sent. If
539such a variable name is followed by a letter or digit or underscore, it must be
540enclosed in curly brackets (braces), for example,
541.code
542${reply_address}
543.endd
544If a &`$`& character is actually required in an expanded string, it must be
545escaped with a backslash, and because backslash is also an escape character in
546quoted input strings, it must be doubled in that case. The following two
547examples illustrate two different ways of testing for a &`$`& character in a
548message:
549.code
550if $message_body contains \$ then ...
551if $message_body contains "\\$" then ...
552.endd
553You can prevent part of a string from being expanded by enclosing it between
554two occurrences of &`\N`&. For example,
555.code
556if $message_body contains \N$$$$\N then ...
557.endd
558tests for a run of four dollar characters.
559
560
4aa45c31 561.section "Some useful general variables" "SEC19"
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562A complete list of the available variables is given in the Exim documentation.
563This shortened list contains the ones that are most likely to be useful in
564personal filter files:
565
566&$body_linecount$&: The number of lines in the body of the message.
567
568&$body_zerocount$&: The number of binary zero characters in the body of the
569message.
570
571&$home$&: In conventional configurations, this variable normally contains the
572user's home directory. The system administrator can, however, change this.
573
574&$local_part$&: The part of the email address that precedes the @ sign &--
575normally the user's login name. If support for multiple personal mailboxes is
576enabled (see section &<<SECTmbox>>& below) and a prefix or suffix for the local
577part was recognized, it is removed from the string in this variable.
578
579&$local_part_prefix$&: If support for multiple personal mailboxes is enabled
580(see section &<<SECTmbox>>& below), and a local part prefix was recognized,
581this variable contains the prefix. Otherwise it contains an empty string.
582
583&$local_part_suffix$&: If support for multiple personal mailboxes is enabled
584(see section &<<SECTmbox>>& below), and a local part suffix was recognized,
585this variable contains the suffix. Otherwise it contains an empty string.
586
587&$message_body$&: The initial portion of the body of the message. By default,
588up to 500 characters are read into this variable, but the system administrator
589can configure this to some other value. Newlines in the body are converted into
590single spaces.
591
592&$message_body_end$&: The final portion of the body of the message, formatted
593and limited in the same way as &$message_body$&.
594
595&$message_body_size$&: The size of the body of the message, in bytes.
596
597&$message_exim_id$&: The message's local identification string, which is unique
598for each message handled by a single host.
599
600&$message_headers$&: The header lines of the message, concatenated into a
601single string, with newline characters between them.
602
603&$message_size$&: The size of the entire message, in bytes.
604
605&$original_local_part$&: When an address that arrived with the message is
606being processed, this contains the same value as the variable &$local_part$&.
607However, if an address generated by an alias, forward, or filter file is being
608processed, this variable contains the local part of the original address.
609
610&$reply_address$&: The contents of the &'Reply-to:'& header, if the message
611has one; otherwise the contents of the &'From:'& header. It is the address to
612which normal replies to the message should be sent.
613
614&$return_path$&: The return path &-- that is, the sender field that will be
615transmitted as part of the message's envelope if the message is sent to another
616host. This is the address to which delivery errors are sent. In many cases,
617this variable has the same value as &$sender_address$&, but if, for example,
618an incoming message to a mailing list has been expanded, &$return_path$& may
619have been changed to contain the address of the list maintainer.
620
621&$sender_address$&: The sender address that was received in the envelope of
622the message. This is not necessarily the same as the contents of the &'From:'&
623or &'Sender:'& header lines. For delivery error messages (&"bounce messages"&)
624there is no sender address, and this variable is empty.
625
626&$tod_full$&: A full version of the time and date, for example: Wed, 18 Oct
6271995 09:51:40 +0100. The timezone is always given as a numerical offset from
628GMT.
629
630&$tod_log$&: The time and date in the format used for writing Exim's log files,
631without the timezone, for example: 1995-10-12 15:32:29.
632
633&$tod_zone$&: The local timezone offset, for example: +0100.
634
635
636
637.section "Header variables" "SECTheadervariables"
638There is a special set of expansion variables containing the header lines of
639the message being processed. These variables have names beginning with
640&$header_$& followed by the name of the header line, terminated by a colon.
641For example,
642.code
643$header_from:
644$header_subject:
645.endd
646The whole item, including the terminating colon, is replaced by the contents of
647the message header line. If there is more than one header line with the same
648name, their contents are concatenated. For header lines whose data consists of
649a list of addresses (for example, &'From:'& and &'To:'&), a comma and newline
650is inserted between each set of data. For all other header lines, just a
651newline is used.
652
653Leading and trailing white space is removed from header line data, and if there
654are any MIME &"words"& that are encoded as defined by RFC 2047 (because they
655contain non-ASCII characters), they are decoded and translated, if possible, to
656a local character set. Translation is attempted only on operating systems that
657have the &[iconv()]& function. This makes the header line look the same as it
658would when displayed by an MUA. The default character set is ISO-8859-1, but
659this can be changed by means of the &(headers)& command (see below).
660
661If you want to see the actual characters that make up a header line, you can
662specify &$rheader_$& instead of &$header_$&. This inserts the &"raw"&
663header line, unmodified.
664
665There is also an intermediate form, requested by &$bheader_$&, which removes
666leading and trailing space and decodes MIME &"words"&, but does not do any
667character translation. If an attempt to decode what looks superficially like a
668MIME &"word"& fails, the raw string is returned. If decoding produces a binary
669zero character, it is replaced by a question mark.
670
671The capitalization of the name following &$header_$& is not significant.
672Because any printing character except colon may appear in the name of a
673message's header (this is a requirement of RFC 2822, the document that
674describes the format of a mail message) curly brackets must &'not'& be used in
675this case, as they will be taken as part of the header name. Two shortcuts are
676allowed in naming header variables:
677
678.ilist
679The initiating &$header_$&, &$rheader_$&, or &$bheader_$& can be
680abbreviated to &$h_$&, &$rh_$&, or &$bh_$&, respectively.
681.next
682The terminating colon can be omitted if the next character is white space. The
683white space character is retained in the expanded string. However, this is not
684recommended, because it makes it easy to forget the colon when it really is
685needed.
686.endlist
687
688If the message does not contain a header of the given name, an empty string is
689substituted. Thus it is important to spell the names of headers correctly. Do
690not use &$header_Reply_to$& when you really mean &$header_Reply-to$&.
691
692
4aa45c31 693.section "User variables" "SEC20"
9b371988
PH
694There are ten user variables with names &$n0$& &-- &$n9$& that can be
695incremented by the &(add)& command (see section &<<SECTadd>>&). These can be
696used for &"scoring"& messages in various ways. If Exim is configured to run a
697&"system filter"& on every message, the values left in these variables are
698copied into the variables &$sn0$& &-- &$sn9$& at the end of the system filter,
699thus making them available to users' filter files. How these values are used is
700entirely up to the individual installation.
701
702
4aa45c31 703.section "Current directory" "SEC21"
9b371988
PH
704The contents of your filter file should not make any assumptions about the
705current directory. It is best to use absolute paths for file names; you can
706normally make use of the &$home$& variable to refer to your home directory. The
707&(save)& command automatically inserts &$home$& at the start of non-absolute
708paths.
709
710
711
712
713.section "Significant deliveries" "SECTsigdel"
714When in the course of delivery a message is processed by a filter file, what
715happens next, that is, after the filter file has been processed, depends on
716whether or not the filter sets up any &'significant deliveries'&. If at least
717one significant delivery is set up, the filter is considered to have handled
718the entire delivery arrangements for the current address, and no further
719processing of the address takes place. If, however, no significant deliveries
720are set up, Exim continues processing the current address as if there were no
721filter file, and typically sets up a delivery of a copy of the message into a
722local mailbox. In particular, this happens in the special case of a filter file
723containing only comments.
724
725The delivery commands &(deliver)&, &(save)&, and &(pipe)& are by default
726significant. However, if such a command is preceded by the word &"unseen"&, its
727delivery is not considered to be significant. In contrast, other commands such
728as &(mail)& and &(vacation)& do not set up significant deliveries unless
729preceded by the word &"seen"&. The following example commands set up
730significant deliveries:
731.code
732deliver jack@beanstalk.example
733pipe $home/bin/mymailscript
734seen mail subject "message discarded"
735seen finish
736.endd
737The following example commands do not set up significant deliveries:
738.code
739unseen deliver jack@beanstalk.example
740unseen pipe $home/bin/mymailscript
741mail subject "message discarded"
742finish
743.endd
744
745
746
4aa45c31 747.section "Filter commands" "SEC222"
9b371988
PH
748The filter commands that are described in subsequent sections are listed
749below, with the section in which they are described in brackets:
750
751.table2
752.row &(add)& "&~&~increment a user variable (section &<<SECTadd>>&)"
753.row &(deliver)& "&~&~deliver to an email address (section &<<SECTdeliver>>&)"
754.row &(fail)& "&~&~force delivery failure (sysadmin use) (section &<<SECTfail>>&)"
755.row &(finish)& "&~&~end processing (section &<<SECTfinish>>&)"
756.row &(freeze)& "&~&~freeze message (sysadmin use) (section &<<SECTfreeze>>&)"
757.row &(headers)& "&~&~set the header character set (section &<<SECTheaders>>&)"
758.row &(if)& "&~&~test condition(s) (section &<<SECTif>>&)"
759.row &(logfile)& "&~&~define log file (section &<<SECTlog>>&)"
760.row &(logwrite)& "&~&~write to log file (section &<<SECTlog>>&)"
761.row &(mail)& "&~&~send a reply message (section &<<SECTmail>>&)"
762.row &(pipe)& "&~&~pipe to a command (section &<<SECTpipe>>&)"
763.row &(save)& "&~&~save to a file (section &<<SECTsave>>&)"
764.row &(testprint)& "&~&~print while testing (section &<<SECTtestprint>>&)"
765.row &(vacation)& "&~&~tailored form of &(mail)& (section &<<SECTmail>>&)"
766.endtable
767
768The &(headers)& command has additional parameters that can be used only in a
769system filter. The &(fail)& and &(freeze)& commands are available only when
770Exim's filtering facilities are being used as a system filter, and are
771therefore usable only by the system administrator and not by ordinary users.
772They are mentioned only briefly in this document; for more information, see the
773main Exim specification.
774
775
776
777.section "The add command" "SECTadd"
778.display
779&` add `&<&'number'&>&` to `&<&'user variable'&>
780&`e.g. add 2 to n3`&
781.endd
782
783There are 10 user variables of this type, with names &$n0$& &-- &$n9$&. Their
784values can be obtained by the normal expansion syntax (for example &$n3$&) in
785other commands. At the start of filtering, these variables all contain zero.
786Both arguments of the &(add)& command are expanded before use, making it
787possible to add variables to each other. Subtraction can be obtained by adding
788negative numbers.
789
790
791
792.section "The deliver command" "SECTdeliver"
793.display
794&` deliver`& <&'mail address'&>
795&`e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"`&
796.endd
797
798This command provides a forwarding operation. The delivery that it sets up is
799significant unless the command is preceded by &"unseen"& (see section
800&<<SECTsigdel>>&). The message is sent on to the given address, exactly as
801happens if the address had appeared in a traditional &_.forward_& file. If you
802want to deliver the message to a number of different addresses, you can use
803more than one &(deliver)& command (each one may have only one address).
804However, duplicate addresses are discarded.
805
806To deliver a copy of the message to your normal mailbox, your login name can be
807given as the address. Once an address has been processed by the filtering
808mechanism, an identical generated address will not be so processed again, so
809doing this does not cause a loop.
810
811However, if you have a mail alias, you should &'not'& refer to it here. For
812example, if the mail address &'L.Gulliver'& is aliased to &'lg303'& then all
813references in Gulliver's &_.forward_& file should be to &'lg303'&. A reference
814to the alias will not work for messages that are addressed to that alias,
815since, like &_.forward_& file processing, aliasing is performed only once on an
816address, in order to avoid looping.
817
818Following the new address, an optional second address, preceded by
819&"errors_to"& may appear. This changes the address to which delivery errors on
820the forwarded message will be sent. Instead of going to the message's original
821sender, they go to this new address. For ordinary users, the only value that is
822permitted for this address is the user whose filter file is being processed.
823For example, the user &'lg303'& whose mailbox is in the domain
824&'lilliput.example'& could have a filter file that contains
825.code
826deliver jon@elsewhere.example errors_to lg303@lilliput.example
827.endd
828Clearly, using this feature makes sense only in situations where not all
829messages are being forwarded. In particular, bounce messages must not be
830forwarded in this way, as this is likely to create a mail loop if something
831goes wrong.
832
833
834
835.section "The save command" "SECTsave"
836.display
837&` save `&<&'file name'&>
838&`e.g. save $home/mail/bookfolder`&
839.endd
840
841This command specifies that a copy of the message is to be appended to the
842given file (that is, the file is to be used as a mail folder). The delivery
843that &(save)& sets up is significant unless the command is preceded by
844&"unseen"& (see section &<<SECTsigdel>>&).
845
846More than one &(save)& command may be obeyed; each one causes a copy of the
847message to be written to its argument file, provided they are different
848(duplicate &(save)& commands are ignored).
849
850If the file name does not start with a / character, the contents of the
f89d2485
PH
851&$home$& variable are prepended, unless it is empty, or the system
852administrator has disabled this feature. In conventional configurations, this
553c0e3a
PH
853variable is normally set in a user filter to the user's home directory, but the
854system administrator may set it to some other path. In some configurations,
f89d2485 855&$home$& may be unset, or prepending may be disabled, in which case a
553c0e3a
PH
856non-absolute path name may be generated. Such configurations convert this to an
857absolute path when the delivery takes place. In a system filter, &$home$& is
858never set.
9b371988
PH
859
860The user must of course have permission to write to the file, and the writing
861of the file takes place in a process that is running as the user, under the
862user's primary group. Any secondary groups to which the user may belong are not
863normally taken into account, though the system administrator can configure Exim
864to set them up. In addition, the ability to use this command at all is
865controlled by the system administrator &-- it may be forbidden on some systems.
866
867An optional mode value may be given after the file name. The value for the mode
868is interpreted as an octal number, even if it does not begin with a zero. For
869example:
870.code
871save /some/folder 640
872.endd
873This makes it possible for users to override the system-wide mode setting for
874file deliveries, which is normally 600. If an existing file does not have the
875correct mode, it is changed.
876
877An alternative form of delivery may be enabled on your system, in which each
878message is delivered into a new file in a given directory. If this is the case,
879this functionality can be requested by giving the directory name terminated by
880a slash after the &(save)& command, for example
881.code
882save separated/messages/
883.endd
884There are several different formats for such deliveries; check with your system
885administrator or local documentation to find out which (if any) are available
886on your system. If this functionality is not enabled, the use of a path name
887ending in a slash causes an error.
888
889
890
891.section "The pipe command" "SECTpipe"
892.display
893&` pipe `&<&'command'&>
894&`e.g. pipe "$home/bin/countmail $sender_address"`&
895.endd
896
897This command specifies that the message is to be delivered to the specified
898command using a pipe. The delivery that it sets up is significant unless the
899command is preceded by &"unseen"& (see section &<<SECTsigdel>>&). Remember,
900however, that no deliveries are done while the filter is being processed. All
901deliveries happen later on. Therefore, the result of running the pipe is not
902available to the filter.
903
904When the deliveries are done, a separate process is run, and a copy of the
905message is passed on its standard input. The process runs as the user, under
906the user's primary group. Any secondary groups to which the user may belong are
907not normally taken into account, though the system administrator can configure
908Exim to set them up. More than one &(pipe)& command may appear; each one causes
909a copy of the message to be written to its argument pipe, provided they are
910different (duplicate &(pipe)& commands are ignored).
911
912When the time comes to transport the message, the command supplied to &(pipe)&
913is split up by Exim into a command name and a number of arguments. These are
914delimited by white space except for arguments enclosed in double quotes, in
915which case backslash is interpreted as an escape, or in single quotes, in which
916case no escaping is recognized. Note that as the whole command is normally
917supplied in double quotes, a second level of quoting is required for internal
918double quotes. For example:
919.code
920pipe "$home/myscript \"size is $message_size\""
921.endd
922String expansion is performed on the separate components after the line has
923been split up, and the command is then run directly by Exim; it is not run
924under a shell. Therefore, substitution cannot change the number of arguments,
925nor can quotes, backslashes or other shell metacharacters in variables cause
926confusion.
927
928Documentation for some programs that are normally run via this kind of pipe
929often suggest that the command should start with
930.code
931IFS=" "
932.endd
933This is a shell command, and should &'not'& be present in Exim filter files,
934since it does not normally run the command under a shell.
935
936However, there is an option that the administrator can set to cause a shell to
937be used. In this case, the entire command is expanded as a single string and
938passed to the shell for interpretation. It is recommended that this be avoided
939if at all possible, since it can lead to problems when inserted variables
940contain shell metacharacters.
941
942The default PATH set up for the command is determined by the system
943administrator, usually containing at least &_/bin_& and &_/usr/bin_& so that
944common commands are available without having to specify an absolute file name.
945However, it is possible for the system administrator to restrict the pipe
946facility so that the command name must not contain any / characters, and must
947be found in one of the directories in the configured PATH. It is also possible
948for the system administrator to lock out the use of the &(pipe)& command
949altogether.
950
951When the command is run, a number of environment variables are set up. The
952complete list for pipe deliveries may be found in the Exim reference manual.
953Those that may be useful for pipe deliveries from user filter files are:
954
955.display
956&`DOMAIN `& the domain of the address
957&`HOME `& your home directory
958&`LOCAL_PART `& see below
959&`LOCAL_PART_PREFIX `& see below
960&`LOCAL_PART_SUFFIX `& see below
961&`LOGNAME `& your login name
962&`MESSAGE_ID `& the unique id of the message
963&`PATH `& the command search path
964&`RECIPIENT `& the complete recipient address
965&`SENDER `& the sender of the message
966&`SHELL `& &`/bin/sh`&
967&`USER `& see below
968.endd
969
970LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
971id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
972recognize prefixes or suffixes in the local parts of addresses. For example, a
973message addressed to &'pat-suf2@domain.example'& may cause the filter for user
974&'pat'& to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
975&`-suf2`& when the pipe command runs. The system administrator has to configure
976Exim specially for this feature to be available.
977
978If you run a command that is a shell script, be very careful in your use of
979data from the incoming message in the commands in your script. RFC 2822 is very
980generous in the characters that are permitted to appear in mail addresses, and
981in particular, an address may begin with a vertical bar or a slash. For this
982reason you should always use quotes round any arguments that involve data from
983the message, like this:
984.code
985/some/command '$SENDER'
986.endd
987so that inserted shell meta-characters do not cause unwanted effects.
988
989Remember that, as was explained earlier, the pipe command is not run at the
990time the filter file is interpreted. The filter just defines what deliveries
991are required for one particular addressee of a message. The deliveries
992themselves happen later, once Exim has decided everything that needs to be done
993for the message.
994
995A consequence of this is that you cannot inspect the return code from the pipe
996command from within the filter. Nevertheless, the code returned by the command
997is important, because Exim uses it to decide whether the delivery has succeeded
998or failed.
999
1000The command should return a zero completion code if all has gone well. Most
1001non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1002treated as a delivery failure, causing the message to be returned to its
1003sender. However, there are some completion codes that are treated as temporary
1004errors. The message remains on Exim's spool disk, and the delivery is tried
1005again later, though it will ultimately time out if the delivery failures go on
1006too long. The completion codes to which this applies can be specified by the
1007system administrator; the default values are 73 and 75.
1008
1009The pipe command should not normally write anything to its standard output or
1010standard error file descriptors. If it does, whatever is written is normally
1011returned to the sender of the message as a delivery error, though this action
1012can be varied by the system administrator.
1013
1014
1015
1016.section "Mail commands" "SECTmail"
1017There are two commands that cause the creation of a new mail message, neither
1018of which count as a significant delivery unless the command is preceded by the
1019word &"seen"& (see section &<<SECTsigdel>>&). This is a powerful facility, but
1020it should be used with care, because of the danger of creating infinite
1021sequences of messages. The system administrator can forbid the use of these
1022commands altogether.
1023
1024To help prevent runaway message sequences, these commands have no effect when
1025the incoming message is a bounce (delivery error) message, and messages sent by
1026this means are treated as if they were reporting delivery errors. Thus, they
1027should never themselves cause a bounce message to be returned. The basic
1028mail-sending command is
1029.display
1030&`mail [to `&<&'address-list'&>&`]`&
1031&` [cc `&<&'address-list'&>&`]`&
1032&` [bcc `&<&'address-list'&>&`]`&
1033&` [from `&<&'address'&>&`]`&
1034&` [reply_to `&<&'address'&>&`]`&
1035&` [subject `&<&'text'&>&`]`&
1036&` [extra_headers `&<&'text'&>&`]`&
1037&` [text `&<&'text'&>&`]`&
1038&` [[expand] file `&<&'filename'&>&`]`&
1039&` [return message]`&
1040&` [log `&<&'log file name'&>&`]`&
1041&` [once `&<&'note file name'&>&`]`&
1042&` [once_repeat `&<&'time interval'&>&`]`&
9b371988
PH
1043&`e.g. mail text "Your message about $h_subject: has been received"`&
1044.endd
1045Each <&'address-list'&> can contain a number of addresses, separated by commas,
1046in the format of a &'To:'& or &'Cc:'& header line. In fact, the text you supply
1047here is copied exactly into the appropriate header line. It may contain
1048additional information as well as email addresses. For example:
1049.code
1050mail to "Julius Caesar <jc@rome.example>, \
1051 <ma@rome.example> (Mark A.)"
1052.endd
1053Similarly, the texts supplied for &%from%& and &%reply_to%& are copied into
1054their respective header lines.
1055
1056As a convenience for use in one common case, there is also a command called
1057&(vacation)&. It behaves in the same way as &(mail)&, except that the defaults
1058for the &%subject%&, &%file%&, &%log%&, &%once%&, and &%once_repeat%& options
1059are
1060.code
1061subject "On vacation"
1062expand file .vacation.msg
1063log .vacation.log
1064once .vacation
1065once_repeat 7d
1066.endd
1067respectively. These are the same file names and repeat period used by the
1068traditional Unix &(vacation)& command. The defaults can be overridden by
1069explicit settings, but if a file name is given its contents are expanded only
1070if explicitly requested.
1071
1072&*Warning*&: The &(vacation)& command should always be used conditionally,
1073subject to at least the &(personal)& condition (see section &<<SECTpersonal>>&
1074below) so as not to send automatic replies to non-personal messages from
1075mailing lists or elsewhere. Sending an automatic response to a mailing list or
1076a mailing list manager is an Internet Sin.
1077
1078For both commands, the key/value argument pairs can appear in any order. At
1079least one of &%text%& or &%file%& must appear (except with &(vacation)&, where
1080there is a default for &%file%&); if both are present, the text string appears
1081first in the message. If &%expand%& precedes &%file%&, each line of the file is
1082subject to string expansion before it is included in the message.
1083
1084Several lines of text can be supplied to &%text%& by including the escape
1085sequence &"\n"& in the string wherever a newline is required. If the command is
1086output during filter file testing, newlines in the text are shown as &"\n"&.
1087
1088Note that the keyword for creating a &'Reply-To:'& header is &%reply_to%&,
1089because Exim keywords may contain underscores, but not hyphens. If the &%from%&
1090keyword is present and the given address does not match the user who owns the
1091forward file, Exim normally adds a &'Sender:'& header to the message, though it
1092can be configured not to do this.
1093
1094The &%extra_headers%& keyword allows you to add custom header lines to the
1095message. The text supplied must be one or more syntactically valid RFC 2822
1096header lines. You can use &"\n"& within quoted text to specify newlines between
1097headers, and also to define continued header lines. For example:
1098.code
1099extra_headers "h1: first\nh2: second\n continued\nh3: third"
1100.endd
1101No newline should appear at the end of the final header line.
1102
1103If no &%to%& argument appears, the message is sent to the address in the
1104&$reply_address$& variable (see section &<<SECTfilterstringexpansion>>& above).
1105An &'In-Reply-To:'& header is automatically included in the created message,
1106giving a reference to the message identification of the incoming message.
1107
1108If &%return message%& is specified, the incoming message that caused the filter
1109file to be run is added to the end of the message, subject to a maximum size
1110limitation.
1111
1112If a log file is specified, a line is added to it for each message sent.
1113
1114If a &%once%& file is specified, it is used to hold a database for remembering
1115who has received a message, and no more than one message is ever sent to any
1116particular address, unless &%once_repeat%& is set. This specifies a time
1117interval after which another copy of the message is sent. The interval is
1118specified as a sequence of numbers, each followed by the initial letter of one
1119of &"seconds"&, &"minutes"&, &"hours"&, &"days"&, or &"weeks"&. For example,
1120.code
1121once_repeat 5d4h
1122.endd
1123causes a new message to be sent if at least 5 days and 4 hours have elapsed
1124since the last one was sent. There must be no white space in a time interval.
1125
1126Commonly, the file name specified for &%once%& is used as the base name for
1127direct-access (DBM) file operations. There are a number of different DBM
1128libraries in existence. Some operating systems provide one as a default, but
1129even in this case a different one may have been used when building Exim. With
1130some DBM libraries, specifying &%once%& results in two files being created,
1131with the suffixes &_.dir_& and &_.pag_& being added to the given name. With
1132some others a single file with the suffix &_.db_& is used, or the name is used
1133unchanged.
1134
1135Using a DBM file for implementing the &%once%& feature means that the file
1136grows as large as necessary. This is not usually a problem, but some system
1137administrators want to put a limit on it. The facility can be configured not to
1138use a DBM file, but instead, to use a regular file with a maximum size. The
1139data in such a file is searched sequentially, and if the file fills up, the
1140oldest entry is deleted to make way for a new one. This means that some
1141correspondents may receive a second copy of the message after an unpredictable
1142interval. Consult your local information to see if your system is configured
1143this way.
1144
1145More than one &(mail)& or &(vacation)& command may be obeyed in a single filter
1146run; they are all honoured, even when they are to the same recipient.
1147
1148
1149
1150.section "Logging commands" "SECTlog"
1151A log can be kept of actions taken by a filter file. This facility is normally
1152available in conventional configurations, but there are some situations where
1153it might not be. Also, the system administrator may choose to disable it. Check
1154your local information if in doubt.
1155
1156Logging takes place while the filter file is being interpreted. It does not
1157queue up for later like the delivery commands. The reason for this is so that a
1158log file need be opened only once for several write operations. There are two
1159commands, neither of which constitutes a significant delivery. The first
1160defines a file to which logging output is subsequently written:
1161.display
1162&` logfile `&<&'file name'&>
1163&`e.g. logfile $home/filter.log`&
1164.endd
1165The file name must be fully qualified. You can use &$home$&, as in this
1166example, to refer to your home directory. The file name may optionally be
1167followed by a mode for the file, which is used if the file has to be created.
1168For example,
1169.code
1170logfile $home/filter.log 0644
1171.endd
1172The number is interpreted as octal, even if it does not begin with a zero.
1173The default for the mode is 600. It is suggested that the &(logfile)& command
1174normally appear as the first command in a filter file. Once a log file has
1175been obeyed, the &(logwrite)& command can be used to write to it:
1176.display
1177&` logwrite "`&<&'some text string'&>&`"`&
1178&`e.g. logwrite "$tod_log $message_id processed"`&
1179.endd
1180It is possible to have more than one &(logfile)& command, to specify writing to
1181different log files in different circumstances. Writing takes place at the end
1182of the file, and a newline character is added to the end of each string if
1183there isn't one already there. Newlines can be put in the middle of the string
1184by using the &"\n"& escape sequence. Lines from simultaneous deliveries may get
1185interleaved in the file, as there is no interlocking, so you should plan your
1186logging with this in mind. However, data should not get lost.
1187
1188
1189
1190.section "The finish command" "SECTfinish"
1191The command &(finish)&, which has no arguments, causes Exim to stop
1192interpreting the filter file. This is not a significant action unless preceded
1193by &"seen"&. A filter file containing only &"seen finish"& is a black hole.
1194
1195
1196.section "The testprint command" "SECTtestprint"
1197It is sometimes helpful to be able to print out the values of variables when
1198testing filter files. The command
1199.display
1200&` testprint `&<&'text'&>
1201&`e.g. testprint "home=$home reply_address=$reply_address"`&
1202.endd
1203does nothing when mail is being delivered. However, when the filtering code is
1204being tested by means of the &%-bf%& option (see section &<<SECTtesting>>&
1205above), the value of the string is written to the standard output.
1206
1207
1208.section "The fail command" "SECTfail"
1209When Exim's filtering facilities are being used as a system filter, the
1210&(fail)& command is available, to force delivery failure. Because this command
1211is normally usable only by the system administrator, and not enabled for use by
1212ordinary users, it is described in more detail in the main Exim specification
1213rather than in this document.
1214
1215
1216.section "The freeze command" "SECTfreeze"
1217When Exim's filtering facilities are being used as a system filter, the
1218&(freeze)& command is available, to freeze a message on the queue. Because this
1219command is normally usable only by the system administrator, and not enabled
1220for use by ordinary users, it is described in more detail in the main Exim
1221specification rather than in this document.
1222
1223
1224
1225.section "The headers command" "SECTheaders"
1226The &(headers)& command can be used to change the target character set that is
1227used when translating the contents of encoded header lines for insertion by the
1228&$header_$& mechanism (see section &<<SECTheadervariables>>& above). The
1229default can be set in the Exim configuration; if not specified, ISO-8859-1 is
1230used. The only currently supported format for the &(headers)& command in user
1231filters is as in this example:
1232.code
1233headers charset "UTF-8"
1234.endd
1235That is, &(headers)& is followed by the word &"charset"& and then the name of a
1236character set. This particular example would be useful if you wanted to compare
1237the contents of a header to a UTF-8 string.
1238
1239In system filter files, the &(headers)& command can be used to add or remove
1240header lines from the message. These features are described in the main Exim
1241specification.
1242
1243
1244
1245.section "Obeying commands conditionally" "SECTif"
1246Most of the power of filtering comes from the ability to test conditions and
1247obey different commands depending on the outcome. The &(if)& command is used to
1248specify conditional execution, and its general form is
1249.display
1250&`if `&<&'condition'&>
1251&`then `&<&'commands'&>
1252&`elif `&<&'condition'&>
1253&`then `&<&'commands'&>
1254&`else `&<&'commands'&>
1255&`endif`&
1256.endd
1257There may be any number of &(elif)& and &(then)& sections (including none) and
1258the &(else)& section is also optional. Any number of commands, including nested
1259&(if)& commands, may appear in any of the <&'commands'&> sections.
1260
1261Conditions can be combined by using the words &(and)& and &(or)&, and round
1262brackets (parentheses) can be used to specify how several conditions are to
1263combine. Without brackets, &(and)& is more binding than &(or)&. For example:
1264.code
1265if
1266$h_subject: contains "Make money" or
1267$h_precedence: is "junk" or
1268($h_sender: matches ^\\d{8}@ and not personal) or
1269$message_body contains "this is not spam"
1270then
1271seen finish
1272endif
1273.endd
1274A condition can be preceded by &(not)& to negate it, and there are also some
1275negative forms of condition that are more English-like.
1276
1277
1278
4aa45c31 1279.section "String testing conditions" "SEC23"
9b371988
PH
1280There are a number of conditions that operate on text strings, using the words
1281&"begins"&, &"ends"&, &"is"&, &"contains"& and &"matches"&. If you want to
1282apply the same test to more than one header line, you can easily concatenate
1283them into a single string for testing, as in this example:
1284.code
1285if "$h_to:, $h_cc:" contains me@domain.example then ...
1286.endd
1287If a string-testing condition name is written in lower case, the testing
1288of letters is done without regard to case; if it is written in upper case
1289(for example, &"CONTAINS"&), the case of letters is taken into account.
1290
1291.display
1292&` `&<&'text1'&>&` begins `&<&'text2'&>
1293&` `&<&'text1'&>&` does not begin `&<&'text2'&>
1294&`e.g. $header_from: begins "Friend@"`&
1295.endd
1296
1297A &"begins"& test checks for the presence of the second string at the start of
1298the first, both strings having been expanded.
1299
1300.display
1301&` `&<&'text1'&>&` ends `&<&'text2'&>
1302&` `&<&'text1'&>&` does not end `&<&'text2'&>
1303&`e.g. $header_from: ends "public.com.example"`&
1304.endd
1305
1306An &"ends"& test checks for the presence of the second string at the end of
1307the first, both strings having been expanded.
1308
1309.display
1310&` `&<&'text1'&>&` is `&<&'text2'&>
1311&` `&<&'text1'&>&` is not `&<&'text2'&>
1312&`e.g. $local_part_suffix is "-foo"`&
1313.endd
1314
1315An &"is"& test does an exact match between the strings, having first expanded
1316both strings.
1317
1318.display
1319&` `&<&'text1'&>&` contains `&<&'text2'&>
1320&` `&<&'text1'&>&` does not contain `&<&'text2'&>
1321&`e.g. $header_subject: contains "evolution"`&
1322.endd
1323
1324A &"contains"& test does a partial string match, having expanded both strings.
1325
1326.display
1327&` `&<&'text1'&>&` matches `&<&'text2'&>
1328&` `&<&'text1'&>&` does not match `&<&'text2'&>
1329&`e.g. $sender_address matches "(bill|john)@"`&
1330.endd
1331
1332For a &"matches"& test, after expansion of both strings, the second one is
1333interpreted as a regular expression. Exim uses the PCRE regular expression
1334library, which provides regular expressions that are compatible with Perl.
1335
1336The match succeeds if the regular expression matches any part of the first
1337string. If you want a regular expression to match only at the start or end of
1338the subject string, you must encode that requirement explicitly, using the
1339&`^`& or &`$`& metacharacters. The above example, which is not so constrained,
1340matches all these addresses:
1341.code
1342bill@test.example
1343john@some.example
1344spoonbill@example.com
1345littlejohn@example.com
1346.endd
1347To match only the first two, you could use this:
1348.code
1349if $sender_address matches "^(bill|john)@" then ...
1350.endd
1351Care must be taken if you need a backslash in a regular expression, because
1352backslashes are interpreted as escape characters both by the string expansion
1353code and by Exim's normal processing of strings in quotes. For example, if you
1354want to test the sender address for a domain ending in &'.com'& the regular
1355expression is
1356.code
1357\.com$
1358.endd
1359The backslash and dollar sign in that expression have to be escaped when used
1360in a filter command, as otherwise they would be interpreted by the expansion
1361code. Thus, what you actually write is
1362.code
1363if $sender_address matches \\.com\$
1364.endd
1365An alternative way of handling this is to make use of the &`\N`& expansion
1366flag for suppressing expansion:
1367.code
1368if $sender_address matches \N\.com$\N
1369.endd
1370Everything between the two occurrences of &`\N`& is copied without change by
1371the string expander (and in fact you do not need the final one, because it is
1372at the end of the string). If the regular expression is given in quotes
1373(mandatory only if it contains white space) you have to write either
1374.code
1375if $sender_address matches "\\\\.com\\$"
1376.endd
1377or
1378.code
1379if $sender_address matches "\\N\\.com$\\N"
1380.endd
1381
1382If the regular expression contains bracketed sub-expressions, numeric
1383variable substitutions such as &$1$& can be used in the subsequent actions
1384after a successful match. If the match fails, the values of the numeric
1385variables remain unchanged. Previous values are not restored after &(endif)&.
1386In other words, only one set of values is ever available. If the condition
1387contains several sub-conditions connected by &(and)& or &(or)&, it is the
1388strings extracted from the last successful match that are available in
1389subsequent actions. Numeric variables from any one sub-condition are also
1390available for use in subsequent sub-conditions, because string expansion of a
1391condition occurs just before it is tested.
1392
1393
4aa45c31 1394.section "Numeric testing conditions" "SEC24"
9b371988
PH
1395The following conditions are available for performing numerical tests:
1396
1397.display
1398&` `&<&'number1'&>&` is above `&<&'number2'&>
1399&` `&<&'number1'&>&` is not above `&<&'number2'&>
1400&` `&<&'number1'&>&` is below `&<&'number2'&>
1401&` `&<&'number1'&>&` is not below `&<&'number2'&>
1402&`e.g. $message_size is not above 10k`&
1403.endd
1404
1405The <&'number'&> arguments must expand to strings of digits, optionally
1406followed by one of the letters K or M (upper case or lower case) which cause
1407multiplication by 1024 and 1024x1024 respectively.
1408
1409
4aa45c31 1410.section "Testing for significant deliveries" "SEC25"
9b371988
PH
1411You can use the &(delivered)& condition to test whether or not any previously
1412obeyed filter commands have set up a significant delivery. For example:
1413.code
1414if not delivered then save mail/anomalous endif
1415.endd
1416&"Delivered"& is perhaps a poor choice of name for this condition, because the
1417message has not actually been delivered; rather, a delivery has been set up for
1418later processing.
1419
1420
4aa45c31 1421.section "Testing for error messages" "SEC26"
9b371988
PH
1422The condition &(error_message)& is true if the incoming message is a bounce
1423(mail delivery error) message. Putting the command
1424.code
1425if error_message then finish endif
1426.endd
1427at the head of your filter file is a useful insurance against things going
1428wrong in such a way that you cannot receive delivery error reports. &*Note*&:
1429&(error_message)& is a condition, not an expansion variable, and therefore is
1430not preceded by &`$`&.
1431
1432
4aa45c31 1433.section "Testing a list of addresses" "SEC27"
9b371988
PH
1434There is a facility for looping through a list of addresses and applying a
1435condition to each of them. It takes the form
1436.display
1437&`foranyaddress `&<&'string'&>&` (`&<&'condition'&>&`)`&
1438.endd
1439where <&'string'&> is interpreted as a list of RFC 2822 addresses, as in a
1440typical header line, and <&'condition'&> is any valid filter condition or
1441combination of conditions. The &"group"& syntax that is defined for certain
1442header lines that contain addresses is supported.
1443
1444The parentheses surrounding the condition are mandatory, to delimit it from
1445possible further sub-conditions of the enclosing &(if)& command. Within the
1446condition, the expansion variable &$thisaddress$& is set to the non-comment
1447portion of each of the addresses in the string in turn. For example, if the
1448string is
1449.code
1450B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1451.endd
1452then &$thisaddress$& would take on the values &`bart@sfld.example`& and
1453&`lisa@sfld.example`& in turn.
1454
1455If there are no valid addresses in the list, the whole condition is false. If
1456the internal condition is true for any one address, the overall condition is
1457true and the loop ends. If the internal condition is false for all addresses in
1458the list, the overall condition is false. This example tests for the presence
1459of an eight-digit local part in any address in a &'To:'& header:
1460.code
1461if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1462.endd
1463When the overall condition is true, the value of &$thisaddress$& in the
1464commands that follow &(then)& is the last value it took on inside the loop. At
1465the end of the &(if)& command, the value of &$thisaddress$& is reset to what it
1466was before. It is best to avoid the use of multiple occurrences of
1467&(foranyaddress)&, nested or otherwise, in a single &(if)& command, if the
1468value of &$thisaddress$& is to be used afterwards, because it isn't always
1469clear what the value will be. Nested &(if)& commands should be used instead.
1470
1471Header lines can be joined together if a check is to be applied to more than
1472one of them. For example:
1473.code
1474if foranyaddress $h_to:,$h_cc: ....
1475.endd
1476This scans through the addresses in both the &'To:'& and the &'Cc:'& headers.
1477
1478
1479.section "Testing for personal mail" "SECTpersonal"
1480A common requirement is to distinguish between incoming personal mail and mail
1481from a mailing list, or from a robot or other automatic process (for example, a
1482bounce message). In particular, this test is normally required for &"vacation
1483messages"&.
1484
1485The &(personal)& condition checks that the message is not a bounce message and
1486that the current user's email address appears in the &'To:'& header. It also
1487checks that the sender is not the current user or one of a number of common
1488daemons, and that there are no header lines starting &'List-'& in the message.
1489Finally, it checks the content of the &'Precedence:'& header line, if there is
1490one.
1491
1492You should always use the &(personal)& condition when generating automatic
1493responses. This example shows the use of &(personal)& in a filter file that is
1494sending out vacation messages:
1495.code
1496if personal then
1497mail to $reply_address
1498subject "I am on holiday"
1499file $home/vacation/message
1500once $home/vacation/once
1501once_repeat 10d
1502endif
1503.endd
1504It is tempting, when writing commands like the above, to quote the original
1505subject in the reply. For example:
1506.code
1507subject "Re: $h_subject:"
1508.endd
1509There is a danger in doing this, however. It may allow a third party to
1510subscribe you to an opt-in mailing list, provided that the list accepts bounce
1511messages as subscription confirmations. (Messages sent from filters are always
1512sent as bounce messages.) Well-managed lists require a non-bounce message to
1513confirm a subscription, so the danger is relatively small.
1514
1515If prefixes or suffixes are in use for local parts &-- something which depends
1516on the configuration of Exim (see section &<<SECTmbox>>& below) &-- the tests
1517for the current user are done with the full address (including the prefix and
1518suffix, if any) as well as with the prefix and suffix removed. If the system is
1519configured to rewrite local parts of mail addresses, for example, to rewrite
1520&`dag46`& as &`Dirk.Gently`&, the rewritten form of the address is also used in
1521the tests.
1522
1523
1524
4aa45c31 1525.section "Alias addresses for the personal condition" "SEC28"
9b371988
PH
1526It is quite common for people who have mail accounts on a number of different
1527systems to forward all their mail to one system, and in this case a check for
1528personal mail should test all their various mail addresses. To allow for this,
1529the &(personal)& condition keyword can be followed by
1530.display
1531&`alias `&<&'address'&>
1532.endd
1533any number of times, for example:
1534.code
1535if personal alias smith@else.where.example
1536 alias jones@other.place.example
1537then ...
1538.endd
1539The alias addresses are treated as alternatives to the current user's email
1540address when testing the contents of header lines.
1541
1542
4aa45c31 1543.section "Details of the personal condition" "SEC29"
9b371988
PH
1544The basic &(personal)& test is roughly equivalent to the following:
1545.code
1546not error_message and
1547$message_headers does not contain "\nList-Id:" and
1548$message_headers does not contain "\nList-Help:" and
1549$message_headers does not contain "\nList-Subscribe:" and
1550$message_headers does not contain "\nList-Unsubscribe:" and
1551$message_headers does not contain "\nList-Post:" and
1552$message_headers does not contain "\nList-Owner:" and
1553$message_headers does not contain "\nList-Archive:" and
1554(
8f3414a1 1555"${if def:h_auto-submitted:{present}{absent}}" is "absent" or
9b371988
PH
1556$header_auto-submitted: is "no"
1557) and
1558$header_precedence: does not contain "bulk" and
1559$header_precedence: does not contain "list" and
1560$header_precedence: does not contain "junk" and
1561foranyaddress $header_to:
1562( $thisaddress contains "$local_part$domain" ) and
1563not foranyaddress $header_from:
1564(
c0712871
PH
1565$thisaddress contains "$local_part@$domain" or
1566$thisaddress contains "server@" or
1567$thisaddress contains "daemon@" or
1568$thisaddress contains "root@" or
1569$thisaddress contains "listserv@" or
1570$thisaddress contains "majordomo@" or
1571$thisaddress contains "-request@" or
1572$thisaddress matches "^owner-[^@]+@"
9b371988
PH
1573)
1574.endd
1575The variable &$local_part$& contains the local part of the mail address of
1576the user whose filter file is being run &-- it is normally your login id. The
1577&$domain$& variable contains the mail domain. As explained above, if aliases
1578or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1579the current user are also done with alternative addresses.
1580
1581
1582
1583
4aa45c31 1584.section "Testing delivery status" "SEC30"
9b371988
PH
1585There are two conditions that are intended mainly for use in system filter
1586files, but which are available in users' filter files as well. The condition
1587&(first_delivery)& is true if this is the first process that is attempting to
1588deliver the message, and false otherwise. This indicator is not reset until the
1589first delivery process successfully terminates; if there is a crash or a power
1590failure (for example), the next delivery attempt is also a &"first delivery"&.
1591
1592In a user filter file &(first_delivery)& will be false if there was previously
1593an error in the filter, or if a delivery for the user failed owing to, for
1594example, a quota error, or if forwarding to a remote address was deferred for
1595some reason.
1596
1597The condition &(manually_thawed)& is true if the message was &"frozen"& for
1598some reason, and was subsequently released by the system administrator. It is
1599unlikely to be of use in users' filter files.
1600
1601
4aa45c31 1602.section "Multiple personal mailboxes" "SECTmbox" "SEC31"
9b371988
PH
1603The system administrator can configure Exim so that users can set up variants
1604on their email addresses and handle them separately. Consult your system
1605administrator or local documentation to see if this facility is enabled on your
1606system, and if so, what the details are.
1607
1608The facility involves the use of a prefix or a suffix on an email address. For
1609example, all mail addressed to &'lg303-'&<&'something'&> would be the property
1610of user &'lg303'&, who could determine how it was to be handled, depending on
1611the value of <&'something'&>.
1612
1613There are two possible ways in which this can be set up. The first possibility
1614is the use of multiple &_.forward_& files. In this case, mail to &'lg303-foo'&,
1615for example, is handled by looking for a file called &_.forward-foo_& in
1616&'lg303'&'s home directory. If such a file does not exist, delivery fails
1617and the message is returned to its sender.
1618
1619The alternative approach is to pass all messages through a single &_.forward_&
1620file, which must be a filter file so that it can distinguish between the
1621different cases by referencing the variables &$local_part_prefix$& or
1622&$local_part_suffix$&, as in the final example in section &<<SECTex>>& below.
1623
1624It is possible to configure Exim to support both schemes at once. In this case,
1625a specific &_.forward-foo_& file is first sought; if it is not found, the basic
1626&_.forward_& file is used.
1627
1628The &(personal)& test (see section &<<SECTpersonal>>&) includes prefixes and
1629suffixes in its checking.
1630
1631
1632
4aa45c31 1633.section "Ignoring delivery errors" "SEC43"
9b371988
PH
1634As was explained above, filtering just sets up addresses for delivery &-- no
1635deliveries are actually done while a filter file is active. If any of the
1636generated addresses subsequently suffers a delivery failure, an error message
1637is generated in the normal way. However, if a filter command that sets up a
1638delivery is preceded by the word &"noerror"&, errors for that delivery,
1639and any deliveries consequent on it (that is, from alias, forwarding, or
1640filter files it invokes) are ignored.
1641
1642
1643
1644.section "Examples of Exim filter commands" "SECTex"
1645Simple forwarding:
1646
1647.code
1648# Exim filter
1649deliver baggins@rivendell.middle-earth.example
1650.endd
1651
1652Vacation handling using traditional means, assuming that the &_.vacation.msg_&
1653and other files have been set up in your home directory:
1654
1655.code
1656# Exim filter
1657unseen pipe "/usr/ucb/vacation \"$local_part\""
1658.endd
1659
1660Vacation handling inside Exim, having first created a file called
1661&_.vacation.msg_& in your home directory:
1662
1663.code
1664# Exim filter
1665if personal then vacation endif
1666.endd
1667
1668File some messages by subject:
1669
1670.code
1671# Exim filter
1672if $header_subject: contains "empire" or
1673$header_subject: contains "foundation"
1674then
1675save $home/mail/f+e
1676endif
1677.endd
1678
1679Save all non-urgent messages by weekday:
1680
1681.code
1682# Exim filter
1683if $header_subject: does not contain "urgent" and
1684$tod_full matches "^(...),"
1685then
1686save $home/mail/$1
1687endif
1688.endd
1689
1690Throw away all mail from one site, except from postmaster:
1691
1692.code
1693# Exim filter
1694if $reply_address contains "@spam.site.example" and
1695$reply_address does not contain "postmaster@"
1696then
1697seen finish
1698endif
1699.endd
1700
1701Handle multiple personal mailboxes:
1702
1703.code
1704# Exim filter
1705if $local_part_suffix is "-foo"
1706then
1707save $home/mail/foo
1708elif $local_part_suffix is "-bar"
1709then
1710save $home/mail/bar
1711endif
1712.endd
1713