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10 toc_title="Exim's interfaces to mail filtering"
14 <title>Exim's interfaces to mail filtering</title>
15 <titleabbrev>Exim filtering</titleabbrev>
16 <date>23 August 2007</date>
17 <author><firstname>Philip</firstname><surname>Hazel</surname></author>
18 <authorinitials>PH</authorinitials>
19 <revhistory><revision>
20 <revnumber>4.69</revnumber>
21 <date>23 August2007</date>
22 <authorinitials>PH</authorinitials>
23 </revision></revhistory>
24 <copyright><year>2007</year><holder>University of Cambridge</holder></copyright>
26 <chapter id="CHAPforandfilt">
27 <title>Forwarding and filtering in Exim</title>
29 This document describes the user interfaces to Exim’s in-built mail filtering
30 facilities, and is copyright © University of Cambridge 2007. It
31 corresponds to Exim version 4.68.
34 <title>Introduction</title>
36 Most Unix mail transfer agents (programs that deliver mail) permit individual
37 users to specify automatic forwarding of their mail, usually by placing a list
38 of forwarding addresses in a file called <filename>.forward</filename> in their home
39 directories. Exim extends this facility by allowing the forwarding instructions
40 to be a set of rules rather than just a list of addresses, in effect providing
41 <quote><filename>.forward</filename> with conditions</quote>. Operating the set of rules is called
42 <emphasis>filtering</emphasis>, and the file that contains them is called a <emphasis>filter file</emphasis>.
45 Exim supports two different kinds of filter file. An <emphasis>Exim filter</emphasis> contains
46 instructions in a format that is unique to Exim. A <emphasis>Sieve filter</emphasis> contains
47 instructions in the Sieve format that is defined by RFC 3028. As this is a
48 standard format, Sieve filter files may already be familiar to some users.
49 Sieve files should also be portable between different environments. However,
50 the Exim filtering facility contains more features (such as variable
51 expansion), and better integration with the host environment (such as the use
52 of external processes and pipes).
55 The choice of which kind of filter to use can be left to the end-user, provided
56 that the system administrator has configured Exim appropriately for both kinds
57 of filter. However, if interoperability is important, Sieve is the only
61 The ability to use filtering or traditional forwarding has to be enabled by the
62 system administrator, and some of the individual facilities can be separately
63 enabled or disabled. A local document should be provided to describe exactly
64 what has been enabled. In the absence of this, consult your system
68 This document describes how to use a filter file and the format of its
69 contents. It is intended for use by end-users. Both Sieve filters and Exim
70 filters are covered. However, for Sieve filters, only issues that relate to the
71 Exim implementation are discussed, since Sieve itself is described elsewhere.
74 The contents of traditional <filename>.forward</filename> files are not described here. They
75 normally contain just a list of addresses, file names, or pipe commands,
76 separated by commas or newlines, but other types of item are also available.
77 The full details can be found in the chapter on the <command>redirect</command> router in the
78 Exim specification, which also describes how the system administrator can set
79 up and control the use of filtering.
83 <title>Filter operation</title>
85 It is important to realize that, in Exim, no deliveries are actually made while
86 a filter or traditional <filename>.forward</filename> file is being processed. Running a filter
87 or processing a traditional <filename>.forward</filename> file sets up future delivery
88 operations, but does not carry them out.
91 The result of filter or <filename>.forward</filename> file processing is a list of destinations
92 to which a message should be delivered. The deliveries themselves take place
93 later, along with all other deliveries for the message. This means that it is
94 not possible to test for successful deliveries while filtering. It also means
95 that any duplicate addresses that are generated are dropped, because Exim never
96 delivers the same message to the same address more than once.
99 <section id="SECTtesting">
100 <title>Testing a new filter file</title>
102 Filter files, especially the more complicated ones, should always be tested, as
103 it is easy to make mistakes. Exim provides a facility for preliminary testing
104 of a filter file before installing it. This tests the syntax of the file and
105 its basic operation, and can also be used with traditional <filename>.forward</filename> files.
108 Because a filter can do tests on the content of messages, a test message is
109 required. Suppose you have a new filter file called <filename>myfilter</filename> and a test
110 message in a file called <filename>test-message</filename>. Assuming that Exim is installed with
111 the conventional path name <filename>/usr/sbin/sendmail</filename> (some operating systems use
112 <filename>/usr/lib/sendmail</filename>), the following command can be used:
114 <literallayout class="monospaced">
115 /usr/sbin/sendmail -bf myfilter <test-message
118 The <option>-bf</option> option tells Exim that the following item on the command line is
119 the name of a filter file that is to be tested. There is also a <option>-bF</option> option,
120 which is similar, but which is used for testing system filter files, as opposed
121 to user filter files, and which is therefore of use only to the system
125 The test message is supplied on the standard input. If there are no
126 message-dependent tests in the filter, an empty file (<filename>/dev/null</filename>) can be
127 used. A supplied message must start with header lines or the <quote>From </quote> message
128 separator line that is found in many multi-message folder files. Note that
129 blank lines at the start terminate the header lines. A warning is given if no
130 header lines are read.
133 The result of running this command, provided no errors are detected in the
134 filter file, is a list of the actions that Exim would try to take if presented
135 with the message for real. For example, for an Exim filter, the output
137 <literallayout class="monospaced">
138 Deliver message to: gulliver@lilliput.fict.example
139 Save message to: /home/lemuel/mail/archive
142 means that one copy of the message would be sent to
143 <emphasis>gulliver@lilliput.fict.example</emphasis>, and another would be added to the file
144 <filename>/home/lemuel/mail/archive</filename>, if all went well.
147 The actions themselves are not attempted while testing a filter file in this
148 way; there is no check, for example, that any forwarding addresses are valid.
149 For an Exim filter, if you want to know why a particular action is being taken,
150 add the <option>-v</option> option to the command. This causes Exim to output the results of
151 any conditional tests and to indent its output according to the depth of
152 nesting of <command>if</command> commands. Further additional output from a filter test can be
153 generated by the <command>testprint</command> command, which is described below.
156 When Exim is outputting a list of the actions it would take, if any text
157 strings are included in the output, non-printing characters therein are
158 converted to escape sequences. In particular, if any text string contains a
159 newline character, this is shown as <quote>\n</quote> in the testing output.
162 When testing a filter in this way, Exim makes up an <quote>envelope</quote> for the
163 message. The recipient is by default the user running the command, and so is
164 the sender, but the command can be run with the <option>-f</option> option to supply a
165 different sender. For example,
167 <literallayout class="monospaced">
168 /usr/sbin/sendmail -bf myfilter \
169 -f islington@never.where <test-message
172 Alternatively, if the <option>-f</option> option is not used, but the first line of the
173 supplied message is a <quote>From </quote> separator from a message folder file (not the
174 same thing as a <emphasis>From:</emphasis> header line), the sender is taken from there. If
175 <option>-f</option> is present, the contents of any <quote>From </quote> line are ignored.
178 The <quote>return path</quote> is the same as the envelope sender, unless the message
179 contains a <emphasis>Return-path:</emphasis> header, in which case it is taken from there. You
180 need not worry about any of this unless you want to test out features of a
181 filter file that rely on the sender address or the return path.
184 It is possible to change the envelope recipient by specifying further options.
185 The <option>-bfd</option> option changes the domain of the recipient address, while the
186 <option>-bfl</option> option changes the <quote>local part</quote>, that is, the part before the @
187 sign. An adviser could make use of these to test someone else’s filter file.
190 The <option>-bfp</option> and <option>-bfs</option> options specify the prefix or suffix for the local
191 part. These are relevant only when support for multiple personal mailboxes is
192 implemented; see the description in section <xref linkend="SECTmbox"/> below.
196 <title>Installing a filter file</title>
198 A filter file is normally installed under the name <filename>.forward</filename> in your home
199 directory – it is distinguished from a conventional <filename>.forward</filename> file by its
200 first line (described below). However, the file name is configurable, and some
201 system administrators may choose to use some different name or location for
206 <title>Testing an installed filter file</title>
208 Testing a filter file before installation cannot find every potential problem;
209 for example, it does not actually run commands to which messages are piped.
210 Some <quote>live</quote> tests should therefore also be done once a filter is installed.
213 If at all possible, test your filter file by sending messages from some other
214 account. If you send a message to yourself from the filtered account, and
215 delivery fails, the error message will be sent back to the same account, which
216 may cause another delivery failure. It won’t cause an infinite sequence of such
217 messages, because delivery failure messages do not themselves generate further
218 messages. However, it does mean that the failure won’t be returned to you, and
219 also that the postmaster will have to investigate the stuck message.
222 If you have to test an Exim filter from the same account, a sensible precaution
223 is to include the line
225 <literallayout class="monospaced">
226 if error_message then finish endif
229 as the first filter command, at least while testing. This causes filtering to
230 be abandoned for a delivery failure message, and since no destinations are
231 generated, the message goes on to be delivered to the original address. Unless
232 there is a good reason for not doing so, it is recommended that the above test
233 be left in all Exim filter files. (This does not apply to Sieve files.)
237 <title>Details of filtering commands</title>
239 The filtering commands for Sieve and Exim filters are completely different in
240 syntax and semantics. The Sieve mechanism is defined in RFC 3028; in the next
241 chapter we describe how it is integrated into Exim. The subsequent chapter
242 covers Exim filtering commands in detail.
247 <chapter id="CHAPsievefilter">
248 <title>Sieve filter files</title>
250 The code for Sieve filtering in Exim was contributed by Michael Haardt, and
251 most of the content of this chapter is taken from the notes he provided. Since
252 Sieve is an extensible language, it is important to understand <quote>Sieve</quote> in
253 this context as <quote>the specific implementation of Sieve for Exim</quote>.
256 This chapter does not contain a description of Sieve, since that can be found
257 in RFC 3028, which should be read in conjunction with these notes.
260 The Exim Sieve implementation offers the core as defined by RFC 3028,
261 comparison tests, the subaddress parameter, the <emphasis role="bold">copy</emphasis>, <emphasis role="bold">envelope</emphasis>,
262 <emphasis role="bold">fileinto</emphasis>, <emphasis role="bold">notify</emphasis>, and <emphasis role="bold">vacation</emphasis> extensions, but not the <emphasis role="bold">reject</emphasis>
263 extension. Exim does not support message delivery notifications (MDNs), so
264 adding it just to the Sieve filter (as required for <emphasis role="bold">reject</emphasis>) makes little
268 In order for Sieve to work properly in Exim, the system administrator needs to
269 make some adjustments to the Exim configuration. These are described in the
270 chapter on the <command>redirect</command> router in the full Exim specification.
273 <title>Recognition of Sieve filters</title>
275 A filter file is interpreted as a Sieve filter if its first line is
277 <literallayout class="monospaced">
281 This is what distinguishes it from a conventional <filename>.forward</filename> file or an Exim
286 <title>Saving to specified folders</title>
288 If the system administrator has set things up as suggested in the Exim
289 specification, and you use <command>keep</command> or <command>fileinto</command> to save a mail into a
290 folder, absolute files are stored where specified, relative files are stored
291 relative to <varname>$home</varname>, and <filename>inbox</filename> goes to the standard mailbox location.
295 <title>Strings containing header names</title>
297 RFC 3028 does not specify what happens if a string denoting a header field does
298 not contain a valid header name, for example, it contains a colon. This
299 implementation generates an error instead of ignoring the header field in order
300 to ease script debugging, which fits in with the common picture of Sieve.
304 <title>Exists test with empty list of headers</title>
306 The <emphasis role="bold">exists</emphasis> test succeeds only if all the specified headers exist. RFC 3028
307 does not explicitly specify what happens on an empty list of headers. This
308 implementation evaluates that condition as true, interpreting the RFC in a
313 <title>Header test with invalid MIME encoding in header</title>
315 Some MUAs process invalid base64 encoded data, generating junk. Others ignore
316 junk after seeing an equal sign in base64 encoded data. RFC 2047 does not
317 specify how to react in this case, other than stating that a client must not
318 forbid to process a message for that reason. RFC 2045 specifies that invalid
319 data should be ignored (apparently looking at end of line characters). It also
320 specifies that invalid data may lead to rejecting messages containing them (and
321 there it appears to talk about true encoding violations), which is a clear
322 contradiction to ignoring them.
325 RFC 3028 does not specify how to process incorrect MIME words. This
326 implementation treats them literally, as it does if the word is correct but its
327 character set cannot be converted to UTF-8.
331 <title>Address test for multiple addresses per header</title>
333 A header may contain multiple addresses. RFC 3028 does not explicitly specify
334 how to deal with them, but since the address test checks if anything matches
335 anything else, matching one address suffices to satisfy the condition. That
336 makes it impossible to test if a header contains a certain set of addresses and
337 no more, but it is more logical than letting the test fail if the header
338 contains an additional address besides the one the test checks for.
342 <title>Semantics of keep</title>
344 The <command>keep</command> command is equivalent to
346 <literallayout class="monospaced">
350 It saves the message and resets the implicit keep flag. It does not set the
351 implicit keep flag; there is no command to set it once it has been reset.
355 <title>Semantics of fileinto</title>
357 RFC 3028 does not specify whether <command>fileinto</command> should try to create a mail
358 folder if it does not exist. This implementation allows the sysadmin to
359 configure that aspect using the <command>appendfile</command> transport options
360 <option>create_directory</option>, <option>create_file</option>, and <option>file_must_exist</option>. See the
361 <command>appendfile</command> transport in the Exim specification for details.
365 <title>Semantics of redirect</title>
367 Sieve scripts are supposed to be interoperable between servers, so this
368 implementation does not allow mail to be redirected to unqualified addresses,
369 because the domain would depend on the system being used. On systems with
370 virtual mail domains, the default domain is probably not what the user expects
375 <title>String arguments</title>
377 There has been confusion if the string arguments to <command>require</command> are to be
378 matched case-sensitively or not. This implementation matches them with the
379 match type <command>:is</command> (default, see section 2.7.1 of the RFC) and the comparator
380 <command>i;ascii-casemap</command> (default, see section 2.7.3 of the RFC). The RFC defines
381 the command defaults clearly, so any different implementations violate RFC
382 3028. The same is valid for comparator names, also specified as strings.
386 <title>Number units</title>
388 There is a mistake in RFC 3028: the suffix G denotes gibi-, not tebibyte.
389 The mistake is obvious, because RFC 3028 specifies G to denote 2^30
390 (which is gibi, not tebi), and that is what this implementation uses as
391 the scaling factor for the suffix G.
395 <title>RFC compliance</title>
397 Exim requires the first line of a Sieve filter to be
399 <literallayout class="monospaced">
403 Of course the RFC does not specify that line. Do not expect examples to work
404 without adding it, though.
407 RFC 3028 requires the use of CRLF to terminate a line. The rationale was that
408 CRLF is universally used in network protocols to mark the end of the line. This
409 implementation does not embed Sieve in a network protocol, but uses Sieve
410 scripts as part of the Exim MTA. Since all parts of Exim use LF as the newline
411 character, this implementation does, too, by default, though the system
412 administrator may choose (at Exim compile time) to use CRLF instead.
415 Exim violates RFC 2822, section 3.6.8, by accepting 8-bit header names, so this
416 implementation repeats this violation to stay consistent with Exim. This is in
417 preparation for UTF-8 data.
420 Sieve scripts cannot contain NUL characters in strings, but mail headers could
421 contain MIME encoded NUL characters, which could never be matched by Sieve
422 scripts using exact comparisons. For that reason, this implementation extends
423 the Sieve quoted string syntax with \0 to describe a NUL character, violating
424 \0 being the same as 0 in RFC 3028. Even without using \0, the following tests
425 are all true in this implementation. Implementations that use C-style strings
426 will only evaluate the first test as true.
428 <literallayout class="monospaced">
429 Subject: =?iso-8859-1?q?abc=00def
431 header :contains "Subject" ["abc"]
432 header :contains "Subject" ["def"]
433 header :matches "Subject" ["abc?def"]
436 Note that by considering Sieve to be an MUA, RFC 2047 can be interpreted in a
437 way that NUL characters truncating strings is allowed for Sieve
438 implementations, although not recommended. It is further allowed to use encoded
439 NUL characters in headers, but that’s not recommended either. The above example
443 RFC 3028 states that if an implementation fails to convert a character set to
444 UTF-8, two strings cannot be equal if one contains octets greater than 127.
445 Assuming that all unknown character sets are one-byte character sets with the
446 lower 128 octets being US-ASCII is not sound, so this implementation violates
447 RFC 3028 and treats such MIME words literally. That way at least something
451 The folder specified by <command>fileinto</command> must not contain the character sequence
452 <quote>..</quote> to avoid security problems. RFC 3028 does not specify the syntax of
453 folders apart from <command>keep</command> being equivalent to
455 <literallayout class="monospaced">
459 This implementation uses <filename>inbox</filename> instead.
462 Sieve script errors currently cause messages to be silently filed into
463 <filename>inbox</filename>. RFC 3028 requires that the user is notified of that condition.
464 This may be implemented in the future by adding a header line to mails that
465 are filed into <filename>inbox</filename> due to an error in the filter.
470 <chapter id="CHAPeximfilter">
471 <title>Exim filter files</title>
473 This chapter contains a full description of the contents of Exim filter files.
476 <title>Format of Exim filter files</title>
478 Apart from leading white space, the first text in an Exim filter file must be
480 <literallayout class="monospaced">
484 This is what distinguishes it from a conventional <filename>.forward</filename> file or a Sieve
485 filter file. If the file does not have this initial line (or the equivalent for
486 a Sieve filter), it is treated as a conventional <filename>.forward</filename> file, both when
487 delivering mail and when using the <option>-bf</option> testing mechanism. The white space
488 in the line is optional, and any capitalization may be used. Further text on
489 the same line is treated as a comment. For example, you could have
491 <literallayout class="monospaced">
492 # Exim filter <<== do not edit or remove this line!
495 The remainder of the file is a sequence of filtering commands, which consist of
496 keywords and data values. For example, in the command
498 <literallayout class="monospaced">
499 deliver gulliver@lilliput.fict.example
502 the keyword is <literal>deliver</literal> and the data value is
503 <literal>gulliver@lilliput.fict.example</literal>. White space or line breaks separate the
504 components of a command, except in the case of conditions for the <command>if</command>
505 command, where round brackets (parentheses) also act as separators. Complete
506 commands are separated from each other by white space or line breaks; there are
507 no special terminators. Thus, several commands may appear on one line, or one
508 command may be spread over a number of lines.
511 If the character # follows a separator anywhere in a command, everything from
512 # up to the next newline is ignored. This provides a way of including comments
517 <title>Data values in filter commands</title>
519 There are two ways in which a data value can be input:
524 If the text contains no white space, it can be typed verbatim. However, if it
525 is part of a condition, it must also be free of round brackets (parentheses),
526 as these are used for grouping in conditions.
531 Otherwise, text must be enclosed in double quotation marks. In this case, the
532 character \ (backslash) is treated as an <quote>escape character</quote> within the
533 string, causing the following character or characters to be treated specially:
536 <literal>\n</literal> is replaced by a newline
537 <literal>\r</literal> is replaced by a carriage return
538 <literal>\t</literal> is replaced by a tab
543 Backslash followed by up to three octal digits is replaced by the character
544 specified by those digits, and <literal>\x</literal> followed by up to two hexadecimal digits
545 is treated similarly. Backslash followed by any other character is replaced by
546 the second character, so that in particular, <literal>\"</literal> becomes <literal>"</literal> and <literal>\\</literal>
547 becomes <literal>\</literal>. A data item enclosed in double quotes can be continued onto the
548 next line by ending the first line with a backslash. Any leading white space at
549 the start of the continuation line is ignored.
552 In addition to the escape character processing that occurs when strings are
553 enclosed in quotes, most data values are also subject to <emphasis>string expansion</emphasis>
554 (as described in the next section), in which case the characters <literal>$</literal> and
555 <literal>\</literal> are also significant. This means that if a single backslash is actually
556 required in such a string, and the string is also quoted, <literal>\\\\</literal> has to be
560 The maximum permitted length of a data string, before expansion, is 1024
564 <section id="SECTfilterstringexpansion">
565 <title>String expansion</title>
567 Most data values are expanded before use. Expansion consists of replacing
568 substrings beginning with <literal>$</literal> with other text. The full expansion facilities
569 available in Exim are extensive. If you want to know everything that Exim can
570 do with strings, you should consult the chapter on string expansion in the Exim
574 In filter files, by far the most common use of string expansion is the
575 substitution of the contents of a variable. For example, the substring
577 <literallayout class="monospaced">
581 is replaced by the address to which replies to the message should be sent. If
582 such a variable name is followed by a letter or digit or underscore, it must be
583 enclosed in curly brackets (braces), for example,
585 <literallayout class="monospaced">
589 If a <literal>$</literal> character is actually required in an expanded string, it must be
590 escaped with a backslash, and because backslash is also an escape character in
591 quoted input strings, it must be doubled in that case. The following two
592 examples illustrate two different ways of testing for a <literal>$</literal> character in a
595 <literallayout class="monospaced">
596 if $message_body contains \$ then ...
597 if $message_body contains "\\$" then ...
600 You can prevent part of a string from being expanded by enclosing it between
601 two occurrences of <literal>\N</literal>. For example,
603 <literallayout class="monospaced">
604 if $message_body contains \N$$$$\N then ...
607 tests for a run of four dollar characters.
611 <title>Some useful general variables</title>
613 A complete list of the available variables is given in the Exim documentation.
614 This shortened list contains the ones that are most likely to be useful in
615 personal filter files:
618 <varname>$body_linecount</varname>: The number of lines in the body of the message.
621 <varname>$body_zerocount</varname>: The number of binary zero characters in the body of the
625 <varname>$home</varname>: In conventional configurations, this variable normally contains the
626 user’s home directory. The system administrator can, however, change this.
629 <varname>$local_part</varname>: The part of the email address that precedes the @ sign –
630 normally the user’s login name. If support for multiple personal mailboxes is
631 enabled (see section <xref linkend="SECTmbox"/> below) and a prefix or suffix for the local
632 part was recognized, it is removed from the string in this variable.
635 <varname>$local_part_prefix</varname>: If support for multiple personal mailboxes is enabled
636 (see section <xref linkend="SECTmbox"/> below), and a local part prefix was recognized,
637 this variable contains the prefix. Otherwise it contains an empty string.
640 <varname>$local_part_suffix</varname>: If support for multiple personal mailboxes is enabled
641 (see section <xref linkend="SECTmbox"/> below), and a local part suffix was recognized,
642 this variable contains the suffix. Otherwise it contains an empty string.
645 <varname>$message_body</varname>: The initial portion of the body of the message. By default,
646 up to 500 characters are read into this variable, but the system administrator
647 can configure this to some other value. Newlines in the body are converted into
651 <varname>$message_body_end</varname>: The final portion of the body of the message, formatted
652 and limited in the same way as <varname>$message_body</varname>.
655 <varname>$message_body_size</varname>: The size of the body of the message, in bytes.
658 <varname>$message_exim_id</varname>: The message’s local identification string, which is unique
659 for each message handled by a single host.
662 <varname>$message_headers</varname>: The header lines of the message, concatenated into a
663 single string, with newline characters between them.
666 <varname>$message_size</varname>: The size of the entire message, in bytes.
669 <varname>$original_local_part</varname>: When an address that arrived with the message is
670 being processed, this contains the same value as the variable <varname>$local_part</varname>.
671 However, if an address generated by an alias, forward, or filter file is being
672 processed, this variable contains the local part of the original address.
675 <varname>$reply_address</varname>: The contents of the <emphasis>Reply-to:</emphasis> header, if the message
676 has one; otherwise the contents of the <emphasis>From:</emphasis> header. It is the address to
677 which normal replies to the message should be sent.
680 <varname>$return_path</varname>: The return path – that is, the sender field that will be
681 transmitted as part of the message’s envelope if the message is sent to another
682 host. This is the address to which delivery errors are sent. In many cases,
683 this variable has the same value as <varname>$sender_address</varname>, but if, for example,
684 an incoming message to a mailing list has been expanded, <varname>$return_path</varname> may
685 have been changed to contain the address of the list maintainer.
688 <varname>$sender_address</varname>: The sender address that was received in the envelope of
689 the message. This is not necessarily the same as the contents of the <emphasis>From:</emphasis>
690 or <emphasis>Sender:</emphasis> header lines. For delivery error messages (<quote>bounce messages</quote>)
691 there is no sender address, and this variable is empty.
694 <varname>$tod_full</varname>: A full version of the time and date, for example: Wed, 18 Oct
695 1995 09:51:40 +0100. The timezone is always given as a numerical offset from
699 <varname>$tod_log</varname>: The time and date in the format used for writing Exim’s log files,
700 without the timezone, for example: 1995-10-12 15:32:29.
703 <varname>$tod_zone</varname>: The local timezone offset, for example: +0100.
706 <section id="SECTheadervariables">
707 <title>Header variables</title>
709 There is a special set of expansion variables containing the header lines of
710 the message being processed. These variables have names beginning with
711 <varname>$header_</varname> followed by the name of the header line, terminated by a colon.
714 <literallayout class="monospaced">
719 The whole item, including the terminating colon, is replaced by the contents of
720 the message header line. If there is more than one header line with the same
721 name, their contents are concatenated. For header lines whose data consists of
722 a list of addresses (for example, <emphasis>From:</emphasis> and <emphasis>To:</emphasis>), a comma and newline
723 is inserted between each set of data. For all other header lines, just a
727 Leading and trailing white space is removed from header line data, and if there
728 are any MIME <quote>words</quote> that are encoded as defined by RFC 2047 (because they
729 contain non-ASCII characters), they are decoded and translated, if possible, to
730 a local character set. Translation is attempted only on operating systems that
731 have the <function>iconv()</function> function. This makes the header line look the same as it
732 would when displayed by an MUA. The default character set is ISO-8859-1, but
733 this can be changed by means of the <command>headers</command> command (see below).
736 If you want to see the actual characters that make up a header line, you can
737 specify <varname>$rheader_</varname> instead of <varname>$header_</varname>. This inserts the <quote>raw</quote>
738 header line, unmodified.
741 There is also an intermediate form, requested by <varname>$bheader_</varname>, which removes
742 leading and trailing space and decodes MIME <quote>words</quote>, but does not do any
743 character translation. If an attempt to decode what looks superficially like a
744 MIME <quote>word</quote> fails, the raw string is returned. If decoding produces a binary
745 zero character, it is replaced by a question mark.
748 The capitalization of the name following <varname>$header_</varname> is not significant.
749 Because any printing character except colon may appear in the name of a
750 message’s header (this is a requirement of RFC 2822, the document that
751 describes the format of a mail message) curly brackets must <emphasis>not</emphasis> be used in
752 this case, as they will be taken as part of the header name. Two shortcuts are
753 allowed in naming header variables:
758 The initiating <varname>$header_</varname>, <varname>$rheader_</varname>, or <varname>$bheader_</varname> can be
759 abbreviated to <varname>$h_</varname>, <varname>$rh_</varname>, or <varname>$bh_</varname>, respectively.
764 The terminating colon can be omitted if the next character is white space. The
765 white space character is retained in the expanded string. However, this is not
766 recommended, because it makes it easy to forget the colon when it really is
772 If the message does not contain a header of the given name, an empty string is
773 substituted. Thus it is important to spell the names of headers correctly. Do
774 not use <varname>$header_Reply_to</varname> when you really mean <varname>$header_Reply-to</varname>.
778 <title>User variables</title>
780 There are ten user variables with names <varname>$n0</varname> – <varname>$n9</varname> that can be
781 incremented by the <command>add</command> command (see section <xref linkend="SECTadd"/>). These can be
782 used for <quote>scoring</quote> messages in various ways. If Exim is configured to run a
783 <quote>system filter</quote> on every message, the values left in these variables are
784 copied into the variables <varname>$sn0</varname> – <varname>$sn9</varname> at the end of the system filter,
785 thus making them available to users’ filter files. How these values are used is
786 entirely up to the individual installation.
790 <title>Current directory</title>
792 The contents of your filter file should not make any assumptions about the
793 current directory. It is best to use absolute paths for file names; you can
794 normally make use of the <varname>$home</varname> variable to refer to your home directory. The
795 <command>save</command> command automatically inserts <varname>$home</varname> at the start of non-absolute
799 <section id="SECTsigdel">
800 <title>Significant deliveries</title>
802 When in the course of delivery a message is processed by a filter file, what
803 happens next, that is, after the filter file has been processed, depends on
804 whether or not the filter sets up any <emphasis>significant deliveries</emphasis>. If at least
805 one significant delivery is set up, the filter is considered to have handled
806 the entire delivery arrangements for the current address, and no further
807 processing of the address takes place. If, however, no significant deliveries
808 are set up, Exim continues processing the current address as if there were no
809 filter file, and typically sets up a delivery of a copy of the message into a
810 local mailbox. In particular, this happens in the special case of a filter file
811 containing only comments.
814 The delivery commands <command>deliver</command>, <command>save</command>, and <command>pipe</command> are by default
815 significant. However, if such a command is preceded by the word <quote>unseen</quote>, its
816 delivery is not considered to be significant. In contrast, other commands such
817 as <command>mail</command> and <command>vacation</command> do not set up significant deliveries unless
818 preceded by the word <quote>seen</quote>. The following example commands set up
819 significant deliveries:
821 <literallayout class="monospaced">
822 deliver jack@beanstalk.example
823 pipe $home/bin/mymailscript
824 seen mail subject "message discarded"
828 The following example commands do not set up significant deliveries:
830 <literallayout class="monospaced">
831 unseen deliver jack@beanstalk.example
832 unseen pipe $home/bin/mymailscript
833 mail subject "message discarded"
837 <section id="SEC222">
838 <title>Filter commands</title>
840 The filter commands that are described in subsequent sections are listed
841 below, with the section in which they are described in brackets:
843 <informaltable frame="none">
844 <tgroup cols="2" colsep="0" rowsep="0">
845 <colspec colwidth="100pt" align="left"/>
846 <colspec colwidth="300pt" align="left"/>
849 <entry><command>add</command></entry>
850 <entry> increment a user variable (section <xref linkend="SECTadd"/>)</entry>
853 <entry><command>deliver</command></entry>
854 <entry> deliver to an email address (section <xref linkend="SECTdeliver"/>)</entry>
857 <entry><command>fail</command></entry>
858 <entry> force delivery failure (sysadmin use) (section <xref linkend="SECTfail"/>)</entry>
861 <entry><command>finish</command></entry>
862 <entry> end processing (section <xref linkend="SECTfinish"/>)</entry>
865 <entry><command>freeze</command></entry>
866 <entry> freeze message (sysadmin use) (section <xref linkend="SECTfreeze"/>)</entry>
869 <entry><command>headers</command></entry>
870 <entry> set the header character set (section <xref linkend="SECTheaders"/>)</entry>
873 <entry><command>if</command></entry>
874 <entry> test condition(s) (section <xref linkend="SECTif"/>)</entry>
877 <entry><command>logfile</command></entry>
878 <entry> define log file (section <xref linkend="SECTlog"/>)</entry>
881 <entry><command>logwrite</command></entry>
882 <entry> write to log file (section <xref linkend="SECTlog"/>)</entry>
885 <entry><command>mail</command></entry>
886 <entry> send a reply message (section <xref linkend="SECTmail"/>)</entry>
889 <entry><command>pipe</command></entry>
890 <entry> pipe to a command (section <xref linkend="SECTpipe"/>)</entry>
893 <entry><command>save</command></entry>
894 <entry> save to a file (section <xref linkend="SECTsave"/>)</entry>
897 <entry><command>testprint</command></entry>
898 <entry> print while testing (section <xref linkend="SECTtestprint"/>)</entry>
901 <entry><command>vacation</command></entry>
902 <entry> tailored form of <command>mail</command> (section <xref linkend="SECTmail"/>)</entry>
908 The <command>headers</command> command has additional parameters that can be used only in a
909 system filter. The <command>fail</command> and <command>freeze</command> commands are available only when
910 Exim’s filtering facilities are being used as a system filter, and are
911 therefore usable only by the system administrator and not by ordinary users.
912 They are mentioned only briefly in this document; for more information, see the
913 main Exim specification.
916 <section id="SECTadd">
917 <title>The add command</title>
919 <literal> add </literal><<emphasis>number</emphasis>><literal> to </literal><<emphasis>user variable</emphasis>>
920 <literal>e.g. add 2 to n3</literal>
923 There are 10 user variables of this type, with names <varname>$n0</varname> – <varname>$n9</varname>. Their
924 values can be obtained by the normal expansion syntax (for example <varname>$n3</varname>) in
925 other commands. At the start of filtering, these variables all contain zero.
926 Both arguments of the <command>add</command> command are expanded before use, making it
927 possible to add variables to each other. Subtraction can be obtained by adding
931 <section id="SECTdeliver">
932 <title>The deliver command</title>
934 <literal> deliver</literal> <<emphasis>mail address</emphasis>>
935 <literal>e.g. deliver "Dr Livingstone <David@somewhere.africa.example>"</literal>
938 This command provides a forwarding operation. The delivery that it sets up is
939 significant unless the command is preceded by <quote>unseen</quote> (see section
940 <xref linkend="SECTsigdel"/>). The message is sent on to the given address, exactly as
941 happens if the address had appeared in a traditional <filename>.forward</filename> file. If you
942 want to deliver the message to a number of different addresses, you can use
943 more than one <command>deliver</command> command (each one may have only one address).
944 However, duplicate addresses are discarded.
947 To deliver a copy of the message to your normal mailbox, your login name can be
948 given as the address. Once an address has been processed by the filtering
949 mechanism, an identical generated address will not be so processed again, so
950 doing this does not cause a loop.
953 However, if you have a mail alias, you should <emphasis>not</emphasis> refer to it here. For
954 example, if the mail address <emphasis>L.Gulliver</emphasis> is aliased to <emphasis>lg303</emphasis> then all
955 references in Gulliver’s <filename>.forward</filename> file should be to <emphasis>lg303</emphasis>. A reference
956 to the alias will not work for messages that are addressed to that alias,
957 since, like <filename>.forward</filename> file processing, aliasing is performed only once on an
958 address, in order to avoid looping.
961 Following the new address, an optional second address, preceded by
962 <quote>errors_to</quote> may appear. This changes the address to which delivery errors on
963 the forwarded message will be sent. Instead of going to the message’s original
964 sender, they go to this new address. For ordinary users, the only value that is
965 permitted for this address is the user whose filter file is being processed.
966 For example, the user <emphasis>lg303</emphasis> whose mailbox is in the domain
967 <emphasis>lilliput.example</emphasis> could have a filter file that contains
969 <literallayout class="monospaced">
970 deliver jon@elsewhere.example errors_to lg303@lilliput.example
973 Clearly, using this feature makes sense only in situations where not all
974 messages are being forwarded. In particular, bounce messages must not be
975 forwarded in this way, as this is likely to create a mail loop if something
979 <section id="SECTsave">
980 <title>The save command</title>
982 <literal> save </literal><<emphasis>file name</emphasis>>
983 <literal>e.g. save $home/mail/bookfolder</literal>
986 This command specifies that a copy of the message is to be appended to the
987 given file (that is, the file is to be used as a mail folder). The delivery
988 that <command>save</command> sets up is significant unless the command is preceded by
989 <quote>unseen</quote> (see section <xref linkend="SECTsigdel"/>).
992 More than one <command>save</command> command may be obeyed; each one causes a copy of the
993 message to be written to its argument file, provided they are different
994 (duplicate <command>save</command> commands are ignored).
997 If the file name does not start with a / character, the contents of the
998 <varname>$home</varname> variable are prepended, unless it is empty, or the system
999 administrator has disabled this feature. In conventional configurations, this
1000 variable is normally set in a user filter to the user’s home directory, but the
1001 system administrator may set it to some other path. In some configurations,
1002 <varname>$home</varname> may be unset, or prepending may be disabled, in which case a
1003 non-absolute path name may be generated. Such configurations convert this to an
1004 absolute path when the delivery takes place. In a system filter, <varname>$home</varname> is
1008 The user must of course have permission to write to the file, and the writing
1009 of the file takes place in a process that is running as the user, under the
1010 user’s primary group. Any secondary groups to which the user may belong are not
1011 normally taken into account, though the system administrator can configure Exim
1012 to set them up. In addition, the ability to use this command at all is
1013 controlled by the system administrator – it may be forbidden on some systems.
1016 An optional mode value may be given after the file name. The value for the mode
1017 is interpreted as an octal number, even if it does not begin with a zero. For
1020 <literallayout class="monospaced">
1021 save /some/folder 640
1024 This makes it possible for users to override the system-wide mode setting for
1025 file deliveries, which is normally 600. If an existing file does not have the
1026 correct mode, it is changed.
1029 An alternative form of delivery may be enabled on your system, in which each
1030 message is delivered into a new file in a given directory. If this is the case,
1031 this functionality can be requested by giving the directory name terminated by
1032 a slash after the <command>save</command> command, for example
1034 <literallayout class="monospaced">
1035 save separated/messages/
1038 There are several different formats for such deliveries; check with your system
1039 administrator or local documentation to find out which (if any) are available
1040 on your system. If this functionality is not enabled, the use of a path name
1041 ending in a slash causes an error.
1044 <section id="SECTpipe">
1045 <title>The pipe command</title>
1047 <literal> pipe </literal><<emphasis>command</emphasis>>
1048 <literal>e.g. pipe "$home/bin/countmail $sender_address"</literal>
1051 This command specifies that the message is to be delivered to the specified
1052 command using a pipe. The delivery that it sets up is significant unless the
1053 command is preceded by <quote>unseen</quote> (see section <xref linkend="SECTsigdel"/>). Remember,
1054 however, that no deliveries are done while the filter is being processed. All
1055 deliveries happen later on. Therefore, the result of running the pipe is not
1056 available to the filter.
1059 When the deliveries are done, a separate process is run, and a copy of the
1060 message is passed on its standard input. The process runs as the user, under
1061 the user’s primary group. Any secondary groups to which the user may belong are
1062 not normally taken into account, though the system administrator can configure
1063 Exim to set them up. More than one <command>pipe</command> command may appear; each one causes
1064 a copy of the message to be written to its argument pipe, provided they are
1065 different (duplicate <command>pipe</command> commands are ignored).
1068 When the time comes to transport the message, the command supplied to <command>pipe</command>
1069 is split up by Exim into a command name and a number of arguments. These are
1070 delimited by white space except for arguments enclosed in double quotes, in
1071 which case backslash is interpreted as an escape, or in single quotes, in which
1072 case no escaping is recognized. Note that as the whole command is normally
1073 supplied in double quotes, a second level of quoting is required for internal
1074 double quotes. For example:
1076 <literallayout class="monospaced">
1077 pipe "$home/myscript \"size is $message_size\""
1080 String expansion is performed on the separate components after the line has
1081 been split up, and the command is then run directly by Exim; it is not run
1082 under a shell. Therefore, substitution cannot change the number of arguments,
1083 nor can quotes, backslashes or other shell metacharacters in variables cause
1087 Documentation for some programs that are normally run via this kind of pipe
1088 often suggest that the command should start with
1090 <literallayout class="monospaced">
1094 This is a shell command, and should <emphasis>not</emphasis> be present in Exim filter files,
1095 since it does not normally run the command under a shell.
1098 However, there is an option that the administrator can set to cause a shell to
1099 be used. In this case, the entire command is expanded as a single string and
1100 passed to the shell for interpretation. It is recommended that this be avoided
1101 if at all possible, since it can lead to problems when inserted variables
1102 contain shell metacharacters.
1105 The default PATH set up for the command is determined by the system
1106 administrator, usually containing at least <filename>/bin</filename> and <filename>/usr/bin</filename> so that
1107 common commands are available without having to specify an absolute file name.
1108 However, it is possible for the system administrator to restrict the pipe
1109 facility so that the command name must not contain any / characters, and must
1110 be found in one of the directories in the configured PATH. It is also possible
1111 for the system administrator to lock out the use of the <command>pipe</command> command
1115 When the command is run, a number of environment variables are set up. The
1116 complete list for pipe deliveries may be found in the Exim reference manual.
1117 Those that may be useful for pipe deliveries from user filter files are:
1120 <literal>DOMAIN </literal> the domain of the address
1121 <literal>HOME </literal> your home directory
1122 <literal>LOCAL_PART </literal> see below
1123 <literal>LOCAL_PART_PREFIX </literal> see below
1124 <literal>LOCAL_PART_SUFFIX </literal> see below
1125 <literal>LOGNAME </literal> your login name
1126 <literal>MESSAGE_ID </literal> the unique id of the message
1127 <literal>PATH </literal> the command search path
1128 <literal>RECIPIENT </literal> the complete recipient address
1129 <literal>SENDER </literal> the sender of the message
1130 <literal>SHELL </literal> <literal>/bin/sh</literal>
1131 <literal>USER </literal> see below
1134 LOCAL_PART, LOGNAME, and USER are all set to the same value, namely, your login
1135 id. LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX may be set if Exim is configured to
1136 recognize prefixes or suffixes in the local parts of addresses. For example, a
1137 message addressed to <emphasis>pat-suf2@domain.example</emphasis> may cause the filter for user
1138 <emphasis>pat</emphasis> to be run. If this sets up a pipe delivery, LOCAL_PART_SUFFIX is
1139 <literal>-suf2</literal> when the pipe command runs. The system administrator has to configure
1140 Exim specially for this feature to be available.
1143 If you run a command that is a shell script, be very careful in your use of
1144 data from the incoming message in the commands in your script. RFC 2822 is very
1145 generous in the characters that are permitted to appear in mail addresses, and
1146 in particular, an address may begin with a vertical bar or a slash. For this
1147 reason you should always use quotes round any arguments that involve data from
1148 the message, like this:
1150 <literallayout class="monospaced">
1151 /some/command '$SENDER'
1154 so that inserted shell meta-characters do not cause unwanted effects.
1157 Remember that, as was explained earlier, the pipe command is not run at the
1158 time the filter file is interpreted. The filter just defines what deliveries
1159 are required for one particular addressee of a message. The deliveries
1160 themselves happen later, once Exim has decided everything that needs to be done
1164 A consequence of this is that you cannot inspect the return code from the pipe
1165 command from within the filter. Nevertheless, the code returned by the command
1166 is important, because Exim uses it to decide whether the delivery has succeeded
1170 The command should return a zero completion code if all has gone well. Most
1171 non-zero codes are treated by Exim as indicating a failure of the pipe. This is
1172 treated as a delivery failure, causing the message to be returned to its
1173 sender. However, there are some completion codes that are treated as temporary
1174 errors. The message remains on Exim’s spool disk, and the delivery is tried
1175 again later, though it will ultimately time out if the delivery failures go on
1176 too long. The completion codes to which this applies can be specified by the
1177 system administrator; the default values are 73 and 75.
1180 The pipe command should not normally write anything to its standard output or
1181 standard error file descriptors. If it does, whatever is written is normally
1182 returned to the sender of the message as a delivery error, though this action
1183 can be varied by the system administrator.
1186 <section id="SECTmail">
1187 <title>Mail commands</title>
1189 There are two commands that cause the creation of a new mail message, neither
1190 of which count as a significant delivery unless the command is preceded by the
1191 word <quote>seen</quote> (see section <xref linkend="SECTsigdel"/>). This is a powerful facility, but
1192 it should be used with care, because of the danger of creating infinite
1193 sequences of messages. The system administrator can forbid the use of these
1194 commands altogether.
1197 To help prevent runaway message sequences, these commands have no effect when
1198 the incoming message is a bounce (delivery error) message, and messages sent by
1199 this means are treated as if they were reporting delivery errors. Thus, they
1200 should never themselves cause a bounce message to be returned. The basic
1201 mail-sending command is
1204 <literal>mail [to </literal><<emphasis>address-list</emphasis>><literal>]</literal>
1205 <literal> [cc </literal><<emphasis>address-list</emphasis>><literal>]</literal>
1206 <literal> [bcc </literal><<emphasis>address-list</emphasis>><literal>]</literal>
1207 <literal> [from </literal><<emphasis>address</emphasis>><literal>]</literal>
1208 <literal> [reply_to </literal><<emphasis>address</emphasis>><literal>]</literal>
1209 <literal> [subject </literal><<emphasis>text</emphasis>><literal>]</literal>
1210 <literal> [extra_headers </literal><<emphasis>text</emphasis>><literal>]</literal>
1211 <literal> [text </literal><<emphasis>text</emphasis>><literal>]</literal>
1212 <literal> [[expand] file </literal><<emphasis>filename</emphasis>><literal>]</literal>
1213 <literal> [return message]</literal>
1214 <literal> [log </literal><<emphasis>log file name</emphasis>><literal>]</literal>
1215 <literal> [once </literal><<emphasis>note file name</emphasis>><literal>]</literal>
1216 <literal> [once_repeat </literal><<emphasis>time interval</emphasis>><literal>]</literal>
1217 <literal>e.g. mail text "Your message about $h_subject: has been received"</literal>
1220 Each <<emphasis>address-list</emphasis>> can contain a number of addresses, separated by commas,
1221 in the format of a <emphasis>To:</emphasis> or <emphasis>Cc:</emphasis> header line. In fact, the text you supply
1222 here is copied exactly into the appropriate header line. It may contain
1223 additional information as well as email addresses. For example:
1225 <literallayout class="monospaced">
1226 mail to "Julius Caesar <jc@rome.example>, \
1227 <ma@rome.example> (Mark A.)"
1230 Similarly, the texts supplied for <option>from</option> and <option>reply_to</option> are copied into
1231 their respective header lines.
1234 As a convenience for use in one common case, there is also a command called
1235 <command>vacation</command>. It behaves in the same way as <command>mail</command>, except that the defaults
1236 for the <option>subject</option>, <option>file</option>, <option>log</option>, <option>once</option>, and <option>once_repeat</option> options
1239 <literallayout class="monospaced">
1240 subject "On vacation"
1241 expand file .vacation.msg
1247 respectively. These are the same file names and repeat period used by the
1248 traditional Unix <command>vacation</command> command. The defaults can be overridden by
1249 explicit settings, but if a file name is given its contents are expanded only
1250 if explicitly requested.
1253 <emphasis role="bold">Warning</emphasis>: The <command>vacation</command> command should always be used conditionally,
1254 subject to at least the <command>personal</command> condition (see section <xref linkend="SECTpersonal"/>
1255 below) so as not to send automatic replies to non-personal messages from
1256 mailing lists or elsewhere. Sending an automatic response to a mailing list or
1257 a mailing list manager is an Internet Sin.
1260 For both commands, the key/value argument pairs can appear in any order. At
1261 least one of <option>text</option> or <option>file</option> must appear (except with <command>vacation</command>, where
1262 there is a default for <option>file</option>); if both are present, the text string appears
1263 first in the message. If <option>expand</option> precedes <option>file</option>, each line of the file is
1264 subject to string expansion before it is included in the message.
1267 Several lines of text can be supplied to <option>text</option> by including the escape
1268 sequence <quote>\n</quote> in the string wherever a newline is required. If the command is
1269 output during filter file testing, newlines in the text are shown as <quote>\n</quote>.
1272 Note that the keyword for creating a <emphasis>Reply-To:</emphasis> header is <option>reply_to</option>,
1273 because Exim keywords may contain underscores, but not hyphens. If the <option>from</option>
1274 keyword is present and the given address does not match the user who owns the
1275 forward file, Exim normally adds a <emphasis>Sender:</emphasis> header to the message, though it
1276 can be configured not to do this.
1279 The <option>extra_headers</option> keyword allows you to add custom header lines to the
1280 message. The text supplied must be one or more syntactically valid RFC 2822
1281 header lines. You can use <quote>\n</quote> within quoted text to specify newlines between
1282 headers, and also to define continued header lines. For example:
1284 <literallayout class="monospaced">
1285 extra_headers "h1: first\nh2: second\n continued\nh3: third"
1288 No newline should appear at the end of the final header line.
1291 If no <option>to</option> argument appears, the message is sent to the address in the
1292 <varname>$reply_address</varname> variable (see section <xref linkend="SECTfilterstringexpansion"/> above).
1293 An <emphasis>In-Reply-To:</emphasis> header is automatically included in the created message,
1294 giving a reference to the message identification of the incoming message.
1297 If <option>return message</option> is specified, the incoming message that caused the filter
1298 file to be run is added to the end of the message, subject to a maximum size
1302 If a log file is specified, a line is added to it for each message sent.
1305 If a <option>once</option> file is specified, it is used to hold a database for remembering
1306 who has received a message, and no more than one message is ever sent to any
1307 particular address, unless <option>once_repeat</option> is set. This specifies a time
1308 interval after which another copy of the message is sent. The interval is
1309 specified as a sequence of numbers, each followed by the initial letter of one
1310 of <quote>seconds</quote>, <quote>minutes</quote>, <quote>hours</quote>, <quote>days</quote>, or <quote>weeks</quote>. For example,
1312 <literallayout class="monospaced">
1316 causes a new message to be sent if at least 5 days and 4 hours have elapsed
1317 since the last one was sent. There must be no white space in a time interval.
1320 Commonly, the file name specified for <option>once</option> is used as the base name for
1321 direct-access (DBM) file operations. There are a number of different DBM
1322 libraries in existence. Some operating systems provide one as a default, but
1323 even in this case a different one may have been used when building Exim. With
1324 some DBM libraries, specifying <option>once</option> results in two files being created,
1325 with the suffixes <filename>.dir</filename> and <filename>.pag</filename> being added to the given name. With
1326 some others a single file with the suffix <filename>.db</filename> is used, or the name is used
1330 Using a DBM file for implementing the <option>once</option> feature means that the file
1331 grows as large as necessary. This is not usually a problem, but some system
1332 administrators want to put a limit on it. The facility can be configured not to
1333 use a DBM file, but instead, to use a regular file with a maximum size. The
1334 data in such a file is searched sequentially, and if the file fills up, the
1335 oldest entry is deleted to make way for a new one. This means that some
1336 correspondents may receive a second copy of the message after an unpredictable
1337 interval. Consult your local information to see if your system is configured
1341 More than one <command>mail</command> or <command>vacation</command> command may be obeyed in a single filter
1342 run; they are all honoured, even when they are to the same recipient.
1345 <section id="SECTlog">
1346 <title>Logging commands</title>
1348 A log can be kept of actions taken by a filter file. This facility is normally
1349 available in conventional configurations, but there are some situations where
1350 it might not be. Also, the system administrator may choose to disable it. Check
1351 your local information if in doubt.
1354 Logging takes place while the filter file is being interpreted. It does not
1355 queue up for later like the delivery commands. The reason for this is so that a
1356 log file need be opened only once for several write operations. There are two
1357 commands, neither of which constitutes a significant delivery. The first
1358 defines a file to which logging output is subsequently written:
1361 <literal> logfile </literal><<emphasis>file name</emphasis>>
1362 <literal>e.g. logfile $home/filter.log</literal>
1365 The file name must be fully qualified. You can use <varname>$home</varname>, as in this
1366 example, to refer to your home directory. The file name may optionally be
1367 followed by a mode for the file, which is used if the file has to be created.
1370 <literallayout class="monospaced">
1371 logfile $home/filter.log 0644
1374 The number is interpreted as octal, even if it does not begin with a zero.
1375 The default for the mode is 600. It is suggested that the <command>logfile</command> command
1376 normally appear as the first command in a filter file. Once a log file has
1377 been obeyed, the <command>logwrite</command> command can be used to write to it:
1380 <literal> logwrite "</literal><<emphasis>some text string</emphasis>><literal>"</literal>
1381 <literal>e.g. logwrite "$tod_log $message_id processed"</literal>
1384 It is possible to have more than one <command>logfile</command> command, to specify writing to
1385 different log files in different circumstances. Writing takes place at the end
1386 of the file, and a newline character is added to the end of each string if
1387 there isn’t one already there. Newlines can be put in the middle of the string
1388 by using the <quote>\n</quote> escape sequence. Lines from simultaneous deliveries may get
1389 interleaved in the file, as there is no interlocking, so you should plan your
1390 logging with this in mind. However, data should not get lost.
1393 <section id="SECTfinish">
1394 <title>The finish command</title>
1396 The command <command>finish</command>, which has no arguments, causes Exim to stop
1397 interpreting the filter file. This is not a significant action unless preceded
1398 by <quote>seen</quote>. A filter file containing only <quote>seen finish</quote> is a black hole.
1401 <section id="SECTtestprint">
1402 <title>The testprint command</title>
1404 It is sometimes helpful to be able to print out the values of variables when
1405 testing filter files. The command
1408 <literal> testprint </literal><<emphasis>text</emphasis>>
1409 <literal>e.g. testprint "home=$home reply_address=$reply_address"</literal>
1412 does nothing when mail is being delivered. However, when the filtering code is
1413 being tested by means of the <option>-bf</option> option (see section <xref linkend="SECTtesting"/>
1414 above), the value of the string is written to the standard output.
1417 <section id="SECTfail">
1418 <title>The fail command</title>
1420 When Exim’s filtering facilities are being used as a system filter, the
1421 <command>fail</command> command is available, to force delivery failure. Because this command
1422 is normally usable only by the system administrator, and not enabled for use by
1423 ordinary users, it is described in more detail in the main Exim specification
1424 rather than in this document.
1427 <section id="SECTfreeze">
1428 <title>The freeze command</title>
1430 When Exim’s filtering facilities are being used as a system filter, the
1431 <command>freeze</command> command is available, to freeze a message on the queue. Because this
1432 command is normally usable only by the system administrator, and not enabled
1433 for use by ordinary users, it is described in more detail in the main Exim
1434 specification rather than in this document.
1437 <section id="SECTheaders">
1438 <title>The headers command</title>
1440 The <command>headers</command> command can be used to change the target character set that is
1441 used when translating the contents of encoded header lines for insertion by the
1442 <varname>$header_</varname> mechanism (see section <xref linkend="SECTheadervariables"/> above). The
1443 default can be set in the Exim configuration; if not specified, ISO-8859-1 is
1444 used. The only currently supported format for the <command>headers</command> command in user
1445 filters is as in this example:
1447 <literallayout class="monospaced">
1448 headers charset "UTF-8"
1451 That is, <command>headers</command> is followed by the word <quote>charset</quote> and then the name of a
1452 character set. This particular example would be useful if you wanted to compare
1453 the contents of a header to a UTF-8 string.
1456 In system filter files, the <command>headers</command> command can be used to add or remove
1457 header lines from the message. These features are described in the main Exim
1461 <section id="SECTif">
1462 <title>Obeying commands conditionally</title>
1464 Most of the power of filtering comes from the ability to test conditions and
1465 obey different commands depending on the outcome. The <command>if</command> command is used to
1466 specify conditional execution, and its general form is
1469 <literal>if </literal><<emphasis>condition</emphasis>>
1470 <literal>then </literal><<emphasis>commands</emphasis>>
1471 <literal>elif </literal><<emphasis>condition</emphasis>>
1472 <literal>then </literal><<emphasis>commands</emphasis>>
1473 <literal>else </literal><<emphasis>commands</emphasis>>
1474 <literal>endif</literal>
1477 There may be any number of <command>elif</command> and <command>then</command> sections (including none) and
1478 the <command>else</command> section is also optional. Any number of commands, including nested
1479 <command>if</command> commands, may appear in any of the <<emphasis>commands</emphasis>> sections.
1482 Conditions can be combined by using the words <command>and</command> and <command>or</command>, and round
1483 brackets (parentheses) can be used to specify how several conditions are to
1484 combine. Without brackets, <command>and</command> is more binding than <command>or</command>. For example:
1486 <literallayout class="monospaced">
1488 $h_subject: contains "Make money" or
1489 $h_precedence: is "junk" or
1490 ($h_sender: matches ^\\d{8}@ and not personal) or
1491 $message_body contains "this is not spam"
1497 A condition can be preceded by <command>not</command> to negate it, and there are also some
1498 negative forms of condition that are more English-like.
1501 <section id="SEC23">
1502 <title>String testing conditions</title>
1504 There are a number of conditions that operate on text strings, using the words
1505 <quote>begins</quote>, <quote>ends</quote>, <quote>is</quote>, <quote>contains</quote> and <quote>matches</quote>. If you want to
1506 apply the same test to more than one header line, you can easily concatenate
1507 them into a single string for testing, as in this example:
1509 <literallayout class="monospaced">
1510 if "$h_to:, $h_cc:" contains me@domain.example then ...
1513 If a string-testing condition name is written in lower case, the testing
1514 of letters is done without regard to case; if it is written in upper case
1515 (for example, <quote>CONTAINS</quote>), the case of letters is taken into account.
1518 <literal> </literal><<emphasis>text1</emphasis>><literal> begins </literal><<emphasis>text2</emphasis>>
1519 <literal> </literal><<emphasis>text1</emphasis>><literal> does not begin </literal><<emphasis>text2</emphasis>>
1520 <literal>e.g. $header_from: begins "Friend@"</literal>
1523 A <quote>begins</quote> test checks for the presence of the second string at the start of
1524 the first, both strings having been expanded.
1527 <literal> </literal><<emphasis>text1</emphasis>><literal> ends </literal><<emphasis>text2</emphasis>>
1528 <literal> </literal><<emphasis>text1</emphasis>><literal> does not end </literal><<emphasis>text2</emphasis>>
1529 <literal>e.g. $header_from: ends "public.com.example"</literal>
1532 An <quote>ends</quote> test checks for the presence of the second string at the end of
1533 the first, both strings having been expanded.
1536 <literal> </literal><<emphasis>text1</emphasis>><literal> is </literal><<emphasis>text2</emphasis>>
1537 <literal> </literal><<emphasis>text1</emphasis>><literal> is not </literal><<emphasis>text2</emphasis>>
1538 <literal>e.g. $local_part_suffix is "-foo"</literal>
1541 An <quote>is</quote> test does an exact match between the strings, having first expanded
1545 <literal> </literal><<emphasis>text1</emphasis>><literal> contains </literal><<emphasis>text2</emphasis>>
1546 <literal> </literal><<emphasis>text1</emphasis>><literal> does not contain </literal><<emphasis>text2</emphasis>>
1547 <literal>e.g. $header_subject: contains "evolution"</literal>
1550 A <quote>contains</quote> test does a partial string match, having expanded both strings.
1553 <literal> </literal><<emphasis>text1</emphasis>><literal> matches </literal><<emphasis>text2</emphasis>>
1554 <literal> </literal><<emphasis>text1</emphasis>><literal> does not match </literal><<emphasis>text2</emphasis>>
1555 <literal>e.g. $sender_address matches "(bill|john)@"</literal>
1558 For a <quote>matches</quote> test, after expansion of both strings, the second one is
1559 interpreted as a regular expression. Exim uses the PCRE regular expression
1560 library, which provides regular expressions that are compatible with Perl.
1563 The match succeeds if the regular expression matches any part of the first
1564 string. If you want a regular expression to match only at the start or end of
1565 the subject string, you must encode that requirement explicitly, using the
1566 <literal>^</literal> or <literal>$</literal> metacharacters. The above example, which is not so constrained,
1567 matches all these addresses:
1569 <literallayout class="monospaced">
1572 spoonbill@example.com
1573 littlejohn@example.com
1576 To match only the first two, you could use this:
1578 <literallayout class="monospaced">
1579 if $sender_address matches "^(bill|john)@" then ...
1582 Care must be taken if you need a backslash in a regular expression, because
1583 backslashes are interpreted as escape characters both by the string expansion
1584 code and by Exim’s normal processing of strings in quotes. For example, if you
1585 want to test the sender address for a domain ending in <emphasis>.com</emphasis> the regular
1588 <literallayout class="monospaced">
1592 The backslash and dollar sign in that expression have to be escaped when used
1593 in a filter command, as otherwise they would be interpreted by the expansion
1594 code. Thus, what you actually write is
1596 <literallayout class="monospaced">
1597 if $sender_address matches \\.com\$
1600 An alternative way of handling this is to make use of the <literal>\N</literal> expansion
1601 flag for suppressing expansion:
1603 <literallayout class="monospaced">
1604 if $sender_address matches \N\.com$\N
1607 Everything between the two occurrences of <literal>\N</literal> is copied without change by
1608 the string expander (and in fact you do not need the final one, because it is
1609 at the end of the string). If the regular expression is given in quotes
1610 (mandatory only if it contains white space) you have to write either
1612 <literallayout class="monospaced">
1613 if $sender_address matches "\\\\.com\\$"
1618 <literallayout class="monospaced">
1619 if $sender_address matches "\\N\\.com$\\N"
1622 If the regular expression contains bracketed sub-expressions, numeric
1623 variable substitutions such as <varname>$1</varname> can be used in the subsequent actions
1624 after a successful match. If the match fails, the values of the numeric
1625 variables remain unchanged. Previous values are not restored after <command>endif</command>.
1626 In other words, only one set of values is ever available. If the condition
1627 contains several sub-conditions connected by <command>and</command> or <command>or</command>, it is the
1628 strings extracted from the last successful match that are available in
1629 subsequent actions. Numeric variables from any one sub-condition are also
1630 available for use in subsequent sub-conditions, because string expansion of a
1631 condition occurs just before it is tested.
1634 <section id="SEC24">
1635 <title>Numeric testing conditions</title>
1637 The following conditions are available for performing numerical tests:
1640 <literal> </literal><<emphasis>number1</emphasis>><literal> is above </literal><<emphasis>number2</emphasis>>
1641 <literal> </literal><<emphasis>number1</emphasis>><literal> is not above </literal><<emphasis>number2</emphasis>>
1642 <literal> </literal><<emphasis>number1</emphasis>><literal> is below </literal><<emphasis>number2</emphasis>>
1643 <literal> </literal><<emphasis>number1</emphasis>><literal> is not below </literal><<emphasis>number2</emphasis>>
1644 <literal>e.g. $message_size is not above 10k</literal>
1647 The <<emphasis>number</emphasis>> arguments must expand to strings of digits, optionally
1648 followed by one of the letters K or M (upper case or lower case) which cause
1649 multiplication by 1024 and 1024x1024 respectively.
1652 <section id="SEC25">
1653 <title>Testing for significant deliveries</title>
1655 You can use the <command>delivered</command> condition to test whether or not any previously
1656 obeyed filter commands have set up a significant delivery. For example:
1658 <literallayout class="monospaced">
1659 if not delivered then save mail/anomalous endif
1662 <quote>Delivered</quote> is perhaps a poor choice of name for this condition, because the
1663 message has not actually been delivered; rather, a delivery has been set up for
1667 <section id="SEC26">
1668 <title>Testing for error messages</title>
1670 The condition <command>error_message</command> is true if the incoming message is a bounce
1671 (mail delivery error) message. Putting the command
1673 <literallayout class="monospaced">
1674 if error_message then finish endif
1677 at the head of your filter file is a useful insurance against things going
1678 wrong in such a way that you cannot receive delivery error reports. <emphasis role="bold">Note</emphasis>:
1679 <command>error_message</command> is a condition, not an expansion variable, and therefore is
1680 not preceded by <literal>$</literal>.
1683 <section id="SEC27">
1684 <title>Testing a list of addresses</title>
1686 There is a facility for looping through a list of addresses and applying a
1687 condition to each of them. It takes the form
1690 <literal>foranyaddress </literal><<emphasis>string</emphasis>><literal> (</literal><<emphasis>condition</emphasis>><literal>)</literal>
1693 where <<emphasis>string</emphasis>> is interpreted as a list of RFC 2822 addresses, as in a
1694 typical header line, and <<emphasis>condition</emphasis>> is any valid filter condition or
1695 combination of conditions. The <quote>group</quote> syntax that is defined for certain
1696 header lines that contain addresses is supported.
1699 The parentheses surrounding the condition are mandatory, to delimit it from
1700 possible further sub-conditions of the enclosing <command>if</command> command. Within the
1701 condition, the expansion variable <varname>$thisaddress</varname> is set to the non-comment
1702 portion of each of the addresses in the string in turn. For example, if the
1705 <literallayout class="monospaced">
1706 B.Simpson <bart@sfld.example>, lisa@sfld.example (his sister)
1709 then <varname>$thisaddress</varname> would take on the values <literal>bart@sfld.example</literal> and
1710 <literal>lisa@sfld.example</literal> in turn.
1713 If there are no valid addresses in the list, the whole condition is false. If
1714 the internal condition is true for any one address, the overall condition is
1715 true and the loop ends. If the internal condition is false for all addresses in
1716 the list, the overall condition is false. This example tests for the presence
1717 of an eight-digit local part in any address in a <emphasis>To:</emphasis> header:
1719 <literallayout class="monospaced">
1720 if foranyaddress $h_to: ( $thisaddress matches ^\\d{8}@ ) then ...
1723 When the overall condition is true, the value of <varname>$thisaddress</varname> in the
1724 commands that follow <command>then</command> is the last value it took on inside the loop. At
1725 the end of the <command>if</command> command, the value of <varname>$thisaddress</varname> is reset to what it
1726 was before. It is best to avoid the use of multiple occurrences of
1727 <command>foranyaddress</command>, nested or otherwise, in a single <command>if</command> command, if the
1728 value of <varname>$thisaddress</varname> is to be used afterwards, because it isn’t always
1729 clear what the value will be. Nested <command>if</command> commands should be used instead.
1732 Header lines can be joined together if a check is to be applied to more than
1733 one of them. For example:
1735 <literallayout class="monospaced">
1736 if foranyaddress $h_to:,$h_cc: ....
1739 This scans through the addresses in both the <emphasis>To:</emphasis> and the <emphasis>Cc:</emphasis> headers.
1742 <section id="SECTpersonal">
1743 <title>Testing for personal mail</title>
1745 A common requirement is to distinguish between incoming personal mail and mail
1746 from a mailing list, or from a robot or other automatic process (for example, a
1747 bounce message). In particular, this test is normally required for <quote>vacation
1751 The <command>personal</command> condition checks that the message is not a bounce message and
1752 that the current user’s email address appears in the <emphasis>To:</emphasis> header. It also
1753 checks that the sender is not the current user or one of a number of common
1754 daemons, and that there are no header lines starting <emphasis>List-</emphasis> in the message.
1755 Finally, it checks the content of the <emphasis>Precedence:</emphasis> header line, if there is
1759 You should always use the <command>personal</command> condition when generating automatic
1760 responses. This example shows the use of <command>personal</command> in a filter file that is
1761 sending out vacation messages:
1763 <literallayout class="monospaced">
1765 mail to $reply_address
1766 subject "I am on holiday"
1767 file $home/vacation/message
1768 once $home/vacation/once
1773 It is tempting, when writing commands like the above, to quote the original
1774 subject in the reply. For example:
1776 <literallayout class="monospaced">
1777 subject "Re: $h_subject:"
1780 There is a danger in doing this, however. It may allow a third party to
1781 subscribe you to an opt-in mailing list, provided that the list accepts bounce
1782 messages as subscription confirmations. (Messages sent from filters are always
1783 sent as bounce messages.) Well-managed lists require a non-bounce message to
1784 confirm a subscription, so the danger is relatively small.
1787 If prefixes or suffixes are in use for local parts – something which depends
1788 on the configuration of Exim (see section <xref linkend="SECTmbox"/> below) – the tests
1789 for the current user are done with the full address (including the prefix and
1790 suffix, if any) as well as with the prefix and suffix removed. If the system is
1791 configured to rewrite local parts of mail addresses, for example, to rewrite
1792 <literal>dag46</literal> as <literal>Dirk.Gently</literal>, the rewritten form of the address is also used in
1796 <section id="SEC28">
1797 <title>Alias addresses for the personal condition</title>
1799 It is quite common for people who have mail accounts on a number of different
1800 systems to forward all their mail to one system, and in this case a check for
1801 personal mail should test all their various mail addresses. To allow for this,
1802 the <command>personal</command> condition keyword can be followed by
1805 <literal>alias </literal><<emphasis>address</emphasis>>
1808 any number of times, for example:
1810 <literallayout class="monospaced">
1811 if personal alias smith@else.where.example
1812 alias jones@other.place.example
1816 The alias addresses are treated as alternatives to the current user’s email
1817 address when testing the contents of header lines.
1820 <section id="SEC29">
1821 <title>Details of the personal condition</title>
1823 The basic <command>personal</command> test is roughly equivalent to the following:
1825 <literallayout class="monospaced">
1826 not error_message and
1827 $message_headers does not contain "\nList-Id:" and
1828 $message_headers does not contain "\nList-Help:" and
1829 $message_headers does not contain "\nList-Subscribe:" and
1830 $message_headers does not contain "\nList-Unsubscribe:" and
1831 $message_headers does not contain "\nList-Post:" and
1832 $message_headers does not contain "\nList-Owner:" and
1833 $message_headers does not contain "\nList-Archive:" and
1835 "${if def h_auto-submitted:{present}{absent}}" is "absent" or
1836 $header_auto-submitted: is "no"
1838 $header_precedence: does not contain "bulk" and
1839 $header_precedence: does not contain "list" and
1840 $header_precedence: does not contain "junk" and
1841 foranyaddress $header_to:
1842 ( $thisaddress contains "$local_part$domain" ) and
1843 not foranyaddress $header_from:
1845 $thisaddress contains "$local_part@$domain" or
1846 $thisaddress contains "server@" or
1847 $thisaddress contains "daemon@" or
1848 $thisaddress contains "root@" or
1849 $thisaddress contains "listserv@" or
1850 $thisaddress contains "majordomo@" or
1851 $thisaddress contains "-request@" or
1852 $thisaddress matches "^owner-[^@]+@"
1856 The variable <varname>$local_part</varname> contains the local part of the mail address of
1857 the user whose filter file is being run – it is normally your login id. The
1858 <varname>$domain</varname> variable contains the mail domain. As explained above, if aliases
1859 or rewriting are defined, or if prefixes or suffixes are in use, the tests for
1860 the current user are also done with alternative addresses.
1863 <section id="SEC30">
1864 <title>Testing delivery status</title>
1866 There are two conditions that are intended mainly for use in system filter
1867 files, but which are available in users’ filter files as well. The condition
1868 <command>first_delivery</command> is true if this is the first process that is attempting to
1869 deliver the message, and false otherwise. This indicator is not reset until the
1870 first delivery process successfully terminates; if there is a crash or a power
1871 failure (for example), the next delivery attempt is also a <quote>first delivery</quote>.
1874 In a user filter file <command>first_delivery</command> will be false if there was previously
1875 an error in the filter, or if a delivery for the user failed owing to, for
1876 example, a quota error, or if forwarding to a remote address was deferred for
1880 The condition <command>manually_thawed</command> is true if the message was <quote>frozen</quote> for
1881 some reason, and was subsequently released by the system administrator. It is
1882 unlikely to be of use in users’ filter files.
1885 <section id="SECTmbox">
1886 <title>Multiple personal mailboxes</title>
1887 <titleabbrev>SEC31</titleabbrev>
1889 The system administrator can configure Exim so that users can set up variants
1890 on their email addresses and handle them separately. Consult your system
1891 administrator or local documentation to see if this facility is enabled on your
1892 system, and if so, what the details are.
1895 The facility involves the use of a prefix or a suffix on an email address. For
1896 example, all mail addressed to <emphasis>lg303-</emphasis><<emphasis>something</emphasis>> would be the property
1897 of user <emphasis>lg303</emphasis>, who could determine how it was to be handled, depending on
1898 the value of <<emphasis>something</emphasis>>.
1901 There are two possible ways in which this can be set up. The first possibility
1902 is the use of multiple <filename>.forward</filename> files. In this case, mail to <emphasis>lg303-foo</emphasis>,
1903 for example, is handled by looking for a file called <filename>.forward-foo</filename> in
1904 <emphasis>lg303</emphasis>’s home directory. If such a file does not exist, delivery fails
1905 and the message is returned to its sender.
1908 The alternative approach is to pass all messages through a single <filename>.forward</filename>
1909 file, which must be a filter file so that it can distinguish between the
1910 different cases by referencing the variables <varname>$local_part_prefix</varname> or
1911 <varname>$local_part_suffix</varname>, as in the final example in section <xref linkend="SECTex"/> below.
1914 It is possible to configure Exim to support both schemes at once. In this case,
1915 a specific <filename>.forward-foo</filename> file is first sought; if it is not found, the basic
1916 <filename>.forward</filename> file is used.
1919 The <command>personal</command> test (see section <xref linkend="SECTpersonal"/>) includes prefixes and
1920 suffixes in its checking.
1923 <section id="SEC43">
1924 <title>Ignoring delivery errors</title>
1926 As was explained above, filtering just sets up addresses for delivery – no
1927 deliveries are actually done while a filter file is active. If any of the
1928 generated addresses subsequently suffers a delivery failure, an error message
1929 is generated in the normal way. However, if a filter command that sets up a
1930 delivery is preceded by the word <quote>noerror</quote>, errors for that delivery,
1931 and any deliveries consequent on it (that is, from alias, forwarding, or
1932 filter files it invokes) are ignored.
1935 <section id="SECTex">
1936 <title>Examples of Exim filter commands</title>
1940 <literallayout class="monospaced">
1942 deliver baggins@rivendell.middle-earth.example
1945 Vacation handling using traditional means, assuming that the <filename>.vacation.msg</filename>
1946 and other files have been set up in your home directory:
1948 <literallayout class="monospaced">
1950 unseen pipe "/usr/ucb/vacation \"$local_part\""
1953 Vacation handling inside Exim, having first created a file called
1954 <filename>.vacation.msg</filename> in your home directory:
1956 <literallayout class="monospaced">
1958 if personal then vacation endif
1961 File some messages by subject:
1963 <literallayout class="monospaced">
1965 if $header_subject: contains "empire" or
1966 $header_subject: contains "foundation"
1972 Save all non-urgent messages by weekday:
1974 <literallayout class="monospaced">
1976 if $header_subject: does not contain "urgent" and
1977 $tod_full matches "^(...),"
1983 Throw away all mail from one site, except from postmaster:
1985 <literallayout class="monospaced">
1987 if $reply_address contains "@spam.site.example" and
1988 $reply_address does not contain "postmaster@"
1994 Handle multiple personal mailboxes:
1996 <literallayout class="monospaced">
1998 if $local_part_suffix is "-foo"
2001 elif $local_part_suffix is "-bar"
git://git.exim.org / exim-website.git / blob