(1) New Wish. (2) Typo and tabs in FAQ source.
[exim.git] / doc / doc-src / filter.src
CommitLineData
4964e932 1. $Cambridge: exim/doc/doc-src/filter.src,v 1.2 2005/01/11 15:17:51 ph10 Exp $
495ae4b0
PH
2.
3.if !set style
4.library "a4ps"
5.linelength ~~sys.linelength + 0.2in
6.emphasis ~~sys.linelength + 0.1in
7.pagedepth ~~sys.pagedepth - 0.2in
8.bindfont 53 "atl/Times-Roman" 7
9.set ssspaceb 1.50
10.fi
11
12.include "markup.sg"
13
14.set sgcal true
15.set html false
16.set texinfo false
17
18
19.if ~~sys.fancy
20.flag $sm{ "$push$g0$f53"
21.
22.else
23.pagedepth ~~sys.pagedepth - 1ld
24.linelength 75em
25.emphasis 77em
26.footdepth 0
27.disable formfeed
28.backspace none
29.set chapspaceb 24
30.set sspacea 24
31.flag $sm{ "$push"
32.fi
33
34.macro tabs 6
35.if ~~sys.fancy
36.tabset ~~1em
37.else
38.set temp (~~1 * 5)/4
39.tabset ~~temp em
40.fi
41.endm
42
43.macro startitems
44.newline
45.push
46.indent 3em
47.endm
48
49.macro enditems
50.newline
51.pop
52.endm
53
54.macro item "item"
55.newpar
56.if ~~sys.leftonpage < 5ld
57.newpage
58.fi
59.tempindent 0
60\~~1\
61.blank
62.endm
63
64.macro index
65.endm
66
67.set contents false
68.set displayindent 2em
69
70
71. ======================================================
72
73
74.if ~~sys.fancy
75.footdepth 2ld
76.foot
77$c[~~sys.pagenumber]$e
78.endfoot
79.fi
80
81
82.set chapter -1
83.chapter Exim's interfaces to mail filtering
84.space -2ld
4964e932
PH
85This document describes the user interfaces to Exim's in-built mail filtering
86facilities, and is copyright (c) University of Cambridge 2005. It corresponds
87to Exim version 4.50.
495ae4b0
PH
88.rule
89
90. ---------------------------------------------------------------------------
91. Some clever jiggery-pokery here. The contents list is known to be less than
92. one page long, so we arrange for it to get onto the rest of the first page.
93. Because we aren't doing any indexing, the z-rawindex file will contain only
94. the TOC entries. The Makefile arranges for it to be empty at the start, then
95. runs SGCAL twice so on the second pass it gets inserted automatically.
96
97.if ~~sgcal
98.space 1ld
4964e932
PH
99. $chead{Contents}
100. space 1ld
495ae4b0
PH
101.tabset 2em 2em
102.push
103.linedepth ~~sys.linedepth - 1
104.include "z-rawindex"
105.newline
106.pop
107.newpage
108.set contents true
109.fi
110. ---------------------------------------------------------------------------
111
112
113.set chapter 0
114.chapter Forwarding and filtering in Exim
115
116
117.section Introduction
118Most Unix mail transfer agents (programs that deliver mail) permit individual
119users to specify automatic forwarding of their mail, usually by placing a list
120of forwarding addresses in a file called \(.forward)\ in their home directories.
121Exim extends this facility by allowing the forwarding instructions to be a set
122of rules rather than just a list of addresses, in effect providing `\(.forward)\
123with conditions'. Operating the set of rules is called $it{filtering}, and the
124file that contains them is called a $it{filter file}.
125
126Exim supports two different kinds of filter file. An \*Exim filter*\ contains
127instructions in a format that is unique to Exim. A \*Sieve filter*\ contains
128instructions in the Sieve format that is defined by RFC 3028. As this is a
129standard format, Sieve filter files may already be familiar to some users.
130Sieve files should also be portable between different environments. However,
131the Exim filtering facility contains more features (such as variable
132expansion), and better integration with the host environment (such as the use
133of external processes and pipes).
134
135The choice of which kind of filter to use can be left to the end-user, provided
136that the system administrator has configured Exim appropriately for both kinds
137of filter. However, if interoperability is important, Sieve is the only
138choice.
139
140The ability to use filtering or traditional forwarding has to be enabled by the
141system administrator, and some of the individual facilities can be separately
142enabled or disabled. A local document should be provided to describe exactly
143what has been enabled. In the absence of this, consult your system
144administrator.
145
495ae4b0
PH
146This document describes how to use a filter file and the format of its
147contents. It is intended for use by end-users. Both Sieve filters and Exim
148filters are covered. However, for Sieve filters, only issues that relate to the
149Exim implementation are discussed, since Sieve itself is described elsewhere.
150
151The contents of traditional \(.forward)\ files are not described here. They
152normally contain just a list of addresses, file names, or pipe commands,
153separated by commas or newlines, but other types of item are also available.
154The full details can be found in the chapter on the \%redirect%\ router in the
155Exim specification, which also describes how the system administrator can set
156up and control the use of filtering.
157
4964e932
PH
158
159.em
160.section Filter operation
161It is important to realize that, in Exim, no deliveries are actually made while
162a filter or traditional \(.forward)\ file is being processed. Running a filter
163or processing a traditional \(.forward)\ file sets up future delivery
164operations, but does not carry them out.
165
166The result of filter or \(.forward)\ file processing is a list of destinations
167to which a message should be delivered. The deliveries themselves take place
168later, along with all other deliveries for the message. This means that it is
169not possible to test for successful deliveries while filtering. It also means
170that any duplicate addresses that are generated are dropped, because Exim never
171delivers the same message to the same address more than once.
172.nem
173
174
495ae4b0
PH
175.section Testing a new filter file
176.rset SECTtesting "~~chapter.~~section"
177Filter files, especially the more complicated ones, should always be tested, as
178it is easy to make mistakes. Exim provides a facility for preliminary testing
179of a filter file before installing it. This tests the syntax of the file and
180its basic operation, and can also be used with traditional \(.forward)\ files.
181
182Because a filter can do tests on the content of messages, a test message is
183required. Suppose you have a new filter file called \(myfilter)\ and a test
184message called \(test-message)\. Assuming that Exim is installed with the
185conventional path name \(/usr/sbin/sendmail)\ (some operating systems use
186\(/usr/lib/sendmail)\), the following command can be used:
187.display asis
188/usr/sbin/sendmail -bf myfilter <test-message
189.endd
190The \-bf-\ option tells Exim that the following item on the command line is the
191name of a filter file that is to be tested. There is also a \-bF-\ option,
192which is similar, but which is used for testing system filter files, as opposed
193to user filter files, and which is therefore of use only to the system
194administrator.
195
196The test message is supplied on the standard input. If there are no
197message-dependent tests in the filter, an empty file (\(/dev/null)\) can be
198used. A supplied message must start with header lines or the `From' message
199separator line which is found in many multi-message folder files. Note that
200blank lines at the start terminate the header lines. A warning is given if no
201header lines are read.
202
203The result of running this command, provided no errors are detected in the
204filter file, is a list of the actions that Exim would try to take if presented
205with the message for real.
206For example, for an Exim filter, the output
207.display asis
208Deliver message to: gulliver@lilliput.fict.example
209Save message to: /home/lemuel/mail/archive
210.endd
211means that one copy of the message would be sent to
212\gulliver@@lilliput.fict.example\, and another would be added to the file
213\(/home/lemuel/mail/archive)\, if all went well.
214
215The actions themselves are not attempted while testing a filter file in this
216way; there is no check, for example, that any forwarding addresses are valid.
217For an Exim filter,
218if you want to know why a particular action is being taken, add the \-v-\
219option to the command. This causes Exim to output the results of any
220conditional tests and to indent its output according to the depth of nesting of
221\"if"\ commands. Further additional output from a filter test can be generated
222by the \"testprint"\ command, which is described below.
223
224When Exim is outputting a list of the actions it would take, if any text
225strings are included in the output, non-printing characters therein are
226converted to escape sequences. In particular, if any text string contains a
227newline character, this is shown as `@\n' in the testing output.
228
229When testing a filter in this way, Exim makes up an `envelope' for the message.
230The recipient is by default the user running the command, and so is the sender,
231but the command can be run with the \-f-\ option to supply a different sender.
232For example,
233.display
234.indent 0
235/usr/sbin/sendmail -bf myfilter -f islington@@never.where <test-message
236.endd
237Alternatively, if the \-f-\ option is not used, but the first line of the
238supplied message is a `From' separator from a message folder file (not the same
239thing as a \"From:"\ header line), the sender is taken from there. If \-f-\ is
240present, the contents of any `From' line are ignored.
241
242The `return path' is the same as the envelope sender, unless the message
243contains a \"Return-path:"\ header, in which case it is taken from there. You
244need not worry about any of this unless you want to test out features of a
245filter file that rely on the sender address or the return path.
246
247It is possible to change the envelope recipient by specifying further options.
248The \-bfd-\ option changes the domain of the recipient address, while the
249\-bfl-\ option changes the `local part', that is, the part before the @@ sign.
250An adviser could make use of these to test someone else's filter file.
251
252The \-bfp-\ and \-bfs-\ options specify the prefix or suffix for the local part.
253These are relevant only when support for multiple personal mailboxes is
254implemented; see the description in section ~~SECTmbox below.
255
256.section Installing a filter file
257A filter file is normally installed under the name \(.forward)\ in your home
258directory -- it is distinguished from a conventional \(.forward)\ file by its
259first line (described below). However, the file name is configurable, and some
260system administrators may choose to use some different name or location for
261filter files.
262
263.section Testing an installed filter file
264Testing a filter file before installation cannot find every potential problem;
265for example, it does not actually run commands to which messages are piped.
266Some `live' tests should therefore also be done once a filter is installed.
267
268If at all possible, test your filter file by sending messages from some other
269account. If you send a message to yourself from the filtered account, and
270delivery fails, the error message will be sent back to the same account, which
271may cause another delivery failure. It won't cause an infinite sequence of such
272messages, because delivery failure messages do not themselves generate further
273messages. However, it does mean that the failure won't be returned to you, and
274also that the postmaster will have to investigate the stuck message.
275
276If you have to test an Exim filter from the same account, a sensible precaution
277is to include the line
278.display asis
279if error_message then finish endif
280.endd
281as the first filter command, at least while testing. This causes filtering to
282be abandoned for a delivery failure message, and since no destinations are
283generated, the message goes on to be delivered to the original address. Unless
284there is a good reason for not doing so, it is recommended that the above test
285be left in all Exim filter files.
286(This does not apply to Sieve files.)
287
288
289.section Details of filtering commands
290The filtering commands for Sieve and Exim filters are completely different in
291syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
292chapter we describe how it is integrated into Exim. The subsequent chapter
293covers Exim filtering commands in detail.
294
295
296.
297.
298.
299.
300.
301.chapter Sieve filter files
302.rset CHAPsievefilter "~~chapter"
303The code for Sieve filtering in Exim was contributed by Michael Haardt, and
304most of the content of this chapter is taken from the notes he provided. Since
305Sieve is a extensible language, it is important to understand `Sieve' in this
306context as `the specific implementation of Sieve for Exim'.
307
308This chapter does not contain a description of Sieve, since that can be found
309in RFC 3028, which should be read in conjunction with these notes.
310
4964e932
PH
311The Exim Sieve implementation offers the core as defined by RFC 3028,
312.em
313comparison tests, the \%copy%\, \%envelope%\, \%fileinto%\, and \%vacation%\
314extensions,
315.nem
316but not the \%reject%\ extension. Exim does not support message delivery
317notifications (MDNs), so adding it just to the Sieve filter (as required for
318\%reject%\) makes little sense.
495ae4b0
PH
319
320In order for Sieve to work properly in Exim, the system administrator needs to
321make some adjustments to the Exim configuration. These are described in the
322chapter on the \%redirect%\ router in the full Exim specification.
323
324.section Recognition of Sieve filters
325A filter file is interpreted as a Sieve filter if its first line is
326.display asis
327# Sieve filter
328.endd
329This is what distinguishes it from a conventional \(.forward)\ file or an Exim
330filter file.
331
332
333.section Saving to specified folders
334If the system administrator has set things up as suggested in the Exim
335specification, and you use \%keep%\ or \%fileinto%\ to save a mail into a
336folder, absolute files are stored where specified, relative files are stored
337relative to \$home$\, and \%inbox%\ goes to the standard mailbox location.
338
339
340.section Strings containing header names
341RFC 3028 does not specify what happens if a string denoting a header field does
342not contain a valid header name, for example, it contains a colon. This
343implementation generates an error instead of ignoring the header field in order
344to ease script debugging, which fits in the common picture of Sieve.
345
346
347.section Exists test with empty list of headers
348The \%exists%\ test succeeds only if all specified headers exist. RFC 3028
349does not explicitly specify what happens on an empty list of headers. This
350implementation evaluates that condition as true, interpreting the RFC in a
351strict sense.
352
353
354.section Header test with invalid MIME encoding in header
355Some MUAs process invalid base64 encoded data, generating junk.
356Others ignore junk after seeing an equal sign in base64 encoded data.
357RFC 2047 does not specify how to react in this case, other than stating
358that a client must not forbid to process a message for that reason.
359RFC 2045 specifies that invalid data should be ignored (apparently
360looking at end of line characters). It also specifies that invalid data
361may lead to rejecting messages containing them (and there it appears to
362talk about true encoding violations), which is a clear contradiction to
363ignoring them.
364
365RFC 3028 does not specify how to process incorrect MIME words.
366This implementation treats them literally, as it does if the word is
367correct but its character set cannot be converted to UTF-8.
368
369
370.section Address test for multiple addresses per header
371A header may contain multiple addresses. RFC 3028 does not explicitly
372specify how to deal with them, but since the address test checks if
373anything matches anything else, matching one address suffices to
374satisfy the condition. That makes it impossible to test if a header
375contains a certain set of addresses and no more, but it is more logical
376than letting the test fail if the header contains an additional address
377besides the one the test checks for.
378
379
380.section Semantics of keep
381The \%keep%\ command is equivalent to
382.display
383fileinto "inbox";
384.endd
385It saves the message and resets the implicit keep flag. It does not set the
386implicit keep flag; there is no command to set it once it has been reset.
387
388
389.section Semantics of fileinto
390RFC 3028 does not specify whether \fileinto\ should try to create a mail folder
391if it does not exist. This implementation allows the sysadmin to configure that
392aspect using the \%appendfile%\ transport options \create@_directory\,
393\create@_file\, and \file@_must@_exist\. See the \%appendfile%\ transport in
394the Exim specification for details.
395
396
397.section Semantics of redirect
398Sieve scripts are supposed to be interoperable between servers, so this
399implementation does not allow mail to be redirected to unqualified addresses,
400because the domain would depend on the system being used. On systems with
401virtual mail domains, the default domain is probably not what the user expects
402it to be.
403
404
405.section String arguments
406There has been confusion if the string arguments to \%require%\ are to be
407matched case-sensitively or not. This implementation matches them with
408the match type \":is"\ (default, see section 2.7.1) and the comparator
409\"i;ascii-casemap"\ (default, see section 2.7.3). The RFC defines the
410command defaults clearly, so any different implementations violate RFC
4113028. The same is valid for comparator names, also specified as strings.
412
413
414.section Number units
415There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
416The mistake is obvious, because RFC 3028 specifies G to denote 2@^30
417(which is gibi, not tebi), and that is what this implementation uses as
418scaling factor for the suffix G.
419
420
421.section RFC compliance
422Exim requires the first line of a Sieve filter to be
423.display asis
424# Sieve filter
425.endd
426Of course the RFC does not specify that line. Do not expect examples to work
427without adding it, though.
428
429RFC 3028 requires the use of CRLF to terminate a line.
430The rationale was that CRLF is universally used in network protocols
431to mark the end of the line. This implementation does not embed Sieve
432in a network protocol, but uses Sieve scripts as part of the Exim MTA.
433Since all parts of Exim use LF as newline character, this implementation
434does, too, by default, though the system administrator may choose (at Exim
435compile time) to use CRLF instead.
436
437Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so
438this implementation repeats this violation to stay consistent with Exim.
439This is in preparation to UTF-8 data.
440
441Sieve scripts cannot contain NUL characters in strings, but mail
442headers could contain MIME encoded NUL characters, which could never
443be matched by Sieve scripts using exact comparisons. For that reason,
444this implementation extends the Sieve quoted string syntax with @\0
445to describe a NUL character, violating @\0 being the same as 0 in
446RFC 3028. Even without using @\0, the following tests are all true in
447this implementation. Implementations that use C-style strings will only
448evaluate the first test as true.
449.display asis
450Subject: =?iso-8859-1?q?abc=00def
451
452header :contains "Subject" ["abc"]
453header :contains "Subject" ["def"]
454header :matches "Subject" ["abc?def"]
455.endd
456
457Note that by considering Sieve to be a MUA, RFC 2047 can be interpreted
458in a way that NUL characters truncating strings is allowed for Sieve
459implementations, although not recommended. It is further allowed to use
460encoded NUL characters in headers, but that's not recommended either.
461The above example shows why.
462
463RFC 3028 states that if an implementation fails to convert a character
464set to UTF-8, two strings cannot be equal if one contains octets greater
465than 127. Assuming that all unknown character sets are one-byte character
466sets with the lower 128 octets being US-ASCII is not sound, so this
467implementation violates RFC 3028 and treats such MIME words literally.
468That way at least something could be matched.
469
470The folder specified by \%fileinto%\ must not contain the character
471sequence \".."\ to avoid security problems. RFC 3028 does not specify the
472syntax of folders apart from \%keep%\ being equivalent to
473.display asis
474fileinto "INBOX";
475.endd
476This implementation uses \"inbox"\ instead.
477
478Sieve script errors currently cause messages to be silently filed into
479\"inbox"\. RFC 3028 requires that the user is notified of that condition.
480This may be implemented in future by adding a header line to mails that
481are filed into \"inbox"\ due to an error in the filter.
482
483
484.
485.
486.
487.
488.
489.chapter Exim filter files
490.rset CHAPeximfilter "~~chapter"
491This chapter contains a full description of the contents of Exim filter files.
492
493.section Format of Exim filter files
494Apart from leading white space, the first text in a filter file must be
495.display asis
496# Exim filter
497.endd
498This is what distinguishes it from a conventional \(.forward)\ file or a Sieve
499filter file. If the file does not have this initial line (or the equivalent for
500a Sieve filter), it is treated as a
501conventional \(.forward)\ file, both when delivering mail and when using the
502\-bf-\ testing mechanism. The white space in the line is optional, and any
503capitalization may be used. Further text on the same line is treated as a
504comment. For example, you could have
505.display asis
506# Exim filter <<== do not edit or remove this line!
507.endd
508The remainder of the file is a sequence of filtering commands, which consist of
509keywords and data values. For example, in the command
510.display asis
511deliver gulliver@lilliput.fict.example
512.endd
513the keyword is \"deliver"\ and the data value is
514\"gulliver@@lilliput.fict.example"\.
515White space or line breaks separate the components of a command, except in the
516case of conditions for the \"if"\ command, where round brackets (parentheses)
517also act as separators. Complete commands are separated from each other by
518white space or line breaks; there are no special terminators. Thus, several
519commands may appear on one line, or one command may be spread over a number of
520lines.
521
522If the character @# follows a separator anywhere in a command, everything from
523@# up to the next newline is ignored. This provides a way of including comments
524in a filter file.
525
526.section Data values in filter commands
527There are two ways in which a data value can be input:
528.numberpars $.
529If the text contains no white space then it can be typed verbatim. However, if
530it is part of a condition, it must also be free of round brackets
531(parentheses), as these are used for grouping in conditions.
532.nextp
533Otherwise, it must be enclosed in double quotation marks. In this case, the
534character @\ (backslash) is treated as an `escape character' within the string,
535causing the following character or characters to be treated specially:
536.display rm
537.tabs 8
538@\n $t is replaced by a newline
539@\r $t is replaced by a carriage return
540@\t $t is replaced by a tab
541.endd
542Backslash followed by up to three octal digits is replaced by the character
543specified by those digits, and @\x followed by up to two hexadecimal digits is
544treated similarly. Backslash followed by any other character is replaced
545by the second character, so that in particular, @\" becomes " and @\@\ becomes
546@\$<. A data item enclosed in double quotes can be continued onto the next line
547by ending the first line with a backslash. Any leading white space at the start
548of the continuation line is ignored.
549.endp
550In addition to the escape character processing that occurs when strings are
551enclosed in quotes, most data values are also subject to $it{string expansion}
552(as described in the next section), in which case the characters \@$\ and \@\\
553are also significant. This means that if a single backslash is actually
554required in such a string, and the string is also quoted, @\@\@\@\ has to be
555entered.
556
557The maximum permitted length of a data string, before expansion, is 1024
558characters.
559
560
561.section String expansion
562.rset SECTfilterstringexpansion "~~chapter.~~section"
563Most data values are expanded before use. Expansion consists of replacing
564substrings beginning with \"@$"\ with other text. The full expansion facilities
565available in Exim are extensive. If you want to know everything that Exim can
566do with strings, you should consult the chapter on string expansion in the Exim
567documentation.
568
569In filter files, by far the most common use of string expansion is the
570substitution of the contents of a variable. For example, the substring
571.display asis
572$reply_address
573.endd
574is replaced by the address to which replies to the message should be sent. If
575such a variable name is followed by a letter or digit or underscore, it must be
576enclosed in curly brackets (braces), for example,
577.display asis
578${reply_address}
579.endd
580If a \"@$"\ character is actually required in an expanded string, it must be
581escaped with a backslash, and because backslash is also an escape character in
582quoted input strings, it must be doubled in that case. The following two
583examples illustrate two different ways of testing for a \"@$"\ character in a
584message:
585.display asis
586if $message_body contains \$ then ...
587if $message_body contains "\\$" then ...
588.endd
589You can prevent part of a string from being expanded by enclosing it between
590two occurrences of \"@\N"\. For example,
591.display asis
592if $message_body contains \N$$$$\N then ...
593.endd
594tests for a run of four dollar characters.
595
596.section Some useful general variables
597A complete list of the available variables is given in the Exim documentation.
598This shortened list contains the ones that are most likely to be useful in
599personal filter files:
600
601\$body@_linecount$\: The number of lines in the body of the message.
602
4964e932
PH
603.em
604\$body@_zerocount$\: The number of binary zero characters in the body of the
605message.
606.nem
607
495ae4b0
PH
608\$home$\: In conventional configurations, this variable normally contains the
609user's home directory. The system administrator can, however, change this.
610
611\$local@_part$\: The part of the email address that precedes the @@ sign --
612normally the user's login name. If support for multiple personal mailboxes is
613enabled (see section ~~SECTmbox below) and a prefix or suffix for the local
614part was recognized, it is removed from the string in this variable.
615
616\$local@_part@_prefix$\: If support for multiple personal mailboxes is enabled
617(see section ~~SECTmbox below), and a local part prefix was recognized,
618this variable contains the prefix. Otherwise it contains an empty string.
619
620\$local@_part@_suffix$\: If support for multiple personal mailboxes is enabled
621(see section ~~SECTmbox below), and a local part suffix was recognized,
622this variable contains the suffix. Otherwise it contains an empty string.
623
624\$message@_body$\: The initial portion of the body of the message. By default,
625up to 500 characters are read into this variable, but the system administrator
626can configure this to some other value. Newlines in the body are converted into
627single spaces.
628
629\$message@_body@_end$\: The final portion of the body of the message, formatted
630and limited in the same way as \$message@_body$\.
631
632\$message@_body@_size$\: The size of the body of the message, in bytes.
633
634\$message@_headers$\: The header lines of the message, concatenated into a
635single string, with newline characters between them.
636
637\$message@_id$\: The message's local identification string, which is unique for
638each message handled by a single host.
639
640\$message@_size$\: The size of the entire message, in bytes.
641
642\$original@_local@_part$\: When an address that arrived with the message is
643being processed, this contains the same value as the variable \$local@_part$\.
644However, if an address generated by an alias, forward, or filter file is being
645processed, this variable contains the local part of the original address.
646
647\$reply@_address$\: The contents of the \"Reply-to:"\ header, if the message
648has one; otherwise the contents of the \"From:"\ header. It is the address to
649which normal replies to the message should be sent.
650
651\$return@_path$\: The return path -- that is, the sender field that will be
652transmitted as part of the message's envelope if the message is sent to another
653host. This is the address to which delivery errors are sent. In many cases,
654this variable has the same value as \$sender@_address$\, but if, for example,
655an incoming message to a mailing list has been expanded, \$return@_path$\ may
656have been changed to contain the address of the list maintainer.
657
658\$sender@_address$\: The sender address that was received in the envelope of
659the message. This is not necessarily the same as the contents of the \"From:"\
660or \"Sender:"\ header lines. For delivery error messages (`bounce messages')
661there is no sender address, and this variable is empty.
662
663\$tod@_full$\: A full version of the time and date, for example: Wed, 18 Oct
6641995 09:51:40 +0100. The timezone is always given as a numerical offset from
665GMT.
666
667\$tod@_log$\: The time and date in the format used for writing Exim's log files,
668without the timezone, for example: 1995-10-12 15:32:29.
669
670\$tod@_zone$\: The local timezone offset, for example: +0100.
671
672
673.section Header variables
674.rset SECTheadervariables "~~chapter.~~section"
675There is a special set of expansion variables containing the header lines of
676the message being processed. These variables have names beginning with
677\"@$header@_"\ followed by the name of the header line, terminated by a colon.
678For example,
679.display asis
680$header_from:
681$header_subject:
682.endd
683The whole item, including the terminating colon, is replaced by the contents of
684the message header line. If there is more than one header line with the same
685name, their contents are concatenated. For header lines whose data consists of
686a list of addresses (for example, ::From:: and ::To::), a comma and newline is
687inserted between each set of data. For all other header lines, just a newline
688is used.
689
690Leading and trailing white space is removed from header line data, and if there
691are any MIME `words' that are encoded as defined by RFC 2047 (because they
692contain non-ASCII characters), they are decoded and translated, if possible, to
693a local character set. Translation is attempted only on operating systems that
694have the \iconv(@)\ function. This makes the header line look the same as it
695would when displayed by an MUA. The default character set is ISO-8859-1, but
696this can be changed by means of the \"headers"\ command (see below).
697
698If you want to see the actual characters that make up a header line, you can
699specify \"@$rheader@_"\ instead of \"@$header@_"\. This inserts the `raw'
700header line, unmodified.
701
702There is also an intermediate form, requested by \"@$bheader@_"\, which removes
703leading and trailing space and decodes MIME `words', but does not do any
704character translation. If an attempt to decode what looks superficially like a
705MIME `word' fails, the raw string is returned. If decoding produces a binary
706zero character, it is replaced by a question mark.
707
708The capitalization of the name following \"@$header@_"\ is not significant.
709Because any printing character except colon may appear in the name of a
710message's header (this is a requirement of RFC 2822, the document that
711describes the format of a mail message) curly brackets must $it{not} be used in
712this case, as they will be taken as part of the header name. Two shortcuts are
713allowed in naming header variables:
714.numberpars $.
715The initiating \"@$header@_"\, \"@$rheader@_"\, or \"@$bheader@_"\ can be
716abbreviated to \"@$h@_"\, \"@$rh@_"\, or \"@$bh@_"\, respectively.
717.nextp
718The terminating colon can be omitted if the next character is white space. The
719white space character is retained in the expanded string. However, this is not
720recommended, because it makes it easy to forget the colon when it really is
721needed.
722.endp
723If the message does not contain a header of the given name, an empty string is
724substituted. Thus it is important to spell the names of headers correctly. Do
725not use \"@$header@_Reply@_to"\ when you really mean \"@$header@_Reply-to"\.
726
727.section User variables
728There are ten user variables with names \$n0$\ -- \$n9$\ that can be
729incremented by the \"add"\ command (see section ~~SECTadd). These can be used
730for `scoring' messages in various ways. If Exim is configured to run a `system
731filter' on every message, the values left in these variables are copied into
732the variables \$sn0$\ -- \$sn9$\ at the end of the system filter, thus making
733them available to users' filter files. How these values are used is entirely up
734to the individual installation.
735
736.section Current directory
737The contents of your filter file should not make any assumptions about the
738current directory. It is best to use absolute paths for file names; you
739can normally make use of the \$home$\ variable to refer to your home directory.
740The \save\ command automatically inserts \$home$\ at the start of non-absolute
741paths.
742
743
744
745.section Significant deliveries
4964e932 746.rset SECTsigdel "~~chapter.~~section"
495ae4b0 747When in the course of delivery a message is processed by a filter file, what
4964e932
PH
748happens next, that is, after the filter file has been processed, depends on
749whether or not the filter sets up any $it{significant deliveries}. If at least
750one significant delivery is set up, the filter is considered to have handled
751the entire delivery arrangements for the current address, and no further
752processing of the address takes place. If, however, no significant deliveries
753are set up, Exim continues processing the current address as if there were no
754filter file, and typically sets up a delivery of a copy of the message into a
755local mailbox. In particular, this happens in the special case of a filter file
756containing only comments.
495ae4b0
PH
757
758The delivery commands \"deliver"\, \"save"\, and \"pipe"\ are by default
759significant. However, if such a command is preceded by the word \"unseen"\, its
760delivery is not considered to be significant. In contrast, other commands such
4964e932 761as \"mail"\ and \"vacation"\ do not set up significant deliveries unless
495ae4b0
PH
762preceded by the word \"seen"\.
763
4964e932
PH
764.em
765The following example commands set up significant deliveries:
766.display asis
767deliver jack@beanstalk.example
768pipe $home/bin/mymailscript
769seen mail subject "message discarded"
770seen finish
771.endd
772The following example commands do not set up significant deliveries:
773.display asis
774unseen deliver jack@beanstalk.example
775unseen pipe $home/bin/mymailscript
776mail subject "message discarded"
777finish
778.endd
779.nem
780
495ae4b0
PH
781
782.section Filter commands
4964e932 783The filter commands that are described in subsequent sections are listed
495ae4b0
PH
784below, with the section in which they are described in brackets:
785.display rm
786.tabs 15
787\add\ $t increment a user variable (section ~~SECTadd)
788\deliver\ $t deliver to an email address (section ~~SECTdeliver)
789\fail\ $t force delivery failure (sysadmin use) (section ~~SECTfail)
790\finish\ $t end processing (section ~~SECTfinish)
791\freeze\ $t freeze message (sysadmin use) (section ~~SECTfreeze)
792\headers\ $t set the header character set (section ~~SECTheaders)
793\if\ $t test condition(s) (section ~~SECTif)
794\logfile\ $t define log file (section ~~SECTlog)
795\logwrite\ $t write to log file (section ~~SECTlog)
796\mail\ $t send a reply message (section ~~SECTmail)
797\pipe\ $t pipe to a command (section ~~SECTpipe)
798\save\ $t save to a file (section ~~SECTsave)
799\testprint\ $t print while testing (section ~~SECTtestprint)
800\vacation\ $t tailored form of \mail\ (section ~~SECTmail)
801.endd
4964e932
PH
802.em
803The \"headers"\ command has additional parameters that can be used only in a
804system filter. The \"fail"\ and \"freeze"\ commands are available only when
805Exim's filtering facilities are being used as a system filter, and are
806therefore usable only by the system administrator and not by ordinary users.
807They are mentioned only briefly in this document; for more information, see the
808main Exim specification.
809.nem
495ae4b0
PH
810
811.section The add command
812.rset SECTadd "~~chapter.~~section"
813.display
814 add <<number>> to <<user variable>>
815e.g. add 2 to n3
816.endd
4964e932
PH
817There are 10 user variables of this type, with names \"n0"\ -- \"n9"\. Their
818values can be obtained by the normal expansion syntax (for example \$n3$\) in
819other commands. At the start of filtering, these variables all contain zero.
820Both arguments of the \"add"\ command are expanded before use, making it
821possible to add variables to each other. Subtraction can be obtained by adding
822negative numbers.
495ae4b0
PH
823
824
825.section The deliver command
826.rset SECTdeliver "~~chapter.~~section"
827.display
828 deliver <<mail address>>
829e.g. deliver "Dr Livingstone <David@@somewhere.africa.example>"
830.endd
4964e932
PH
831This command provides a forwarding operation.
832.em
833The delivery that it sets up is significant unless the command is preceded by
834\"unseen"\ (see section ~~SECTsigdel).
835.nem
836The message is sent on to the given address, exactly as happens if the address
837had appeared in a traditional \(.forward)\ file. If you want to deliver the
838message to a number of different addresses, you can use more than one
839\"deliver"\ command (each one may have only one address). However, duplicate
840addresses are discarded.
495ae4b0
PH
841
842To deliver a copy of the message to your normal mailbox, your login name can be
843given as the address. Once an address has been processed by the filtering
844mechanism, an identical generated address will not be so processed again, so
845doing this does not cause a loop.
846
847However, if you have a mail alias, you should $it{not} refer to it here. For
4964e932
PH
848example, if the mail address \"L.Gulliver"\ is aliased to \"lg303"\ then all
849references in Gulliver's \(.forward)\ file should be to \"lg303"\. A reference
495ae4b0
PH
850to the alias will not work for messages that are addressed to that alias,
851since, like \(.forward)\ file processing, aliasing is performed only once on an
852address, in order to avoid looping.
853
854Following the new address, an optional second address, preceded by
855\"errors@_to"\ may appear. This changes the address to which delivery errors on
856the forwarded message will be sent. Instead of going to the message's original
857sender, they go to this new address. For ordinary users, the only value that is
858permitted for this address is the user whose filter file is being processed.
4964e932 859For example, the user \"lg303"\ whose mailbox is in the domain
495ae4b0
PH
860\lilliput.example\ could have a filter file that contains
861.display asis
4964e932 862 deliver jon@elsewhere.example errors_to lg303@lilliput.example
495ae4b0
PH
863.endd
864Clearly, using this feature makes sense only in situations where not all
865messages are being forwarded. In particular, bounce messages must not be
866forwarded in this way, as this is likely to create a mail loop if something
867goes wrong.
868
869
870.section The save command
871.rset SECTsave "~~chapter.~~section"
872.display
873 save <<file name>>
874e.g. save @$home/mail/bookfolder
875.endd
4964e932
PH
876.em
877This command specifies that a copy of the message is to be appended to the
878given file (that is, the file is to be used as a mail folder). The delivery
879that \"save"\ sets up is significant unless the command is preceded by
880\"unseen"\ (see section ~~SECTsigdel).
881.nem
882More than one \"save"\ command may be obeyed; each one causes a copy of the
883message to be written to its argument file, provided they are different
884(duplicate \"save"\ commands are ignored).
495ae4b0
PH
885
886If the file name does not start with a / character, the contents of the
887\$home$\ variable are prepended, unless it is empty. In conventional
888configurations, this variable is normally set in a user filter to the user's
889home directory, but the system administrator may set it to some other path. In
890some configurations, \$home$\ may be unset, in which case a non-absolute path
891name may be generated. Such configurations convert this to an absolute path
892when the delivery takes place. In a system filter, \$home$\ is never set.
893
894The user must of course have permission to write to the file, and the writing
895of the file takes place in a process that is running as the user, under the
896user's primary group. Any secondary groups to which the user may belong are not
897normally taken into account, though the system administrator can configure Exim
898to set them up. In addition, the ability to use this command at all is
899controlled by the system administrator -- it may be forbidden on some systems.
900
901An optional mode value may be given after the file name. The value for the mode
902is interpreted as an octal number, even if it does not begin with a zero. For
903example:
904.display
905 save /some/folder 640
906.endd
907This makes it possible for users to override the system-wide mode setting for
908file deliveries, which is normally 600. If an existing file does not have the
909correct mode, it is changed.
910
911An alternative form of delivery may be enabled on your system, in which each
912message is delivered into a new file in a given directory. If this is the case,
913this functionality can be requested by giving the directory name terminated by
914a slash after the \"save"\ command, for example
915.display
916 save separated/messages/
917.endd
918There are several different formats for such deliveries; check with your system
919administrator or local documentation to find out which (if any) are available
920on your system. If this functionality is not enabled, the use of a path name
921ending in a slash causes an error.
922
923
924.section The pipe command
925.rset SECTpipe "~~chapter.~~section"
926.display
927 pipe <<command>>
928e.g. pipe "@$home/bin/countmail @$sender@_address"
929.endd
4964e932
PH
930.em
931This command specifies that the message is to be delivered to the specified
932command using a pipe. The delivery that it sets up is significant unless the
933command is preceded by \"unseen"\ (see section ~~SECTsigdel).
934.nem
935Remember, however, that no deliveries are done while the filter is being
936processed. All deliveries happen later on. Therefore, the result of running the
937pipe is not available to the filter.
495ae4b0
PH
938
939When the deliveries are done, a separate process is run, and a copy of the
940message is passed on its standard input. The process runs as the user, under
941the user's primary group. Any secondary groups to which the user may belong are
942not normally taken into account, though the system administrator can configure
943Exim to set them up. More than one \"pipe"\ command may appear; each one causes
944a copy of the message to be written to its argument pipe, provided they are
945different (duplicate \"pipe"\ commands are ignored).
946
947When the time comes to transport the message,
948the command supplied to \"pipe"\ is split up by Exim into a command name and a
949number of arguments. These are delimited by white space except for arguments
950enclosed in double quotes, in which case backslash is interpreted as an escape,
951or in single quotes, in which case no escaping is recognized. Note that as the
952whole command is normally supplied in double quotes, a second level of quoting
953is required for internal double quotes. For example:
954.display asis
955 pipe "$home/myscript \"size is $message_size\""
956.endd
957String expansion is performed on the separate components after the line has
958been split up, and the command is then run directly by Exim; it is not run
959under a shell. Therefore, substitution cannot change the number of arguments,
960nor can quotes, backslashes or other shell metacharacters in variables cause
961confusion.
962
963Documentation for some programs that are normally run via this kind of pipe
964often suggest that the command should start with
965.display asis
966IFS=" "
967.endd
968This is a shell command, and should $it{not} be present in Exim filter files,
969since it does not normally run the command under a shell.
970
971However, there is an option that the administrator can set to cause a shell to
972be used. In this case, the entire command is expanded as a single string and
973passed to the shell for interpretation. It is recommended that this be avoided
974if at all possible, since it can lead to problems when inserted variables
975contain shell metacharacters.
976
977The default \\PATH\\ set up for the command is determined by the system
978administrator, usually containing at least \/usr/bin\ so that common commands
979are available without having to specify an absolute file name. However, it is
980possible for the system administrator to restrict the pipe facility so that the
981command name must not contain any / characters, and must be found in one of the
982directories in the configured \\PATH\\. It is also possible for the system
983administrator to lock out the use of the \"pipe"\ command altogether.
984
985When the command is run, a number of environment variables are set up. The
986complete list for pipe deliveries may be found in the Exim reference manual.
987Those that may be useful for pipe deliveries from user filter files are:
988.display
989.tabs 20
990DOMAIN $t $rm{the domain of the address}
991HOME $t $rm{your home directory}
992LOCAL@_PART $t $rm{see below}
993LOCAL@_PART@_PREFIX $t $rm{see below}
994LOCAL@_PART@_SUFFIX $t $rm{see below}
995LOGNAME $t $rm{your login name}
996MESSAGE@_ID $t $rm{the message's unique id}
997PATH $t $rm{the command search path}
998RECIPIENT $t $rm{the complete recipient address}
999SENDER $t $rm{the sender of the message}
1000SHELL $t $bf{/bin/sh}
1001USER $t $rm{see below}
1002.endd
1003\\LOCAL@_PART\\, \\LOGNAME\\, and \\USER\\ are all set to the same value,
1004namely, your login id. \\LOCAL@_PART@_PREFIX\\ and \\LOCAL@_PART@_SUFFIX\\ may
1005be set if Exim is configured to recognize prefixes or suffixes in the local
1006parts of addresses. For example, a message addressed to
1007\*pat-suf2@@domain.example*\ may cause user \*pat*\'s filter file to be run. If
1008this sets up a pipe delivery, \\LOCAL@_PART@_SUFFIX\\ is \"-suf2"\ when the
1009pipe command runs. The system administrator has to configure Exim specially for
1010this feature to be available.
1011
1012If you run a command that is a shell script, be very careful in your use of
1013data from the incoming message in the commands in your script. RFC 2822 is very
1014generous in the characters that are legally permitted to appear in mail
1015addresses, and in particular, an address may begin with a vertical bar or a
1016slash. For this reason you should always use quotes round any arguments that
1017involve data from the message, like this:
1018.display asis
1019/some/command '$SENDER'
1020.endd
1021so that inserted shell meta-characters do not cause unwanted effects.
1022
1023Remember that, as was explained earlier, the pipe command is not run at the
1024time the filter file is interpreted. The filter just defines what deliveries
1025are required for one particular addressee of a message. The deliveries
1026themselves happen later, once Exim has decided everything that needs to be done
1027for the message.
1028
1029A consequence of this is that you cannot inspect the return code from the pipe
1030command from within the filter. Nevertheless, the code returned by the command
1031is important, because Exim uses it to decide whether the delivery has succeeded
1032or failed.
1033
1034The command should return a zero completion code if all has gone well. Most
1035non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1036treated as a delivery failure, causing the message to be returned to its
4964e932 1037sender. However, there are some completion codes that are treated as temporary
495ae4b0
PH
1038errors. The message remains on Exim's spool disk, and the delivery is tried
1039again later, though it will ultimately time out if the delivery failures go on
1040too long. The completion codes to which this applies can be specified by the
1041system administrator; the default values are 73 and 75.
1042
1043The pipe command should not normally write anything to its standard output or
1044standard error file descriptors. If it does, whatever is written is normally
1045returned to the sender of the message as a delivery error, though this action
1046can be varied by the system administrator.
1047
1048
1049.section Mail commands
1050.rset SECTmail "~~chapter.~~section"
4964e932 1051There are two commands that cause the creation of a new mail message, neither
495ae4b0 1052of which count as a significant delivery unless the command is preceded by the
4964e932
PH
1053word \"seen"\ (see section ~~SECTsigdel). This is a powerful facility, but it
1054should be used with care, because of the danger of creating infinite sequences
1055of messages. The system administrator can forbid the use of these commands
1056altogether.
495ae4b0
PH
1057
1058To help prevent runaway message sequences, these commands have no effect when
4964e932
PH
1059the incoming message is a bounce (delivery error) message, and messages sent by
1060this means are treated as if they were reporting delivery errors. Thus, they
1061should never themselves cause a bounce message to be returned. The basic
495ae4b0
PH
1062mail-sending command is
1063.display
1064 mail [to <<address-list>>]
1065 [cc <<address-list>>]
1066 [bcc <<address-list>>]
1067 [from <<address>>]
1068 [reply@_to <<address>>]
1069 [subject <<text>>]
1070 [extra@_headers <<text>>]
1071 [text <<text>>]
1072 [[expand] file <<filename>>]
1073 [return message]
1074 [log <<log file name>>]
1075 [once <<note file name>>]
1076 [once@_repeat <<time interval>>]
1077.blank
1078e.g. mail text "Your message about @$h@_subject: has been received"
1079.endd
1080
1081Each <<address-list>> can contain a number of addresses, separated by commas,
1082in the format of a ::To:: or ::Cc:: header line. In fact, the text you supply
4964e932 1083here is copied exactly into the appropriate header line. It may contain
495ae4b0
PH
1084additional information as well as email addresses. For example:
1085.display asis
1086mail to "Julius Caesar <jc@rome.example>, \
1087 <ma@rome.example> (Mark A.)"
1088.endd
4964e932 1089Similarly, the texts supplied for \"from"\ and \"reply@_to"\ are copied into
495ae4b0
PH
1090their respective header lines.
1091
1092As a convenience for use in one common case, there is also a command called
1093\vacation\. It behaves in the same way as \mail\, except that the defaults for
1094the
1095\"subject"\,
1096\"file"\, \"log"\, \"once"\, and \"once@_repeat"\ options are
1097.display
1098subject "On vacation"
1099expand file .vacation.msg
1100log .vacation.log
1101once .vacation
1102once@_repeat 7d
1103.endd
1104respectively. These are the same file names and repeat period used by the
1105traditional Unix \"vacation"\ command. The defaults can be overridden by
1106explicit settings, but if a file name is given its contents are expanded only
1107if explicitly requested.
1108
1109\**Warning**\: The \"vacation"\ command should always be used conditionally,
1110subject to at least the \"personal"\ condition (see section ~~SECTpersonal
1111below) so as not to send automatic replies to non-personal messages from
1112mailing lists or elsewhere. Sending an automatic response to a mailing list or
1113a mailing list manager is an Internet Sin.
1114
1115For both commands, the key/value argument pairs can appear in any order. At
4964e932
PH
1116least one of \"text"\ or \"file"\ must appear (except with \"vacation"\, where
1117there is a default for \"file"\); if both are present, the text string appears
1118first in the message. If \"expand"\ precedes \"file"\, each line of the file is
1119subject to string expansion before it is included in the message.
495ae4b0
PH
1120
1121Several lines of text can be supplied to \"text"\ by including the escape
4964e932 1122sequence `@\n' in the string wherever a newline is required. If the command is
495ae4b0
PH
1123output during filter file testing, newlines in the text are shown as `@\n'.
1124
1125Note that the keyword for creating a \"Reply-To:"\ header is \reply@_to\,
1126because Exim keywords may contain underscores, but not hyphens. If the \"from"\
1127keyword is present and the given address does not match the user who owns the
1128forward file, Exim normally adds a \"Sender:"\ header to the message,
1129though it can be configured not to do this.
1130
1131The \extra@_headers\ keyword allows you to add custom header lines to the
1132message. The text supplied must be one or more syntactically valid RFC 2882
1133header lines. You can use `@\n' within quoted text to specify newlines between
1134headers, and also to define continued header lines. For example:
1135.display asis
1136extra_headers "h1: first\nh2: second\n continued\nh3: third"
1137.endd
1138No newline should appear at the end of the final header line.
1139
1140If no \"to"\ argument appears, the message is sent to the address in the
1141\"@$reply@_address"\ variable (see section ~~SECTfilterstringexpansion above).
1142An \"In-Reply-To:"\ header is automatically included in the created message,
1143giving a reference to the message identification of the incoming message.
1144
1145If \"return message"\ is specified, the incoming message that caused the filter
1146file to be run is added to the end of the message, subject to a maximum size
1147limitation.
1148
1149If a log file is specified, a line is added to it for each message sent.
1150
1151If a \"once"\ file is specified, it is used to hold a database for remembering
1152who has received a message, and no more than one message is ever sent to any
1153particular address, unless \"once@_repeat"\ is set. This specifies a time
1154interval after which another copy of the message is sent. The interval is
1155specified as a sequence of numbers, each followed by the initial letter of one
1156of `seconds', `minutes', `hours', `days', or `weeks'. For example,
1157.display asis
1158once_repeat 5d4h
1159.endd
1160causes a new message to be sent if 5 days and 4 hours have elapsed since the
1161last one was sent. There must be no white space in a time interval.
1162
1163Commonly, the file name specified for \"once"\ is used as the base name for
1164direct-access (DBM) file operations. There are a number of different DBM
1165libraries in existence. Some operating systems provide one as a default, but
1166even in this case a different one may have been used when building Exim. With
1167some DBM libraries, specifying \"once"\ results in two files being created,
1168with the suffixes \".dir"\ and \".pag"\ being added to the given name. With
1169some others a single file with the suffix \".db"\ is used, or the name is used
1170unchanged.
1171
1172Using a DBM file for implementing the \"once"\ feature means that the file
1173grows as large as necessary. This is not usually a problem, but some system
1174administrators want to put a limit on it. The facility can be configured not to
1175use a DBM file, but instead, to use a regular file with a maximum size. The
1176data in such a file is searched sequentially, and if the file fills up, the
1177oldest entry is deleted to make way for a new one. This means that some
1178correspondents may receive a second copy of the message after an unpredictable
1179interval. Consult your local information to see if your system is configured
1180this way.
1181
1182More than one \"mail"\ or \"vacation"\ command may be obeyed in a single filter
1183run; they are all honoured, even when they are to the same recipient.
1184
1185
1186.section Logging commands
1187.rset SECTlog "~~chapter.~~section"
1188A log can be kept of actions taken by a filter file. This facility is normally
1189available in conventional configurations, but there are some situations where
1190it might not be. Also, the system administrator may choose to disable it. Check
1191your local information if in doubt.
1192
1193Logging takes place while the filter file is being interpreted. It does not
1194queue up for later like the delivery commands. The reason for this is so that a
1195log file need be opened only once for several write operations. There are two
1196commands, neither of which constitutes a significant delivery. The first
1197defines a file to which logging output is subsequently written:
1198.display
1199 logfile <<file name>>
1200e.g. logfile @$home/filter.log
1201.endd
1202The file name must be fully qualified. You can use \$home$\, as in this
1203example, to refer to your home directory. The file name may optionally be
1204followed by a mode for the file, which is used if the file has to be created.
1205For example,
1206.display
1207 logfile @$home/filter.log 0644
1208.endd
1209The number is interpreted as octal, even if it does not begin with a zero.
1210The default for the mode is 600. It is suggested that the \"logfile"\ command
1211normally appear as the first command in a filter file. Once \"logfile"\ has
1212been obeyed, the \"logwrite"\ command can be used to write to the log file:
1213.display
1214 logwrite "<<some text string>>"
1215e.g. logwrite "@$tod@_log @$message@_id processed"
1216.endd
1217It is possible to have more than one \"logfile"\ command, to specify writing to
1218different log files in different circumstances. Writing takes place at the end
1219of the file, and a newline character is added to the end of each string if
1220there isn't one already there. Newlines can be put in the middle of the string
1221by using the `@\n' escape sequence. Lines from simultaneous deliveries may get
1222interleaved in the file, as there is no interlocking, so you should plan your
1223logging with this in mind. However, data should not get lost.
1224
1225
1226.section The finish command
1227.rset SECTfinish "~~chapter.~~section"
1228The command \"finish"\, which has no arguments, causes Exim to stop
1229interpreting the filter file. This is not a significant action unless preceded
1230by \"seen"\. A filter file containing only \"seen finish"\ is a black hole.
1231
1232.section The testprint command
1233.rset SECTtestprint "~~chapter.~~section"
1234It is sometimes helpful to be able to print out the values of variables when
1235testing filter files. The command
1236.display
1237 testprint <<text>>
1238e.g. testprint "home=@$home reply@_address=@$reply@_address"
1239.endd
1240does nothing when mail is being delivered. However, when the filtering code is
1241being tested by means of the \-bf-\ option (see section ~~SECTtesting above),
1242the value of the string is written to the standard output.
1243
1244.section The fail command
1245.rset SECTfail "~~chapter.~~section"
1246When Exim's filtering facilities are being used as a system filter, the
1247\"fail"\ command is available, to force delivery failure. Because this command
1248is normally usable only by the system administrator, and not enabled for use by
1249ordinary users, it is described in more detail in the main Exim specification
1250rather than in this document.
1251
1252.section The freeze command
1253.rset SECTfreeze "~~chapter.~~section"
1254When Exim's filtering facilities are being used as a system filter, the
1255\"freeze"\ command is available, to freeze a message on the queue. Because this
1256command is normally usable only by the system administrator, and not enabled
1257for use by ordinary users, it is described in more detail in the main Exim
1258specification rather than in this document.
1259
1260
1261.section The headers command
1262.rset SECTheaders "~~chapter.~~section"
4964e932 1263The \"headers"\ command can be used to change the target character set that is
495ae4b0
PH
1264used when translating the contents of encoded header lines for insertion by the
1265\"@$header@_"\ mechanism (see section ~~SECTheadervariables above). The default
1266can be set in the Exim configuration; if not specified, ISO-8859-1 is used. The
4964e932
PH
1267only currently supported format for the \"headers"\ command
1268.em
1269in user filters
1270.nem
1271is as in this example:
495ae4b0
PH
1272.display asis
1273headers charset "UTF-8"
1274.endd
1275That is, \"headers"\ is followed by the word \"charset"\ and then the name of a
1276character set. This particular example would be useful if you wanted to compare
1277the contents of a header to a UTF-8 string.
1278
4964e932
PH
1279.em
1280In system filter files, the \"headers"\ command can be used to add or remove
1281header lines from the message. These features are described in the main Exim
1282specification.
1283.nem
1284
1285
495ae4b0
PH
1286
1287.section Obeying commands conditionally
1288.rset SECTif "~~chapter.~~section"
1289Most of the power of filtering comes from the ability to test conditions and
1290obey different commands depending on the outcome. The \"if"\ command is used to
1291specify conditional execution, and its general form is
1292.display
1293if <<condition>>
1294then <<commands>>
1295elif <<condition>>
1296then <<commands>>
1297else <<commands>>
1298endif
1299.endd
1300There may be any number of \"elif"\ and \"then"\ sections (including none) and
1301the \"else"\ section is also optional. Any number of commands, including nested
1302\"if"\ commands, may appear in any of the <<commands>> sections.
1303
1304Conditions can be combined by using the words \"and"\ and \"or"\, and round
1305brackets (parentheses) can be used to specify how several conditions are to
1306combine. Without brackets, \"and"\ is more binding than \"or"\.
1307For example,
1308.display asis
1309if
1310 $h_subject: contains "Make money" or
1311 $h_precedence: is "junk" or
1312 ($h_sender: matches ^\\d{8}@ and not personal) or
1313 $message_body contains "this is spam"
1314then
1315 seen finish
1316endif
1317.endd
1318A condition can be preceded by \"not"\ to negate it, and there are also some
1319negative forms of condition that are more English-like.
1320
1321
1322
1323.section String testing conditions
1324There are a number of conditions that operate on text strings, using the words
4964e932
PH
1325`begins', `ends', `is', `contains' and `matches'. If you want to apply the same
1326test to more than one header line, you can easily concatenate them into a
1327single string for testing, as in this example:
495ae4b0
PH
1328.display asis
1329if "$h_to:, $h_cc:" contains me@domain.example then ...
1330.endd
1331
4964e932
PH
1332If a string-testing condition name is written in lower case, the testing
1333of letters is done without regard to case; if it is written in upper case
1334(for example, `CONTAINS'), the case of letters is taken into account.
495ae4b0
PH
1335.display
1336 <<text1>> begins <<text2>>
1337 <<text1>> does not begin <<text2>>
1338e.g. @$header@_from: begins "Friend@@"
1339.endd
1340A `begins' test checks for the presence of the second string at the start of
1341the first, both strings having been expanded.
1342.display
1343 <<text1>> ends <<text2>>
1344 <<text1>> does not end <<text2>>
1345e.g. @$header@_from: ends "@public.com.example"
1346.endd
1347An `ends' test checks for the presence of the second string at the end of
1348the first, both strings having been expanded.
1349.display
1350 <<text1>> is <<text2>>
1351 <<text1>> is not <<text2>>
1352e.g. @$local@_part@_suffix is "-foo"
1353.endd
1354An `is' test does an exact match between the strings, having first expanded
1355both strings.
1356.display
1357 <<text1>> contains <<text2>>
1358 <<text1>> does not contain <<text2>>
1359e.g. @$header@_subject: contains "evolution"
1360.endd
1361A `contains' test does a partial string match, having expanded both strings.
1362.display
1363 <<text1>> matches <<text2>>
1364 <<text1>> does not match <<text2>>
1365e.g. @$sender@_address matches "(bill|john)@@"
1366.endd
1367For a `matches' test, after expansion of both strings, the second one is
1368interpreted as a regular expression. Exim uses the PCRE regular expression
1369library, which provides regular expressions that are compatible with Perl.
1370
495ae4b0
PH
1371The match succeeds if the regular expression matches any part of the first
1372string. If you want a regular expression to match only at the start or end of
1373the subject string, you must encode that requirement explicitly, using the @^
1374or @$ metacharacters. The above example, which is not so constrained, matches
1375all these addresses:
1376.display asis
1377bill@test.example
1378john@some.example
1379spoonbill@example.com
1380littlejohn@example.com
1381.endd
1382To match only the first two, you could use this:
1383.display asis
1384if $sender_address matches "^(bill|john)@" then ...
1385.endd
495ae4b0
PH
1386
1387Care must be taken if you need a backslash in a regular expression, because
1388backslashes are interpreted as escape characters both by the string expansion
1389code and by Exim's normal processing of strings in quotes. For example, if you
1390want to test the sender address for a domain ending in \".com"\ the regular
1391expression is
1392.display asis
1393\.com$
1394.endd
1395The backslash and dollar sign in that expression have to be escaped when used
1396in a filter command, as otherwise they would be interpreted by the expansion
1397code. Thus what you actually write is
1398.display asis
1399if $sender_address matches \\.com\$
1400.endd
1401An alternative way of handling this is to make use of the \"@\N"\ expansion
1402flag for suppressing expansion:
1403.display asis
1404if $sender_address matches \N\.com$\N
1405.endd
1406Everything between the two occurrences of \"@\N"\ is copied without change by
1407the string expander (and in fact you do not need the final one, because it is
1408at the end of the string).
1409
1410If the regular expression is given in quotes (mandatory only if it contains
1411white space) you have to write either
1412.display asis
1413if $sender_address matches "\\\\.com\\$"
1414.endd
1415or
1416.display asis
1417if $sender_address matches "\\N\\.com$\\N"
1418.endd
1419
495ae4b0
PH
1420If the regular expression contains bracketed sub-expressions, numeric
1421variable substitutions such as \$1$\ can be used in the subsequent actions
1422after a successful match. If the match fails, the values of the numeric
4964e932
PH
1423variables remain unchanged. Previous values are not restored after \"endif"\.
1424In other words, only one set of values is ever available. If the condition
495ae4b0
PH
1425contains several sub-conditions connected by \"and"\ or \"or"\, it is the
1426strings extracted from the last successful match that are available in
1427subsequent actions. Numeric variables from any one sub-condition are also
4964e932 1428available for use in subsequent sub-conditions, because string expansion of a
495ae4b0
PH
1429condition occurs just before it is tested.
1430
1431.section Numeric testing conditions
1432The following conditions are available for performing numerical tests:
1433.display
1434 <<number1>> is above <<number2>>
1435 <<number1>> is not above <<number2>>
1436 <<number1>> is below <<number2>>
1437 <<number1>> is not below <<number2>>
1438e.g. @$message@_size is not above 10k
1439.endd
1440The <<number>> arguments must expand to strings of digits, optionally followed
1441by one of the letters K or M (upper case or lower case) which cause
1442multiplication by 1024 and 1024x1024 respectively.
1443
1444.section Testing for significant deliveries
4964e932
PH
1445You can use the \"delivered"\ condition to test whether or not any previously
1446obeyed filter commands have set up a significant delivery. For example:
495ae4b0
PH
1447.display asis
1448if not delivered then save mail/anomalous endif
1449.endd
1450
1451.section Testing for error messages
4964e932
PH
1452The condition \"error@_message"\ is true if the incoming message is a bounce
1453(mail delivery error) message. Putting the command
495ae4b0
PH
1454.display asis
1455if error_message then finish endif
1456.endd
1457at the head of your filter file is a useful insurance against things going
4964e932
PH
1458wrong in such a way that you cannot receive delivery error reports. \**Note**\:
1459\"error@_message"\ is a condition, not an expansion variable, and therefore is
1460not preceded by \@$\.
495ae4b0
PH
1461
1462.section Testing a list of addresses
1463There is a facility for looping through a list of addresses and applying a
1464condition to each of them. It takes the form
1465.display
1466foranyaddress <<string>> (<<condition>>)
1467.endd
1468where <<string>> is interpreted as a list of RFC 2822 addresses, as in a
1469typical header line, and <<condition>> is any valid filter condition or
1470combination of conditions. The `group' syntax that is defined for certain
1471header lines that contain addresses is supported.
1472
1473The parentheses surrounding the condition are mandatory, to delimit it from
1474possible further sub-conditions of the enclosing \"if"\ command. Within the
1475condition, the expansion variable \$thisaddress$\ is set to the non-comment
1476portion of each of the addresses in the string in turn. For example, if the
1477string is
1478.display asis
1479B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1480.endd
1481then \$thisaddress$\ would take on the values \"bart@@sfld.example"\ and
1482\"lisa@@sfld.example"\ in turn.
1483
1484If there are no valid addresses in the list, the whole condition is false. If
1485the internal condition is true for any one address, the overall condition is
1486true and the loop ends. If the internal condition is false for all addresses in
1487the list, the overall condition is false. This example tests for the presence
1488of an eight-digit local part in any address in a \To:\ header:
1489.display asis
1490if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1491.endd
1492When the overall condition is true, the value of \$thisaddress$\ in the
1493commands that follow \"then"\ is the last value it took on inside the loop. At
1494the end of the \"if"\ command, the value of \$thisaddress$\ is reset to what it
1495was before. It is best to avoid the use of multiple occurrences of
1496\"foranyaddress"\, nested or otherwise, in a single \"if"\ command, if the
1497value of \$thisaddress$\ is to be used afterwards, because it isn't always
1498clear what the value will be. Nested \"if"\ commands should be used instead.
1499
1500Header lines can be joined together if a check is to be applied to more than
1501one of them. For example:
1502.display asis
1503if foranyaddress $h_to:,$h_cc: ....
1504.endd
1505scans through the addresses in both the \To:\ and the \Cc:\ headers.
1506
4964e932
PH
1507.section Testing for personal mail
1508.rset SECTpersonal "~~chapter.~~section"
1509A common requirement is to distinguish between incoming personal mail and mail
1510from a mailing list, or from a robot or other automatic process (for example, a
1511bounce message). In particular, this test is normally required for `vacation
1512messages'.
1513
1514.em
1515The \"personal"\ condition checks that the message is not a bounce message and
1516that the current user's email address appears in the \"To:"\ header. It also
1517checks that the sender is not the current user or one of a number of common
1518daemons, and that there are no header lines starting \"List-"\ in the message.
1519Finally, it checks the content of the \"Precedence:"\ header line, if there is
1520one.
1521
1522You should always use the \"personal"\ condition when generating automatic
1523responses.
1524.nem
1525This example shows the use of \"personal"\ in a filter file that is sending out
1526vacation messages:
1527.display asis
1528if personal then
1529 mail
1530 to $reply_address
1531.newline
1532.em
1533 subject "I am on holiday"
1534.nem
1535.newline
1536 file $home/vacation/message
1537 once $home/vacation/once
1538 once_repeat 10d
1539endif
1540.endd
1541.em
1542It is tempting, when writing commands like the above, to quote the original
1543subject in the reply. For example:
1544.display asis
1545subject "Re: $h_subject:"
1546.endd
1547There is a danger in doing this, however. It may allow a third party to
1548subscribe you to an opt-in mailing list, provided that the list accepts bounce
1549messages as subscription confirmations. (Messages sent from filters are always
1550sent as bounce messages.) Well-managed lists require a non-bounce message to
1551confirm a subscription, so the danger is relatively small.
1552
1553If prefixes or suffixes are in use for local parts -- something which depends
1554on the configuration of Exim (see section ~~SECTmbox below) -- the tests for
1555the current user are done with the full address (including the prefix and
1556suffix, if any) as well as with the prefix and suffix removed. If the system is
1557configured to rewrite local parts of mail addresses, for example, to rewrite
1558`dag46' as `Dirk.Gently', the rewritten form of the address is also used in the
1559tests.
1560.nem
1561
1562.em
1563.section Alias addresses for the personal condition
1564It is quite common for people who have mail accounts on a number of different
1565systems to forward all their mail to one system, and in this case a check for
1566personal mail should test all their various mail addresses. To allow for this,
1567the \"personal"\ condition keyword can be followed by
1568.display
1569alias <<address>>
1570.endd
1571any number of times, for example
1572.display asis
1573if personal alias smith@else.where.example
1574 alias jones@other.place.example
1575then ...
1576.endd
1577The alias addresses are treated as alternatives to the current user's email
1578address when testing the contents of header lines.
1579.nem
1580
1581
1582.em
1583.section Details of the personal condition
1584The basic \"personal"\ test is roughly equivalent to the following:
1585.display flow asis
1586not error_message and
1587$message_headers does not contain "\nList-" and
1588$header_auto-submitted: does not contain "auto-" and
1589$header_precedence: does not contain "bulk" and
1590$header_precedence: does not contain "list" and
1591$header_precedence: does not contain "junk" and
1592foranyaddress $header_to:
1593 ( $thisaddress contains "$local_part@$domain" ) and
1594not foranyaddress $header_from:
1595 (
1596 $thisaddress contains "$local_part@domain" or
1597 $thisaddress contains "server@" or
1598 $thisaddress contains "daemon@" or
1599 $thisaddress contains "root@" or
1600 $thisaddress contains "listserv@" or
1601 $thisaddress contains "majordomo@" or
1602 $thisaddress contains "-request@" or
1603 $thisaddress matches "^owner-[^@]+@"
1604 )
1605.endd
1606The variable \$local@_part$\ contains the local part of the mail address of
1607the user whose filter file is being run -- it is normally your login id. The
1608\$domain$\ variable contains the mail domain. As explained above, if aliases
1609or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1610the current user are also done with alternative addresses.
1611.nem
1612
1613
1614.section Testing delivery status
1615There are two conditions that are intended mainly for use in system filter
1616files, but which are available in users' filter files as well. The condition
1617\"first@_delivery"\ is true if this is the first process that is attempting to
1618deliver the message, and false otherwise. This indicator is not reset until the
1619first delivery process successfully terminates; if there is a crash or a power
1620failure (for example), the next delivery attempt is also a `first delivery'.
1621
1622In a user filter file \"first@_delivery"\ will be false only if
1623there was previously an error in the filter, or if a delivery for the user
1624failed owing to, for example, a quota error, or if forwarding to a remote
1625address was deferred for some reason.
1626
1627The condition \"manually@_thawed"\ is true only if the message was `frozen' for
1628some reason, and was subsequently released by the system administrator. It is
1629unlikely to be of use in users' filter files.
1630
495ae4b0
PH
1631.section Multiple personal mailboxes
1632.rset SECTmbox "~~chapter.~~section"
1633The system administrator can configure Exim so that users can set up variants
1634on their email addresses and handle them separately. Consult your system
1635administrator or local documentation to see if this facility is enabled on your
1636system, and if so, what the details are.
1637
1638The facility involves the use of a prefix or a suffix on an email address. For
4964e932
PH
1639example, all mail addressed to \lg303-<<something>>\ would be the property of
1640user \lg303\, who could determine how it was to be handled, depending on the
495ae4b0
PH
1641value of <<something>>.
1642
1643There are two possible ways in which this can be set up. The first possibility
4964e932 1644is the use of multiple \(.forward)\ files. In this case, mail to \lg303-foo\,
495ae4b0 1645for example, is handled by looking for a file called \.forward-foo\ in
4964e932 1646\lg303's\ home directory. If such a file does not exist, delivery fails and the
495ae4b0
PH
1647message is returned to its sender.
1648
1649The alternative approach is to pass all messages through a single \(.forward)\
4964e932
PH
1650file, which must be a filter file so that it can distinguish between the
1651different cases by referencing the variables \$local@_part@_prefix$\ or
1652\$local@_part@_suffix$\, as in the final example in section ~~SECTex below.
495ae4b0
PH
1653
1654It is possible to configure Exim to support both schemes at once. In this case,
1655a specific \.forward-foo\ file is first sought; if it is not found, the basic
1656\(.forward)\ file is used.
1657
1658The \"personal"\ test (see section ~~SECTpersonal) includes prefixes and
1659suffixes in its checking.
1660
1661
1662.section Ignoring delivery errors
1663As was explained above, filtering just sets up addresses for delivery -- no
1664deliveries are actually done while a filter file is active. If any of the
1665generated addresses subsequently suffers a delivery failure, an error message
4964e932 1666is generated in the normal way. However, if a filter command that sets up a
495ae4b0
PH
1667delivery is preceded by the word \"noerror"\, errors for that delivery,
1668$it{and any deliveries consequent on it} (that is, from alias, forwarding, or
1669filter files it invokes) are ignored.
1670
1671
1672.section Examples of Exim filter commands
1673.rset SECTex "~~chapter.~~section"
1674Simple forwarding:
1675.display asis
1676# Exim filter
1677deliver baggins@rivendell.middle-earth.example
1678.endd
1679Vacation handling using traditional means, assuming that the \.vacation.msg\
1680and other files have been set up in your home directory:
1681.display asis
1682# Exim filter
1683unseen pipe "/usr/ucb/vacation \"$local_part\""
1684.endd
1685Vacation handling inside Exim, having first created a file called
1686\.vacation.msg\ in your home directory:
1687.display asis
1688# Exim filter
1689if personal then vacation endif
1690.endd
1691File some messages by subject:
1692.display asis
1693# Exim filter
1694if $header_subject: contains "empire" or
1695 $header_subject: contains "foundation"
1696then
1697 save $home/mail/f+e
1698endif
1699.endd
1700Save all non-urgent messages by weekday:
1701.display asis
1702# Exim filter
1703if $header_subject: does not contain "urgent" and
1704 $tod_full matches "^(...),"
1705then
1706 save $home/mail/$1
1707endif
1708.endd
1709Throw away all mail from one site, except from postmaster:
1710.display asis
1711# Exim filter
1712if $reply_address contains "@spam.site.example" and
1713 $reply_address does not contain "postmaster@"
1714then
1715 seen finish
1716endif
1717.endd
1718.if ~~sgcal
1719.if ~~sys.leftonpage < 6ld
1720.newpage
1721.fi
1722.fi
1723Handle multiple personal mailboxes
1724.display asis
1725# Exim filter
1726if $local_part_suffix is "-foo"
1727then
1728 save $home/mail/foo
1729elif $local_part_suffix is "-bar"
1730then
1731 save $home/mail/bar
1732endif
1733.endd
1734
1735. End of filter