Updated filter source; preliminary update of ACL chapter and addition of
[exim.git] / doc / doc-src / filter.src
1 . $Cambridge: exim/doc/doc-src/filter.src,v 1.2 2005/01/11 15:17:51 ph10 Exp $
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82 .set chapter -1
83 .chapter Exim's interfaces to mail filtering
84 .space -2ld
85 This document describes the user interfaces to Exim's in-built mail filtering
86 facilities, and is copyright (c) University of Cambridge 2005. It corresponds
87 to Exim version 4.50.
88 .rule
90 . ---------------------------------------------------------------------------
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110 . ---------------------------------------------------------------------------
113 .set chapter 0
114 .chapter Forwarding and filtering in Exim
117 .section Introduction
118 Most Unix mail transfer agents (programs that deliver mail) permit individual
119 users to specify automatic forwarding of their mail, usually by placing a list
120 of forwarding addresses in a file called \(.forward)\ in their home directories.
121 Exim extends this facility by allowing the forwarding instructions to be a set
122 of rules rather than just a list of addresses, in effect providing `\(.forward)\
123 with conditions'. Operating the set of rules is called $it{filtering}, and the
124 file that contains them is called a $it{filter file}.
126 Exim supports two different kinds of filter file. An \*Exim filter*\ contains
127 instructions in a format that is unique to Exim. A \*Sieve filter*\ contains
128 instructions in the Sieve format that is defined by RFC 3028. As this is a
129 standard format, Sieve filter files may already be familiar to some users.
130 Sieve files should also be portable between different environments. However,
131 the Exim filtering facility contains more features (such as variable
132 expansion), and better integration with the host environment (such as the use
133 of external processes and pipes).
135 The choice of which kind of filter to use can be left to the end-user, provided
136 that the system administrator has configured Exim appropriately for both kinds
137 of filter. However, if interoperability is important, Sieve is the only
138 choice.
140 The ability to use filtering or traditional forwarding has to be enabled by the
141 system administrator, and some of the individual facilities can be separately
142 enabled or disabled. A local document should be provided to describe exactly
143 what has been enabled. In the absence of this, consult your system
144 administrator.
146 This document describes how to use a filter file and the format of its
147 contents. It is intended for use by end-users. Both Sieve filters and Exim
148 filters are covered. However, for Sieve filters, only issues that relate to the
149 Exim implementation are discussed, since Sieve itself is described elsewhere.
151 The contents of traditional \(.forward)\ files are not described here. They
152 normally contain just a list of addresses, file names, or pipe commands,
153 separated by commas or newlines, but other types of item are also available.
154 The full details can be found in the chapter on the \%redirect%\ router in the
155 Exim specification, which also describes how the system administrator can set
156 up and control the use of filtering.
159 .em
160 .section Filter operation
161 It is important to realize that, in Exim, no deliveries are actually made while
162 a filter or traditional \(.forward)\ file is being processed. Running a filter
163 or processing a traditional \(.forward)\ file sets up future delivery
164 operations, but does not carry them out.
166 The result of filter or \(.forward)\ file processing is a list of destinations
167 to which a message should be delivered. The deliveries themselves take place
168 later, along with all other deliveries for the message. This means that it is
169 not possible to test for successful deliveries while filtering. It also means
170 that any duplicate addresses that are generated are dropped, because Exim never
171 delivers the same message to the same address more than once.
172 .nem
175 .section Testing a new filter file
176 .rset SECTtesting "~~chapter.~~section"
177 Filter files, especially the more complicated ones, should always be tested, as
178 it is easy to make mistakes. Exim provides a facility for preliminary testing
179 of a filter file before installing it. This tests the syntax of the file and
180 its basic operation, and can also be used with traditional \(.forward)\ files.
182 Because a filter can do tests on the content of messages, a test message is
183 required. Suppose you have a new filter file called \(myfilter)\ and a test
184 message called \(test-message)\. Assuming that Exim is installed with the
185 conventional 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
190 The \-bf-\ option tells Exim that the following item on the command line is the
191 name of a filter file that is to be tested. There is also a \-bF-\ option,
192 which is similar, but which is used for testing system filter files, as opposed
193 to user filter files, and which is therefore of use only to the system
194 administrator.
196 The test message is supplied on the standard input. If there are no
197 message-dependent tests in the filter, an empty file (\(/dev/null)\) can be
198 used. A supplied message must start with header lines or the `From' message
199 separator line which is found in many multi-message folder files. Note that
200 blank lines at the start terminate the header lines. A warning is given if no
201 header lines are read.
203 The result of running this command, provided no errors are detected in the
204 filter file, is a list of the actions that Exim would try to take if presented
205 with the message for real.
206 For example, for an Exim filter, the output
207 .display asis
208 Deliver message to: gulliver@lilliput.fict.example
209 Save message to: /home/lemuel/mail/archive
210 .endd
211 means 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.
215 The actions themselves are not attempted while testing a filter file in this
216 way; there is no check, for example, that any forwarding addresses are valid.
217 For an Exim filter,
218 if you want to know why a particular action is being taken, add the \-v-\
219 option to the command. This causes Exim to output the results of any
220 conditional 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
222 by the \"testprint"\ command, which is described below.
224 When Exim is outputting a list of the actions it would take, if any text
225 strings are included in the output, non-printing characters therein are
226 converted to escape sequences. In particular, if any text string contains a
227 newline character, this is shown as `@\n' in the testing output.
229 When testing a filter in this way, Exim makes up an `envelope' for the message.
230 The recipient is by default the user running the command, and so is the sender,
231 but the command can be run with the \-f-\ option to supply a different sender.
232 For example,
233 .display
234 .indent 0
235 /usr/sbin/sendmail -bf myfilter -f islington@@never.where <test-message
236 .endd
237 Alternatively, if the \-f-\ option is not used, but the first line of the
238 supplied message is a `From' separator from a message folder file (not the same
239 thing as a \"From:"\ header line), the sender is taken from there. If \-f-\ is
240 present, the contents of any `From' line are ignored.
242 The `return path' is the same as the envelope sender, unless the message
243 contains a \"Return-path:"\ header, in which case it is taken from there. You
244 need not worry about any of this unless you want to test out features of a
245 filter file that rely on the sender address or the return path.
247 It is possible to change the envelope recipient by specifying further options.
248 The \-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.
250 An adviser could make use of these to test someone else's filter file.
252 The \-bfp-\ and \-bfs-\ options specify the prefix or suffix for the local part.
253 These are relevant only when support for multiple personal mailboxes is
254 implemented; see the description in section ~~SECTmbox below.
256 .section Installing a filter file
257 A filter file is normally installed under the name \(.forward)\ in your home
258 directory -- it is distinguished from a conventional \(.forward)\ file by its
259 first line (described below). However, the file name is configurable, and some
260 system administrators may choose to use some different name or location for
261 filter files.
263 .section Testing an installed filter file
264 Testing a filter file before installation cannot find every potential problem;
265 for example, it does not actually run commands to which messages are piped.
266 Some `live' tests should therefore also be done once a filter is installed.
268 If at all possible, test your filter file by sending messages from some other
269 account. If you send a message to yourself from the filtered account, and
270 delivery fails, the error message will be sent back to the same account, which
271 may cause another delivery failure. It won't cause an infinite sequence of such
272 messages, because delivery failure messages do not themselves generate further
273 messages. However, it does mean that the failure won't be returned to you, and
274 also that the postmaster will have to investigate the stuck message.
276 If you have to test an Exim filter from the same account, a sensible precaution
277 is to include the line
278 .display asis
279 if error_message then finish endif
280 .endd
281 as the first filter command, at least while testing. This causes filtering to
282 be abandoned for a delivery failure message, and since no destinations are
283 generated, the message goes on to be delivered to the original address. Unless
284 there is a good reason for not doing so, it is recommended that the above test
285 be left in all Exim filter files.
286 (This does not apply to Sieve files.)
289 .section Details of filtering commands
290 The filtering commands for Sieve and Exim filters are completely different in
291 syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
292 chapter we describe how it is integrated into Exim. The subsequent chapter
293 covers Exim filtering commands in detail.
296 .
297 .
298 .
299 .
300 .
301 .chapter Sieve filter files
302 .rset CHAPsievefilter "~~chapter"
303 The code for Sieve filtering in Exim was contributed by Michael Haardt, and
304 most of the content of this chapter is taken from the notes he provided. Since
305 Sieve is a extensible language, it is important to understand `Sieve' in this
306 context as `the specific implementation of Sieve for Exim'.
308 This chapter does not contain a description of Sieve, since that can be found
309 in RFC 3028, which should be read in conjunction with these notes.
311 The Exim Sieve implementation offers the core as defined by RFC 3028,
312 .em
313 comparison tests, the \%copy%\, \%envelope%\, \%fileinto%\, and \%vacation%\
314 extensions,
315 .nem
316 but not the \%reject%\ extension. Exim does not support message delivery
317 notifications (MDNs), so adding it just to the Sieve filter (as required for
318 \%reject%\) makes little sense.
320 In order for Sieve to work properly in Exim, the system administrator needs to
321 make some adjustments to the Exim configuration. These are described in the
322 chapter on the \%redirect%\ router in the full Exim specification.
324 .section Recognition of Sieve filters
325 A filter file is interpreted as a Sieve filter if its first line is
326 .display asis
327 # Sieve filter
328 .endd
329 This is what distinguishes it from a conventional \(.forward)\ file or an Exim
330 filter file.
333 .section Saving to specified folders
334 If the system administrator has set things up as suggested in the Exim
335 specification, and you use \%keep%\ or \%fileinto%\ to save a mail into a
336 folder, absolute files are stored where specified, relative files are stored
337 relative to \$home$\, and \%inbox%\ goes to the standard mailbox location.
340 .section Strings containing header names
341 RFC 3028 does not specify what happens if a string denoting a header field does
342 not contain a valid header name, for example, it contains a colon. This
343 implementation generates an error instead of ignoring the header field in order
344 to ease script debugging, which fits in the common picture of Sieve.
347 .section Exists test with empty list of headers
348 The \%exists%\ test succeeds only if all specified headers exist. RFC 3028
349 does not explicitly specify what happens on an empty list of headers. This
350 implementation evaluates that condition as true, interpreting the RFC in a
351 strict sense.
354 .section Header test with invalid MIME encoding in header
355 Some MUAs process invalid base64 encoded data, generating junk.
356 Others ignore junk after seeing an equal sign in base64 encoded data.
357 RFC 2047 does not specify how to react in this case, other than stating
358 that a client must not forbid to process a message for that reason.
359 RFC 2045 specifies that invalid data should be ignored (apparently
360 looking at end of line characters). It also specifies that invalid data
361 may lead to rejecting messages containing them (and there it appears to
362 talk about true encoding violations), which is a clear contradiction to
363 ignoring them.
365 RFC 3028 does not specify how to process incorrect MIME words.
366 This implementation treats them literally, as it does if the word is
367 correct but its character set cannot be converted to UTF-8.
370 .section Address test for multiple addresses per header
371 A header may contain multiple addresses. RFC 3028 does not explicitly
372 specify how to deal with them, but since the address test checks if
373 anything matches anything else, matching one address suffices to
374 satisfy the condition. That makes it impossible to test if a header
375 contains a certain set of addresses and no more, but it is more logical
376 than letting the test fail if the header contains an additional address
377 besides the one the test checks for.
380 .section Semantics of keep
381 The \%keep%\ command is equivalent to
382 .display
383 fileinto "inbox";
384 .endd
385 It saves the message and resets the implicit keep flag. It does not set the
386 implicit keep flag; there is no command to set it once it has been reset.
389 .section Semantics of fileinto
390 RFC 3028 does not specify whether \fileinto\ should try to create a mail folder
391 if it does not exist. This implementation allows the sysadmin to configure that
392 aspect using the \%appendfile%\ transport options \create@_directory\,
393 \create@_file\, and \file@_must@_exist\. See the \%appendfile%\ transport in
394 the Exim specification for details.
397 .section Semantics of redirect
398 Sieve scripts are supposed to be interoperable between servers, so this
399 implementation does not allow mail to be redirected to unqualified addresses,
400 because the domain would depend on the system being used. On systems with
401 virtual mail domains, the default domain is probably not what the user expects
402 it to be.
405 .section String arguments
406 There has been confusion if the string arguments to \%require%\ are to be
407 matched case-sensitively or not. This implementation matches them with
408 the 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
410 command defaults clearly, so any different implementations violate RFC
411 3028. The same is valid for comparator names, also specified as strings.
414 .section Number units
415 There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
416 The 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
418 scaling factor for the suffix G.
421 .section RFC compliance
422 Exim requires the first line of a Sieve filter to be
423 .display asis
424 # Sieve filter
425 .endd
426 Of course the RFC does not specify that line. Do not expect examples to work
427 without adding it, though.
429 RFC 3028 requires the use of CRLF to terminate a line.
430 The rationale was that CRLF is universally used in network protocols
431 to mark the end of the line. This implementation does not embed Sieve
432 in a network protocol, but uses Sieve scripts as part of the Exim MTA.
433 Since all parts of Exim use LF as newline character, this implementation
434 does, too, by default, though the system administrator may choose (at Exim
435 compile time) to use CRLF instead.
437 Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so
438 this implementation repeats this violation to stay consistent with Exim.
439 This is in preparation to UTF-8 data.
441 Sieve scripts cannot contain NUL characters in strings, but mail
442 headers could contain MIME encoded NUL characters, which could never
443 be matched by Sieve scripts using exact comparisons. For that reason,
444 this implementation extends the Sieve quoted string syntax with @\0
445 to describe a NUL character, violating @\0 being the same as 0 in
446 RFC 3028. Even without using @\0, the following tests are all true in
447 this implementation. Implementations that use C-style strings will only
448 evaluate the first test as true.
449 .display asis
450 Subject: =?iso-8859-1?q?abc=00def
452 header :contains "Subject" ["abc"]
453 header :contains "Subject" ["def"]
454 header :matches "Subject" ["abc?def"]
455 .endd
457 Note that by considering Sieve to be a MUA, RFC 2047 can be interpreted
458 in a way that NUL characters truncating strings is allowed for Sieve
459 implementations, although not recommended. It is further allowed to use
460 encoded NUL characters in headers, but that's not recommended either.
461 The above example shows why.
463 RFC 3028 states that if an implementation fails to convert a character
464 set to UTF-8, two strings cannot be equal if one contains octets greater
465 than 127. Assuming that all unknown character sets are one-byte character
466 sets with the lower 128 octets being US-ASCII is not sound, so this
467 implementation violates RFC 3028 and treats such MIME words literally.
468 That way at least something could be matched.
470 The folder specified by \%fileinto%\ must not contain the character
471 sequence \".."\ to avoid security problems. RFC 3028 does not specify the
472 syntax of folders apart from \%keep%\ being equivalent to
473 .display asis
474 fileinto "INBOX";
475 .endd
476 This implementation uses \"inbox"\ instead.
478 Sieve script errors currently cause messages to be silently filed into
479 \"inbox"\. RFC 3028 requires that the user is notified of that condition.
480 This may be implemented in future by adding a header line to mails that
481 are filed into \"inbox"\ due to an error in the filter.
484 .
485 .
486 .
487 .
488 .
489 .chapter Exim filter files
490 .rset CHAPeximfilter "~~chapter"
491 This chapter contains a full description of the contents of Exim filter files.
493 .section Format of Exim filter files
494 Apart from leading white space, the first text in a filter file must be
495 .display asis
496 # Exim filter
497 .endd
498 This is what distinguishes it from a conventional \(.forward)\ file or a Sieve
499 filter file. If the file does not have this initial line (or the equivalent for
500 a Sieve filter), it is treated as a
501 conventional \(.forward)\ file, both when delivering mail and when using the
502 \-bf-\ testing mechanism. The white space in the line is optional, and any
503 capitalization may be used. Further text on the same line is treated as a
504 comment. For example, you could have
505 .display asis
506 # Exim filter <<== do not edit or remove this line!
507 .endd
508 The remainder of the file is a sequence of filtering commands, which consist of
509 keywords and data values. For example, in the command
510 .display asis
511 deliver gulliver@lilliput.fict.example
512 .endd
513 the keyword is \"deliver"\ and the data value is
514 \"gulliver@@lilliput.fict.example"\.
515 White space or line breaks separate the components of a command, except in the
516 case of conditions for the \"if"\ command, where round brackets (parentheses)
517 also act as separators. Complete commands are separated from each other by
518 white space or line breaks; there are no special terminators. Thus, several
519 commands may appear on one line, or one command may be spread over a number of
520 lines.
522 If 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
524 in a filter file.
526 .section Data values in filter commands
527 There are two ways in which a data value can be input:
528 .numberpars $.
529 If the text contains no white space then it can be typed verbatim. However, if
530 it 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
533 Otherwise, it must be enclosed in double quotation marks. In this case, the
534 character @\ (backslash) is treated as an `escape character' within the string,
535 causing 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
542 Backslash followed by up to three octal digits is replaced by the character
543 specified by those digits, and @\x followed by up to two hexadecimal digits is
544 treated similarly. Backslash followed by any other character is replaced
545 by 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
547 by ending the first line with a backslash. Any leading white space at the start
548 of the continuation line is ignored.
549 .endp
550 In addition to the escape character processing that occurs when strings are
551 enclosed 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 \@\\
553 are also significant. This means that if a single backslash is actually
554 required in such a string, and the string is also quoted, @\@\@\@\ has to be
555 entered.
557 The maximum permitted length of a data string, before expansion, is 1024
558 characters.
561 .section String expansion
562 .rset SECTfilterstringexpansion "~~chapter.~~section"
563 Most data values are expanded before use. Expansion consists of replacing
564 substrings beginning with \"@$"\ with other text. The full expansion facilities
565 available in Exim are extensive. If you want to know everything that Exim can
566 do with strings, you should consult the chapter on string expansion in the Exim
567 documentation.
569 In filter files, by far the most common use of string expansion is the
570 substitution of the contents of a variable. For example, the substring
571 .display asis
572 $reply_address
573 .endd
574 is replaced by the address to which replies to the message should be sent. If
575 such a variable name is followed by a letter or digit or underscore, it must be
576 enclosed in curly brackets (braces), for example,
577 .display asis
578 ${reply_address}
579 .endd
580 If a \"@$"\ character is actually required in an expanded string, it must be
581 escaped with a backslash, and because backslash is also an escape character in
582 quoted input strings, it must be doubled in that case. The following two
583 examples illustrate two different ways of testing for a \"@$"\ character in a
584 message:
585 .display asis
586 if $message_body contains \$ then ...
587 if $message_body contains "\\$" then ...
588 .endd
589 You can prevent part of a string from being expanded by enclosing it between
590 two occurrences of \"@\N"\. For example,
591 .display asis
592 if $message_body contains \N$$$$\N then ...
593 .endd
594 tests for a run of four dollar characters.
596 .section Some useful general variables
597 A complete list of the available variables is given in the Exim documentation.
598 This shortened list contains the ones that are most likely to be useful in
599 personal filter files:
601 \$body@_linecount$\: The number of lines in the body of the message.
603 .em
604 \$body@_zerocount$\: The number of binary zero characters in the body of the
605 message.
606 .nem
608 \$home$\: In conventional configurations, this variable normally contains the
609 user's home directory. The system administrator can, however, change this.
611 \$local@_part$\: The part of the email address that precedes the @@ sign --
612 normally the user's login name. If support for multiple personal mailboxes is
613 enabled (see section ~~SECTmbox below) and a prefix or suffix for the local
614 part was recognized, it is removed from the string in this variable.
616 \$local@_part@_prefix$\: If support for multiple personal mailboxes is enabled
617 (see section ~~SECTmbox below), and a local part prefix was recognized,
618 this variable contains the prefix. Otherwise it contains an empty string.
620 \$local@_part@_suffix$\: If support for multiple personal mailboxes is enabled
621 (see section ~~SECTmbox below), and a local part suffix was recognized,
622 this variable contains the suffix. Otherwise it contains an empty string.
624 \$message@_body$\: The initial portion of the body of the message. By default,
625 up to 500 characters are read into this variable, but the system administrator
626 can configure this to some other value. Newlines in the body are converted into
627 single spaces.
629 \$message@_body@_end$\: The final portion of the body of the message, formatted
630 and limited in the same way as \$message@_body$\.
632 \$message@_body@_size$\: The size of the body of the message, in bytes.
634 \$message@_headers$\: The header lines of the message, concatenated into a
635 single string, with newline characters between them.
637 \$message@_id$\: The message's local identification string, which is unique for
638 each message handled by a single host.
640 \$message@_size$\: The size of the entire message, in bytes.
642 \$original@_local@_part$\: When an address that arrived with the message is
643 being processed, this contains the same value as the variable \$local@_part$\.
644 However, if an address generated by an alias, forward, or filter file is being
645 processed, this variable contains the local part of the original address.
647 \$reply@_address$\: The contents of the \"Reply-to:"\ header, if the message
648 has one; otherwise the contents of the \"From:"\ header. It is the address to
649 which normal replies to the message should be sent.
651 \$return@_path$\: The return path -- that is, the sender field that will be
652 transmitted as part of the message's envelope if the message is sent to another
653 host. This is the address to which delivery errors are sent. In many cases,
654 this variable has the same value as \$sender@_address$\, but if, for example,
655 an incoming message to a mailing list has been expanded, \$return@_path$\ may
656 have been changed to contain the address of the list maintainer.
658 \$sender@_address$\: The sender address that was received in the envelope of
659 the message. This is not necessarily the same as the contents of the \"From:"\
660 or \"Sender:"\ header lines. For delivery error messages (`bounce messages')
661 there is no sender address, and this variable is empty.
663 \$tod@_full$\: A full version of the time and date, for example: Wed, 18 Oct
664 1995 09:51:40 +0100. The timezone is always given as a numerical offset from
665 GMT.
667 \$tod@_log$\: The time and date in the format used for writing Exim's log files,
668 without the timezone, for example: 1995-10-12 15:32:29.
670 \$tod@_zone$\: The local timezone offset, for example: +0100.
673 .section Header variables
674 .rset SECTheadervariables "~~chapter.~~section"
675 There is a special set of expansion variables containing the header lines of
676 the message being processed. These variables have names beginning with
677 \"@$header@_"\ followed by the name of the header line, terminated by a colon.
678 For example,
679 .display asis
680 $header_from:
681 $header_subject:
682 .endd
683 The whole item, including the terminating colon, is replaced by the contents of
684 the message header line. If there is more than one header line with the same
685 name, their contents are concatenated. For header lines whose data consists of
686 a list of addresses (for example, ::From:: and ::To::), a comma and newline is
687 inserted between each set of data. For all other header lines, just a newline
688 is used.
690 Leading and trailing white space is removed from header line data, and if there
691 are any MIME `words' that are encoded as defined by RFC 2047 (because they
692 contain non-ASCII characters), they are decoded and translated, if possible, to
693 a local character set. Translation is attempted only on operating systems that
694 have the \iconv(@)\ function. This makes the header line look the same as it
695 would when displayed by an MUA. The default character set is ISO-8859-1, but
696 this can be changed by means of the \"headers"\ command (see below).
698 If you want to see the actual characters that make up a header line, you can
699 specify \"@$rheader@_"\ instead of \"@$header@_"\. This inserts the `raw'
700 header line, unmodified.
702 There is also an intermediate form, requested by \"@$bheader@_"\, which removes
703 leading and trailing space and decodes MIME `words', but does not do any
704 character translation. If an attempt to decode what looks superficially like a
705 MIME `word' fails, the raw string is returned. If decoding produces a binary
706 zero character, it is replaced by a question mark.
708 The capitalization of the name following \"@$header@_"\ is not significant.
709 Because any printing character except colon may appear in the name of a
710 message's header (this is a requirement of RFC 2822, the document that
711 describes the format of a mail message) curly brackets must $it{not} be used in
712 this case, as they will be taken as part of the header name. Two shortcuts are
713 allowed in naming header variables:
714 .numberpars $.
715 The initiating \"@$header@_"\, \"@$rheader@_"\, or \"@$bheader@_"\ can be
716 abbreviated to \"@$h@_"\, \"@$rh@_"\, or \"@$bh@_"\, respectively.
717 .nextp
718 The terminating colon can be omitted if the next character is white space. The
719 white space character is retained in the expanded string. However, this is not
720 recommended, because it makes it easy to forget the colon when it really is
721 needed.
722 .endp
723 If the message does not contain a header of the given name, an empty string is
724 substituted. Thus it is important to spell the names of headers correctly. Do
725 not use \"@$header@_Reply@_to"\ when you really mean \"@$header@_Reply-to"\.
727 .section User variables
728 There are ten user variables with names \$n0$\ -- \$n9$\ that can be
729 incremented by the \"add"\ command (see section ~~SECTadd). These can be used
730 for `scoring' messages in various ways. If Exim is configured to run a `system
731 filter' on every message, the values left in these variables are copied into
732 the variables \$sn0$\ -- \$sn9$\ at the end of the system filter, thus making
733 them available to users' filter files. How these values are used is entirely up
734 to the individual installation.
736 .section Current directory
737 The contents of your filter file should not make any assumptions about the
738 current directory. It is best to use absolute paths for file names; you
739 can normally make use of the \$home$\ variable to refer to your home directory.
740 The \save\ command automatically inserts \$home$\ at the start of non-absolute
741 paths.
745 .section Significant deliveries
746 .rset SECTsigdel "~~chapter.~~section"
747 When in the course of delivery a message is processed by a filter file, what
748 happens next, that is, after the filter file has been processed, depends on
749 whether or not the filter sets up any $it{significant deliveries}. If at least
750 one significant delivery is set up, the filter is considered to have handled
751 the entire delivery arrangements for the current address, and no further
752 processing of the address takes place. If, however, no significant deliveries
753 are set up, Exim continues processing the current address as if there were no
754 filter file, and typically sets up a delivery of a copy of the message into a
755 local mailbox. In particular, this happens in the special case of a filter file
756 containing only comments.
758 The delivery commands \"deliver"\, \"save"\, and \"pipe"\ are by default
759 significant. However, if such a command is preceded by the word \"unseen"\, its
760 delivery is not considered to be significant. In contrast, other commands such
761 as \"mail"\ and \"vacation"\ do not set up significant deliveries unless
762 preceded by the word \"seen"\.
764 .em
765 The following example commands set up significant deliveries:
766 .display asis
767 deliver jack@beanstalk.example
768 pipe $home/bin/mymailscript
769 seen mail subject "message discarded"
770 seen finish
771 .endd
772 The following example commands do not set up significant deliveries:
773 .display asis
774 unseen deliver jack@beanstalk.example
775 unseen pipe $home/bin/mymailscript
776 mail subject "message discarded"
777 finish
778 .endd
779 .nem
782 .section Filter commands
783 The filter commands that are described in subsequent sections are listed
784 below, 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\ $t tailored form of \mail\ (section ~~SECTmail)
801 .endd
802 .em
803 The \"headers"\ command has additional parameters that can be used only in a
804 system filter. The \"fail"\ and \"freeze"\ commands are available only when
805 Exim's filtering facilities are being used as a system filter, and are
806 therefore usable only by the system administrator and not by ordinary users.
807 They are mentioned only briefly in this document; for more information, see the
808 main Exim specification.
809 .nem
811 .section The add command
812 .rset SECTadd "~~chapter.~~section"
813 .display
814 add <<number>> to <<user variable>>
815 e.g. add 2 to n3
816 .endd
817 There are 10 user variables of this type, with names \"n0"\ -- \"n9"\. Their
818 values can be obtained by the normal expansion syntax (for example \$n3$\) in
819 other commands. At the start of filtering, these variables all contain zero.
820 Both arguments of the \"add"\ command are expanded before use, making it
821 possible to add variables to each other. Subtraction can be obtained by adding
822 negative numbers.
825 .section The deliver command
826 .rset SECTdeliver "~~chapter.~~section"
827 .display
828 deliver <<mail address>>
829 e.g. deliver "Dr Livingstone <David@@somewhere.africa.example>"
830 .endd
831 This command provides a forwarding operation.
832 .em
833 The delivery that it sets up is significant unless the command is preceded by
834 \"unseen"\ (see section ~~SECTsigdel).
835 .nem
836 The message is sent on to the given address, exactly as happens if the address
837 had appeared in a traditional \(.forward)\ file. If you want to deliver the
838 message to a number of different addresses, you can use more than one
839 \"deliver"\ command (each one may have only one address). However, duplicate
840 addresses are discarded.
842 To deliver a copy of the message to your normal mailbox, your login name can be
843 given as the address. Once an address has been processed by the filtering
844 mechanism, an identical generated address will not be so processed again, so
845 doing this does not cause a loop.
847 However, if you have a mail alias, you should $it{not} refer to it here. For
848 example, if the mail address \"L.Gulliver"\ is aliased to \"lg303"\ then all
849 references in Gulliver's \(.forward)\ file should be to \"lg303"\. A reference
850 to the alias will not work for messages that are addressed to that alias,
851 since, like \(.forward)\ file processing, aliasing is performed only once on an
852 address, in order to avoid looping.
854 Following the new address, an optional second address, preceded by
855 \"errors@_to"\ may appear. This changes the address to which delivery errors on
856 the forwarded message will be sent. Instead of going to the message's original
857 sender, they go to this new address. For ordinary users, the only value that is
858 permitted for this address is the user whose filter file is being processed.
859 For example, the user \"lg303"\ whose mailbox is in the domain
860 \lilliput.example\ could have a filter file that contains
861 .display asis
862 deliver jon@elsewhere.example errors_to lg303@lilliput.example
863 .endd
864 Clearly, using this feature makes sense only in situations where not all
865 messages are being forwarded. In particular, bounce messages must not be
866 forwarded in this way, as this is likely to create a mail loop if something
867 goes wrong.
870 .section The save command
871 .rset SECTsave "~~chapter.~~section"
872 .display
873 save <<file name>>
874 e.g. save @$home/mail/bookfolder
875 .endd
876 .em
877 This command specifies that a copy of the message is to be appended to the
878 given file (that is, the file is to be used as a mail folder). The delivery
879 that \"save"\ sets up is significant unless the command is preceded by
880 \"unseen"\ (see section ~~SECTsigdel).
881 .nem
882 More than one \"save"\ command may be obeyed; each one causes a copy of the
883 message to be written to its argument file, provided they are different
884 (duplicate \"save"\ commands are ignored).
886 If the file name does not start with a / character, the contents of the
887 \$home$\ variable are prepended, unless it is empty. In conventional
888 configurations, this variable is normally set in a user filter to the user's
889 home directory, but the system administrator may set it to some other path. In
890 some configurations, \$home$\ may be unset, in which case a non-absolute path
891 name may be generated. Such configurations convert this to an absolute path
892 when the delivery takes place. In a system filter, \$home$\ is never set.
894 The user must of course have permission to write to the file, and the writing
895 of the file takes place in a process that is running as the user, under the
896 user's primary group. Any secondary groups to which the user may belong are not
897 normally taken into account, though the system administrator can configure Exim
898 to set them up. In addition, the ability to use this command at all is
899 controlled by the system administrator -- it may be forbidden on some systems.
901 An optional mode value may be given after the file name. The value for the mode
902 is interpreted as an octal number, even if it does not begin with a zero. For
903 example:
904 .display
905 save /some/folder 640
906 .endd
907 This makes it possible for users to override the system-wide mode setting for
908 file deliveries, which is normally 600. If an existing file does not have the
909 correct mode, it is changed.
911 An alternative form of delivery may be enabled on your system, in which each
912 message is delivered into a new file in a given directory. If this is the case,
913 this functionality can be requested by giving the directory name terminated by
914 a slash after the \"save"\ command, for example
915 .display
916 save separated/messages/
917 .endd
918 There are several different formats for such deliveries; check with your system
919 administrator or local documentation to find out which (if any) are available
920 on your system. If this functionality is not enabled, the use of a path name
921 ending in a slash causes an error.
924 .section The pipe command
925 .rset SECTpipe "~~chapter.~~section"
926 .display
927 pipe <<command>>
928 e.g. pipe "@$home/bin/countmail @$sender@_address"
929 .endd
930 .em
931 This command specifies that the message is to be delivered to the specified
932 command using a pipe. The delivery that it sets up is significant unless the
933 command is preceded by \"unseen"\ (see section ~~SECTsigdel).
934 .nem
935 Remember, however, that no deliveries are done while the filter is being
936 processed. All deliveries happen later on. Therefore, the result of running the
937 pipe is not available to the filter.
939 When the deliveries are done, a separate process is run, and a copy of the
940 message is passed on its standard input. The process runs as the user, under
941 the user's primary group. Any secondary groups to which the user may belong are
942 not normally taken into account, though the system administrator can configure
943 Exim to set them up. More than one \"pipe"\ command may appear; each one causes
944 a copy of the message to be written to its argument pipe, provided they are
945 different (duplicate \"pipe"\ commands are ignored).
947 When the time comes to transport the message,
948 the command supplied to \"pipe"\ is split up by Exim into a command name and a
949 number of arguments. These are delimited by white space except for arguments
950 enclosed in double quotes, in which case backslash is interpreted as an escape,
951 or in single quotes, in which case no escaping is recognized. Note that as the
952 whole command is normally supplied in double quotes, a second level of quoting
953 is required for internal double quotes. For example:
954 .display asis
955 pipe "$home/myscript \"size is $message_size\""
956 .endd
957 String expansion is performed on the separate components after the line has
958 been split up, and the command is then run directly by Exim; it is not run
959 under a shell. Therefore, substitution cannot change the number of arguments,
960 nor can quotes, backslashes or other shell metacharacters in variables cause
961 confusion.
963 Documentation for some programs that are normally run via this kind of pipe
964 often suggest that the command should start with
965 .display asis
966 IFS=" "
967 .endd
968 This is a shell command, and should $it{not} be present in Exim filter files,
969 since it does not normally run the command under a shell.
971 However, there is an option that the administrator can set to cause a shell to
972 be used. In this case, the entire command is expanded as a single string and
973 passed to the shell for interpretation. It is recommended that this be avoided
974 if at all possible, since it can lead to problems when inserted variables
975 contain shell metacharacters.
977 The default \\PATH\\ set up for the command is determined by the system
978 administrator, usually containing at least \/usr/bin\ so that common commands
979 are available without having to specify an absolute file name. However, it is
980 possible for the system administrator to restrict the pipe facility so that the
981 command name must not contain any / characters, and must be found in one of the
982 directories in the configured \\PATH\\. It is also possible for the system
983 administrator to lock out the use of the \"pipe"\ command altogether.
985 When the command is run, a number of environment variables are set up. The
986 complete list for pipe deliveries may be found in the Exim reference manual.
987 Those that may be useful for pipe deliveries from user filter files are:
988 .display
989 .tabs 20
990 DOMAIN $t $rm{the domain of the address}
991 HOME $t $rm{your home directory}
992 LOCAL@_PART $t $rm{see below}
993 LOCAL@_PART@_PREFIX $t $rm{see below}
994 LOCAL@_PART@_SUFFIX $t $rm{see below}
995 LOGNAME $t $rm{your login name}
996 MESSAGE@_ID $t $rm{the message's unique id}
997 PATH $t $rm{the command search path}
998 RECIPIENT $t $rm{the complete recipient address}
999 SENDER $t $rm{the sender of the message}
1000 SHELL $t $bf{/bin/sh}
1001 USER $t $rm{see below}
1002 .endd
1003 \\LOCAL@_PART\\, \\LOGNAME\\, and \\USER\\ are all set to the same value,
1004 namely, your login id. \\LOCAL@_PART@_PREFIX\\ and \\LOCAL@_PART@_SUFFIX\\ may
1005 be set if Exim is configured to recognize prefixes or suffixes in the local
1006 parts of addresses. For example, a message addressed to
1007 \*pat-suf2@@domain.example*\ may cause user \*pat*\'s filter file to be run. If
1008 this sets up a pipe delivery, \\LOCAL@_PART@_SUFFIX\\ is \"-suf2"\ when the
1009 pipe command runs. The system administrator has to configure Exim specially for
1010 this feature to be available.
1012 If you run a command that is a shell script, be very careful in your use of
1013 data from the incoming message in the commands in your script. RFC 2822 is very
1014 generous in the characters that are legally permitted to appear in mail
1015 addresses, and in particular, an address may begin with a vertical bar or a
1016 slash. For this reason you should always use quotes round any arguments that
1017 involve data from the message, like this:
1018 .display asis
1019 /some/command '$SENDER'
1020 .endd
1021 so that inserted shell meta-characters do not cause unwanted effects.
1023 Remember that, as was explained earlier, the pipe command is not run at the
1024 time the filter file is interpreted. The filter just defines what deliveries
1025 are required for one particular addressee of a message. The deliveries
1026 themselves happen later, once Exim has decided everything that needs to be done
1027 for the message.
1029 A consequence of this is that you cannot inspect the return code from the pipe
1030 command from within the filter. Nevertheless, the code returned by the command
1031 is important, because Exim uses it to decide whether the delivery has succeeded
1032 or failed.
1034 The command should return a zero completion code if all has gone well. Most
1035 non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1036 treated as a delivery failure, causing the message to be returned to its
1037 sender. However, there are some completion codes that are treated as temporary
1038 errors. The message remains on Exim's spool disk, and the delivery is tried
1039 again later, though it will ultimately time out if the delivery failures go on
1040 too long. The completion codes to which this applies can be specified by the
1041 system administrator; the default values are 73 and 75.
1043 The pipe command should not normally write anything to its standard output or
1044 standard error file descriptors. If it does, whatever is written is normally
1045 returned to the sender of the message as a delivery error, though this action
1046 can be varied by the system administrator.
1049 .section Mail commands
1050 .rset SECTmail "~~chapter.~~section"
1051 There are two commands that cause the creation of a new mail message, neither
1052 of which count as a significant delivery unless the command is preceded by the
1053 word \"seen"\ (see section ~~SECTsigdel). This is a powerful facility, but it
1054 should be used with care, because of the danger of creating infinite sequences
1055 of messages. The system administrator can forbid the use of these commands
1056 altogether.
1058 To help prevent runaway message sequences, these commands have no effect when
1059 the incoming message is a bounce (delivery error) message, and messages sent by
1060 this means are treated as if they were reporting delivery errors. Thus, they
1061 should never themselves cause a bounce message to be returned. The basic
1062 mail-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
1078 e.g. mail text "Your message about @$h@_subject: has been received"
1079 .endd
1081 Each <<address-list>> can contain a number of addresses, separated by commas,
1082 in the format of a ::To:: or ::Cc:: header line. In fact, the text you supply
1083 here is copied exactly into the appropriate header line. It may contain
1084 additional information as well as email addresses. For example:
1085 .display asis
1086 mail to "Julius Caesar <jc@rome.example>, \
1087 <ma@rome.example> (Mark A.)"
1088 .endd
1089 Similarly, the texts supplied for \"from"\ and \"reply@_to"\ are copied into
1090 their respective header lines.
1092 As 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
1094 the
1095 \"subject"\,
1096 \"file"\, \"log"\, \"once"\, and \"once@_repeat"\ options are
1097 .display
1098 subject "On vacation"
1099 expand file .vacation.msg
1100 log .vacation.log
1101 once .vacation
1102 once@_repeat 7d
1103 .endd
1104 respectively. These are the same file names and repeat period used by the
1105 traditional Unix \"vacation"\ command. The defaults can be overridden by
1106 explicit settings, but if a file name is given its contents are expanded only
1107 if explicitly requested.
1109 \**Warning**\: The \"vacation"\ command should always be used conditionally,
1110 subject to at least the \"personal"\ condition (see section ~~SECTpersonal
1111 below) so as not to send automatic replies to non-personal messages from
1112 mailing lists or elsewhere. Sending an automatic response to a mailing list or
1113 a mailing list manager is an Internet Sin.
1115 For both commands, the key/value argument pairs can appear in any order. At
1116 least one of \"text"\ or \"file"\ must appear (except with \"vacation"\, where
1117 there is a default for \"file"\); if both are present, the text string appears
1118 first in the message. If \"expand"\ precedes \"file"\, each line of the file is
1119 subject to string expansion before it is included in the message.
1121 Several lines of text can be supplied to \"text"\ by including the escape
1122 sequence `@\n' in the string wherever a newline is required. If the command is
1123 output during filter file testing, newlines in the text are shown as `@\n'.
1125 Note that the keyword for creating a \"Reply-To:"\ header is \reply@_to\,
1126 because Exim keywords may contain underscores, but not hyphens. If the \"from"\
1127 keyword is present and the given address does not match the user who owns the
1128 forward file, Exim normally adds a \"Sender:"\ header to the message,
1129 though it can be configured not to do this.
1131 The \extra@_headers\ keyword allows you to add custom header lines to the
1132 message. The text supplied must be one or more syntactically valid RFC 2882
1133 header lines. You can use `@\n' within quoted text to specify newlines between
1134 headers, and also to define continued header lines. For example:
1135 .display asis
1136 extra_headers "h1: first\nh2: second\n continued\nh3: third"
1137 .endd
1138 No newline should appear at the end of the final header line.
1140 If no \"to"\ argument appears, the message is sent to the address in the
1141 \"@$reply@_address"\ variable (see section ~~SECTfilterstringexpansion above).
1142 An \"In-Reply-To:"\ header is automatically included in the created message,
1143 giving a reference to the message identification of the incoming message.
1145 If \"return message"\ is specified, the incoming message that caused the filter
1146 file to be run is added to the end of the message, subject to a maximum size
1147 limitation.
1149 If a log file is specified, a line is added to it for each message sent.
1151 If a \"once"\ file is specified, it is used to hold a database for remembering
1152 who has received a message, and no more than one message is ever sent to any
1153 particular address, unless \"once@_repeat"\ is set. This specifies a time
1154 interval after which another copy of the message is sent. The interval is
1155 specified as a sequence of numbers, each followed by the initial letter of one
1156 of `seconds', `minutes', `hours', `days', or `weeks'. For example,
1157 .display asis
1158 once_repeat 5d4h
1159 .endd
1160 causes a new message to be sent if 5 days and 4 hours have elapsed since the
1161 last one was sent. There must be no white space in a time interval.
1163 Commonly, the file name specified for \"once"\ is used as the base name for
1164 direct-access (DBM) file operations. There are a number of different DBM
1165 libraries in existence. Some operating systems provide one as a default, but
1166 even in this case a different one may have been used when building Exim. With
1167 some DBM libraries, specifying \"once"\ results in two files being created,
1168 with the suffixes \".dir"\ and \".pag"\ being added to the given name. With
1169 some others a single file with the suffix \".db"\ is used, or the name is used
1170 unchanged.
1172 Using a DBM file for implementing the \"once"\ feature means that the file
1173 grows as large as necessary. This is not usually a problem, but some system
1174 administrators want to put a limit on it. The facility can be configured not to
1175 use a DBM file, but instead, to use a regular file with a maximum size. The
1176 data in such a file is searched sequentially, and if the file fills up, the
1177 oldest entry is deleted to make way for a new one. This means that some
1178 correspondents may receive a second copy of the message after an unpredictable
1179 interval. Consult your local information to see if your system is configured
1180 this way.
1182 More than one \"mail"\ or \"vacation"\ command may be obeyed in a single filter
1183 run; they are all honoured, even when they are to the same recipient.
1186 .section Logging commands
1187 .rset SECTlog "~~chapter.~~section"
1188 A log can be kept of actions taken by a filter file. This facility is normally
1189 available in conventional configurations, but there are some situations where
1190 it might not be. Also, the system administrator may choose to disable it. Check
1191 your local information if in doubt.
1193 Logging takes place while the filter file is being interpreted. It does not
1194 queue up for later like the delivery commands. The reason for this is so that a
1195 log file need be opened only once for several write operations. There are two
1196 commands, neither of which constitutes a significant delivery. The first
1197 defines a file to which logging output is subsequently written:
1198 .display
1199 logfile <<file name>>
1200 e.g. logfile @$home/filter.log
1201 .endd
1202 The file name must be fully qualified. You can use \$home$\, as in this
1203 example, to refer to your home directory. The file name may optionally be
1204 followed by a mode for the file, which is used if the file has to be created.
1205 For example,
1206 .display
1207 logfile @$home/filter.log 0644
1208 .endd
1209 The number is interpreted as octal, even if it does not begin with a zero.
1210 The default for the mode is 600. It is suggested that the \"logfile"\ command
1211 normally appear as the first command in a filter file. Once \"logfile"\ has
1212 been obeyed, the \"logwrite"\ command can be used to write to the log file:
1213 .display
1214 logwrite "<<some text string>>"
1215 e.g. logwrite "@$tod@_log @$message@_id processed"
1216 .endd
1217 It is possible to have more than one \"logfile"\ command, to specify writing to
1218 different log files in different circumstances. Writing takes place at the end
1219 of the file, and a newline character is added to the end of each string if
1220 there isn't one already there. Newlines can be put in the middle of the string
1221 by using the `@\n' escape sequence. Lines from simultaneous deliveries may get
1222 interleaved in the file, as there is no interlocking, so you should plan your
1223 logging with this in mind. However, data should not get lost.
1226 .section The finish command
1227 .rset SECTfinish "~~chapter.~~section"
1228 The command \"finish"\, which has no arguments, causes Exim to stop
1229 interpreting the filter file. This is not a significant action unless preceded
1230 by \"seen"\. A filter file containing only \"seen finish"\ is a black hole.
1232 .section The testprint command
1233 .rset SECTtestprint "~~chapter.~~section"
1234 It is sometimes helpful to be able to print out the values of variables when
1235 testing filter files. The command
1236 .display
1237 testprint <<text>>
1238 e.g. testprint "home=@$home reply@_address=@$reply@_address"
1239 .endd
1240 does nothing when mail is being delivered. However, when the filtering code is
1241 being tested by means of the \-bf-\ option (see section ~~SECTtesting above),
1242 the value of the string is written to the standard output.
1244 .section The fail command
1245 .rset SECTfail "~~chapter.~~section"
1246 When Exim's filtering facilities are being used as a system filter, the
1247 \"fail"\ command is available, to force delivery failure. Because this command
1248 is normally usable only by the system administrator, and not enabled for use by
1249 ordinary users, it is described in more detail in the main Exim specification
1250 rather than in this document.
1252 .section The freeze command
1253 .rset SECTfreeze "~~chapter.~~section"
1254 When 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
1256 command is normally usable only by the system administrator, and not enabled
1257 for use by ordinary users, it is described in more detail in the main Exim
1258 specification rather than in this document.
1261 .section The headers command
1262 .rset SECTheaders "~~chapter.~~section"
1263 The \"headers"\ command can be used to change the target character set that is
1264 used when translating the contents of encoded header lines for insertion by the
1265 \"@$header@_"\ mechanism (see section ~~SECTheadervariables above). The default
1266 can be set in the Exim configuration; if not specified, ISO-8859-1 is used. The
1267 only currently supported format for the \"headers"\ command
1268 .em
1269 in user filters
1270 .nem
1271 is as in this example:
1272 .display asis
1273 headers charset "UTF-8"
1274 .endd
1275 That is, \"headers"\ is followed by the word \"charset"\ and then the name of a
1276 character set. This particular example would be useful if you wanted to compare
1277 the contents of a header to a UTF-8 string.
1279 .em
1280 In system filter files, the \"headers"\ command can be used to add or remove
1281 header lines from the message. These features are described in the main Exim
1282 specification.
1283 .nem
1287 .section Obeying commands conditionally
1288 .rset SECTif "~~chapter.~~section"
1289 Most of the power of filtering comes from the ability to test conditions and
1290 obey different commands depending on the outcome. The \"if"\ command is used to
1291 specify conditional execution, and its general form is
1292 .display
1293 if <<condition>>
1294 then <<commands>>
1295 elif <<condition>>
1296 then <<commands>>
1297 else <<commands>>
1298 endif
1299 .endd
1300 There may be any number of \"elif"\ and \"then"\ sections (including none) and
1301 the \"else"\ section is also optional. Any number of commands, including nested
1302 \"if"\ commands, may appear in any of the <<commands>> sections.
1304 Conditions can be combined by using the words \"and"\ and \"or"\, and round
1305 brackets (parentheses) can be used to specify how several conditions are to
1306 combine. Without brackets, \"and"\ is more binding than \"or"\.
1307 For example,
1308 .display asis
1309 if
1310 $h_subject: contains "Make money" or
1311 $h_precedence: is "junk" or
1312 ($h_sender: matches ^\\d{8}@ and not personal) or
1313 $message_body contains "this is spam"
1314 then
1315 seen finish
1316 endif
1317 .endd
1318 A condition can be preceded by \"not"\ to negate it, and there are also some
1319 negative forms of condition that are more English-like.
1323 .section String testing conditions
1324 There are a number of conditions that operate on text strings, using the words
1325 `begins', `ends', `is', `contains' and `matches'. If you want to apply the same
1326 test to more than one header line, you can easily concatenate them into a
1327 single string for testing, as in this example:
1328 .display asis
1329 if "$h_to:, $h_cc:" contains me@domain.example then ...
1330 .endd
1332 If a string-testing condition name is written in lower case, the testing
1333 of letters is done without regard to case; if it is written in upper case
1334 (for example, `CONTAINS'), the case of letters is taken into account.
1335 .display
1336 <<text1>> begins <<text2>>
1337 <<text1>> does not begin <<text2>>
1338 e.g. @$header@_from: begins "Friend@@"
1339 .endd
1340 A `begins' test checks for the presence of the second string at the start of
1341 the first, both strings having been expanded.
1342 .display
1343 <<text1>> ends <<text2>>
1344 <<text1>> does not end <<text2>>
1345 e.g. @$header@_from: ends "@public.com.example"
1346 .endd
1347 An `ends' test checks for the presence of the second string at the end of
1348 the first, both strings having been expanded.
1349 .display
1350 <<text1>> is <<text2>>
1351 <<text1>> is not <<text2>>
1352 e.g. @$local@_part@_suffix is "-foo"
1353 .endd
1354 An `is' test does an exact match between the strings, having first expanded
1355 both strings.
1356 .display
1357 <<text1>> contains <<text2>>
1358 <<text1>> does not contain <<text2>>
1359 e.g. @$header@_subject: contains "evolution"
1360 .endd
1361 A `contains' test does a partial string match, having expanded both strings.
1362 .display
1363 <<text1>> matches <<text2>>
1364 <<text1>> does not match <<text2>>
1365 e.g. @$sender@_address matches "(bill|john)@@"
1366 .endd
1367 For a `matches' test, after expansion of both strings, the second one is
1368 interpreted as a regular expression. Exim uses the PCRE regular expression
1369 library, which provides regular expressions that are compatible with Perl.
1371 The match succeeds if the regular expression matches any part of the first
1372 string. If you want a regular expression to match only at the start or end of
1373 the subject string, you must encode that requirement explicitly, using the @^
1374 or @$ metacharacters. The above example, which is not so constrained, matches
1375 all these addresses:
1376 .display asis
1377 bill@test.example
1378 john@some.example
1379 spoonbill@example.com
1380 littlejohn@example.com
1381 .endd
1382 To match only the first two, you could use this:
1383 .display asis
1384 if $sender_address matches "^(bill|john)@" then ...
1385 .endd
1387 Care must be taken if you need a backslash in a regular expression, because
1388 backslashes are interpreted as escape characters both by the string expansion
1389 code and by Exim's normal processing of strings in quotes. For example, if you
1390 want to test the sender address for a domain ending in \".com"\ the regular
1391 expression is
1392 .display asis
1393 \.com$
1394 .endd
1395 The backslash and dollar sign in that expression have to be escaped when used
1396 in a filter command, as otherwise they would be interpreted by the expansion
1397 code. Thus what you actually write is
1398 .display asis
1399 if $sender_address matches \\.com\$
1400 .endd
1401 An alternative way of handling this is to make use of the \"@\N"\ expansion
1402 flag for suppressing expansion:
1403 .display asis
1404 if $sender_address matches \N\.com$\N
1405 .endd
1406 Everything between the two occurrences of \"@\N"\ is copied without change by
1407 the string expander (and in fact you do not need the final one, because it is
1408 at the end of the string).
1410 If the regular expression is given in quotes (mandatory only if it contains
1411 white space) you have to write either
1412 .display asis
1413 if $sender_address matches "\\\\.com\\$"
1414 .endd
1415 or
1416 .display asis
1417 if $sender_address matches "\\N\\.com$\\N"
1418 .endd
1420 If the regular expression contains bracketed sub-expressions, numeric
1421 variable substitutions such as \$1$\ can be used in the subsequent actions
1422 after a successful match. If the match fails, the values of the numeric
1423 variables remain unchanged. Previous values are not restored after \"endif"\.
1424 In other words, only one set of values is ever available. If the condition
1425 contains several sub-conditions connected by \"and"\ or \"or"\, it is the
1426 strings extracted from the last successful match that are available in
1427 subsequent actions. Numeric variables from any one sub-condition are also
1428 available for use in subsequent sub-conditions, because string expansion of a
1429 condition occurs just before it is tested.
1431 .section Numeric testing conditions
1432 The following conditions are available for performing numerical tests:
1433 .display
1434 <<number1>> is above <<number2>>
1435 <<number1>> is not above <<number2>>
1436 <<number1>> is below <<number2>>
1437 <<number1>> is not below <<number2>>
1438 e.g. @$message@_size is not above 10k
1439 .endd
1440 The <<number>> arguments must expand to strings of digits, optionally followed
1441 by one of the letters K or M (upper case or lower case) which cause
1442 multiplication by 1024 and 1024x1024 respectively.
1444 .section Testing for significant deliveries
1445 You can use the \"delivered"\ condition to test whether or not any previously
1446 obeyed filter commands have set up a significant delivery. For example:
1447 .display asis
1448 if not delivered then save mail/anomalous endif
1449 .endd
1451 .section Testing for error messages
1452 The condition \"error@_message"\ is true if the incoming message is a bounce
1453 (mail delivery error) message. Putting the command
1454 .display asis
1455 if error_message then finish endif
1456 .endd
1457 at the head of your filter file is a useful insurance against things going
1458 wrong 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
1460 not preceded by \@$\.
1462 .section Testing a list of addresses
1463 There is a facility for looping through a list of addresses and applying a
1464 condition to each of them. It takes the form
1465 .display
1466 foranyaddress <<string>> (<<condition>>)
1467 .endd
1468 where <<string>> is interpreted as a list of RFC 2822 addresses, as in a
1469 typical header line, and <<condition>> is any valid filter condition or
1470 combination of conditions. The `group' syntax that is defined for certain
1471 header lines that contain addresses is supported.
1473 The parentheses surrounding the condition are mandatory, to delimit it from
1474 possible further sub-conditions of the enclosing \"if"\ command. Within the
1475 condition, the expansion variable \$thisaddress$\ is set to the non-comment
1476 portion of each of the addresses in the string in turn. For example, if the
1477 string is
1478 .display asis
1479 B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1480 .endd
1481 then \$thisaddress$\ would take on the values \"bart@@sfld.example"\ and
1482 \"lisa@@sfld.example"\ in turn.
1484 If there are no valid addresses in the list, the whole condition is false. If
1485 the internal condition is true for any one address, the overall condition is
1486 true and the loop ends. If the internal condition is false for all addresses in
1487 the list, the overall condition is false. This example tests for the presence
1488 of an eight-digit local part in any address in a \To:\ header:
1489 .display asis
1490 if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1491 .endd
1492 When the overall condition is true, the value of \$thisaddress$\ in the
1493 commands that follow \"then"\ is the last value it took on inside the loop. At
1494 the end of the \"if"\ command, the value of \$thisaddress$\ is reset to what it
1495 was before. It is best to avoid the use of multiple occurrences of
1496 \"foranyaddress"\, nested or otherwise, in a single \"if"\ command, if the
1497 value of \$thisaddress$\ is to be used afterwards, because it isn't always
1498 clear what the value will be. Nested \"if"\ commands should be used instead.
1500 Header lines can be joined together if a check is to be applied to more than
1501 one of them. For example:
1502 .display asis
1503 if foranyaddress $h_to:,$h_cc: ....
1504 .endd
1505 scans through the addresses in both the \To:\ and the \Cc:\ headers.
1507 .section Testing for personal mail
1508 .rset SECTpersonal "~~chapter.~~section"
1509 A common requirement is to distinguish between incoming personal mail and mail
1510 from a mailing list, or from a robot or other automatic process (for example, a
1511 bounce message). In particular, this test is normally required for `vacation
1512 messages'.
1514 .em
1515 The \"personal"\ condition checks that the message is not a bounce message and
1516 that the current user's email address appears in the \"To:"\ header. It also
1517 checks that the sender is not the current user or one of a number of common
1518 daemons, and that there are no header lines starting \"List-"\ in the message.
1519 Finally, it checks the content of the \"Precedence:"\ header line, if there is
1520 one.
1522 You should always use the \"personal"\ condition when generating automatic
1523 responses.
1524 .nem
1525 This example shows the use of \"personal"\ in a filter file that is sending out
1526 vacation messages:
1527 .display asis
1528 if 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
1539 endif
1540 .endd
1541 .em
1542 It is tempting, when writing commands like the above, to quote the original
1543 subject in the reply. For example:
1544 .display asis
1545 subject "Re: $h_subject:"
1546 .endd
1547 There is a danger in doing this, however. It may allow a third party to
1548 subscribe you to an opt-in mailing list, provided that the list accepts bounce
1549 messages as subscription confirmations. (Messages sent from filters are always
1550 sent as bounce messages.) Well-managed lists require a non-bounce message to
1551 confirm a subscription, so the danger is relatively small.
1553 If prefixes or suffixes are in use for local parts -- something which depends
1554 on the configuration of Exim (see section ~~SECTmbox below) -- the tests for
1555 the current user are done with the full address (including the prefix and
1556 suffix, if any) as well as with the prefix and suffix removed. If the system is
1557 configured 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
1559 tests.
1560 .nem
1562 .em
1563 .section Alias addresses for the personal condition
1564 It is quite common for people who have mail accounts on a number of different
1565 systems to forward all their mail to one system, and in this case a check for
1566 personal mail should test all their various mail addresses. To allow for this,
1567 the \"personal"\ condition keyword can be followed by
1568 .display
1569 alias <<address>>
1570 .endd
1571 any number of times, for example
1572 .display asis
1573 if personal alias smith@else.where.example
1574 alias jones@other.place.example
1575 then ...
1576 .endd
1577 The alias addresses are treated as alternatives to the current user's email
1578 address when testing the contents of header lines.
1579 .nem
1582 .em
1583 .section Details of the personal condition
1584 The basic \"personal"\ test is roughly equivalent to the following:
1585 .display flow asis
1586 not 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
1592 foranyaddress $header_to:
1593 ( $thisaddress contains "$local_part@$domain" ) and
1594 not 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 $thisaddress matches "^owner-[^@]+@"
1604 )
1605 .endd
1606 The variable \$local@_part$\ contains the local part of the mail address of
1607 the 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
1609 or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1610 the current user are also done with alternative addresses.
1611 .nem
1614 .section Testing delivery status
1615 There are two conditions that are intended mainly for use in system filter
1616 files, 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
1618 deliver the message, and false otherwise. This indicator is not reset until the
1619 first delivery process successfully terminates; if there is a crash or a power
1620 failure (for example), the next delivery attempt is also a `first delivery'.
1622 In a user filter file \"first@_delivery"\ will be false only if
1623 there was previously an error in the filter, or if a delivery for the user
1624 failed owing to, for example, a quota error, or if forwarding to a remote
1625 address was deferred for some reason.
1627 The condition \"manually@_thawed"\ is true only if the message was `frozen' for
1628 some reason, and was subsequently released by the system administrator. It is
1629 unlikely to be of use in users' filter files.
1631 .section Multiple personal mailboxes
1632 .rset SECTmbox "~~chapter.~~section"
1633 The system administrator can configure Exim so that users can set up variants
1634 on their email addresses and handle them separately. Consult your system
1635 administrator or local documentation to see if this facility is enabled on your
1636 system, and if so, what the details are.
1638 The facility involves the use of a prefix or a suffix on an email address. For
1639 example, all mail addressed to \lg303-<<something>>\ would be the property of
1640 user \lg303\, who could determine how it was to be handled, depending on the
1641 value of <<something>>.
1643 There are two possible ways in which this can be set up. The first possibility
1644 is the use of multiple \(.forward)\ files. In this case, mail to \lg303-foo\,
1645 for example, is handled by looking for a file called \.forward-foo\ in
1646 \lg303's\ home directory. If such a file does not exist, delivery fails and the
1647 message is returned to its sender.
1649 The alternative approach is to pass all messages through a single \(.forward)\
1650 file, which must be a filter file so that it can distinguish between the
1651 different cases by referencing the variables \$local@_part@_prefix$\ or
1652 \$local@_part@_suffix$\, as in the final example in section ~~SECTex below.
1654 It is possible to configure Exim to support both schemes at once. In this case,
1655 a specific \.forward-foo\ file is first sought; if it is not found, the basic
1656 \(.forward)\ file is used.
1658 The \"personal"\ test (see section ~~SECTpersonal) includes prefixes and
1659 suffixes in its checking.
1662 .section Ignoring delivery errors
1663 As was explained above, filtering just sets up addresses for delivery -- no
1664 deliveries are actually done while a filter file is active. If any of the
1665 generated addresses subsequently suffers a delivery failure, an error message
1666 is generated in the normal way. However, if a filter command that sets up a
1667 delivery is preceded by the word \"noerror"\, errors for that delivery,
1668 $it{and any deliveries consequent on it} (that is, from alias, forwarding, or
1669 filter files it invokes) are ignored.
1672 .section Examples of Exim filter commands
1673 .rset SECTex "~~chapter.~~section"
1674 Simple forwarding:
1675 .display asis
1676 # Exim filter
1677 deliver baggins@rivendell.middle-earth.example
1678 .endd
1679 Vacation handling using traditional means, assuming that the \.vacation.msg\
1680 and other files have been set up in your home directory:
1681 .display asis
1682 # Exim filter
1683 unseen pipe "/usr/ucb/vacation \"$local_part\""
1684 .endd
1685 Vacation handling inside Exim, having first created a file called
1686 \.vacation.msg\ in your home directory:
1687 .display asis
1688 # Exim filter
1689 if personal then vacation endif
1690 .endd
1691 File some messages by subject:
1692 .display asis
1693 # Exim filter
1694 if $header_subject: contains "empire" or
1695 $header_subject: contains "foundation"
1696 then
1697 save $home/mail/f+e
1698 endif
1699 .endd
1700 Save all non-urgent messages by weekday:
1701 .display asis
1702 # Exim filter
1703 if $header_subject: does not contain "urgent" and
1704 $tod_full matches "^(...),"
1705 then
1706 save $home/mail/$1
1707 endif
1708 .endd
1709 Throw away all mail from one site, except from postmaster:
1710 .display asis
1711 # Exim filter
1712 if $reply_address contains "@spam.site.example" and
1713 $reply_address does not contain "postmaster@"
1714 then
1715 seen finish
1716 endif
1717 .endd
1718 .if ~~sgcal
1719 .if ~~sys.leftonpage < 6ld
1720 .newpage
1721 .fi
1722 .fi
1723 Handle multiple personal mailboxes
1724 .display asis
1725 # Exim filter
1726 if $local_part_suffix is "-foo"
1727 then
1728 save $home/mail/foo
1729 elif $local_part_suffix is "-bar"
1730 then
1731 save $home/mail/bar
1732 endif
1733 .endd
1735 . End of filter