Update for eximstats 1.58
[exim.git] / doc / doc-docbook / filter.xfpt
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553c0e3a 1. $Cambridge: exim/doc/doc-docbook/filter.xfpt,v 1.4 2006/07/31 13:28:49 ph10 Exp $
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2
3. /////////////////////////////////////////////////////////////////////////////
4. This is the primary source of the document that describes Exim's filtering
5. facilities. It is an xfpt document that is converted into DocBook XML for
6. subsequent conversion into printing and online formats. The markup used
7. herein is "standard" xfpt markup, with some extras. The markup is summarized
8. in a file called Markup.txt.
9. /////////////////////////////////////////////////////////////////////////////
10
11.include stdflags
12.include stdmacs
13.docbook
14.book
15
16. ===========================================================================
17. Additional xfpt markup used by this document, over and above the default
18. provided in the xfpt library.
19
20. Override the &$ flag to automatically insert a $ with the variable name
21
22.flag &$ $& "<varname>$" "</varname>"
23
24. A macro for the common 2-column tables
25
26.macro table2 100pt 300pt
27.itable none 0 0 2 $1 left $2 left
28.endmacro
29. ===========================================================================
30
31
32. This preliminary stuff creates a <bookinfo> entry in the XML. This is removed
33. when creating the PostScript/PDF output, because we do not want a full-blown
34. title page created for those versions. The stylesheet fudges up a title line
35. to replace the text "Table of contents". However, for the other forms of
36. output, the <bookinfo> element is retained and used.
37
38.literal xml
39<bookinfo>
40<title>Exim's interfaces to mail filtering</title>
41<titleabbrev>Exim filtering</titleabbrev>
553c0e3a 42<date>31 July</date>
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43<author><firstname>Philip</firstname><surname>Hazel</surname></author>
44<authorinitials>PH</authorinitials>
45<revhistory><revision>
553c0e3a
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46 <revnumber>4.63</revnumber>
47 <date>31 July 2006</date>
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48 <authorinitials>PH</authorinitials>
49</revision></revhistory>
50<copyright><year>2006</year><holder>University of Cambridge</holder></copyright>
51</bookinfo>
52.literal off
53
54
55.chapter "Forwarding and filtering in Exim"
56This document describes the user interfaces to Exim's in-built mail filtering
57facilities, and is copyright &copy; University of Cambridge 2006. It
553c0e3a 58corresponds to Exim version 4.63.
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59
60
61
62.section "Introduction"
63Most Unix mail transfer agents (programs that deliver mail) permit individual
64users to specify automatic forwarding of their mail, usually by placing a list
65of forwarding addresses in a file called &_.forward_& in their home
66directories. Exim extends this facility by allowing the forwarding instructions
67to be a set of rules rather than just a list of addresses, in effect providing
68&"&_.forward_& with conditions"&. Operating the set of rules is called
69&'filtering'&, and the file that contains them is called a &'filter file'&.
70
71Exim supports two different kinds of filter file. An &'Exim filter'& contains
72instructions in a format that is unique to Exim. A &'Sieve filter'& contains
73instructions in the Sieve format that is defined by RFC 3028. As this is a
74standard format, Sieve filter files may already be familiar to some users.
75Sieve files should also be portable between different environments. However,
76the Exim filtering facility contains more features (such as variable
77expansion), and better integration with the host environment (such as the use
78of external processes and pipes).
79
80The choice of which kind of filter to use can be left to the end-user, provided
81that the system administrator has configured Exim appropriately for both kinds
82of filter. However, if interoperability is important, Sieve is the only
83choice.
84
85The ability to use filtering or traditional forwarding has to be enabled by the
86system administrator, and some of the individual facilities can be separately
87enabled or disabled. A local document should be provided to describe exactly
88what has been enabled. In the absence of this, consult your system
89administrator.
90
91This document describes how to use a filter file and the format of its
92contents. It is intended for use by end-users. Both Sieve filters and Exim
93filters are covered. However, for Sieve filters, only issues that relate to the
94Exim implementation are discussed, since Sieve itself is described elsewhere.
95
96The contents of traditional &_.forward_& files are not described here. They
97normally contain just a list of addresses, file names, or pipe commands,
98separated by commas or newlines, but other types of item are also available.
99The full details can be found in the chapter on the &(redirect)& router in the
100Exim specification, which also describes how the system administrator can set
101up and control the use of filtering.
102
103
104
105.section "Filter operation"
106It is important to realize that, in Exim, no deliveries are actually made while
107a filter or traditional &_.forward_& file is being processed. Running a filter
108or processing a traditional &_.forward_& file sets up future delivery
109operations, but does not carry them out.
110
111The result of filter or &_.forward_& file processing is a list of destinations
112to which a message should be delivered. The deliveries themselves take place
113later, along with all other deliveries for the message. This means that it is
114not possible to test for successful deliveries while filtering. It also means
115that any duplicate addresses that are generated are dropped, because Exim never
116delivers the same message to the same address more than once.
117
118
119
120
121.section "Testing a new filter file" "SECTtesting"
122Filter files, especially the more complicated ones, should always be tested, as
123it is easy to make mistakes. Exim provides a facility for preliminary testing
124of a filter file before installing it. This tests the syntax of the file and
125its basic operation, and can also be used with traditional &_.forward_& files.
126
127Because a filter can do tests on the content of messages, a test message is
128required. Suppose you have a new filter file called &_myfilter_& and a test
129message in a file called &_test-message_&. Assuming that Exim is installed with
130the conventional path name &_/usr/sbin/sendmail_& (some operating systems use
131&_/usr/lib/sendmail_&), the following command can be used:
132.code
133/usr/sbin/sendmail -bf myfilter <test-message
134.endd
135The &%-bf%& option tells Exim that the following item on the command line is
136the name of a filter file that is to be tested. There is also a &%-bF%& option,
137which is similar, but which is used for testing system filter files, as opposed
138to user filter files, and which is therefore of use only to the system
139administrator.
140
141The test message is supplied on the standard input. If there are no
142message-dependent tests in the filter, an empty file (&_/dev/null_&) can be
143used. A supplied message must start with header lines or the &"From&~"& message
144separator line that is found in many multi-message folder files. Note that
145blank lines at the start terminate the header lines. A warning is given if no
146header lines are read.
147
148The result of running this command, provided no errors are detected in the
149filter file, is a list of the actions that Exim would try to take if presented
150with the message for real. For example, for an Exim filter, the output
151.code
152Deliver message to: gulliver@lilliput.fict.example
153Save message to: /home/lemuel/mail/archive
154.endd
155means that one copy of the message would be sent to
156&'gulliver@lilliput.fict.example'&, and another would be added to the file
157&_/home/lemuel/mail/archive_&, if all went well.
158
159The actions themselves are not attempted while testing a filter file in this
160way; there is no check, for example, that any forwarding addresses are valid.
161For an Exim filter, if you want to know why a particular action is being taken,
162add the &%-v%& option to the command. This causes Exim to output the results of
163any conditional tests and to indent its output according to the depth of
164nesting of &(if)& commands. Further additional output from a filter test can be
165generated by the &(testprint)& command, which is described below.
166
167When Exim is outputting a list of the actions it would take, if any text
168strings are included in the output, non-printing characters therein are
169converted to escape sequences. In particular, if any text string contains a
170newline character, this is shown as &"\n"& in the testing output.
171
172When testing a filter in this way, Exim makes up an &"envelope"& for the
173message. The recipient is by default the user running the command, and so is
174the sender, but the command can be run with the &%-f%& option to supply a
175different sender. For example,
176.code
177/usr/sbin/sendmail -bf myfilter \
178 -f islington@never.where <test-message
179.endd
180Alternatively, if the &%-f%& option is not used, but the first line of the
181supplied message is a &"From&~"& separator from a message folder file (not the
182same thing as a &'From:'& header line), the sender is taken from there. If
183&%-f%& is present, the contents of any &"From&~"& line are ignored.
184
185The &"return path"& is the same as the envelope sender, unless the message
186contains a &'Return-path:'& header, in which case it is taken from there. You
187need not worry about any of this unless you want to test out features of a
188filter file that rely on the sender address or the return path.
189
190It is possible to change the envelope recipient by specifying further options.
191The &%-bfd%& option changes the domain of the recipient address, while the
192&%-bfl%& option changes the &"local part"&, that is, the part before the @
193sign. An adviser could make use of these to test someone else's filter file.
194
195The &%-bfp%& and &%-bfs%& options specify the prefix or suffix for the local
196part. These are relevant only when support for multiple personal mailboxes is
197implemented; see the description in section &<<SECTmbox>>& below.
198
199
200.section "Installing a filter file"
201A filter file is normally installed under the name &_.forward_& in your home
202directory &-- it is distinguished from a conventional &_.forward_& file by its
203first line (described below). However, the file name is configurable, and some
204system administrators may choose to use some different name or location for
205filter files.
206
207
208.section "Testing an installed filter file"
209Testing a filter file before installation cannot find every potential problem;
210for example, it does not actually run commands to which messages are piped.
211Some &"live"& tests should therefore also be done once a filter is installed.
212
213If at all possible, test your filter file by sending messages from some other
214account. If you send a message to yourself from the filtered account, and
215delivery fails, the error message will be sent back to the same account, which
216may cause another delivery failure. It won't cause an infinite sequence of such
217messages, because delivery failure messages do not themselves generate further
218messages. However, it does mean that the failure won't be returned to you, and
219also that the postmaster will have to investigate the stuck message.
220
221If you have to test an Exim filter from the same account, a sensible precaution
222is to include the line
223.code
224if error_message then finish endif
225.endd
226as the first filter command, at least while testing. This causes filtering to
227be abandoned for a delivery failure message, and since no destinations are
228generated, the message goes on to be delivered to the original address. Unless
229there is a good reason for not doing so, it is recommended that the above test
230be left in all Exim filter files. (This does not apply to Sieve files.)
231
232
233
234.section "Details of filtering commands"
235The filtering commands for Sieve and Exim filters are completely different in
236syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
237chapter we describe how it is integrated into Exim. The subsequent chapter
238covers Exim filtering commands in detail.
239
240
241
242.chapter "Sieve filter files" "CHAPsievefilter"
243The code for Sieve filtering in Exim was contributed by Michael Haardt, and
244most of the content of this chapter is taken from the notes he provided. Since
245Sieve is an extensible language, it is important to understand &"Sieve"& in
246this context as &"the specific implementation of Sieve for Exim"&.
247
248This chapter does not contain a description of Sieve, since that can be found
249in RFC 3028, which should be read in conjunction with these notes.
250
251The Exim Sieve implementation offers the core as defined by RFC 3028,
252comparison tests, the &*copy*&, &*envelope*&, &*fileinto*&, and &*vacation*&
253extensions, but not the &*reject*& extension. Exim does not support message
254delivery notifications (MDNs), so adding it just to the Sieve filter (as
255required for &*reject*&) makes little sense.
256
257In order for Sieve to work properly in Exim, the system administrator needs to
258make some adjustments to the Exim configuration. These are described in the
259chapter on the &(redirect)& router in the full Exim specification.
260
261
262.section "Recognition of Sieve filters"
263A filter file is interpreted as a Sieve filter if its first line is
264.code
265# Sieve filter
266.endd
267This is what distinguishes it from a conventional &_.forward_& file or an Exim
268filter file.
269
270
271
272.section "Saving to specified folders"
273If the system administrator has set things up as suggested in the Exim
274specification, and you use &(keep)& or &(fileinto)& to save a mail into a
275folder, absolute files are stored where specified, relative files are stored
276relative to &$home$&, and &_inbox_& goes to the standard mailbox location.
277
278
279
280.section "Strings containing header names"
281RFC 3028 does not specify what happens if a string denoting a header field does
282not contain a valid header name, for example, it contains a colon. This
283implementation generates an error instead of ignoring the header field in order
284to ease script debugging, which fits in with the common picture of Sieve.
285
286
287
288.section "Exists test with empty list of headers"
289The &*exists*& test succeeds only if all the specified headers exist. RFC 3028
290does not explicitly specify what happens on an empty list of headers. This
291implementation evaluates that condition as true, interpreting the RFC in a
292strict sense.
293
294
295
296.section "Header test with invalid MIME encoding in header"
297Some MUAs process invalid base64 encoded data, generating junk. Others ignore
298junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
299specify how to react in this case, other than stating that a client must not
300forbid to process a message for that reason. RFC 2045 specifies that invalid
301data should be ignored (apparently looking at end of line characters). It also
302specifies that invalid data may lead to rejecting messages containing them (and
303there it appears to talk about true encoding violations), which is a clear
304contradiction to ignoring them.
305
306RFC 3028 does not specify how to process incorrect MIME words. This
307implementation treats them literally, as it does if the word is correct but its
308character set cannot be converted to UTF-8.
309
310
311
312.section "Address test for multiple addresses per header"
313A header may contain multiple addresses. RFC 3028 does not explicitly specify
314how to deal with them, but since the address test checks if anything matches
315anything else, matching one address suffices to satisfy the condition. That
316makes it impossible to test if a header contains a certain set of addresses and
317no more, but it is more logical than letting the test fail if the header
318contains an additional address besides the one the test checks for.
319
320
321
322.section "Semantics of keep"
323The &(keep)& command is equivalent to
324.code
325fileinto "inbox";
326.endd
327It saves the message and resets the implicit keep flag. It does not set the
328implicit keep flag; there is no command to set it once it has been reset.
329
330
331
332.section "Semantics of fileinto"
333RFC 3028 does not specify whether &(fileinto)& should try to create a mail
334folder if it does not exist. This implementation allows the sysadmin to
335configure that aspect using the &(appendfile)& transport options
336&%create_directory%&, &%create_file%&, and &%file_must_exist%&. See the
337&(appendfile)& transport in the Exim specification for details.
338
339
340
341.section "Semantics of redirect"
342Sieve scripts are supposed to be interoperable between servers, so this
343implementation does not allow mail to be redirected to unqualified addresses,
344because the domain would depend on the system being used. On systems with
345virtual mail domains, the default domain is probably not what the user expects
346it to be.
347
348
349
350.section "String arguments"
351There has been confusion if the string arguments to &(require)& are to be
352matched case-sensitively or not. This implementation matches them with the
353match type &(:is)& (default, see section 2.7.1 of the RFC) and the comparator
354&(i;ascii-casemap)& (default, see section 2.7.3 of the RFC). The RFC defines
355the command defaults clearly, so any different implementations violate RFC
3563028. The same is valid for comparator names, also specified as strings.
357
358
359
360.section "Number units"
361There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
362The mistake is obvious, because RFC 3028 specifies G to denote 2^30
363(which is gibi, not tebi), and that is what this implementation uses as
364the scaling factor for the suffix G.
365
366
367
368.section "RFC compliance"
369Exim requires the first line of a Sieve filter to be
370.code
371# Sieve filter
372.endd
373Of course the RFC does not specify that line. Do not expect examples to work
374without adding it, though.
375
376RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
377CRLF is universally used in network protocols to mark the end of the line. This
378implementation does not embed Sieve in a network protocol, but uses Sieve
379scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
380character, this implementation does, too, by default, though the system
381administrator may choose (at Exim compile time) to use CRLF instead.
382
383Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
384implementation repeats this violation to stay consistent with Exim. This is in
385preparation for UTF-8 data.
386
387Sieve scripts cannot contain NUL characters in strings, but mail headers could
388contain MIME encoded NUL characters, which could never be matched by Sieve
389scripts using exact comparisons. For that reason, this implementation extends
390the Sieve quoted string syntax with \0 to describe a NUL character, violating
391\0 being the same as 0 in RFC 3028. Even without using \0, the following tests
392are all true in this implementation. Implementations that use C-style strings
393will only evaluate the first test as true.
394.code
395Subject: =?iso-8859-1?q?abc=00def
396
397header :contains "Subject" ["abc"]
398header :contains "Subject" ["def"]
399header :matches "Subject" ["abc?def"]
400.endd
401Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
402way that NUL characters truncating strings is allowed for Sieve
403implementations, although not recommended. It is further allowed to use encoded
404NUL characters in headers, but that's not recommended either. The above example
405shows why.
406
407RFC 3028 states that if an implementation fails to convert a character set to
408UTF-8, two strings cannot be equal if one contains octets greater than 127.
409Assuming that all unknown character sets are one-byte character sets with the
410lower 128 octets being US-ASCII is not sound, so this implementation violates
411RFC 3028 and treats such MIME words literally. That way at least something
412could be matched.
413
414The folder specified by &(fileinto)& must not contain the character sequence
415&".."& to avoid security problems. RFC 3028 does not specify the syntax of
416folders apart from &(keep)& being equivalent to
417.code
418fileinto "INBOX";
419.endd
420This implementation uses &_inbox_& instead.
421
422Sieve script errors currently cause messages to be silently filed into
423&_inbox_&. RFC 3028 requires that the user is notified of that condition.
424This may be implemented in the future by adding a header line to mails that
425are filed into &_inbox_& due to an error in the filter.
426
427
428
429.chapter "Exim filter files" "CHAPeximfilter"
430This chapter contains a full description of the contents of Exim filter files.
431
432
433.section "Format of Exim filter files"
434Apart from leading white space, the first text in an Exim filter file must be
435.code
436# Exim filter
437.endd
438This is what distinguishes it from a conventional &_.forward_& file or a Sieve
439filter file. If the file does not have this initial line (or the equivalent for
440a Sieve filter), it is treated as a conventional &_.forward_& file, both when
441delivering mail and when using the &%-bf%& testing mechanism. The white space
442in the line is optional, and any capitalization may be used. Further text on
443the same line is treated as a comment. For example, you could have
444.code
445# Exim filter <<== do not edit or remove this line!
446.endd
447The remainder of the file is a sequence of filtering commands, which consist of
448keywords and data values. For example, in the command
449.code
450deliver gulliver@lilliput.fict.example
451.endd
452the keyword is &`deliver`& and the data value is
453&`gulliver@lilliput.fict.example`&. White space or line breaks separate the
454components of a command, except in the case of conditions for the &(if)&
455command, where round brackets (parentheses) also act as separators. Complete
456commands are separated from each other by white space or line breaks; there are
457no special terminators. Thus, several commands may appear on one line, or one
458command may be spread over a number of lines.
459
460If the character # follows a separator anywhere in a command, everything from
461# up to the next newline is ignored. This provides a way of including comments
462in a filter file.
463
464
465.section "Data values in filter commands"
466There are two ways in which a data value can be input:
467
468.ilist
469If the text contains no white space, it can be typed verbatim. However, if it
470is part of a condition, it must also be free of round brackets (parentheses),
471as these are used for grouping in conditions.
472.next
473Otherwise, text must be enclosed in double quotation marks. In this case, the
474character \ (backslash) is treated as an &"escape character"& within the
475string, causing the following character or characters to be treated specially:
476.display
477&`\n`& is replaced by a newline
478&`\r`& is replaced by a carriage return
479&`\t`& is replaced by a tab
480.endd
481.endlist
482
483Backslash followed by up to three octal digits is replaced by the character
484specified by those digits, and &`\x`& followed by up to two hexadecimal digits
485is treated similarly. Backslash followed by any other character is replaced by
486the second character, so that in particular, &`\"`& becomes &`"`& and &`\\`&
487becomes &`\`&. A data item enclosed in double quotes can be continued onto the
488next line by ending the first line with a backslash. Any leading white space at
489the start of the continuation line is ignored.
490
491In addition to the escape character processing that occurs when strings are
492enclosed in quotes, most data values are also subject to &'string expansion'&
493(as described in the next section), in which case the characters &`$`& and
494&`\`& are also significant. This means that if a single backslash is actually
495required in such a string, and the string is also quoted, &`\\\\`& has to be
496entered.
497
498The maximum permitted length of a data string, before expansion, is 1024
499characters.
500
501
502.section "String expansion" "SECTfilterstringexpansion"
503Most data values are expanded before use. Expansion consists of replacing
504substrings beginning with &`$`& with other text. The full expansion facilities
505available in Exim are extensive. If you want to know everything that Exim can
506do with strings, you should consult the chapter on string expansion in the Exim
507documentation.
508
509In filter files, by far the most common use of string expansion is the
510substitution of the contents of a variable. For example, the substring
511.code
512$reply_address
513.endd
514is replaced by the address to which replies to the message should be sent. If
515such a variable name is followed by a letter or digit or underscore, it must be
516enclosed in curly brackets (braces), for example,
517.code
518${reply_address}
519.endd
520If a &`$`& character is actually required in an expanded string, it must be
521escaped with a backslash, and because backslash is also an escape character in
522quoted input strings, it must be doubled in that case. The following two
523examples illustrate two different ways of testing for a &`$`& character in a
524message:
525.code
526if $message_body contains \$ then ...
527if $message_body contains "\\$" then ...
528.endd
529You can prevent part of a string from being expanded by enclosing it between
530two occurrences of &`\N`&. For example,
531.code
532if $message_body contains \N$$$$\N then ...
533.endd
534tests for a run of four dollar characters.
535
536
537.section "Some useful general variables"
538A complete list of the available variables is given in the Exim documentation.
539This shortened list contains the ones that are most likely to be useful in
540personal filter files:
541
542&$body_linecount$&: The number of lines in the body of the message.
543
544&$body_zerocount$&: The number of binary zero characters in the body of the
545message.
546
547&$home$&: In conventional configurations, this variable normally contains the
548user's home directory. The system administrator can, however, change this.
549
550&$local_part$&: The part of the email address that precedes the @ sign &--
551normally the user's login name. If support for multiple personal mailboxes is
552enabled (see section &<<SECTmbox>>& below) and a prefix or suffix for the local
553part was recognized, it is removed from the string in this variable.
554
555&$local_part_prefix$&: If support for multiple personal mailboxes is enabled
556(see section &<<SECTmbox>>& below), and a local part prefix was recognized,
557this variable contains the prefix. Otherwise it contains an empty string.
558
559&$local_part_suffix$&: If support for multiple personal mailboxes is enabled
560(see section &<<SECTmbox>>& below), and a local part suffix was recognized,
561this variable contains the suffix. Otherwise it contains an empty string.
562
563&$message_body$&: The initial portion of the body of the message. By default,
564up to 500 characters are read into this variable, but the system administrator
565can configure this to some other value. Newlines in the body are converted into
566single spaces.
567
568&$message_body_end$&: The final portion of the body of the message, formatted
569and limited in the same way as &$message_body$&.
570
571&$message_body_size$&: The size of the body of the message, in bytes.
572
573&$message_exim_id$&: The message's local identification string, which is unique
574for each message handled by a single host.
575
576&$message_headers$&: The header lines of the message, concatenated into a
577single string, with newline characters between them.
578
579&$message_size$&: The size of the entire message, in bytes.
580
581&$original_local_part$&: When an address that arrived with the message is
582being processed, this contains the same value as the variable &$local_part$&.
583However, if an address generated by an alias, forward, or filter file is being
584processed, this variable contains the local part of the original address.
585
586&$reply_address$&: The contents of the &'Reply-to:'& header, if the message
587has one; otherwise the contents of the &'From:'& header. It is the address to
588which normal replies to the message should be sent.
589
590&$return_path$&: The return path &-- that is, the sender field that will be
591transmitted as part of the message's envelope if the message is sent to another
592host. This is the address to which delivery errors are sent. In many cases,
593this variable has the same value as &$sender_address$&, but if, for example,
594an incoming message to a mailing list has been expanded, &$return_path$& may
595have been changed to contain the address of the list maintainer.
596
597&$sender_address$&: The sender address that was received in the envelope of
598the message. This is not necessarily the same as the contents of the &'From:'&
599or &'Sender:'& header lines. For delivery error messages (&"bounce messages"&)
600there is no sender address, and this variable is empty.
601
602&$tod_full$&: A full version of the time and date, for example: Wed, 18 Oct
6031995 09:51:40 +0100. The timezone is always given as a numerical offset from
604GMT.
605
606&$tod_log$&: The time and date in the format used for writing Exim's log files,
607without the timezone, for example: 1995-10-12 15:32:29.
608
609&$tod_zone$&: The local timezone offset, for example: +0100.
610
611
612
613.section "Header variables" "SECTheadervariables"
614There is a special set of expansion variables containing the header lines of
615the message being processed. These variables have names beginning with
616&$header_$& followed by the name of the header line, terminated by a colon.
617For example,
618.code
619$header_from:
620$header_subject:
621.endd
622The whole item, including the terminating colon, is replaced by the contents of
623the message header line. If there is more than one header line with the same
624name, their contents are concatenated. For header lines whose data consists of
625a list of addresses (for example, &'From:'& and &'To:'&), a comma and newline
626is inserted between each set of data. For all other header lines, just a
627newline is used.
628
629Leading and trailing white space is removed from header line data, and if there
630are any MIME &"words"& that are encoded as defined by RFC 2047 (because they
631contain non-ASCII characters), they are decoded and translated, if possible, to
632a local character set. Translation is attempted only on operating systems that
633have the &[iconv()]& function. This makes the header line look the same as it
634would when displayed by an MUA. The default character set is ISO-8859-1, but
635this can be changed by means of the &(headers)& command (see below).
636
637If you want to see the actual characters that make up a header line, you can
638specify &$rheader_$& instead of &$header_$&. This inserts the &"raw"&
639header line, unmodified.
640
641There is also an intermediate form, requested by &$bheader_$&, which removes
642leading and trailing space and decodes MIME &"words"&, but does not do any
643character translation. If an attempt to decode what looks superficially like a
644MIME &"word"& fails, the raw string is returned. If decoding produces a binary
645zero character, it is replaced by a question mark.
646
647The capitalization of the name following &$header_$& is not significant.
648Because any printing character except colon may appear in the name of a
649message's header (this is a requirement of RFC 2822, the document that
650describes the format of a mail message) curly brackets must &'not'& be used in
651this case, as they will be taken as part of the header name. Two shortcuts are
652allowed in naming header variables:
653
654.ilist
655The initiating &$header_$&, &$rheader_$&, or &$bheader_$& can be
656abbreviated to &$h_$&, &$rh_$&, or &$bh_$&, respectively.
657.next
658The terminating colon can be omitted if the next character is white space. The
659white space character is retained in the expanded string. However, this is not
660recommended, because it makes it easy to forget the colon when it really is
661needed.
662.endlist
663
664If the message does not contain a header of the given name, an empty string is
665substituted. Thus it is important to spell the names of headers correctly. Do
666not use &$header_Reply_to$& when you really mean &$header_Reply-to$&.
667
668
669.section "User variables"
670There are ten user variables with names &$n0$& &-- &$n9$& that can be
671incremented by the &(add)& command (see section &<<SECTadd>>&). These can be
672used for &"scoring"& messages in various ways. If Exim is configured to run a
673&"system filter"& on every message, the values left in these variables are
674copied into the variables &$sn0$& &-- &$sn9$& at the end of the system filter,
675thus making them available to users' filter files. How these values are used is
676entirely up to the individual installation.
677
678
679.section "Current directory"
680The contents of your filter file should not make any assumptions about the
681current directory. It is best to use absolute paths for file names; you can
682normally make use of the &$home$& variable to refer to your home directory. The
683&(save)& command automatically inserts &$home$& at the start of non-absolute
684paths.
685
686
687
688
689.section "Significant deliveries" "SECTsigdel"
690When in the course of delivery a message is processed by a filter file, what
691happens next, that is, after the filter file has been processed, depends on
692whether or not the filter sets up any &'significant deliveries'&. If at least
693one significant delivery is set up, the filter is considered to have handled
694the entire delivery arrangements for the current address, and no further
695processing of the address takes place. If, however, no significant deliveries
696are set up, Exim continues processing the current address as if there were no
697filter file, and typically sets up a delivery of a copy of the message into a
698local mailbox. In particular, this happens in the special case of a filter file
699containing only comments.
700
701The delivery commands &(deliver)&, &(save)&, and &(pipe)& are by default
702significant. However, if such a command is preceded by the word &"unseen"&, its
703delivery is not considered to be significant. In contrast, other commands such
704as &(mail)& and &(vacation)& do not set up significant deliveries unless
705preceded by the word &"seen"&. The following example commands set up
706significant deliveries:
707.code
708deliver jack@beanstalk.example
709pipe $home/bin/mymailscript
710seen mail subject "message discarded"
711seen finish
712.endd
713The following example commands do not set up significant deliveries:
714.code
715unseen deliver jack@beanstalk.example
716unseen pipe $home/bin/mymailscript
717mail subject "message discarded"
718finish
719.endd
720
721
722
723.section "Filter commands"
724The filter commands that are described in subsequent sections are listed
725below, with the section in which they are described in brackets:
726
727.table2
728.row &(add)& "&~&~increment a user variable (section &<<SECTadd>>&)"
729.row &(deliver)& "&~&~deliver to an email address (section &<<SECTdeliver>>&)"
730.row &(fail)& "&~&~force delivery failure (sysadmin use) (section &<<SECTfail>>&)"
731.row &(finish)& "&~&~end processing (section &<<SECTfinish>>&)"
732.row &(freeze)& "&~&~freeze message (sysadmin use) (section &<<SECTfreeze>>&)"
733.row &(headers)& "&~&~set the header character set (section &<<SECTheaders>>&)"
734.row &(if)& "&~&~test condition(s) (section &<<SECTif>>&)"
735.row &(logfile)& "&~&~define log file (section &<<SECTlog>>&)"
736.row &(logwrite)& "&~&~write to log file (section &<<SECTlog>>&)"
737.row &(mail)& "&~&~send a reply message (section &<<SECTmail>>&)"
738.row &(pipe)& "&~&~pipe to a command (section &<<SECTpipe>>&)"
739.row &(save)& "&~&~save to a file (section &<<SECTsave>>&)"
740.row &(testprint)& "&~&~print while testing (section &<<SECTtestprint>>&)"
741.row &(vacation)& "&~&~tailored form of &(mail)& (section &<<SECTmail>>&)"
742.endtable
743
744The &(headers)& command has additional parameters that can be used only in a
745system filter. The &(fail)& and &(freeze)& commands are available only when
746Exim's filtering facilities are being used as a system filter, and are
747therefore usable only by the system administrator and not by ordinary users.
748They are mentioned only briefly in this document; for more information, see the
749main Exim specification.
750
751
752
753.section "The add command" "SECTadd"
754.display
755&` add `&<&'number'&>&` to `&<&'user variable'&>
756&`e.g. add 2 to n3`&
757.endd
758
759There are 10 user variables of this type, with names &$n0$& &-- &$n9$&. Their
760values can be obtained by the normal expansion syntax (for example &$n3$&) in
761other commands. At the start of filtering, these variables all contain zero.
762Both arguments of the &(add)& command are expanded before use, making it
763possible to add variables to each other. Subtraction can be obtained by adding
764negative numbers.
765
766
767
768.section "The deliver command" "SECTdeliver"
769.display
770&` deliver`& <&'mail address'&>
771&`e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"`&
772.endd
773
774This command provides a forwarding operation. The delivery that it sets up is
775significant unless the command is preceded by &"unseen"& (see section
776&<<SECTsigdel>>&). The message is sent on to the given address, exactly as
777happens if the address had appeared in a traditional &_.forward_& file. If you
778want to deliver the message to a number of different addresses, you can use
779more than one &(deliver)& command (each one may have only one address).
780However, duplicate addresses are discarded.
781
782To deliver a copy of the message to your normal mailbox, your login name can be
783given as the address. Once an address has been processed by the filtering
784mechanism, an identical generated address will not be so processed again, so
785doing this does not cause a loop.
786
787However, if you have a mail alias, you should &'not'& refer to it here. For
788example, if the mail address &'L.Gulliver'& is aliased to &'lg303'& then all
789references in Gulliver's &_.forward_& file should be to &'lg303'&. A reference
790to the alias will not work for messages that are addressed to that alias,
791since, like &_.forward_& file processing, aliasing is performed only once on an
792address, in order to avoid looping.
793
794Following the new address, an optional second address, preceded by
795&"errors_to"& may appear. This changes the address to which delivery errors on
796the forwarded message will be sent. Instead of going to the message's original
797sender, they go to this new address. For ordinary users, the only value that is
798permitted for this address is the user whose filter file is being processed.
799For example, the user &'lg303'& whose mailbox is in the domain
800&'lilliput.example'& could have a filter file that contains
801.code
802deliver jon@elsewhere.example errors_to lg303@lilliput.example
803.endd
804Clearly, using this feature makes sense only in situations where not all
805messages are being forwarded. In particular, bounce messages must not be
806forwarded in this way, as this is likely to create a mail loop if something
807goes wrong.
808
809
810
811.section "The save command" "SECTsave"
812.display
813&` save `&<&'file name'&>
814&`e.g. save $home/mail/bookfolder`&
815.endd
816
817This command specifies that a copy of the message is to be appended to the
818given file (that is, the file is to be used as a mail folder). The delivery
819that &(save)& sets up is significant unless the command is preceded by
820&"unseen"& (see section &<<SECTsigdel>>&).
821
822More than one &(save)& command may be obeyed; each one causes a copy of the
823message to be written to its argument file, provided they are different
824(duplicate &(save)& commands are ignored).
825
826If the file name does not start with a / character, the contents of the
553c0e3a
PH
827&$home$& variable are prepended, unless it is empty, &new("or the system
828administrator has disabled this feature.") In conventional configurations, this
829variable is normally set in a user filter to the user's home directory, but the
830system administrator may set it to some other path. In some configurations,
831&$home$& may be unset, &new("or prepending may be disabled,") in which case a
832non-absolute path name may be generated. Such configurations convert this to an
833absolute path when the delivery takes place. In a system filter, &$home$& is
834never set.
9b371988
PH
835
836The user must of course have permission to write to the file, and the writing
837of the file takes place in a process that is running as the user, under the
838user's primary group. Any secondary groups to which the user may belong are not
839normally taken into account, though the system administrator can configure Exim
840to set them up. In addition, the ability to use this command at all is
841controlled by the system administrator &-- it may be forbidden on some systems.
842
843An optional mode value may be given after the file name. The value for the mode
844is interpreted as an octal number, even if it does not begin with a zero. For
845example:
846.code
847save /some/folder 640
848.endd
849This makes it possible for users to override the system-wide mode setting for
850file deliveries, which is normally 600. If an existing file does not have the
851correct mode, it is changed.
852
853An alternative form of delivery may be enabled on your system, in which each
854message is delivered into a new file in a given directory. If this is the case,
855this functionality can be requested by giving the directory name terminated by
856a slash after the &(save)& command, for example
857.code
858save separated/messages/
859.endd
860There are several different formats for such deliveries; check with your system
861administrator or local documentation to find out which (if any) are available
862on your system. If this functionality is not enabled, the use of a path name
863ending in a slash causes an error.
864
865
866
867.section "The pipe command" "SECTpipe"
868.display
869&` pipe `&<&'command'&>
870&`e.g. pipe "$home/bin/countmail $sender_address"`&
871.endd
872
873This command specifies that the message is to be delivered to the specified
874command using a pipe. The delivery that it sets up is significant unless the
875command is preceded by &"unseen"& (see section &<<SECTsigdel>>&). Remember,
876however, that no deliveries are done while the filter is being processed. All
877deliveries happen later on. Therefore, the result of running the pipe is not
878available to the filter.
879
880When the deliveries are done, a separate process is run, and a copy of the
881message is passed on its standard input. The process runs as the user, under
882the user's primary group. Any secondary groups to which the user may belong are
883not normally taken into account, though the system administrator can configure
884Exim to set them up. More than one &(pipe)& command may appear; each one causes
885a copy of the message to be written to its argument pipe, provided they are
886different (duplicate &(pipe)& commands are ignored).
887
888When the time comes to transport the message, the command supplied to &(pipe)&
889is split up by Exim into a command name and a number of arguments. These are
890delimited by white space except for arguments enclosed in double quotes, in
891which case backslash is interpreted as an escape, or in single quotes, in which
892case no escaping is recognized. Note that as the whole command is normally
893supplied in double quotes, a second level of quoting is required for internal
894double quotes. For example:
895.code
896pipe "$home/myscript \"size is $message_size\""
897.endd
898String expansion is performed on the separate components after the line has
899been split up, and the command is then run directly by Exim; it is not run
900under a shell. Therefore, substitution cannot change the number of arguments,
901nor can quotes, backslashes or other shell metacharacters in variables cause
902confusion.
903
904Documentation for some programs that are normally run via this kind of pipe
905often suggest that the command should start with
906.code
907IFS=" "
908.endd
909This is a shell command, and should &'not'& be present in Exim filter files,
910since it does not normally run the command under a shell.
911
912However, there is an option that the administrator can set to cause a shell to
913be used. In this case, the entire command is expanded as a single string and
914passed to the shell for interpretation. It is recommended that this be avoided
915if at all possible, since it can lead to problems when inserted variables
916contain shell metacharacters.
917
918The default PATH set up for the command is determined by the system
919administrator, usually containing at least &_/bin_& and &_/usr/bin_& so that
920common commands are available without having to specify an absolute file name.
921However, it is possible for the system administrator to restrict the pipe
922facility so that the command name must not contain any / characters, and must
923be found in one of the directories in the configured PATH. It is also possible
924for the system administrator to lock out the use of the &(pipe)& command
925altogether.
926
927When the command is run, a number of environment variables are set up. The
928complete list for pipe deliveries may be found in the Exim reference manual.
929Those that may be useful for pipe deliveries from user filter files are:
930
931.display
932&`DOMAIN `& the domain of the address
933&`HOME `& your home directory
934&`LOCAL_PART `& see below
935&`LOCAL_PART_PREFIX `& see below
936&`LOCAL_PART_SUFFIX `& see below
937&`LOGNAME `& your login name
938&`MESSAGE_ID `& the unique id of the message
939&`PATH `& the command search path
940&`RECIPIENT `& the complete recipient address
941&`SENDER `& the sender of the message
942&`SHELL `& &`/bin/sh`&
943&`USER `& see below
944.endd
945
946LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
947id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
948recognize prefixes or suffixes in the local parts of addresses. For example, a
949message addressed to &'pat-suf2@domain.example'& may cause the filter for user
950&'pat'& to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
951&`-suf2`& when the pipe command runs. The system administrator has to configure
952Exim specially for this feature to be available.
953
954If you run a command that is a shell script, be very careful in your use of
955data from the incoming message in the commands in your script. RFC 2822 is very
956generous in the characters that are permitted to appear in mail addresses, and
957in particular, an address may begin with a vertical bar or a slash. For this
958reason you should always use quotes round any arguments that involve data from
959the message, like this:
960.code
961/some/command '$SENDER'
962.endd
963so that inserted shell meta-characters do not cause unwanted effects.
964
965Remember that, as was explained earlier, the pipe command is not run at the
966time the filter file is interpreted. The filter just defines what deliveries
967are required for one particular addressee of a message. The deliveries
968themselves happen later, once Exim has decided everything that needs to be done
969for the message.
970
971A consequence of this is that you cannot inspect the return code from the pipe
972command from within the filter. Nevertheless, the code returned by the command
973is important, because Exim uses it to decide whether the delivery has succeeded
974or failed.
975
976The command should return a zero completion code if all has gone well. Most
977non-zero codes are treated by Exim as indicating a failure of the pipe. This is
978treated as a delivery failure, causing the message to be returned to its
979sender. However, there are some completion codes that are treated as temporary
980errors. The message remains on Exim's spool disk, and the delivery is tried
981again later, though it will ultimately time out if the delivery failures go on
982too long. The completion codes to which this applies can be specified by the
983system administrator; the default values are 73 and 75.
984
985The pipe command should not normally write anything to its standard output or
986standard error file descriptors. If it does, whatever is written is normally
987returned to the sender of the message as a delivery error, though this action
988can be varied by the system administrator.
989
990
991
992.section "Mail commands" "SECTmail"
993There are two commands that cause the creation of a new mail message, neither
994of which count as a significant delivery unless the command is preceded by the
995word &"seen"& (see section &<<SECTsigdel>>&). This is a powerful facility, but
996it should be used with care, because of the danger of creating infinite
997sequences of messages. The system administrator can forbid the use of these
998commands altogether.
999
1000To help prevent runaway message sequences, these commands have no effect when
1001the incoming message is a bounce (delivery error) message, and messages sent by
1002this means are treated as if they were reporting delivery errors. Thus, they
1003should never themselves cause a bounce message to be returned. The basic
1004mail-sending command is
1005.display
1006&`mail [to `&<&'address-list'&>&`]`&
1007&` [cc `&<&'address-list'&>&`]`&
1008&` [bcc `&<&'address-list'&>&`]`&
1009&` [from `&<&'address'&>&`]`&
1010&` [reply_to `&<&'address'&>&`]`&
1011&` [subject `&<&'text'&>&`]`&
1012&` [extra_headers `&<&'text'&>&`]`&
1013&` [text `&<&'text'&>&`]`&
1014&` [[expand] file `&<&'filename'&>&`]`&
1015&` [return message]`&
1016&` [log `&<&'log file name'&>&`]`&
1017&` [once `&<&'note file name'&>&`]`&
1018&` [once_repeat `&<&'time interval'&>&`]`&
1019
1020&`e.g. mail text "Your message about $h_subject: has been received"`&
1021.endd
1022Each <&'address-list'&> can contain a number of addresses, separated by commas,
1023in the format of a &'To:'& or &'Cc:'& header line. In fact, the text you supply
1024here is copied exactly into the appropriate header line. It may contain
1025additional information as well as email addresses. For example:
1026.code
1027mail to "Julius Caesar <jc@rome.example>, \
1028 <ma@rome.example> (Mark A.)"
1029.endd
1030Similarly, the texts supplied for &%from%& and &%reply_to%& are copied into
1031their respective header lines.
1032
1033As a convenience for use in one common case, there is also a command called
1034&(vacation)&. It behaves in the same way as &(mail)&, except that the defaults
1035for the &%subject%&, &%file%&, &%log%&, &%once%&, and &%once_repeat%& options
1036are
1037.code
1038subject "On vacation"
1039expand file .vacation.msg
1040log .vacation.log
1041once .vacation
1042once_repeat 7d
1043.endd
1044respectively. These are the same file names and repeat period used by the
1045traditional Unix &(vacation)& command. The defaults can be overridden by
1046explicit settings, but if a file name is given its contents are expanded only
1047if explicitly requested.
1048
1049&*Warning*&: The &(vacation)& command should always be used conditionally,
1050subject to at least the &(personal)& condition (see section &<<SECTpersonal>>&
1051below) so as not to send automatic replies to non-personal messages from
1052mailing lists or elsewhere. Sending an automatic response to a mailing list or
1053a mailing list manager is an Internet Sin.
1054
1055For both commands, the key/value argument pairs can appear in any order. At
1056least one of &%text%& or &%file%& must appear (except with &(vacation)&, where
1057there is a default for &%file%&); if both are present, the text string appears
1058first in the message. If &%expand%& precedes &%file%&, each line of the file is
1059subject to string expansion before it is included in the message.
1060
1061Several lines of text can be supplied to &%text%& by including the escape
1062sequence &"\n"& in the string wherever a newline is required. If the command is
1063output during filter file testing, newlines in the text are shown as &"\n"&.
1064
1065Note that the keyword for creating a &'Reply-To:'& header is &%reply_to%&,
1066because Exim keywords may contain underscores, but not hyphens. If the &%from%&
1067keyword is present and the given address does not match the user who owns the
1068forward file, Exim normally adds a &'Sender:'& header to the message, though it
1069can be configured not to do this.
1070
1071The &%extra_headers%& keyword allows you to add custom header lines to the
1072message. The text supplied must be one or more syntactically valid RFC 2822
1073header lines. You can use &"\n"& within quoted text to specify newlines between
1074headers, and also to define continued header lines. For example:
1075.code
1076extra_headers "h1: first\nh2: second\n continued\nh3: third"
1077.endd
1078No newline should appear at the end of the final header line.
1079
1080If no &%to%& argument appears, the message is sent to the address in the
1081&$reply_address$& variable (see section &<<SECTfilterstringexpansion>>& above).
1082An &'In-Reply-To:'& header is automatically included in the created message,
1083giving a reference to the message identification of the incoming message.
1084
1085If &%return message%& is specified, the incoming message that caused the filter
1086file to be run is added to the end of the message, subject to a maximum size
1087limitation.
1088
1089If a log file is specified, a line is added to it for each message sent.
1090
1091If a &%once%& file is specified, it is used to hold a database for remembering
1092who has received a message, and no more than one message is ever sent to any
1093particular address, unless &%once_repeat%& is set. This specifies a time
1094interval after which another copy of the message is sent. The interval is
1095specified as a sequence of numbers, each followed by the initial letter of one
1096of &"seconds"&, &"minutes"&, &"hours"&, &"days"&, or &"weeks"&. For example,
1097.code
1098once_repeat 5d4h
1099.endd
1100causes a new message to be sent if at least 5 days and 4 hours have elapsed
1101since the last one was sent. There must be no white space in a time interval.
1102
1103Commonly, the file name specified for &%once%& is used as the base name for
1104direct-access (DBM) file operations. There are a number of different DBM
1105libraries in existence. Some operating systems provide one as a default, but
1106even in this case a different one may have been used when building Exim. With
1107some DBM libraries, specifying &%once%& results in two files being created,
1108with the suffixes &_.dir_& and &_.pag_& being added to the given name. With
1109some others a single file with the suffix &_.db_& is used, or the name is used
1110unchanged.
1111
1112Using a DBM file for implementing the &%once%& feature means that the file
1113grows as large as necessary. This is not usually a problem, but some system
1114administrators want to put a limit on it. The facility can be configured not to
1115use a DBM file, but instead, to use a regular file with a maximum size. The
1116data in such a file is searched sequentially, and if the file fills up, the
1117oldest entry is deleted to make way for a new one. This means that some
1118correspondents may receive a second copy of the message after an unpredictable
1119interval. Consult your local information to see if your system is configured
1120this way.
1121
1122More than one &(mail)& or &(vacation)& command may be obeyed in a single filter
1123run; they are all honoured, even when they are to the same recipient.
1124
1125
1126
1127.section "Logging commands" "SECTlog"
1128A log can be kept of actions taken by a filter file. This facility is normally
1129available in conventional configurations, but there are some situations where
1130it might not be. Also, the system administrator may choose to disable it. Check
1131your local information if in doubt.
1132
1133Logging takes place while the filter file is being interpreted. It does not
1134queue up for later like the delivery commands. The reason for this is so that a
1135log file need be opened only once for several write operations. There are two
1136commands, neither of which constitutes a significant delivery. The first
1137defines a file to which logging output is subsequently written:
1138.display
1139&` logfile `&<&'file name'&>
1140&`e.g. logfile $home/filter.log`&
1141.endd
1142The file name must be fully qualified. You can use &$home$&, as in this
1143example, to refer to your home directory. The file name may optionally be
1144followed by a mode for the file, which is used if the file has to be created.
1145For example,
1146.code
1147logfile $home/filter.log 0644
1148.endd
1149The number is interpreted as octal, even if it does not begin with a zero.
1150The default for the mode is 600. It is suggested that the &(logfile)& command
1151normally appear as the first command in a filter file. Once a log file has
1152been obeyed, the &(logwrite)& command can be used to write to it:
1153.display
1154&` logwrite "`&<&'some text string'&>&`"`&
1155&`e.g. logwrite "$tod_log $message_id processed"`&
1156.endd
1157It is possible to have more than one &(logfile)& command, to specify writing to
1158different log files in different circumstances. Writing takes place at the end
1159of the file, and a newline character is added to the end of each string if
1160there isn't one already there. Newlines can be put in the middle of the string
1161by using the &"\n"& escape sequence. Lines from simultaneous deliveries may get
1162interleaved in the file, as there is no interlocking, so you should plan your
1163logging with this in mind. However, data should not get lost.
1164
1165
1166
1167.section "The finish command" "SECTfinish"
1168The command &(finish)&, which has no arguments, causes Exim to stop
1169interpreting the filter file. This is not a significant action unless preceded
1170by &"seen"&. A filter file containing only &"seen finish"& is a black hole.
1171
1172
1173.section "The testprint command" "SECTtestprint"
1174It is sometimes helpful to be able to print out the values of variables when
1175testing filter files. The command
1176.display
1177&` testprint `&<&'text'&>
1178&`e.g. testprint "home=$home reply_address=$reply_address"`&
1179.endd
1180does nothing when mail is being delivered. However, when the filtering code is
1181being tested by means of the &%-bf%& option (see section &<<SECTtesting>>&
1182above), the value of the string is written to the standard output.
1183
1184
1185.section "The fail command" "SECTfail"
1186When Exim's filtering facilities are being used as a system filter, the
1187&(fail)& command is available, to force delivery failure. Because this command
1188is normally usable only by the system administrator, and not enabled for use by
1189ordinary users, it is described in more detail in the main Exim specification
1190rather than in this document.
1191
1192
1193.section "The freeze command" "SECTfreeze"
1194When Exim's filtering facilities are being used as a system filter, the
1195&(freeze)& command is available, to freeze a message on the queue. Because this
1196command is normally usable only by the system administrator, and not enabled
1197for use by ordinary users, it is described in more detail in the main Exim
1198specification rather than in this document.
1199
1200
1201
1202.section "The headers command" "SECTheaders"
1203The &(headers)& command can be used to change the target character set that is
1204used when translating the contents of encoded header lines for insertion by the
1205&$header_$& mechanism (see section &<<SECTheadervariables>>& above). The
1206default can be set in the Exim configuration; if not specified, ISO-8859-1 is
1207used. The only currently supported format for the &(headers)& command in user
1208filters is as in this example:
1209.code
1210headers charset "UTF-8"
1211.endd
1212That is, &(headers)& is followed by the word &"charset"& and then the name of a
1213character set. This particular example would be useful if you wanted to compare
1214the contents of a header to a UTF-8 string.
1215
1216In system filter files, the &(headers)& command can be used to add or remove
1217header lines from the message. These features are described in the main Exim
1218specification.
1219
1220
1221
1222.section "Obeying commands conditionally" "SECTif"
1223Most of the power of filtering comes from the ability to test conditions and
1224obey different commands depending on the outcome. The &(if)& command is used to
1225specify conditional execution, and its general form is
1226.display
1227&`if `&<&'condition'&>
1228&`then `&<&'commands'&>
1229&`elif `&<&'condition'&>
1230&`then `&<&'commands'&>
1231&`else `&<&'commands'&>
1232&`endif`&
1233.endd
1234There may be any number of &(elif)& and &(then)& sections (including none) and
1235the &(else)& section is also optional. Any number of commands, including nested
1236&(if)& commands, may appear in any of the <&'commands'&> sections.
1237
1238Conditions can be combined by using the words &(and)& and &(or)&, and round
1239brackets (parentheses) can be used to specify how several conditions are to
1240combine. Without brackets, &(and)& is more binding than &(or)&. For example:
1241.code
1242if
1243$h_subject: contains "Make money" or
1244$h_precedence: is "junk" or
1245($h_sender: matches ^\\d{8}@ and not personal) or
1246$message_body contains "this is not spam"
1247then
1248seen finish
1249endif
1250.endd
1251A condition can be preceded by &(not)& to negate it, and there are also some
1252negative forms of condition that are more English-like.
1253
1254
1255
1256.section "String testing conditions"
1257There are a number of conditions that operate on text strings, using the words
1258&"begins"&, &"ends"&, &"is"&, &"contains"& and &"matches"&. If you want to
1259apply the same test to more than one header line, you can easily concatenate
1260them into a single string for testing, as in this example:
1261.code
1262if "$h_to:, $h_cc:" contains me@domain.example then ...
1263.endd
1264If a string-testing condition name is written in lower case, the testing
1265of letters is done without regard to case; if it is written in upper case
1266(for example, &"CONTAINS"&), the case of letters is taken into account.
1267
1268.display
1269&` `&<&'text1'&>&` begins `&<&'text2'&>
1270&` `&<&'text1'&>&` does not begin `&<&'text2'&>
1271&`e.g. $header_from: begins "Friend@"`&
1272.endd
1273
1274A &"begins"& test checks for the presence of the second string at the start of
1275the first, both strings having been expanded.
1276
1277.display
1278&` `&<&'text1'&>&` ends `&<&'text2'&>
1279&` `&<&'text1'&>&` does not end `&<&'text2'&>
1280&`e.g. $header_from: ends "public.com.example"`&
1281.endd
1282
1283An &"ends"& test checks for the presence of the second string at the end of
1284the first, both strings having been expanded.
1285
1286.display
1287&` `&<&'text1'&>&` is `&<&'text2'&>
1288&` `&<&'text1'&>&` is not `&<&'text2'&>
1289&`e.g. $local_part_suffix is "-foo"`&
1290.endd
1291
1292An &"is"& test does an exact match between the strings, having first expanded
1293both strings.
1294
1295.display
1296&` `&<&'text1'&>&` contains `&<&'text2'&>
1297&` `&<&'text1'&>&` does not contain `&<&'text2'&>
1298&`e.g. $header_subject: contains "evolution"`&
1299.endd
1300
1301A &"contains"& test does a partial string match, having expanded both strings.
1302
1303.display
1304&` `&<&'text1'&>&` matches `&<&'text2'&>
1305&` `&<&'text1'&>&` does not match `&<&'text2'&>
1306&`e.g. $sender_address matches "(bill|john)@"`&
1307.endd
1308
1309For a &"matches"& test, after expansion of both strings, the second one is
1310interpreted as a regular expression. Exim uses the PCRE regular expression
1311library, which provides regular expressions that are compatible with Perl.
1312
1313The match succeeds if the regular expression matches any part of the first
1314string. If you want a regular expression to match only at the start or end of
1315the subject string, you must encode that requirement explicitly, using the
1316&`^`& or &`$`& metacharacters. The above example, which is not so constrained,
1317matches all these addresses:
1318.code
1319bill@test.example
1320john@some.example
1321spoonbill@example.com
1322littlejohn@example.com
1323.endd
1324To match only the first two, you could use this:
1325.code
1326if $sender_address matches "^(bill|john)@" then ...
1327.endd
1328Care must be taken if you need a backslash in a regular expression, because
1329backslashes are interpreted as escape characters both by the string expansion
1330code and by Exim's normal processing of strings in quotes. For example, if you
1331want to test the sender address for a domain ending in &'.com'& the regular
1332expression is
1333.code
1334\.com$
1335.endd
1336The backslash and dollar sign in that expression have to be escaped when used
1337in a filter command, as otherwise they would be interpreted by the expansion
1338code. Thus, what you actually write is
1339.code
1340if $sender_address matches \\.com\$
1341.endd
1342An alternative way of handling this is to make use of the &`\N`& expansion
1343flag for suppressing expansion:
1344.code
1345if $sender_address matches \N\.com$\N
1346.endd
1347Everything between the two occurrences of &`\N`& is copied without change by
1348the string expander (and in fact you do not need the final one, because it is
1349at the end of the string). If the regular expression is given in quotes
1350(mandatory only if it contains white space) you have to write either
1351.code
1352if $sender_address matches "\\\\.com\\$"
1353.endd
1354or
1355.code
1356if $sender_address matches "\\N\\.com$\\N"
1357.endd
1358
1359If the regular expression contains bracketed sub-expressions, numeric
1360variable substitutions such as &$1$& can be used in the subsequent actions
1361after a successful match. If the match fails, the values of the numeric
1362variables remain unchanged. Previous values are not restored after &(endif)&.
1363In other words, only one set of values is ever available. If the condition
1364contains several sub-conditions connected by &(and)& or &(or)&, it is the
1365strings extracted from the last successful match that are available in
1366subsequent actions. Numeric variables from any one sub-condition are also
1367available for use in subsequent sub-conditions, because string expansion of a
1368condition occurs just before it is tested.
1369
1370
1371.section "Numeric testing conditions"
1372The following conditions are available for performing numerical tests:
1373
1374.display
1375&` `&<&'number1'&>&` is above `&<&'number2'&>
1376&` `&<&'number1'&>&` is not above `&<&'number2'&>
1377&` `&<&'number1'&>&` is below `&<&'number2'&>
1378&` `&<&'number1'&>&` is not below `&<&'number2'&>
1379&`e.g. $message_size is not above 10k`&
1380.endd
1381
1382The <&'number'&> arguments must expand to strings of digits, optionally
1383followed by one of the letters K or M (upper case or lower case) which cause
1384multiplication by 1024 and 1024x1024 respectively.
1385
1386
1387.section "Testing for significant deliveries"
1388You can use the &(delivered)& condition to test whether or not any previously
1389obeyed filter commands have set up a significant delivery. For example:
1390.code
1391if not delivered then save mail/anomalous endif
1392.endd
1393&"Delivered"& is perhaps a poor choice of name for this condition, because the
1394message has not actually been delivered; rather, a delivery has been set up for
1395later processing.
1396
1397
1398.section "Testing for error messages"
1399The condition &(error_message)& is true if the incoming message is a bounce
1400(mail delivery error) message. Putting the command
1401.code
1402if error_message then finish endif
1403.endd
1404at the head of your filter file is a useful insurance against things going
1405wrong in such a way that you cannot receive delivery error reports. &*Note*&:
1406&(error_message)& is a condition, not an expansion variable, and therefore is
1407not preceded by &`$`&.
1408
1409
1410.section "Testing a list of addresses"
1411There is a facility for looping through a list of addresses and applying a
1412condition to each of them. It takes the form
1413.display
1414&`foranyaddress `&<&'string'&>&` (`&<&'condition'&>&`)`&
1415.endd
1416where <&'string'&> is interpreted as a list of RFC 2822 addresses, as in a
1417typical header line, and <&'condition'&> is any valid filter condition or
1418combination of conditions. The &"group"& syntax that is defined for certain
1419header lines that contain addresses is supported.
1420
1421The parentheses surrounding the condition are mandatory, to delimit it from
1422possible further sub-conditions of the enclosing &(if)& command. Within the
1423condition, the expansion variable &$thisaddress$& is set to the non-comment
1424portion of each of the addresses in the string in turn. For example, if the
1425string is
1426.code
1427B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1428.endd
1429then &$thisaddress$& would take on the values &`bart@sfld.example`& and
1430&`lisa@sfld.example`& in turn.
1431
1432If there are no valid addresses in the list, the whole condition is false. If
1433the internal condition is true for any one address, the overall condition is
1434true and the loop ends. If the internal condition is false for all addresses in
1435the list, the overall condition is false. This example tests for the presence
1436of an eight-digit local part in any address in a &'To:'& header:
1437.code
1438if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1439.endd
1440When the overall condition is true, the value of &$thisaddress$& in the
1441commands that follow &(then)& is the last value it took on inside the loop. At
1442the end of the &(if)& command, the value of &$thisaddress$& is reset to what it
1443was before. It is best to avoid the use of multiple occurrences of
1444&(foranyaddress)&, nested or otherwise, in a single &(if)& command, if the
1445value of &$thisaddress$& is to be used afterwards, because it isn't always
1446clear what the value will be. Nested &(if)& commands should be used instead.
1447
1448Header lines can be joined together if a check is to be applied to more than
1449one of them. For example:
1450.code
1451if foranyaddress $h_to:,$h_cc: ....
1452.endd
1453This scans through the addresses in both the &'To:'& and the &'Cc:'& headers.
1454
1455
1456.section "Testing for personal mail" "SECTpersonal"
1457A common requirement is to distinguish between incoming personal mail and mail
1458from a mailing list, or from a robot or other automatic process (for example, a
1459bounce message). In particular, this test is normally required for &"vacation
1460messages"&.
1461
1462The &(personal)& condition checks that the message is not a bounce message and
1463that the current user's email address appears in the &'To:'& header. It also
1464checks that the sender is not the current user or one of a number of common
1465daemons, and that there are no header lines starting &'List-'& in the message.
1466Finally, it checks the content of the &'Precedence:'& header line, if there is
1467one.
1468
1469You should always use the &(personal)& condition when generating automatic
1470responses. This example shows the use of &(personal)& in a filter file that is
1471sending out vacation messages:
1472.code
1473if personal then
1474mail to $reply_address
1475subject "I am on holiday"
1476file $home/vacation/message
1477once $home/vacation/once
1478once_repeat 10d
1479endif
1480.endd
1481It is tempting, when writing commands like the above, to quote the original
1482subject in the reply. For example:
1483.code
1484subject "Re: $h_subject:"
1485.endd
1486There is a danger in doing this, however. It may allow a third party to
1487subscribe you to an opt-in mailing list, provided that the list accepts bounce
1488messages as subscription confirmations. (Messages sent from filters are always
1489sent as bounce messages.) Well-managed lists require a non-bounce message to
1490confirm a subscription, so the danger is relatively small.
1491
1492If prefixes or suffixes are in use for local parts &-- something which depends
1493on the configuration of Exim (see section &<<SECTmbox>>& below) &-- the tests
1494for the current user are done with the full address (including the prefix and
1495suffix, if any) as well as with the prefix and suffix removed. If the system is
1496configured to rewrite local parts of mail addresses, for example, to rewrite
1497&`dag46`& as &`Dirk.Gently`&, the rewritten form of the address is also used in
1498the tests.
1499
1500
1501
1502.section "Alias addresses for the personal condition"
1503It is quite common for people who have mail accounts on a number of different
1504systems to forward all their mail to one system, and in this case a check for
1505personal mail should test all their various mail addresses. To allow for this,
1506the &(personal)& condition keyword can be followed by
1507.display
1508&`alias `&<&'address'&>
1509.endd
1510any number of times, for example:
1511.code
1512if personal alias smith@else.where.example
1513 alias jones@other.place.example
1514then ...
1515.endd
1516The alias addresses are treated as alternatives to the current user's email
1517address when testing the contents of header lines.
1518
1519
1520.section "Details of the personal condition"
1521The basic &(personal)& test is roughly equivalent to the following:
1522.code
1523not error_message and
1524$message_headers does not contain "\nList-Id:" and
1525$message_headers does not contain "\nList-Help:" and
1526$message_headers does not contain "\nList-Subscribe:" and
1527$message_headers does not contain "\nList-Unsubscribe:" and
1528$message_headers does not contain "\nList-Post:" and
1529$message_headers does not contain "\nList-Owner:" and
1530$message_headers does not contain "\nList-Archive:" and
1531(
1532"${if def h_auto-submitted:{present}{absent}}" is "absent" or
1533$header_auto-submitted: is "no"
1534) and
1535$header_precedence: does not contain "bulk" and
1536$header_precedence: does not contain "list" and
1537$header_precedence: does not contain "junk" and
1538foranyaddress $header_to:
1539( $thisaddress contains "$local_part$domain" ) and
1540not foranyaddress $header_from:
1541(
c0712871
PH
1542$thisaddress contains "$local_part@$domain" or
1543$thisaddress contains "server@" or
1544$thisaddress contains "daemon@" or
1545$thisaddress contains "root@" or
1546$thisaddress contains "listserv@" or
1547$thisaddress contains "majordomo@" or
1548$thisaddress contains "-request@" or
1549$thisaddress matches "^owner-[^@]+@"
9b371988
PH
1550)
1551.endd
1552The variable &$local_part$& contains the local part of the mail address of
1553the user whose filter file is being run &-- it is normally your login id. The
1554&$domain$& variable contains the mail domain. As explained above, if aliases
1555or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1556the current user are also done with alternative addresses.
1557
1558
1559
1560
1561.section "Testing delivery status"
1562There are two conditions that are intended mainly for use in system filter
1563files, but which are available in users' filter files as well. The condition
1564&(first_delivery)& is true if this is the first process that is attempting to
1565deliver the message, and false otherwise. This indicator is not reset until the
1566first delivery process successfully terminates; if there is a crash or a power
1567failure (for example), the next delivery attempt is also a &"first delivery"&.
1568
1569In a user filter file &(first_delivery)& will be false if there was previously
1570an error in the filter, or if a delivery for the user failed owing to, for
1571example, a quota error, or if forwarding to a remote address was deferred for
1572some reason.
1573
1574The condition &(manually_thawed)& is true if the message was &"frozen"& for
1575some reason, and was subsequently released by the system administrator. It is
1576unlikely to be of use in users' filter files.
1577
1578
1579.section "Multiple personal mailboxes" "SECTmbox"
1580The system administrator can configure Exim so that users can set up variants
1581on their email addresses and handle them separately. Consult your system
1582administrator or local documentation to see if this facility is enabled on your
1583system, and if so, what the details are.
1584
1585The facility involves the use of a prefix or a suffix on an email address. For
1586example, all mail addressed to &'lg303-'&<&'something'&> would be the property
1587of user &'lg303'&, who could determine how it was to be handled, depending on
1588the value of <&'something'&>.
1589
1590There are two possible ways in which this can be set up. The first possibility
1591is the use of multiple &_.forward_& files. In this case, mail to &'lg303-foo'&,
1592for example, is handled by looking for a file called &_.forward-foo_& in
1593&'lg303'&'s home directory. If such a file does not exist, delivery fails
1594and the message is returned to its sender.
1595
1596The alternative approach is to pass all messages through a single &_.forward_&
1597file, which must be a filter file so that it can distinguish between the
1598different cases by referencing the variables &$local_part_prefix$& or
1599&$local_part_suffix$&, as in the final example in section &<<SECTex>>& below.
1600
1601It is possible to configure Exim to support both schemes at once. In this case,
1602a specific &_.forward-foo_& file is first sought; if it is not found, the basic
1603&_.forward_& file is used.
1604
1605The &(personal)& test (see section &<<SECTpersonal>>&) includes prefixes and
1606suffixes in its checking.
1607
1608
1609
1610.section "Ignoring delivery errors"
1611As was explained above, filtering just sets up addresses for delivery &-- no
1612deliveries are actually done while a filter file is active. If any of the
1613generated addresses subsequently suffers a delivery failure, an error message
1614is generated in the normal way. However, if a filter command that sets up a
1615delivery is preceded by the word &"noerror"&, errors for that delivery,
1616and any deliveries consequent on it (that is, from alias, forwarding, or
1617filter files it invokes) are ignored.
1618
1619
1620
1621.section "Examples of Exim filter commands" "SECTex"
1622Simple forwarding:
1623
1624.code
1625# Exim filter
1626deliver baggins@rivendell.middle-earth.example
1627.endd
1628
1629Vacation handling using traditional means, assuming that the &_.vacation.msg_&
1630and other files have been set up in your home directory:
1631
1632.code
1633# Exim filter
1634unseen pipe "/usr/ucb/vacation \"$local_part\""
1635.endd
1636
1637Vacation handling inside Exim, having first created a file called
1638&_.vacation.msg_& in your home directory:
1639
1640.code
1641# Exim filter
1642if personal then vacation endif
1643.endd
1644
1645File some messages by subject:
1646
1647.code
1648# Exim filter
1649if $header_subject: contains "empire" or
1650$header_subject: contains "foundation"
1651then
1652save $home/mail/f+e
1653endif
1654.endd
1655
1656Save all non-urgent messages by weekday:
1657
1658.code
1659# Exim filter
1660if $header_subject: does not contain "urgent" and
1661$tod_full matches "^(...),"
1662then
1663save $home/mail/$1
1664endif
1665.endd
1666
1667Throw away all mail from one site, except from postmaster:
1668
1669.code
1670# Exim filter
1671if $reply_address contains "@spam.site.example" and
1672$reply_address does not contain "postmaster@"
1673then
1674seen finish
1675endif
1676.endd
1677
1678Handle multiple personal mailboxes:
1679
1680.code
1681# Exim filter
1682if $local_part_suffix is "-foo"
1683then
1684save $home/mail/foo
1685elif $local_part_suffix is "-bar"
1686then
1687save $home/mail/bar
1688endif
1689.endd
1690