[exim.git] / doc / doc-src / filter.src
1 . $Cambridge: exim/doc/doc-src/filter.src,v 1.1 2004/10/07 15:04:35 ph10 Exp $
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82 .set chapter -1
83 .chapter Exim's interfaces to mail filtering
84 .space -2ld
85 Exim is a mail transfer agent for Unix-like systems. This document describes
86 the user interfaces to its in-built mail filtering facilities, and is copyright
87 (c) University of Cambridge 2004. It corresponds to Exim version 4.40.
88 .rule
90 . ---------------------------------------------------------------------------
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92 . one page long, so we arrange for it to get onto the rest of the first page.
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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 It is important to realize that, in Exim, no deliveries are actually made while
147 a filter or traditional \(.forward)\ file is being processed. The result of
148 such processing is a list of destinations to which a message should be
149 delivered -- the deliveries themselves take place later, along with all other
150 deliveries for the message. This means that it is not possible to test for
151 successful deliveries while filtering. It also means that any duplicate
152 addresses that are generated are dropped, since Exim never delivers the same
153 message to the same address more than once.
155 This document describes how to use a filter file and the format of its
156 contents. It is intended for use by end-users. Both Sieve filters and Exim
157 filters are covered. However, for Sieve filters, only issues that relate to the
158 Exim implementation are discussed, since Sieve itself is described elsewhere.
160 The contents of traditional \(.forward)\ files are not described here. They
161 normally contain just a list of addresses, file names, or pipe commands,
162 separated by commas or newlines, but other types of item are also available.
163 The full details can be found in the chapter on the \%redirect%\ router in the
164 Exim specification, which also describes how the system administrator can set
165 up and control the use of filtering.
167 .section Testing a new filter file
168 .rset SECTtesting "~~chapter.~~section"
169 Filter files, especially the more complicated ones, should always be tested, as
170 it is easy to make mistakes. Exim provides a facility for preliminary testing
171 of a filter file before installing it. This tests the syntax of the file and
172 its basic operation, and can also be used with traditional \(.forward)\ files.
174 Because a filter can do tests on the content of messages, a test message is
175 required. Suppose you have a new filter file called \(myfilter)\ and a test
176 message called \(test-message)\. Assuming that Exim is installed with the
177 conventional path name \(/usr/sbin/sendmail)\ (some operating systems use
178 \(/usr/lib/sendmail)\), the following command can be used:
179 .display asis
180 /usr/sbin/sendmail -bf myfilter <test-message
181 .endd
182 The \-bf-\ option tells Exim that the following item on the command line is the
183 name of a filter file that is to be tested. There is also a \-bF-\ option,
184 which is similar, but which is used for testing system filter files, as opposed
185 to user filter files, and which is therefore of use only to the system
186 administrator.
188 The test message is supplied on the standard input. If there are no
189 message-dependent tests in the filter, an empty file (\(/dev/null)\) can be
190 used. A supplied message must start with header lines or the `From' message
191 separator line which is found in many multi-message folder files. Note that
192 blank lines at the start terminate the header lines. A warning is given if no
193 header lines are read.
195 The result of running this command, provided no errors are detected in the
196 filter file, is a list of the actions that Exim would try to take if presented
197 with the message for real.
198 For example, for an Exim filter, the output
199 .display asis
200 Deliver message to: gulliver@lilliput.fict.example
201 Save message to: /home/lemuel/mail/archive
202 .endd
203 means that one copy of the message would be sent to
204 \gulliver@@lilliput.fict.example\, and another would be added to the file
205 \(/home/lemuel/mail/archive)\, if all went well.
207 The actions themselves are not attempted while testing a filter file in this
208 way; there is no check, for example, that any forwarding addresses are valid.
209 For an Exim filter,
210 if you want to know why a particular action is being taken, add the \-v-\
211 option to the command. This causes Exim to output the results of any
212 conditional tests and to indent its output according to the depth of nesting of
213 \"if"\ commands. Further additional output from a filter test can be generated
214 by the \"testprint"\ command, which is described below.
216 When Exim is outputting a list of the actions it would take, if any text
217 strings are included in the output, non-printing characters therein are
218 converted to escape sequences. In particular, if any text string contains a
219 newline character, this is shown as `@\n' in the testing output.
221 When testing a filter in this way, Exim makes up an `envelope' for the message.
222 The recipient is by default the user running the command, and so is the sender,
223 but the command can be run with the \-f-\ option to supply a different sender.
224 For example,
225 .display
226 .indent 0
227 /usr/sbin/sendmail -bf myfilter -f islington@@never.where <test-message
228 .endd
229 Alternatively, if the \-f-\ option is not used, but the first line of the
230 supplied message is a `From' separator from a message folder file (not the same
231 thing as a \"From:"\ header line), the sender is taken from there. If \-f-\ is
232 present, the contents of any `From' line are ignored.
234 The `return path' is the same as the envelope sender, unless the message
235 contains a \"Return-path:"\ header, in which case it is taken from there. You
236 need not worry about any of this unless you want to test out features of a
237 filter file that rely on the sender address or the return path.
239 It is possible to change the envelope recipient by specifying further options.
240 The \-bfd-\ option changes the domain of the recipient address, while the
241 \-bfl-\ option changes the `local part', that is, the part before the @@ sign.
242 An adviser could make use of these to test someone else's filter file.
244 The \-bfp-\ and \-bfs-\ options specify the prefix or suffix for the local part.
245 These are relevant only when support for multiple personal mailboxes is
246 implemented; see the description in section ~~SECTmbox below.
248 .section Installing a filter file
249 A filter file is normally installed under the name \(.forward)\ in your home
250 directory -- it is distinguished from a conventional \(.forward)\ file by its
251 first line (described below). However, the file name is configurable, and some
252 system administrators may choose to use some different name or location for
253 filter files.
255 .section Testing an installed filter file
256 Testing a filter file before installation cannot find every potential problem;
257 for example, it does not actually run commands to which messages are piped.
258 Some `live' tests should therefore also be done once a filter is installed.
260 If at all possible, test your filter file by sending messages from some other
261 account. If you send a message to yourself from the filtered account, and
262 delivery fails, the error message will be sent back to the same account, which
263 may cause another delivery failure. It won't cause an infinite sequence of such
264 messages, because delivery failure messages do not themselves generate further
265 messages. However, it does mean that the failure won't be returned to you, and
266 also that the postmaster will have to investigate the stuck message.
268 If you have to test an Exim filter from the same account, a sensible precaution
269 is to include the line
270 .display asis
271 if error_message then finish endif
272 .endd
273 as the first filter command, at least while testing. This causes filtering to
274 be abandoned for a delivery failure message, and since no destinations are
275 generated, the message goes on to be delivered to the original address. Unless
276 there is a good reason for not doing so, it is recommended that the above test
277 be left in all Exim filter files.
278 (This does not apply to Sieve files.)
281 .section Details of filtering commands
282 The filtering commands for Sieve and Exim filters are completely different in
283 syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
284 chapter we describe how it is integrated into Exim. The subsequent chapter
285 covers Exim filtering commands in detail.
288 .
289 .
290 .
291 .
292 .
293 .chapter Sieve filter files
294 .rset CHAPsievefilter "~~chapter"
295 The code for Sieve filtering in Exim was contributed by Michael Haardt, and
296 most of the content of this chapter is taken from the notes he provided. Since
297 Sieve is a extensible language, it is important to understand `Sieve' in this
298 context as `the specific implementation of Sieve for Exim'.
300 This chapter does not contain a description of Sieve, since that can be found
301 in RFC 3028, which should be read in conjunction with these notes.
303 The Exim Sieve implementation offers the core as defined by RFC 3028, the
304 \%envelope%\ and the \%fileinto%\ extensions, but not the \%reject%\ extension.
305 Exim does not support message delivery notifications (MDNs), so adding it just
306 to the Sieve filter (as required for \%reject%\) makes little sense.
308 In order for Sieve to work properly in Exim, the system administrator needs to
309 make some adjustments to the Exim configuration. These are described in the
310 chapter on the \%redirect%\ router in the full Exim specification.
312 .section Recognition of Sieve filters
313 A filter file is interpreted as a Sieve filter if its first line is
314 .display asis
315 # Sieve filter
316 .endd
317 This is what distinguishes it from a conventional \(.forward)\ file or an Exim
318 filter file.
321 .section Saving to specified folders
322 If the system administrator has set things up as suggested in the Exim
323 specification, and you use \%keep%\ or \%fileinto%\ to save a mail into a
324 folder, absolute files are stored where specified, relative files are stored
325 relative to \$home$\, and \%inbox%\ goes to the standard mailbox location.
328 .section Strings containing header names
329 RFC 3028 does not specify what happens if a string denoting a header field does
330 not contain a valid header name, for example, it contains a colon. This
331 implementation generates an error instead of ignoring the header field in order
332 to ease script debugging, which fits in the common picture of Sieve.
335 .section Exists test with empty list of headers
336 The \%exists%\ test succeeds only if all specified headers exist. RFC 3028
337 does not explicitly specify what happens on an empty list of headers. This
338 implementation evaluates that condition as true, interpreting the RFC in a
339 strict sense.
342 .section Header test with invalid MIME encoding in header
343 Some MUAs process invalid base64 encoded data, generating junk.
344 Others ignore junk after seeing an equal sign in base64 encoded data.
345 RFC 2047 does not specify how to react in this case, other than stating
346 that a client must not forbid to process a message for that reason.
347 RFC 2045 specifies that invalid data should be ignored (apparently
348 looking at end of line characters). It also specifies that invalid data
349 may lead to rejecting messages containing them (and there it appears to
350 talk about true encoding violations), which is a clear contradiction to
351 ignoring them.
353 RFC 3028 does not specify how to process incorrect MIME words.
354 This implementation treats them literally, as it does if the word is
355 correct but its character set cannot be converted to UTF-8.
358 .section Address test for multiple addresses per header
359 A header may contain multiple addresses. RFC 3028 does not explicitly
360 specify how to deal with them, but since the address test checks if
361 anything matches anything else, matching one address suffices to
362 satisfy the condition. That makes it impossible to test if a header
363 contains a certain set of addresses and no more, but it is more logical
364 than letting the test fail if the header contains an additional address
365 besides the one the test checks for.
368 .section Semantics of keep
369 The \%keep%\ command is equivalent to
370 .display
371 fileinto "inbox";
372 .endd
373 It saves the message and resets the implicit keep flag. It does not set the
374 implicit keep flag; there is no command to set it once it has been reset.
377 .section Semantics of fileinto
378 RFC 3028 does not specify whether \fileinto\ should try to create a mail folder
379 if it does not exist. This implementation allows the sysadmin to configure that
380 aspect using the \%appendfile%\ transport options \create@_directory\,
381 \create@_file\, and \file@_must@_exist\. See the \%appendfile%\ transport in
382 the Exim specification for details.
385 .section Semantics of redirect
386 Sieve scripts are supposed to be interoperable between servers, so this
387 implementation does not allow mail to be redirected to unqualified addresses,
388 because the domain would depend on the system being used. On systems with
389 virtual mail domains, the default domain is probably not what the user expects
390 it to be.
393 .section String arguments
394 There has been confusion if the string arguments to \%require%\ are to be
395 matched case-sensitively or not. This implementation matches them with
396 the match type \":is"\ (default, see section 2.7.1) and the comparator
397 \"i;ascii-casemap"\ (default, see section 2.7.3). The RFC defines the
398 command defaults clearly, so any different implementations violate RFC
399 3028. The same is valid for comparator names, also specified as strings.
402 .section Number units
403 There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
404 The mistake is obvious, because RFC 3028 specifies G to denote 2@^30
405 (which is gibi, not tebi), and that is what this implementation uses as
406 scaling factor for the suffix G.
409 .section RFC compliance
410 Exim requires the first line of a Sieve filter to be
411 .display asis
412 # Sieve filter
413 .endd
414 Of course the RFC does not specify that line. Do not expect examples to work
415 without adding it, though.
417 RFC 3028 requires the use of CRLF to terminate a line.
418 The rationale was that CRLF is universally used in network protocols
419 to mark the end of the line. This implementation does not embed Sieve
420 in a network protocol, but uses Sieve scripts as part of the Exim MTA.
421 Since all parts of Exim use LF as newline character, this implementation
422 does, too, by default, though the system administrator may choose (at Exim
423 compile time) to use CRLF instead.
425 Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so
426 this implementation repeats this violation to stay consistent with Exim.
427 This is in preparation to UTF-8 data.
429 Sieve scripts cannot contain NUL characters in strings, but mail
430 headers could contain MIME encoded NUL characters, which could never
431 be matched by Sieve scripts using exact comparisons. For that reason,
432 this implementation extends the Sieve quoted string syntax with @\0
433 to describe a NUL character, violating @\0 being the same as 0 in
434 RFC 3028. Even without using @\0, the following tests are all true in
435 this implementation. Implementations that use C-style strings will only
436 evaluate the first test as true.
437 .display asis
438 Subject: =?iso-8859-1?q?abc=00def
440 header :contains "Subject" ["abc"]
441 header :contains "Subject" ["def"]
442 header :matches "Subject" ["abc?def"]
443 .endd
445 Note that by considering Sieve to be a MUA, RFC 2047 can be interpreted
446 in a way that NUL characters truncating strings is allowed for Sieve
447 implementations, although not recommended. It is further allowed to use
448 encoded NUL characters in headers, but that's not recommended either.
449 The above example shows why.
451 RFC 3028 states that if an implementation fails to convert a character
452 set to UTF-8, two strings cannot be equal if one contains octets greater
453 than 127. Assuming that all unknown character sets are one-byte character
454 sets with the lower 128 octets being US-ASCII is not sound, so this
455 implementation violates RFC 3028 and treats such MIME words literally.
456 That way at least something could be matched.
458 The folder specified by \%fileinto%\ must not contain the character
459 sequence \".."\ to avoid security problems. RFC 3028 does not specify the
460 syntax of folders apart from \%keep%\ being equivalent to
461 .display asis
462 fileinto "INBOX";
463 .endd
464 This implementation uses \"inbox"\ instead.
466 Sieve script errors currently cause messages to be silently filed into
467 \"inbox"\. RFC 3028 requires that the user is notified of that condition.
468 This may be implemented in future by adding a header line to mails that
469 are filed into \"inbox"\ due to an error in the filter.
472 .
473 .
474 .
475 .
476 .
477 .chapter Exim filter files
478 .rset CHAPeximfilter "~~chapter"
479 This chapter contains a full description of the contents of Exim filter files.
481 .section Format of Exim filter files
482 Apart from leading white space, the first text in a filter file must be
483 .display asis
484 # Exim filter
485 .endd
486 This is what distinguishes it from a conventional \(.forward)\ file or a Sieve
487 filter file. If the file does not have this initial line (or the equivalent for
488 a Sieve filter), it is treated as a
489 conventional \(.forward)\ file, both when delivering mail and when using the
490 \-bf-\ testing mechanism. The white space in the line is optional, and any
491 capitalization may be used. Further text on the same line is treated as a
492 comment. For example, you could have
493 .display asis
494 # Exim filter <<== do not edit or remove this line!
495 .endd
496 The remainder of the file is a sequence of filtering commands, which consist of
497 keywords and data values. For example, in the command
498 .display asis
499 deliver gulliver@lilliput.fict.example
500 .endd
501 the keyword is \"deliver"\ and the data value is
502 \"gulliver@@lilliput.fict.example"\.
503 White space or line breaks separate the components of a command, except in the
504 case of conditions for the \"if"\ command, where round brackets (parentheses)
505 also act as separators. Complete commands are separated from each other by
506 white space or line breaks; there are no special terminators. Thus, several
507 commands may appear on one line, or one command may be spread over a number of
508 lines.
510 If the character @# follows a separator anywhere in a command, everything from
511 @# up to the next newline is ignored. This provides a way of including comments
512 in a filter file.
514 .section Data values in filter commands
515 There are two ways in which a data value can be input:
516 .numberpars $.
517 If the text contains no white space then it can be typed verbatim. However, if
518 it is part of a condition, it must also be free of round brackets
519 (parentheses), as these are used for grouping in conditions.
520 .nextp
521 Otherwise, it must be enclosed in double quotation marks. In this case, the
522 character @\ (backslash) is treated as an `escape character' within the string,
523 causing the following character or characters to be treated specially:
524 .display rm
525 .tabs 8
526 @\n $t is replaced by a newline
527 @\r $t is replaced by a carriage return
528 @\t $t is replaced by a tab
529 .endd
530 Backslash followed by up to three octal digits is replaced by the character
531 specified by those digits, and @\x followed by up to two hexadecimal digits is
532 treated similarly. Backslash followed by any other character is replaced
533 by the second character, so that in particular, @\" becomes " and @\@\ becomes
534 @\$<. A data item enclosed in double quotes can be continued onto the next line
535 by ending the first line with a backslash. Any leading white space at the start
536 of the continuation line is ignored.
537 .endp
538 In addition to the escape character processing that occurs when strings are
539 enclosed in quotes, most data values are also subject to $it{string expansion}
540 (as described in the next section), in which case the characters \@$\ and \@\\
541 are also significant. This means that if a single backslash is actually
542 required in such a string, and the string is also quoted, @\@\@\@\ has to be
543 entered.
545 The maximum permitted length of a data string, before expansion, is 1024
546 characters.
549 .section String expansion
550 .rset SECTfilterstringexpansion "~~chapter.~~section"
551 Most data values are expanded before use. Expansion consists of replacing
552 substrings beginning with \"@$"\ with other text. The full expansion facilities
553 available in Exim are extensive. If you want to know everything that Exim can
554 do with strings, you should consult the chapter on string expansion in the Exim
555 documentation.
557 In filter files, by far the most common use of string expansion is the
558 substitution of the contents of a variable. For example, the substring
559 .display asis
560 $reply_address
561 .endd
562 is replaced by the address to which replies to the message should be sent. If
563 such a variable name is followed by a letter or digit or underscore, it must be
564 enclosed in curly brackets (braces), for example,
565 .display asis
566 ${reply_address}
567 .endd
568 If a \"@$"\ character is actually required in an expanded string, it must be
569 escaped with a backslash, and because backslash is also an escape character in
570 quoted input strings, it must be doubled in that case. The following two
571 examples illustrate two different ways of testing for a \"@$"\ character in a
572 message:
573 .display asis
574 if $message_body contains \$ then ...
575 if $message_body contains "\\$" then ...
576 .endd
577 You can prevent part of a string from being expanded by enclosing it between
578 two occurrences of \"@\N"\. For example,
579 .display asis
580 if $message_body contains \N$$$$\N then ...
581 .endd
582 tests for a run of four dollar characters.
584 .section Some useful general variables
585 A complete list of the available variables is given in the Exim documentation.
586 This shortened list contains the ones that are most likely to be useful in
587 personal filter files:
589 \$body@_linecount$\: The number of lines in the body of the message.
591 \$home$\: In conventional configurations, this variable normally contains the
592 user's home directory. The system administrator can, however, change this.
594 \$local@_part$\: The part of the email address that precedes the @@ sign --
595 normally the user's login name. If support for multiple personal mailboxes is
596 enabled (see section ~~SECTmbox below) and a prefix or suffix for the local
597 part was recognized, it is removed from the string in this variable.
599 \$local@_part@_prefix$\: If support for multiple personal mailboxes is enabled
600 (see section ~~SECTmbox below), and a local part prefix was recognized,
601 this variable contains the prefix. Otherwise it contains an empty string.
603 \$local@_part@_suffix$\: If support for multiple personal mailboxes is enabled
604 (see section ~~SECTmbox below), and a local part suffix was recognized,
605 this variable contains the suffix. Otherwise it contains an empty string.
607 \$message@_body$\: The initial portion of the body of the message. By default,
608 up to 500 characters are read into this variable, but the system administrator
609 can configure this to some other value. Newlines in the body are converted into
610 single spaces.
612 \$message@_body@_end$\: The final portion of the body of the message, formatted
613 and limited in the same way as \$message@_body$\.
615 \$message@_body@_size$\: The size of the body of the message, in bytes.
617 \$message@_headers$\: The header lines of the message, concatenated into a
618 single string, with newline characters between them.
620 \$message@_id$\: The message's local identification string, which is unique for
621 each message handled by a single host.
623 \$message@_size$\: The size of the entire message, in bytes.
625 \$original@_local@_part$\: When an address that arrived with the message is
626 being processed, this contains the same value as the variable \$local@_part$\.
627 However, if an address generated by an alias, forward, or filter file is being
628 processed, this variable contains the local part of the original address.
630 \$reply@_address$\: The contents of the \"Reply-to:"\ header, if the message
631 has one; otherwise the contents of the \"From:"\ header. It is the address to
632 which normal replies to the message should be sent.
634 \$return@_path$\: The return path -- that is, the sender field that will be
635 transmitted as part of the message's envelope if the message is sent to another
636 host. This is the address to which delivery errors are sent. In many cases,
637 this variable has the same value as \$sender@_address$\, but if, for example,
638 an incoming message to a mailing list has been expanded, \$return@_path$\ may
639 have been changed to contain the address of the list maintainer.
641 \$sender@_address$\: The sender address that was received in the envelope of
642 the message. This is not necessarily the same as the contents of the \"From:"\
643 or \"Sender:"\ header lines. For delivery error messages (`bounce messages')
644 there is no sender address, and this variable is empty.
646 \$tod@_full$\: A full version of the time and date, for example: Wed, 18 Oct
647 1995 09:51:40 +0100. The timezone is always given as a numerical offset from
648 GMT.
650 \$tod@_log$\: The time and date in the format used for writing Exim's log files,
651 without the timezone, for example: 1995-10-12 15:32:29.
653 \$tod@_zone$\: The local timezone offset, for example: +0100.
656 .section Header variables
657 .rset SECTheadervariables "~~chapter.~~section"
658 There is a special set of expansion variables containing the header lines of
659 the message being processed. These variables have names beginning with
660 \"@$header@_"\ followed by the name of the header line, terminated by a colon.
661 For example,
662 .display asis
663 $header_from:
664 $header_subject:
665 .endd
666 The whole item, including the terminating colon, is replaced by the contents of
667 the message header line. If there is more than one header line with the same
668 name, their contents are concatenated. For header lines whose data consists of
669 a list of addresses (for example, ::From:: and ::To::), a comma and newline is
670 inserted between each set of data. For all other header lines, just a newline
671 is used.
673 Leading and trailing white space is removed from header line data, and if there
674 are any MIME `words' that are encoded as defined by RFC 2047 (because they
675 contain non-ASCII characters), they are decoded and translated, if possible, to
676 a local character set. Translation is attempted only on operating systems that
677 have the \iconv(@)\ function. This makes the header line look the same as it
678 would when displayed by an MUA. The default character set is ISO-8859-1, but
679 this can be changed by means of the \"headers"\ command (see below).
681 If you want to see the actual characters that make up a header line, you can
682 specify \"@$rheader@_"\ instead of \"@$header@_"\. This inserts the `raw'
683 header line, unmodified.
685 There is also an intermediate form, requested by \"@$bheader@_"\, which removes
686 leading and trailing space and decodes MIME `words', but does not do any
687 character translation. If an attempt to decode what looks superficially like a
688 MIME `word' fails, the raw string is returned. If decoding produces a binary
689 zero character, it is replaced by a question mark.
691 The capitalization of the name following \"@$header@_"\ is not significant.
692 Because any printing character except colon may appear in the name of a
693 message's header (this is a requirement of RFC 2822, the document that
694 describes the format of a mail message) curly brackets must $it{not} be used in
695 this case, as they will be taken as part of the header name. Two shortcuts are
696 allowed in naming header variables:
697 .numberpars $.
698 The initiating \"@$header@_"\, \"@$rheader@_"\, or \"@$bheader@_"\ can be
699 abbreviated to \"@$h@_"\, \"@$rh@_"\, or \"@$bh@_"\, respectively.
700 .nextp
701 The terminating colon can be omitted if the next character is white space. The
702 white space character is retained in the expanded string. However, this is not
703 recommended, because it makes it easy to forget the colon when it really is
704 needed.
705 .endp
706 If the message does not contain a header of the given name, an empty string is
707 substituted. Thus it is important to spell the names of headers correctly. Do
708 not use \"@$header@_Reply@_to"\ when you really mean \"@$header@_Reply-to"\.
710 .section User variables
711 There are ten user variables with names \$n0$\ -- \$n9$\ that can be
712 incremented by the \"add"\ command (see section ~~SECTadd). These can be used
713 for `scoring' messages in various ways. If Exim is configured to run a `system
714 filter' on every message, the values left in these variables are copied into
715 the variables \$sn0$\ -- \$sn9$\ at the end of the system filter, thus making
716 them available to users' filter files. How these values are used is entirely up
717 to the individual installation.
719 .section Current directory
720 The contents of your filter file should not make any assumptions about the
721 current directory. It is best to use absolute paths for file names; you
722 can normally make use of the \$home$\ variable to refer to your home directory.
723 The \save\ command automatically inserts \$home$\ at the start of non-absolute
724 paths.
728 .section Significant deliveries
729 When in the course of delivery a message is processed by a filter file, what
730 happens next, that is, after the whole filter file has been processed, depends
731 on whether the filter has set up any $it{significant deliveries} or not. If
732 there is at least one significant delivery, the filter is considered to
733 have handled the entire delivery arrangements for the current address, and no
734 further processing of the address takes place. If, however, no significant
735 deliveries have been set up, Exim continues processing the current address as
736 if there were no filter file, and typically sets up a delivery of a copy of the
737 message into a local mailbox. In particular, this happens in the special case
738 of a filter file containing only comments.
740 The delivery commands \"deliver"\, \"save"\, and \"pipe"\ are by default
741 significant. However, if such a command is preceded by the word \"unseen"\, its
742 delivery is not considered to be significant. In contrast, other commands such
743 as \"mail"\ and \"vacation"\ do not count as significant deliveries unless
744 preceded by the word \"seen"\.
747 .section Filter commands
748 The filter commands which are described in subsequent sections are listed
749 below, with the section in which they are described in brackets:
750 .display rm
751 .tabs 15
752 \add\ $t increment a user variable (section ~~SECTadd)
753 \deliver\ $t deliver to an email address (section ~~SECTdeliver)
754 \fail\ $t force delivery failure (sysadmin use) (section ~~SECTfail)
755 \finish\ $t end processing (section ~~SECTfinish)
756 \freeze\ $t freeze message (sysadmin use) (section ~~SECTfreeze)
757 \headers\ $t set the header character set (section ~~SECTheaders)
758 \if\ $t test condition(s) (section ~~SECTif)
759 \logfile\ $t define log file (section ~~SECTlog)
760 \logwrite\ $t write to log file (section ~~SECTlog)
761 \mail\ $t send a reply message (section ~~SECTmail)
762 \pipe\ $t pipe to a command (section ~~SECTpipe)
763 \save\ $t save to a file (section ~~SECTsave)
764 \testprint\ $t print while testing (section ~~SECTtestprint)
765 \vacation\ $t tailored form of \mail\ (section ~~SECTmail)
766 .endd
767 In addition, when Exim's filtering facilities are being used as a system
768 filter, the \"fail"\, \"freeze"\, and \"headers"\ commands are available.
769 However, since they are usable only by the system administrator and not by
770 ordinary users, they are described in the main Exim specification rather than
771 in this document.
773 .section The add command
774 .rset SECTadd "~~chapter.~~section"
775 .display
776 add <<number>> to <<user variable>>
777 e.g. add 2 to n3
778 .endd
779 There are 10 user variables of this type, and their values can be obtained by
780 the normal expansion syntax (for example \$n3$\) in other commands. At the
781 start of filtering, these variables all contain zero. Both arguments of the
782 \"add"\ command are expanded before use, making it possible to add variables to
783 each other. Subtraction can be obtained by adding negative numbers.
786 .section The deliver command
787 .rset SECTdeliver "~~chapter.~~section"
788 .display
789 deliver <<mail address>>
790 e.g. deliver "Dr Livingstone <>"
791 .endd
792 This provides a forwarding operation. The message is sent on to the given
793 address, exactly as happens if the address had appeared in a traditional
794 \(.forward)\ file. If you want to deliver the message to a number of different
795 addresses, you can use more than one \"deliver"\ command (each one may have
796 only one address). However, duplicate addresses are discarded.
798 To deliver a copy of the message to your normal mailbox, your login name can be
799 given as the address. Once an address has been processed by the filtering
800 mechanism, an identical generated address will not be so processed again, so
801 doing this does not cause a loop.
803 However, if you have a mail alias, you should $it{not} refer to it here. For
804 example, if the mail address \"L.Gulliver"\ is aliased to \"lg103"\ then all
805 references in Gulliver's \(.forward)\ file should be to \"lg103"\. A reference
806 to the alias will not work for messages that are addressed to that alias,
807 since, like \(.forward)\ file processing, aliasing is performed only once on an
808 address, in order to avoid looping.
810 Following the new address, an optional second address, preceded by
811 \"errors@_to"\ may appear. This changes the address to which delivery errors on
812 the forwarded message will be sent. Instead of going to the message's original
813 sender, they go to this new address. For ordinary users, the only value that is
814 permitted for this address is the user whose filter file is being processed.
815 For example, the user \"lg103"\ whose mailbox is in the domain
816 \lilliput.example\ could have a filter file that contains
817 .display asis
818 deliver jon@elsewhere.example errors_to lg103@lilliput.example
819 .endd
820 Clearly, using this feature makes sense only in situations where not all
821 messages are being forwarded. In particular, bounce messages must not be
822 forwarded in this way, as this is likely to create a mail loop if something
823 goes wrong.
826 .section The save command
827 .rset SECTsave "~~chapter.~~section"
828 .display
829 save <<file name>>
830 e.g. save @$home/mail/bookfolder
831 .endd
832 This causes a copy of the message to be appended to the given file (that is,
833 the file is used as a mail folder). More than one \"save"\ command may appear;
834 each one causes a copy of the message to be written to its argument file,
835 provided they are different (duplicate \"save"\ commands are ignored).
837 If the file name does not start with a / character, the contents of the
838 \$home$\ variable are prepended, unless it is empty. In conventional
839 configurations, this variable is normally set in a user filter to the user's
840 home directory, but the system administrator may set it to some other path. In
841 some configurations, \$home$\ may be unset, in which case a non-absolute path
842 name may be generated. Such configurations convert this to an absolute path
843 when the delivery takes place. In a system filter, \$home$\ is never set.
845 The user must of course have permission to write to the file, and the writing
846 of the file takes place in a process that is running as the user, under the
847 user's primary group. Any secondary groups to which the user may belong are not
848 normally taken into account, though the system administrator can configure Exim
849 to set them up. In addition, the ability to use this command at all is
850 controlled by the system administrator -- it may be forbidden on some systems.
852 An optional mode value may be given after the file name. The value for the mode
853 is interpreted as an octal number, even if it does not begin with a zero. For
854 example:
855 .display
856 save /some/folder 640
857 .endd
858 This makes it possible for users to override the system-wide mode setting for
859 file deliveries, which is normally 600. If an existing file does not have the
860 correct mode, it is changed.
862 An alternative form of delivery may be enabled on your system, in which each
863 message is delivered into a new file in a given directory. If this is the case,
864 this functionality can be requested by giving the directory name terminated by
865 a slash after the \"save"\ command, for example
866 .display
867 save separated/messages/
868 .endd
869 There are several different formats for such deliveries; check with your system
870 administrator or local documentation to find out which (if any) are available
871 on your system. If this functionality is not enabled, the use of a path name
872 ending in a slash causes an error.
875 .section The pipe command
876 .rset SECTpipe "~~chapter.~~section"
877 .display
878 pipe <<command>>
879 e.g. pipe "@$home/bin/countmail @$sender@_address"
880 .endd
881 This command sets up delivery to a specified command using a pipe. Remember,
882 however, that no deliveries are done while the filter is being processed. All
883 deliveries happen later on. Therefore, the result of running the pipe is not
884 available to the filter.
886 When the deliveries are done, a separate process is run, and a copy of the
887 message is passed on its standard input. The process runs as the user, under
888 the user's primary group. Any secondary groups to which the user may belong are
889 not normally taken into account, though the system administrator can configure
890 Exim to set them up. More than one \"pipe"\ command may appear; each one causes
891 a copy of the message to be written to its argument pipe, provided they are
892 different (duplicate \"pipe"\ commands are ignored).
894 When the time comes to transport the message,
895 the command supplied to \"pipe"\ is split up by Exim into a command name and a
896 number of arguments. These are delimited by white space except for arguments
897 enclosed in double quotes, in which case backslash is interpreted as an escape,
898 or in single quotes, in which case no escaping is recognized. Note that as the
899 whole command is normally supplied in double quotes, a second level of quoting
900 is required for internal double quotes. For example:
901 .display asis
902 pipe "$home/myscript \"size is $message_size\""
903 .endd
904 String expansion is performed on the separate components after the line has
905 been split up, and the command is then run directly by Exim; it is not run
906 under a shell. Therefore, substitution cannot change the number of arguments,
907 nor can quotes, backslashes or other shell metacharacters in variables cause
908 confusion.
910 Documentation for some programs that are normally run via this kind of pipe
911 often suggest that the command should start with
912 .display asis
913 IFS=" "
914 .endd
915 This is a shell command, and should $it{not} be present in Exim filter files,
916 since it does not normally run the command under a shell.
918 However, there is an option that the administrator can set to cause a shell to
919 be used. In this case, the entire command is expanded as a single string and
920 passed to the shell for interpretation. It is recommended that this be avoided
921 if at all possible, since it can lead to problems when inserted variables
922 contain shell metacharacters.
924 The default \\PATH\\ set up for the command is determined by the system
925 administrator, usually containing at least \/usr/bin\ so that common commands
926 are available without having to specify an absolute file name. However, it is
927 possible for the system administrator to restrict the pipe facility so that the
928 command name must not contain any / characters, and must be found in one of the
929 directories in the configured \\PATH\\. It is also possible for the system
930 administrator to lock out the use of the \"pipe"\ command altogether.
932 When the command is run, a number of environment variables are set up. The
933 complete list for pipe deliveries may be found in the Exim reference manual.
934 Those that may be useful for pipe deliveries from user filter files are:
935 .display
936 .tabs 20
937 DOMAIN $t $rm{the domain of the address}
938 HOME $t $rm{your home directory}
939 LOCAL@_PART $t $rm{see below}
940 LOCAL@_PART@_PREFIX $t $rm{see below}
941 LOCAL@_PART@_SUFFIX $t $rm{see below}
942 LOGNAME $t $rm{your login name}
943 MESSAGE@_ID $t $rm{the message's unique id}
944 PATH $t $rm{the command search path}
945 RECIPIENT $t $rm{the complete recipient address}
946 SENDER $t $rm{the sender of the message}
947 SHELL $t $bf{/bin/sh}
948 USER $t $rm{see below}
949 .endd
950 \\LOCAL@_PART\\, \\LOGNAME\\, and \\USER\\ are all set to the same value,
951 namely, your login id. \\LOCAL@_PART@_PREFIX\\ and \\LOCAL@_PART@_SUFFIX\\ may
952 be set if Exim is configured to recognize prefixes or suffixes in the local
953 parts of addresses. For example, a message addressed to
954 \*pat-suf2@@domain.example*\ may cause user \*pat*\'s filter file to be run. If
955 this sets up a pipe delivery, \\LOCAL@_PART@_SUFFIX\\ is \"-suf2"\ when the
956 pipe command runs. The system administrator has to configure Exim specially for
957 this feature to be available.
959 If you run a command that is a shell script, be very careful in your use of
960 data from the incoming message in the commands in your script. RFC 2822 is very
961 generous in the characters that are legally permitted to appear in mail
962 addresses, and in particular, an address may begin with a vertical bar or a
963 slash. For this reason you should always use quotes round any arguments that
964 involve data from the message, like this:
965 .display asis
966 /some/command '$SENDER'
967 .endd
968 so that inserted shell meta-characters do not cause unwanted effects.
970 Remember that, as was explained earlier, the pipe command is not run at the
971 time the filter file is interpreted. The filter just defines what deliveries
972 are required for one particular addressee of a message. The deliveries
973 themselves happen later, once Exim has decided everything that needs to be done
974 for the message.
976 A consequence of this is that you cannot inspect the return code from the pipe
977 command from within the filter. Nevertheless, the code returned by the command
978 is important, because Exim uses it to decide whether the delivery has succeeded
979 or failed.
981 The command should return a zero completion code if all has gone well. Most
982 non-zero codes are treated by Exim as indicating a failure of the pipe. This is
983 treated as a delivery failure, causing the message to be returned to its
984 sender. However, there are some completion codes which are treated as temporary
985 errors. The message remains on Exim's spool disk, and the delivery is tried
986 again later, though it will ultimately time out if the delivery failures go on
987 too long. The completion codes to which this applies can be specified by the
988 system administrator; the default values are 73 and 75.
990 The pipe command should not normally write anything to its standard output or
991 standard error file descriptors. If it does, whatever is written is normally
992 returned to the sender of the message as a delivery error, though this action
993 can be varied by the system administrator.
996 .section Mail commands
997 .rset SECTmail "~~chapter.~~section"
998 There are two commands which cause the creation of a new mail message, neither
999 of which count as a significant delivery unless the command is preceded by the
1000 word \"seen"\. This is a powerful facility, but it should be used with care,
1001 because of the danger of creating infinite sequences of messages. The system
1002 administrator can forbid the use of these commands altogether.
1004 To help prevent runaway message sequences, these commands have no effect when
1005 the incoming message is a delivery error message, and messages sent by this
1006 means are treated as if they were reporting delivery errors. Thus they should
1007 never themselves cause a delivery error message to be returned. The basic
1008 mail-sending command is
1009 .display
1010 mail [to <<address-list>>]
1011 [cc <<address-list>>]
1012 [bcc <<address-list>>]
1013 [from <<address>>]
1014 [reply@_to <<address>>]
1015 [subject <<text>>]
1016 [extra@_headers <<text>>]
1017 [text <<text>>]
1018 [[expand] file <<filename>>]
1019 [return message]
1020 [log <<log file name>>]
1021 [once <<note file name>>]
1022 [once@_repeat <<time interval>>]
1023 .blank
1024 e.g. mail text "Your message about @$h@_subject: has been received"
1025 .endd
1027 Each <<address-list>> can contain a number of addresses, separated by commas,
1028 in the format of a ::To:: or ::Cc:: header line. In fact, the text you supply
1029 here is copied exactly into the appropriate header line. Thus, it may contain
1030 additional information as well as email addresses. For example:
1031 .display asis
1032 mail to "Julius Caesar <jc@rome.example>, \
1033 <ma@rome.example> (Mark A.)"
1034 .endd
1035 Similarly, the texts supplied for ::From:: and ::Reply-to:: are copied into
1036 their respective header lines.
1038 As a convenience for use in one common case, there is also a command called
1039 \vacation\. It behaves in the same way as \mail\, except that the defaults for
1040 the
1041 \"subject"\,
1042 \"file"\, \"log"\, \"once"\, and \"once@_repeat"\ options are
1043 .display
1044 subject "On vacation"
1045 expand file .vacation.msg
1046 log .vacation.log
1047 once .vacation
1048 once@_repeat 7d
1049 .endd
1050 respectively. These are the same file names and repeat period used by the
1051 traditional Unix \"vacation"\ command. The defaults can be overridden by
1052 explicit settings, but if a file name is given its contents are expanded only
1053 if explicitly requested.
1055 \**Warning**\: The \"vacation"\ command should always be used conditionally,
1056 subject to at least the \"personal"\ condition (see section ~~SECTpersonal
1057 below) so as not to send automatic replies to non-personal messages from
1058 mailing lists or elsewhere. Sending an automatic response to a mailing list or
1059 a mailing list manager is an Internet Sin.
1061 For both commands, the key/value argument pairs can appear in any order. At
1062 least one of \"text"\ or \"file"\ must appear (except with \"vacation"\); if
1063 both are present, the text string appears first in the message. If \"expand"\
1064 precedes \"file"\, each line of the file is subject to string expansion as
1065 it is included in the message.
1067 Several lines of text can be supplied to \"text"\ by including the escape
1068 sequence `@\n' in the string where newlines are required. If the command is
1069 output during filter file testing, newlines in the text are shown as `@\n'.
1071 Note that the keyword for creating a \"Reply-To:"\ header is \reply@_to\,
1072 because Exim keywords may contain underscores, but not hyphens. If the \"from"\
1073 keyword is present and the given address does not match the user who owns the
1074 forward file, Exim normally adds a \"Sender:"\ header to the message,
1075 though it can be configured not to do this.
1077 The \extra@_headers\ keyword allows you to add custom header lines to the
1078 message. The text supplied must be one or more syntactically valid RFC 2882
1079 header lines. You can use `@\n' within quoted text to specify newlines between
1080 headers, and also to define continued header lines. For example:
1081 .display asis
1082 extra_headers "h1: first\nh2: second\n continued\nh3: third"
1083 .endd
1084 No newline should appear at the end of the final header line.
1086 If no \"to"\ argument appears, the message is sent to the address in the
1087 \"@$reply@_address"\ variable (see section ~~SECTfilterstringexpansion above).
1088 An \"In-Reply-To:"\ header is automatically included in the created message,
1089 giving a reference to the message identification of the incoming message.
1091 If \"return message"\ is specified, the incoming message that caused the filter
1092 file to be run is added to the end of the message, subject to a maximum size
1093 limitation.
1095 If a log file is specified, a line is added to it for each message sent.
1097 If a \"once"\ file is specified, it is used to hold a database for remembering
1098 who has received a message, and no more than one message is ever sent to any
1099 particular address, unless \"once@_repeat"\ is set. This specifies a time
1100 interval after which another copy of the message is sent. The interval is
1101 specified as a sequence of numbers, each followed by the initial letter of one
1102 of `seconds', `minutes', `hours', `days', or `weeks'. For example,
1103 .display asis
1104 once_repeat 5d4h
1105 .endd
1106 causes a new message to be sent if 5 days and 4 hours have elapsed since the
1107 last one was sent. There must be no white space in a time interval.
1109 Commonly, the file name specified for \"once"\ is used as the base name for
1110 direct-access (DBM) file operations. There are a number of different DBM
1111 libraries in existence. Some operating systems provide one as a default, but
1112 even in this case a different one may have been used when building Exim. With
1113 some DBM libraries, specifying \"once"\ results in two files being created,
1114 with the suffixes \".dir"\ and \".pag"\ being added to the given name. With
1115 some others a single file with the suffix \".db"\ is used, or the name is used
1116 unchanged.
1118 Using a DBM file for implementing the \"once"\ feature means that the file
1119 grows as large as necessary. This is not usually a problem, but some system
1120 administrators want to put a limit on it. The facility can be configured not to
1121 use a DBM file, but instead, to use a regular file with a maximum size. The
1122 data in such a file is searched sequentially, and if the file fills up, the
1123 oldest entry is deleted to make way for a new one. This means that some
1124 correspondents may receive a second copy of the message after an unpredictable
1125 interval. Consult your local information to see if your system is configured
1126 this way.
1128 More than one \"mail"\ or \"vacation"\ command may be obeyed in a single filter
1129 run; they are all honoured, even when they are to the same recipient.
1132 .section Logging commands
1133 .rset SECTlog "~~chapter.~~section"
1134 A log can be kept of actions taken by a filter file. This facility is normally
1135 available in conventional configurations, but there are some situations where
1136 it might not be. Also, the system administrator may choose to disable it. Check
1137 your local information if in doubt.
1139 Logging takes place while the filter file is being interpreted. It does not
1140 queue up for later like the delivery commands. The reason for this is so that a
1141 log file need be opened only once for several write operations. There are two
1142 commands, neither of which constitutes a significant delivery. The first
1143 defines a file to which logging output is subsequently written:
1144 .display
1145 logfile <<file name>>
1146 e.g. logfile @$home/filter.log
1147 .endd
1148 The file name must be fully qualified. You can use \$home$\, as in this
1149 example, to refer to your home directory. The file name may optionally be
1150 followed by a mode for the file, which is used if the file has to be created.
1151 For example,
1152 .display
1153 logfile @$home/filter.log 0644
1154 .endd
1155 The number is interpreted as octal, even if it does not begin with a zero.
1156 The default for the mode is 600. It is suggested that the \"logfile"\ command
1157 normally appear as the first command in a filter file. Once \"logfile"\ has
1158 been obeyed, the \"logwrite"\ command can be used to write to the log file:
1159 .display
1160 logwrite "<<some text string>>"
1161 e.g. logwrite "@$tod@_log @$message@_id processed"
1162 .endd
1163 It is possible to have more than one \"logfile"\ command, to specify writing to
1164 different log files in different circumstances. Writing takes place at the end
1165 of the file, and a newline character is added to the end of each string if
1166 there isn't one already there. Newlines can be put in the middle of the string
1167 by using the `@\n' escape sequence. Lines from simultaneous deliveries may get
1168 interleaved in the file, as there is no interlocking, so you should plan your
1169 logging with this in mind. However, data should not get lost.
1172 .section The finish command
1173 .rset SECTfinish "~~chapter.~~section"
1174 The command \"finish"\, which has no arguments, causes Exim to stop
1175 interpreting the filter file. This is not a significant action unless preceded
1176 by \"seen"\. A filter file containing only \"seen finish"\ is a black hole.
1178 .section The testprint command
1179 .rset SECTtestprint "~~chapter.~~section"
1180 It is sometimes helpful to be able to print out the values of variables when
1181 testing filter files. The command
1182 .display
1183 testprint <<text>>
1184 e.g. testprint "home=@$home reply@_address=@$reply@_address"
1185 .endd
1186 does nothing when mail is being delivered. However, when the filtering code is
1187 being tested by means of the \-bf-\ option (see section ~~SECTtesting above),
1188 the value of the string is written to the standard output.
1190 .section The fail command
1191 .rset SECTfail "~~chapter.~~section"
1192 When Exim's filtering facilities are being used as a system filter, the
1193 \"fail"\ command is available, to force delivery failure. Because this command
1194 is normally usable only by the system administrator, and not enabled for use by
1195 ordinary users, it is described in more detail in the main Exim specification
1196 rather than in this document.
1198 .section The freeze command
1199 .rset SECTfreeze "~~chapter.~~section"
1200 When Exim's filtering facilities are being used as a system filter, the
1201 \"freeze"\ command is available, to freeze a message on the queue. Because this
1202 command is normally usable only by the system administrator, and not enabled
1203 for use by ordinary users, it is described in more detail in the main Exim
1204 specification rather than in this document.
1207 .section The headers command
1208 .rset SECTheaders "~~chapter.~~section"
1209 The \"headers"\ command can be used to change the target character set which is
1210 used when translating the contents of encoded header lines for insertion by the
1211 \"@$header@_"\ mechanism (see section ~~SECTheadervariables above). The default
1212 can be set in the Exim configuration; if not specified, ISO-8859-1 is used. The
1213 only currently supported format for the \"headers"\ command is as in this
1214 example:
1215 .display asis
1216 headers charset "UTF-8"
1217 .endd
1218 That is, \"headers"\ is followed by the word \"charset"\ and then the name of a
1219 character set. This particular example would be useful if you wanted to compare
1220 the contents of a header to a UTF-8 string.
1223 .section Obeying commands conditionally
1224 .rset SECTif "~~chapter.~~section"
1225 Most of the power of filtering comes from the ability to test conditions and
1226 obey different commands depending on the outcome. The \"if"\ command is used to
1227 specify conditional execution, and its general form is
1228 .display
1229 if <<condition>>
1230 then <<commands>>
1231 elif <<condition>>
1232 then <<commands>>
1233 else <<commands>>
1234 endif
1235 .endd
1236 There may be any number of \"elif"\ and \"then"\ sections (including none) and
1237 the \"else"\ section is also optional. Any number of commands, including nested
1238 \"if"\ commands, may appear in any of the <<commands>> sections.
1240 Conditions can be combined by using the words \"and"\ and \"or"\, and round
1241 brackets (parentheses) can be used to specify how several conditions are to
1242 combine. Without brackets, \"and"\ is more binding than \"or"\.
1243 For example,
1244 .display asis
1245 if
1246 $h_subject: contains "Make money" or
1247 $h_precedence: is "junk" or
1248 ($h_sender: matches ^\\d{8}@ and not personal) or
1249 $message_body contains "this is spam"
1250 then
1251 seen finish
1252 endif
1253 .endd
1254 A condition can be preceded by \"not"\ to negate it, and there are also some
1255 negative forms of condition that are more English-like.
1259 .section String testing conditions
1260 There are a number of conditions that operate on text strings, using the words
1261 `begins', `ends', `is', `contains' and `matches'.
1263 Note that if you want to apply the same test to more than one header line, you
1264 can easily concatenate them into a single string for testing, as in this
1265 example:
1266 .display asis
1267 if "$h_to:, $h_cc:" contains me@domain.example then ...
1268 .endd
1270 If any of the condition names are written in lower case, the testing of letters
1271 is done without regard to case; if they are written in upper case (for example,
1272 `CONTAINS') then the case of letters is significant.
1273 .display
1274 <<text1>> begins <<text2>>
1275 <<text1>> does not begin <<text2>>
1276 e.g. @$header@_from: begins "Friend@@"
1277 .endd
1278 A `begins' test checks for the presence of the second string at the start of
1279 the first, both strings having been expanded.
1280 .display
1281 <<text1>> ends <<text2>>
1282 <<text1>> does not end <<text2>>
1283 e.g. @$header@_from: ends ""
1284 .endd
1285 An `ends' test checks for the presence of the second string at the end of
1286 the first, both strings having been expanded.
1287 .display
1288 <<text1>> is <<text2>>
1289 <<text1>> is not <<text2>>
1290 e.g. @$local@_part@_suffix is "-foo"
1291 .endd
1292 An `is' test does an exact match between the strings, having first expanded
1293 both strings.
1294 .display
1295 <<text1>> contains <<text2>>
1296 <<text1>> does not contain <<text2>>
1297 e.g. @$header@_subject: contains "evolution"
1298 .endd
1299 A `contains' test does a partial string match, having expanded both strings.
1300 .display
1301 <<text1>> matches <<text2>>
1302 <<text1>> does not match <<text2>>
1303 e.g. @$sender@_address matches "(bill|john)@@"
1304 .endd
1305 For a `matches' test, after expansion of both strings, the second one is
1306 interpreted as a regular expression. Exim uses the PCRE regular expression
1307 library, which provides regular expressions that are compatible with Perl.
1309 .em
1310 The match succeeds if the regular expression matches any part of the first
1311 string. If you want a regular expression to match only at the start or end of
1312 the subject string, you must encode that requirement explicitly, using the @^
1313 or @$ metacharacters. The above example, which is not so constrained, matches
1314 all these addresses:
1315 .display asis
1316 bill@test.example
1317 john@some.example
1320 .endd
1321 To match only the first two, you could use this:
1322 .display asis
1323 if $sender_address matches "^(bill|john)@" then ...
1324 .endd
1325 .nem
1327 Care must be taken if you need a backslash in a regular expression, because
1328 backslashes are interpreted as escape characters both by the string expansion
1329 code and by Exim's normal processing of strings in quotes. For example, if you
1330 want to test the sender address for a domain ending in \".com"\ the regular
1331 expression is
1332 .display asis
1333 \.com$
1334 .endd
1335 The backslash and dollar sign in that expression have to be escaped when used
1336 in a filter command, as otherwise they would be interpreted by the expansion
1337 code. Thus what you actually write is
1338 .display asis
1339 if $sender_address matches \\.com\$
1340 .endd
1341 An alternative way of handling this is to make use of the \"@\N"\ expansion
1342 flag for suppressing expansion:
1343 .display asis
1344 if $sender_address matches \N\.com$\N
1345 .endd
1346 Everything between the two occurrences of \"@\N"\ is copied without change by
1347 the string expander (and in fact you do not need the final one, because it is
1348 at the end of the string).
1350 If the regular expression is given in quotes (mandatory only if it contains
1351 white space) you have to write either
1352 .display asis
1353 if $sender_address matches "\\\\.com\\$"
1354 .endd
1355 or
1356 .display asis
1357 if $sender_address matches "\\N\\.com$\\N"
1358 .endd
1361 If the regular expression contains bracketed sub-expressions, numeric
1362 variable substitutions such as \$1$\ can be used in the subsequent actions
1363 after a successful match. If the match fails, the values of the numeric
1364 variables remain unchanged. Previous values are not restored after \"endif"\ --
1365 in other words, only one set of values is ever available. If the condition
1366 contains several sub-conditions connected by \"and"\ or \"or"\, it is the
1367 strings extracted from the last successful match that are available in
1368 subsequent actions. Numeric variables from any one sub-condition are also
1369 available for use in subsequent sub-conditions, since string expansion of a
1370 condition occurs just before it is tested.
1372 .section Numeric testing conditions
1373 The following conditions are available for performing numerical tests:
1374 .display
1375 <<number1>> is above <<number2>>
1376 <<number1>> is not above <<number2>>
1377 <<number1>> is below <<number2>>
1378 <<number1>> is not below <<number2>>
1379 e.g. @$message@_size is not above 10k
1380 .endd
1381 The <<number>> arguments must expand to strings of digits, optionally followed
1382 by one of the letters K or M (upper case or lower case) which cause
1383 multiplication by 1024 and 1024x1024 respectively.
1385 .section Testing for significant deliveries
1386 Whether or not any previously obeyed filter commands have resulted in a
1387 significant delivery can be tested by the condition \"delivered"\, for example:
1388 .display asis
1389 if not delivered then save mail/anomalous endif
1390 .endd
1392 .section Testing for error messages
1393 The condition \"error@_message"\ is true if the incoming message is a mail
1394 delivery error message (bounce message). Putting the command
1395 .display asis
1396 if error_message then finish endif
1397 .endd
1398 at the head of your filter file is a useful insurance against things going
1399 wrong in such a way that you cannot receive delivery error reports, and is
1400 highly recommended. Note that \"error@_message"\ is a condition, not an
1401 expansion variable, and therefore is not preceded by \@$\.
1403 .section Testing for personal mail
1404 .rset SECTpersonal "~~chapter.~~section"
1405 A common requirement is to distinguish between incoming personal mail and mail
1406 from a mailing list,
1407 or from a robot or other automatic process (for example, a bounce message).
1408 In particular, this test is normally required for so-called `vacation
1409 messages'. The condition
1410 .display
1411 personal
1412 .endd
1413 is a shorthand for
1414 .display
1415 not error@_message and
1416 @$header@_to: contains "@$local@_part@@@$domain" and
1417 @$header@_from: does not contain "@$local@_part@@@$domain" and
1418 @$header@_from: does not contain "server@@" and
1419 @$header@_from: does not contain "daemon@@" and
1420 @$header@_from: does not contain "root@@" and
1421 @$header@_auto-submitted: does not contain "auto-" and
1422 @$header@_subject: does not contain "circular" and
1423 @$header@_precedence: does not contain "bulk" and
1424 @$header@_precedence: does not contain "list" and
1425 @$header@_precedence: does not contain "junk"
1426 .endd
1427 The variable \$local@_part$\ contains the local part of the mail address of
1428 the user whose filter file is being run -- it is normally your login id. The
1429 \$domain$\ variable contains the mail domain. This condition tests for the
1430 appearance of the current user in the \"To:"\ header, checks that the sender is
1431 not the current user or one of a number of common daemons, and checks the
1432 content of the \"Subject:"\ and \"Precedence:"\ headers.
1434 If prefixes or suffixes are in use for local parts -- something which depends
1435 on the configuration of Exim (see section ~~SECTmbox below) -- the first two
1436 tests above are also done with
1437 .display asis
1438 $local_part_prefix$local_part$local_part_suffix
1439 .endd
1440 instead of just \$local@_part$\. If the system is configured to rewrite local
1441 parts of mail addresses, for example, to rewrite `dag46' as `Dirk.Gently',
1442 the rewritten form of the address is also used in the tests.
1444 This example shows the use of \"personal"\ in a filter file that is sending out
1445 vacation messages:
1446 .display asis
1447 if personal then
1448 mail
1449 to $reply_address
1450 subject "Re: $h_subject:"
1451 file $home/vacation/message
1452 once $home/vacation/once
1453 once_repeat 10d
1454 endif
1455 .endd
1457 It is quite common for people who have mail accounts on a number of different
1458 systems to forward all their mail to one system, and in this case a check for
1459 personal mail should test all their various mail addresses. To allow for this,
1460 the \"personal"\ condition keyword can be followed by
1461 .display
1462 alias <<address>>
1463 .endd
1464 any number of times, for example
1465 .display asis
1466 if personal alias smith@else.where.example
1467 alias
1468 then ...
1469 .endd
1470 This causes messages containing the alias addresses in any places where the
1471 local address is tested to be treated as personal.
1473 .section Testing delivery status
1474 There are two conditions which are intended mainly for use in system filter
1475 files, but which are available in users' filter files as well. The condition
1476 \"first@_delivery"\ is true if this is the first attempt to deliver the
1477 message, and false otherwise.
1478 .em
1479 This indicator is not reset until the first delivery process successfully
1480 terminates; if there is a crash or a power failure (for example), the next
1481 delivery attempt is also a `first delivery'.
1482 .nem
1484 In a user filter file it will be false only if
1485 there was previously an error in the filter, or if a delivery for the user
1486 failed owing to, for example, a quota error, or forwarding to a remote
1487 address that was deferred for some reason.
1489 The condition \"manually@_thawed"\ is true only if the message was `frozen' for
1490 some reason, and was subsequently released by the system administrator. It is
1491 unlikely to be of use in users' filter files.
1493 .section Testing a list of addresses
1494 There is a facility for looping through a list of addresses and applying a
1495 condition to each of them. It takes the form
1496 .display
1497 foranyaddress <<string>> (<<condition>>)
1498 .endd
1499 where <<string>> is interpreted as a list of RFC 2822 addresses, as in a
1500 typical header line, and <<condition>> is any valid filter condition or
1501 combination of conditions. The `group' syntax that is defined for certain
1502 header lines that contain addresses is supported.
1504 The parentheses surrounding the condition are mandatory, to delimit it from
1505 possible further sub-conditions of the enclosing \"if"\ command. Within the
1506 condition, the expansion variable \$thisaddress$\ is set to the non-comment
1507 portion of each of the addresses in the string in turn. For example, if the
1508 string is
1509 .display asis
1510 B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1511 .endd
1512 then \$thisaddress$\ would take on the values \"bart@@sfld.example"\ and
1513 \"lisa@@sfld.example"\ in turn.
1515 If there are no valid addresses in the list, the whole condition is false. If
1516 the internal condition is true for any one address, the overall condition is
1517 true and the loop ends. If the internal condition is false for all addresses in
1518 the list, the overall condition is false. This example tests for the presence
1519 of an eight-digit local part in any address in a \To:\ header:
1520 .display asis
1521 if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1522 .endd
1523 When the overall condition is true, the value of \$thisaddress$\ in the
1524 commands that follow \"then"\ is the last value it took on inside the loop. At
1525 the end of the \"if"\ command, the value of \$thisaddress$\ is reset to what it
1526 was before. It is best to avoid the use of multiple occurrences of
1527 \"foranyaddress"\, nested or otherwise, in a single \"if"\ command, if the
1528 value of \$thisaddress$\ is to be used afterwards, because it isn't always
1529 clear what the value will be. Nested \"if"\ commands should be used instead.
1531 Header lines can be joined together if a check is to be applied to more than
1532 one of them. For example:
1533 .display asis
1534 if foranyaddress $h_to:,$h_cc: ....
1535 .endd
1536 scans through the addresses in both the \To:\ and the \Cc:\ headers.
1538 .section Multiple personal mailboxes
1539 .rset SECTmbox "~~chapter.~~section"
1540 The system administrator can configure Exim so that users can set up variants
1541 on their email addresses and handle them separately. Consult your system
1542 administrator or local documentation to see if this facility is enabled on your
1543 system, and if so, what the details are.
1545 The facility involves the use of a prefix or a suffix on an email address. For
1546 example, all mail addressed to \lg103-<<something>>\ would be the property of
1547 user \lg103\, who could determine how it was to be handled, depending on the
1548 value of <<something>>.
1550 There are two possible ways in which this can be set up. The first possibility
1551 is the use of multiple \(.forward)\ files. In this case, mail to \lg103-foo\,
1552 for example, is handled by looking for a file called \.forward-foo\ in
1553 \lg103's\ home directory. If such a file does not exist, delivery fails and the
1554 message is returned to its sender.
1556 The alternative approach is to pass all messages through a single \(.forward)\
1557 file, which must be a filter file in order to distinguish between the different
1558 cases by referencing the variables \$local@_part@_prefix$\ or
1559 \$local@_part@_suffix$\, as in the final example in section ~~SECTex below. If
1560 the filter file does not handle a prefixed or suffixed address, delivery fails
1561 and the message is returned to its sender.
1563 It is possible to configure Exim to support both schemes at once. In this case,
1564 a specific \.forward-foo\ file is first sought; if it is not found, the basic
1565 \(.forward)\ file is used.
1567 The \"personal"\ test (see section ~~SECTpersonal) includes prefixes and
1568 suffixes in its checking.
1571 .section Ignoring delivery errors
1572 As was explained above, filtering just sets up addresses for delivery -- no
1573 deliveries are actually done while a filter file is active. If any of the
1574 generated addresses subsequently suffers a delivery failure, an error message
1575 is generated in the normal way. However, if the filter command which sets up a
1576 delivery is preceded by the word \"noerror"\, errors for that delivery,
1577 $it{and any deliveries consequent on it} (that is, from alias, forwarding, or
1578 filter files it invokes) are ignored.
1581 .section Examples of Exim filter commands
1582 .rset SECTex "~~chapter.~~section"
1583 Simple forwarding:
1584 .display asis
1585 # Exim filter
1586 deliver baggins@rivendell.middle-earth.example
1587 .endd
1588 Vacation handling using traditional means, assuming that the \.vacation.msg\
1589 and other files have been set up in your home directory:
1590 .display asis
1591 # Exim filter
1592 unseen pipe "/usr/ucb/vacation \"$local_part\""
1593 .endd
1594 Vacation handling inside Exim, having first created a file called
1595 \.vacation.msg\ in your home directory:
1596 .display asis
1597 # Exim filter
1598 if personal then vacation endif
1599 .endd
1600 File some messages by subject:
1601 .display asis
1602 # Exim filter
1603 if $header_subject: contains "empire" or
1604 $header_subject: contains "foundation"
1605 then
1606 save $home/mail/f+e
1607 endif
1608 .endd
1609 Save all non-urgent messages by weekday:
1610 .display asis
1611 # Exim filter
1612 if $header_subject: does not contain "urgent" and
1613 $tod_full matches "^(...),"
1614 then
1615 save $home/mail/$1
1616 endif
1617 .endd
1618 Throw away all mail from one site, except from postmaster:
1619 .display asis
1620 # Exim filter
1621 if $reply_address contains "" and
1622 $reply_address does not contain "postmaster@"
1623 then
1624 seen finish
1625 endif
1626 .endd
1627 .if ~~sgcal
1628 .if ~~sys.leftonpage < 6ld
1629 .newpage
1630 .fi
1631 .fi
1632 Handle multiple personal mailboxes
1633 .display asis
1634 # Exim filter
1635 if $local_part_suffix is "-foo"
1636 then
1637 save $home/mail/foo
1638 elif $local_part_suffix is "-bar"
1639 then
1640 save $home/mail/bar
1641 endif
1642 .endd
1644 . End of filter