1MAILDROPFILTER(7) Double Precision, Inc. MAILDROPFILTER(7)
2
6 maildropfilter - maildrop's filtering language
7
9 /etc/maildroprc, $HOME/.mailfilter, $HOME/.mailfilters/*, and
10 friends...
11
13 This manual page describes the language used by maildrop to filter
14 E-mail messages. The mail filtering instructions are read from a file.
15 The language is loosely structured, it is based on pattern matching.
16 The language has a distinct lexical and syntactical structure, very
17 similar to Perl's, but it is important to note that it is not Perl, and
18 is very different from Perl, in certain cases.
19 If the filtering instructions do not exist, maildrop delivers the
21 message to the default mailbox without doing any additional processing,
22 making it indistinguishable from the usual mail delivery agent.
23 It is important to note that maildrop reads and parses the filter file
25 before doing anything. If there are any errors maildrop prints an error
26 message, and terminates with the exit code set to EX_TEMPFAIL. A
27 compliant mail transport agent should re-queue the message for a later
28 delivery attempt. Hopefully, most simple syntax errors will not cause
29 mail to be bounced back if the error is caught and fixed quickly.
30 Environment
32 maildrop uses variables to access and manipulate messages. Variables
33 are arbitrary text accessed by referring to the name of the variable,
34 such as HOME, or DEFAULT. Text is placed into a variable by using an
35 assignment statement, such as:
36 FILE="IN.junk"
38 This statement puts the text "IN.junk" (without the quotes) into a
41 variable whose name is FILE. Later, the contents of a variable are
42 accessed by using the $ symbol and the name for the variable. For
43 example:
44 to $FILE
46 This will deliver the current message to the mailbox file (or a maildir
49 directory) named "IN.junk".
50 maildrop initially creates variables from the environment variables of
52 the operating system, UNLESS maildrop runs in delivery mode. Each
53 operating system environment variable becomes a maildrop variable. When
54 running in delivery mode, maildrop does not import the environment for
55 security reasons, except for the environment variables that define the
56 process locale (LANG, LANGUAGE, and LC_*), which are still imported.
57 In all cases maildrop resets the following variables to their default
59 values: HOME, DEFAULT, SHELL, PATH, LOCKEXT, LOCKREFRESH, LOCKSLEEP,
60 LOCKTIMEOUT, MAILDIRQUOTA, SENDMAIL and LOGNAME.
61 There's one exception to this rule which applies to the version of
63 maildrop that comes with the Courier mail server[1]. The following does
64 not apply to the standalone version of maildrop: when running in
65 delivery mode, if the -d flag was not used, or if it specifies the same
66 userid as the one that's running maildrop: the following variables are
67 automatically imported from the environment: HOME, SHELL, LOGNAME and
68 MAILDIRQUOTA. These environment variables are initialized by the
69 Courier mail server prior to running maildrop. Additionally, the
70 initial value for the DEFAULT maildrop variable is imported from the
71 MAILDROPDEFAULT environment variable. This is because the Courier mail
72 server overloads the DEFAULT environment variable to store the
73 defaulted portion of the local mailbox address. See the
74 dot-courier(5)[2] man page in the Courier mail server distribution. You
75 can get the Courier mail server's DEFAULT value by using the import
76 command. Note, however, that this will clobber the old contents of
77 DEFAULT, which is probably not what you want. The right way to do this
78 would be something like this:
79 SAVEDEFAULT=$DEFAULT
81 import DEFAULT
82 LOCALDEFAULT=$DEFAULT
83 DEFAULT=$SAVEDEFAULT
84 All internal variables are exported back as environment variables when
87 maildrop runs an external command. Changes to internal variables, made
88 by the filter file, are reflected in the exported environment.
89 Lexical structure
91 Most whitespace is generally ignored. The # character introduces a
92 comment running to the end of the line, which is also ignored. Unlike
93 other mail filters, maildrop parses the filter file before taking any
94 action with the message. If there are syntax errors in the file,
95 maildrop displays an error message, and returns EX_TEMPFAIL. That
96 should cause the mail message to remain in the queue, and, hopefully
97 allow the problem to be corrected, without bouncing any mail.
98 Note
100 In maildrop, the end of line is a lexical token. In order to
101 continue a long statement on the next line, terminate the line with
102 a backslash character.
103 Literal text
105 Literal text in the maildrop filtering language is surrounded by either
106 single or double quotes. In order to enter a single quote into a text
107 literal surrounded by single quotes, or a double quote into a literal
108 surrounded by double quotes, prefix it with a backslash character. Use
109 two backslash characters characters to enter one backslash character in
110 the text literal.
111 Note
113 A backslash followed by either a backslash, or a matching quote, is
114 the only situation where the backslash character is actually
115 removed, leaving only the following character in the actual text
116 literal. If a backslash character is followed by any other
117 character, the backslash is NOT removed.
118 Multiple text literals in a row are automatically concatenated, even if
120 they use different quotes. For example:
121 FOOBAR="Foo"'bar'
123 SAVEDEFAULT=$DEFAULT
124 import DEFAULT
125 LOCALDEFAULT=$DEFAULT
126 DEFAULT=$SAVEDEFAULT
127 This sets the variable FOOBAR to the text "Foobar".
130 Variable substitution
132 Variable substitution is performed on text literals that's surrounded
133 by double quotation marks. The "$" character, followed by a variable
134 name, is replaced by that variable's contents.
135 MAILBOX="$HOME/Mailbox"
137 This sets the variable MAILBOX to the contents of the variable HOME
140 followed by "/Mailbox". Variable names must begin with an uppercase
141 letter, a lowercase letter, or an underscore. Following that, all
142 letters, digits, and underscores are taken as a variable name, and its
143 contents replace the $ sign, and the variable name. It is possible to
144 access variables whose name includes other characters, by using braces
145 as follows:
146 MAILBOX="${HOME-WORD}/Mailbox"
148 Inserts the contents of the HOME-WORD variable. If the variable does
151 not exist, the empty text literal is used to replace the variable name.
152 It is not possible to access variables whose names include the }
153 character.
154 If the $ character is not followed by a left brace, letter, or an
156 underscore, the $ character remains unmolested in the text literal. A
157 backslash followed by the $ character results in a $ character in the
158 text literal, without doing any variable substitution.
159 Variable substitution is not done in text literals which are surrounded
161 by single quotes (apostrophes).
162 Command line arguments
164 maildrop initializes special variables: $1, $2, and so on, with
165 additional parameters specified on the maildrop command line. A filter
166 file may use those variables just like any other variables.
167 Predefined variables
169 The following variables are automatically defined by maildrop. The
170 default values for the following variables may be changed by the system
171 administrator. For security reasons, the values of the following
172 variables are always reset to their default values, and are never
173 imported from the environment:
174 DEFAULT
176 The default mailbox to deliver the message to. If the filter file
177 does not indicate a mailbox to deliver this message to, the message
178 is delivered to this mailbox. The default mailbox is defined by the
179 system administrator.
180 FROM
182 Message envelope sender. This is usually the same address as what
183 appears in the From: header, but may not be. This information may
184 or may not be available to maildrop on your system. The message
185 envelope sender is usually specified with the -f option to
186 maildrop. If the -f option is not given, maildrop looks for the
187 Return-Path: header in the message. As the last resort, FROM
188 defaults to “MAILER-DAEMON”. Note that FROM may be empty - the
189 message envelope sender is empty for bounce messages.
190 HOME
192 Home directory of the user running maildrop.
193 HOSTNAME
195 Network name of the machine running maildrop. Obtained from
196 gethostname(3).
197 LOCKEXT
199 Extension for dot-lock files (default: .lock).
200 LOCKREFRESH
202 Refresh interval, in seconds, for dot-locks (default: 15). When
203 maildrop dot-locks a mailbox, maildrop tries to refresh the lock
204 periodically in order to keep other programs from removing a stale
205 dot-lock. This is only required if a dot-lock exists for a
206 prolonged period of time, which should be discouraged anyway.
207 LOCKSLEEP
209 Number of seconds to wait to try again to create a dot-lock file,
210 if one already exists (default: 5).
211 LOCKTIMEOUT
213 Number of seconds to wait before removing a stale dot-lock file
214 (default: 60). If a dot-lock file still exists after LOCKTIMEOUT
215 seconds, maildrop assumes that the process holding the lock no
216 longer exists, and the dot-lock file can be safely removed. After
217 removing the dot-lock file, maildrop waits LOCKSLEEP seconds before
218 trying to create its own dot-lock file, in order to avoid a race
219 condition with another process which is also trying to remove the
220 same stale dot-lock, at the same time.
221 LOGNAME
223 Name of the user to who the message is being delivered.
224 MAILDROP_OLD_REGEXP
226 Revert to using the old legacy pattern matching engine. Versions of
227 maildrop prior to version 2.0 (included in the Courier mail server
228 0.51, and earlier), used a built-in pattern matching engine,
229 instead of using the PCRE library (see the “Patterns” section).
230 maildrop 1.x used a different syntax for patterns, which is no
231 longer described in this manual page. The old pattern matching
232 engine is still available, by setting MAILDROP_OLD_REGEXP to “1”.
233 Setting this variable will use the legacy pattern matching engine
234 for the rest of the maildrop recipe file.
235 The pattern matching engine will be removed completely in a future
237 version of maildrop. This setting provides for a transitional
238 period of converting old recipes. MAILDROP_OLD_REGEXP can be set
239 to “1” in the global maildroprc file, then reset to “0” in each
240 individual maildrop recipe file, after it gets converted to the new
241 syntax.
242 MAILFILTER
244 This is the name of the original filter file that was given to
245 maildrop on the command line. This is mostly useful to -default
246 filter files, it allows them to obtain the value of the -M
247 option[3] specified on the command line.
248 PATH
250 Command execution path. maildrop resets PATH to the system default
251 (usually /bin:/usr/bin:/usr/local/bin).
252 SENDMAIL
254 The mail delivery agent. When maildrop is instructed to deliver the
255 message to a mailbox whose name begins with the ! character, this
256 is interpreted as a request to forward the message. The SENDMAIL
257 command is executed to forward the message.
258 SHELL
260 The login shell. The shell is used to execute all commands invoked
261 by maildrop.
262 VERBOSE
264 Current Debug level (default: 0). Setting VERBOSE to progressive
265 higher values, between 1 and 9, produces debugging output on
266 standard error. maildrop ignores the VERBOSE variable in delivery
267 mode (in order not to confuse the mail transport agent).
268 UMASK
270 The file creation mode mask, in octal. The default setting of 077
271 creates mailboxes that are readable and writable by the owner only.
272 Use 007 to create mailboxes that are readable/writable by both
273 owner and the group. Use 037 to create mailboxes that are readable
274 by both owner and group, but writable by owner only. Permissions on
275 existing mailboxes are not changed, this setting affects only new
276 mailboxes. When delivering to maildirs this setting sets the
277 permissions on new messages only. Access permissions on messages in
278 maildirs are also affected by the permissions on the maildir
279 directories.
280 Other special variables
282 The following variables are automatically used by maildrop when the
283 filter file is being processed:
284 EXITCODE
286 Return code for maildrop. When maildrop successfully delivers a
287 message, it terminates with this exit code, which defaults to 0.
288 When the to or the cc command is used to deliver the message to an
289 external process, via a pipe, maildrop will set this variable to
290 the exit code of the external process. Since maildrop immediately
291 terminates after completing the to command this means that
292 maildrop's exit code will be the exit code of the external process.
293 If the to command does not deliver the message to a process you
294 must set EXITCODE before the to command, since maildrop terminates
295 immediately after finishing the delivery.
296 FLAGS
298 The FLAGS variable is used only when delivering a message to a
299 maildir, and may contain only the following letters: “D”, “F”, “R”,
300 and “S”. They may appear in any order. When the message gets
301 delivered to the maildir, the message will be marked with a draft,
302 flag, replied, or seen, attribute, correspondingly.
303 FLAGS must be set before the message is delivered to a maildir. The
305 contents of FLAGS are ignored, when delivering on an mbox folder.
306 KEYWORDS
308 The KEYWORDS variable is used only when delivering a message to a
309 maildir, and implements the optional IMAP keyword extension as
310 implemented in the Courier IMAP server[1]. It may be optionally
311 initialized to contain a comma-separate list of keywords. The to,
312 or the cc command, delivers the message to the maildir normally,
313 but also associated the list of keywords in KEYWORDS with the newly
314 delivered message.
315 KEYWORDS must be set before the message is delivered to a maildir.
317 The contents of KEYWORDS are ignored, when delivering on an mbox
318 folder.
319 LINES
321 Number of lines in the current message. Note that this may be an
322 approximation. It may or may not take into account the -A option.
323 Use this as criteria for filtering, nothing more.
324 MAILDIRQUOTA
326 Set this variable in order to manually enforce a maximum size on
327 ANY maildir where the message is delivered. This is an optional
328 feature that must be enabled by the system administrator, see
329 maildirquota(8)[4] for more information.
330 RETURNCODE
332 This variable is set when maildrop runs the system[5] command,
333 xfilter[6] command, or a command that's specified within a pair of
334 backtick characters ( command substitution ). The RETURNCODE
335 variable will be set to the exit code of the command, after it
336 completes.
337 SIZE
339 Number of bytes in the message. This may or may not include the -A
340 option. Use this as a criteria for filtering, nothing more.
341 Unquoted text
343 All text strings in filter files should be in single, or double quotes.
344 However, for convenience sake, quotes can be omitted under certain
345 circumstances.
346 Text that includes ONLY letters, digits, and the following characters:
348 _-.:/${}@ may appear without quotes. Note that this does not allow
349 spaces, or backslashes to be entered, however the text is still
350 variable-substituted, and the substituted text may contain other
351 characters.
352 Also, note that patterns (see below) begin with the slash character.
354 Normally, anything that begins with the slash is interpreted as a
355 pattern. However, text immediately after “VARIABLE=” is interpreted as
356 a string even if it begins with a slash. This is why something like:
357 MAILDIR=/var/mail
359 works as expected. Using quotes, though, is highly recommended. You
362 must use quotes to set a variable to a lone slash, because an unquoted
363 slash is interpreted as a division sign.
364 Long double or singly-quoted text can be broken across multiple lines
366 by ending the line with a lone backslash character, like this:
367 TEXT="This is a long \
369 text string"
370 The backslash, the newline, and all leading whitespace on the next line
373 is removed, resulting in "This is a long text string".
374 Command substitution
376 Text enclosed in back-tick characters is interpreted as a shell
377 command. The shell command is executed as a child process by maildrop.
378 Its output is used in place of the command. For example:
379 DIR=`ls`
381 places the names of the files in the current directory into the DIR
384 variable.
385 The output of the command will have all newline characters replaced by
387 spaces, and leading and trailing spaces will be stripped (multiple
388 spaces are not removed, though). Also, the contents of the message
389 being delivered is made available to the command on standard input.
390 Patterns
392 The pattern syntax in maildrop is similar to the grep command's syntax,
393 with some minor differences. A pattern takes the following form in the
394 filter file:
395 /pattern/:options
397 pattern specifies the text to look for in the message, in the UTF-8
400 codeset. pattern must not begin with a space, otherwise the leading
401 slash will then be interpreted as a division sign. If you must search
402 for text that starts with a space, use something like "/[ ] ... /".
403 The general syntax of maildrop's patterns is described in the
405 pcrepattern(3) manual page, with certain exceptions noted below.
406 maildrop uses the PCRE[7] library to implement pattern matching. Not
407 all features in PCRE are available in maildrop, and the “options” part,
408 which follows the pattern specification, changes the pattern matching
409 further. Consult the pcrepattern(3) manual page for more information,
410 but note the following exceptions:
411 · Internal options settings are not supported (but see the “D”
413 maildrop option, below). Do not include option settings in the
414 pattern, doing so will lead to undefined results.
415 · Named subpatterns are not implemented. Numbered subpatterns are
417 implemented, see “Pattern Match Results”, below.
418 · The search pattern gets executed not against the raw message text,
420 but the message transcoded into a canonical UTF-8-based format.
421 This process involves transcoding any non-UTF-8 message content
422 into UTF-8. Additionally, message headers get converted into a
423 canonical format before the search pattern gets executed.
424 For structured headers with email addresses, the process involves
426 removing extraneous punctuation, or adding missing ones (in
427 situations where a missing punctuation character can be deduced).
428 Additionally certain pre-RFC822 obsolete header formats get
429 converted to canonical form.
430 This means that header search patterns that include punctuation
432 character may appear not to work against obviously-matching message
433 text. Use “reformime -u <message.txt”, with message.txt containing
434 the sample message, to see exactly the actual text that gets
435 searched by patterns.
436 Pattern options
438 Following /pattern/, there may be an optional colon, followed by one.
439 or more options. The following options may be specified in any order:
440 h
442 Match this pattern against the message header.
443 b
445 Match this pattern against the message body.
446 D
448 This is a case sensitive match. Normally the patterns match either
449 uppercase or lowercase text. /john/ will match "John", "john", or
450 "JOHN". Specify the D option for a case-sensitive search: lowercase
451 letters in the pattern must match lowercase letters in the message;
452 ditto for uppercase.
453 If neither 'h' or 'b' is specified, the pattern is matched against the
455 header only. Specifying the 'b' option causes the pattern to be matched
456 against the message body. Specifying both causes the pattern to be
457 matched against the entire message.
458 Normally, each line in the message gets matched against the pattern
460 individually. When applying patterns to a header, multi-line headers
461 (headers split on several lines by beginning each continuation line
462 with whitespace) are silently combined into a single line, before the
463 pattern is applied.
464 MIME encoding
466 The pattern must be a valid text string in the UTF-8 codeset, and
467 maildrop should handle messages that use MIME encodings in other known
468 character sets. Options that specify a message header search result in
469 maildrop searching the initial message headers, and any headers of
470 additional MIME sections, in a multipart MIME message. Options that
471 specify a message body search will search through all "text" MIME
472 content.
473 For a MIME search to succeed, the message must be a well-formed MIME
475 message (with a Mime-Version: 1.0 header).
476 Weighted scoring
478 Patterns are evaluated by maildrop as any other numerical expression.
479 If a pattern is found, maildrop's filter interprets the results of the
480 pattern match as number 1, or true, for filtering purposes. If a
481 pattern is not found the results of the pattern search is zero. Once a
482 pattern is found, the search stops. Second, and subsequent occurrences
483 of the same pattern are NOT searched for.
484 maildrop can also do weighted scoring. In weighted scoring, multiple
486 occurrences of the same pattern are used to calculate a numerical
487 score.
488 To use a weighted search, specify the pattern as follows:
490 /pattern/:options,xxx,yyy
492 where xxx and yyy are two numbers. yyy is optional -- it will default
495 to 1, if missing.
496 The first occurrence of the pattern is evaluated as xxx. The second
498 occurrence of the pattern is evaluated as xxx*yyy, the third as
499 xxx*yyy*yyy, etc... All occurrences of the pattern are added up to
500 calculate the final score.
501 Note
503 maildrop does not recognize multiple occurrences of the same
504 pattern in the same line. Multiple occurences of the same pattern
505 in one line count as one occurence.
506 Pattern Match Results
508 After a pattern is successfully matched, the actual text that is
509 matched is placed in the MATCH variable. For example:
510 /^From:.*/
512 matches a line of the form:
515 From: postmaster@localhost
517 Here the variable MATCH will be set to "From: postmaster@localhost",
520 which can be used in subsequent statements.
521 If the pattern contains subpatterns, the portions of the text that
523 match the first subpattern is placed in the MATCH1 variable. The second
524 subpattern, if any, is placed in MATCH2, and so on:
525 /^From:\s+(.*)@(.*)/
527 matched against the same line will set MATCH to “From:
530 postmaster@localhost”, MATCH1 to “postmaster”, and MATCH2 to
531 “localhost”. Of course, in real world the “From:” header is usually
532 much more complicated, and can't be handled that easily. This is just
533 an illustrative example.
534 Note
536 Subpatterns are not processed in the foreach statement.
537 Conversion of maildrop 1.x patterns to 2.0
539 Although the new PCRE-based pattern matching code in maildrop is
540 completely different from the built-in pattern matching code in
541 maildrop 1.x, very few changes will be required to convert recipes to
542 the new syntax. The only major differences are:
543 · The subexpression format has changed. Any pattern that uses
545 subexpression needs to be converted. Additionally, references to
546 MATCH2 must be replaced with MATCH1, MATCH3 to MATCH2, and so on.
547 References to plain old MATCH will remain the same.
548 · The “w” pattern option is no longer possible, with PCRE. The very
550 few recipes that use this option, if any actually exist, will have
551 to be rewritten in some other fashion.
552 Expressions
554 Although maildrop evaluates expressions numerically, results of
555 expressions are stored as text literals. When necessary, text literals
556 are converted to numbers, then the results of a mathematical operation
557 is converted back into a text literal.
558 Operators
560 The following operators carry their usual meaning, and are listed
561 in order from lowest precedence, to the highest:
562 ||
565 &&
566 < <= > >= == != lt le gt ge eq ne
567 |
568 &
569 + -
570 * /
571 =~ /pattern/
572 /pattern/ ! ~ function()
573 Variable assignment
576 VARIABLE=expression
577 Assigns the result of the expression to VARIABLE (note no leading $
580 in front of variable).
581 Note
583 If VARIABLE is NOT surrounded by quotes, then it may contain
584 only letters, numbers, underscores, dashes, and a selected few
585 other characters. In order to initialize a variable whose name
586 contains non-standard punctuation marks, surround the name of
587 the variable with quotes.
588 cc - deliver a copy of the message
590 cc expression
591 The cc statement is very similar to the to statement, except that
594 after delivering the message maildrop continues to process the
595 filter file, unlike the to statement which immediately terminates
596 maildrop after the delivery is complete. Essentially, the message
597 is carbon copied to the given mailbox, and may be delivered again
598 to another mailbox by another cc or to statement.
599 See the to statement[8] for more details. When cc is used to
601 deliver a message to a process maildrop will set the EXITCODE
602 variable to the process's exit code.
603 dotlock - create a manual dot-lock
605 dotlock expression {
606 ...
608 }
610 maildrop automatically creates a lock when a message is delivered
613 to a mailbox. Depending upon your system configuration, maildrop
614 will use either dot-locks, or the flock() system call.
615 The dotlock statement creates an explicit dot-lock file. Use the
617 flock statement[9] to create an explicit flock() lock.
618 The expression is a filename that should be used as a lock file.
620 maildrop creates the indicated dot-lock, executes the filtering
621 instructions contained within the { ... } block, and removes the
622 lock. The expression must be the name of the dot-lock file itself,
623 NOT the name of the mailbox file you want to lock.
624 Note
626 With manual locking, it is possible to deadlock multiple
627 maildrop processes (or any other processes that try to claim
628 the same locks).
629 No deadlock detection is possible with dot-locks, and since
631 maildrop automatically refreshes all of its dot-locks
632 regularly, they will never go stale. You'll have maildrop
633 processes hanging in limbo, until their watchdog timers go off,
634 aborting the mail delivery.
635 echo - output diagnostic information
637 echo expression
638 maildrop will print the given text. This is usually used when
641 maildrop runs in embedded mode, but can be used for debugging
642 purposes. Normally, a newline is printed after the text. If text is
643 terminated with a \c, no newline will be printed.
644 exception - trap fatal errors
646 exception {
647 ...
649 }
651 The exception statement traps errors that would normally cause
654 maildrop to terminate. If a fatal error is encountered anywhere
655 within the block of statements enclosed by the exception clause,
656 execution will resume immediately following the exception clause.
657 exit - terminate filtering unconditionally
659 exit
660 The exit statement immediately terminates filtering. maildrop's
663 return code is set to the value of the EXITCODE variable. Normally,
664 maildrop terminates immediately after successfully delivering the
665 message[8] to a mailbox. The exit statement causes maildrop to
666 terminate without delivering the message anywhere.
667 The exit statement is usually used when maildrop runs in embedded
669 mode[10], when message delivery instructions are not allowed.
670 flock - create an manual flock() lock
672 flock expression {
673 ...
675 }
677 maildrop automatically creates a lock when a message is delivered
680 to a mailbox. Depending upon your system configuration, maildrop
681 will use either dot-locks, or the flock() system call.
682 The flock statement creates a manual flock() lock. Use the dotlock
684 statement[11] to create a manual dot-lock file.
685 The expression is the name of the file that should be locked.
687 maildrop creates the lock on the indicated file, executes the
688 filtering instructions contained within the { ... } block, and
689 removes the lock.
690 Note
692 With manual locking, it is possible to deadlock multiple
693 maildrop processes (or any other processes that try to claim
694 the same locks). The operating system will automatically break
695 flock() deadlocks. When that happens, one of the maildrop
696 processes will terminate immediately. Use the exception
697 statement in order to trap this exception condition, and
698 execute an alternative set of filtering instructions.
699 foreach - iterate over text sections matched by a pattern
701 foreach /pattern/:options
702 {
703 ...
704 }
705 foreach (expression) =~ /pattern/:options
707 {
708 ...
709 }
710 The foreach statement executes a block of statements for each
713 occurrence of the given pattern in the given message, or
714 expression. On every iteration MATCH variable will be set to the
715 matched string. All the usual options may be applied to the pattern
716 match, EXCEPT the following:
717 ,xxx,yyy
719 Weighted scoring is meaningless, in this context.
720 ( ... )
722 Subpatterns are not processed. Only the MATCH variable will be
723 set for each found pattern.
724 if - conditional execution
726 if (expression)
727 {
728 ...
729 }
730 else
731 {
732 ...
733 }
734 Conditional execution. If expression evaluates to a logical true
737 (note - parenthesis are required) then the first set of statements
738 is executed. The else keyword, and the subsequent statements, are
739 optional. If present, and the expression evaluates to a logical
740 false, the else part is executed.
741 maildrop evaluates all expression as text strings. In the context
743 of a logical expression, an empty string, or the number 0
744 constitutes a logical false value, anything else is a logical true
745 value.
746 If the if part, or the else part consists of only one statement,
748 the braces may be omitted.
749 Note
751 The grammar of this if statement is stricter than usual. If you
752 get baffling syntax errors from maildrop, make sure that the
753 braces, and the if statement, appear on separate lines.
754 Specifically: the closing parenthesis, the closing braces, and
755 the else statement, must be at the end of the line (comments
756 are allowed), and there may not be any blank lines in between
757 (not even ones containing comments only).
758 If the else part contains a single if, and nothing else, this may
760 be combined into an elsif:
761 if (expression)
763 {
764 ...
765 }
766 elsif (expression)
767 {
768 ...
769 }
770 The above example is logically identical to:
773 if (expression)
775 {
776 ...
777 }
778 else
779 {
780 if (expression)
781 {
782 ...
783 }
784 }
785 Consecutive elsif sequences are allowed:
788 if (expression)
790 {
791 ...
792 }
793 elsif (expression)
794 {
795 ...
796 }
797 elsif (expression)
798 {
799 ...
800 }
801 Consecutive occurences of elsif commands eliminate a significant
804 amount of indentation, and the resulting code is more readable.
805 import - access original environment variable
807 import variable
808 When maildrop starts, it normally imports the contents of the
811 environment variables, and assigns them to internal maildrop
812 variables. For example, if there was an environment variable FOO,
813 the internal maildrop variable FOO will have the contents of the
814 environment variable. From then on, FOO will be no different than
815 any other variable, and when maildrop runs an external command, the
816 contents of maildrop's variables will be exported as the
817 environment for the command.
818 Certain variables, like HOME and PATH, are always reset to fixed
820 defaults, for security reasons. Also, in delivery and embedded
821 modes, the environment is not imported at all (with the exception
822 of system locale environment variables), and maildrop starts with
823 only the fixed default variables.
824 The import statement initializes the specified variable with the
826 contents of the original environment variable when maildrop
827 started. For example:
828 echo "PATH is $PATH"
830 PATH="/bin"
831 echo "PATH is $PATH"
832 import PATH
833 echo "PATH is $PATH"
834 exit
835 This results in the following output:
838 PATH is /bin:/usr/bin:/usr/local/bin
840 PATH is /bin
841 PATH is /home/root/bin:/sbin:/usr/sbin:/bin:/usr/bin:/usr/local/bin
842 This shows that when maildrop starts PATH is set to the fixed
845 default of /bin:/usr/bin:/usr/local/bin. However, the original
846 contents of the PATH environment variable we different, and the
847 import statement shows what it was.
848 include - execute filtering instructions from another file
850 include expression
851 The include statement reads a file, and executes filtering
854 instructions contained in that file. Note that the include
855 statement is processed when the current filter file is being
856 executed. When maildrop reads the initial filter file, any syntax
857 errors in the filtering instructions are immediately reported, and
858 maildrop will terminate with a return code of EX_TEMPFAIL. Any
859 errors in files specified by include statements are NOT reported,
860 because those files will not be read until the include statement is
861 itself executed.
862 If the specified file does not exist, or if there are any syntax
864 errors in the file, maildrop reports the error, and terminates with
865 a return code of EX_TEMPFAIL.
866 log, logfile - log message deliveries
868 logfile expression
869 log expression
871 Logging in maildrop is normally turned off. The logfile statement
874 specifies the file where maildrop will log how the message has been
875 disposed of. The parameter is then name of the file. If the file
876 exists maildrop appends to the file.
877 For each delivery (the to[8] and cc[12] statements, and default
879 deliveries) maildrop records the From: and the Subject: fields,
880 together with the current time, in the log file.
881 The log statement adds additional logging text to the log file. The
883 log statement works exactly like the echo statement, except that
884 the text is written to the logfile, instead of standard output.
885 system - execute a system command
887 system expression
888 expression specifies an external program that maildrop runs as a
891 subprocess. The subprocess's standard input gets connected to
892 /dev/null, and the subprocess inherits the standard output and
893 error from maildrop.
894 to - deliver message to a mailbox
896 to expression
897 The to statement delivers the message to a mailbox. expression
900 must evaluate to a valid mailbox. A valid mailbox is either a
901 mailbox file, a maildir, or an external program (which includes
902 forwarding to another address).
903 The to statement is the final delivery statement. maildrop
905 delivers message, then immediately terminates, with its return code
906 set to the EXITCODE variable. If there was an error while
907 delivering the message, maildrop terminates with the EX_TEMPFAIL
908 exit code. A properly-written mail transport agent should re-queue
909 the message, and re-attempt delivery at some later time.
910 An expression that begins with the "|" character specifies an
912 external program to run to handle the actual delivery. The SHELL
913 variable specifies the shell to execute the given command. The
914 message is provided to the command on standard input. maildrop's
915 exit code will be the process's exit code.
916 An expression that begins with an exclamation mark, "!" specifies a
918 whitespace-delimited list of E-mail addresses to forward the
919 message to. The program specified by the SENDMAIL variable is run
920 as an external program, with the list of E-mail addresses provided
921 as parameters to the program.
922 Otherwise, expression names the mailbox where maildrop delivers the
924 message. If expression is a directory, maildrop assumes that the
925 directory is a maildir directory. Otherwise, maildrop will deliver
926 the message to a file, formatted in traditional mailbox format.
927 maildrop will use either dot-locking, or flock()-locking when
928 delivering the message to the file.
929 while - repeatedly execute a block of statements
931 while (expression)
932 {
933 ...
934 }
935 The expression is repeatedly evaluated. Each time it evaluates to a
938 logical true[13], the statements inside the braces are executed.
939 When expression evaluates to a logical false, the while loop is
940 over. Take care to avoid infinite loops.
941 xfilter - filter message through another program
943 xfilter expression
944 expression specifies an external program that maildrop runs to
947 filter the current message. The current message will be piped to
948 the filter program as standard input. The output of the filter
949 program replaces the current message being delivered. The external
950 program must terminate with an exit code of 0. If the external
951 program does not terminate with an exit code of 0, or if it does
952 not read the message from the standard input, maildrop terminates
953 with an exit code of EX_TEMPFAIL.
954 || - logical or
956 expression1 || expression2
957 If expression1 evaluates to a logical true, the result of the || is
961 expression1, otherwise it's expression2, which is evaluated.
962 maildrop uses the following concept of true/false: an empty text
964 literal, or a text literal that consists of the single character
965 "0" is a logical false value. Anything else is a logical true
966 value.
967 && - logical and
969 expression1 && expression2
970 If expression1 evaluates to a logical false, the result of the &&
974 is expression1, otherwise it's expression2, which is evaluated.
975 maildrop uses the following concept of true/false: an empty text
977 literal, or a text literal that consists of the single character
978 "0" is a logical false value. Anything else is a logical true
979 value.
980 <, <=, >, >=, ==, != - numerical comparison
982 expression1 < expression2
983 expression1 <= expression2
985 expression1 > expression2
987 expression1 >= expression2
989 expression1 == expression2
991 expression1 != expression2
993 These operators compare their left hand side expression against
997 their right hand side. These operators compare the numerical values
998 of each side, as floating point numbers. If the numbers compare as
999 indicated, the result of the comparison is the text string "1",
1000 otherwise it is the text string 0.
1001 Note
1003 Ccomparisons are not associative: "a < b < c" is an error. If
1004 it is absolutely necessary, use "(a < b) < c".
1005 lt, le, gt, ge, eq, ne - text comparison
1007 expression1 lt expression2
1008 expression1 le expression2
1010 expression1 gt expression2
1012 expression1 ge expression2
1014 expression1 eq expression2
1016 expression1 ne expression2
1018 These operators compare their left hand side expression against
1022 their right hand side. These operators compare each side as text
1023 strings (alphabetically, although the text may include anything).
1024 If the text strings compare as indicated, the result of the
1025 comparison is the text string "1", otherwise it is the text string
1026 0.
1027 Note
1029 Comparisons are not associative: "a lt b lt c" is an error. If
1030 it is absolutely necessary, use "(a lt b) lt c". (But why would
1031 you?).
1032 | - bitwise or
1034 expression1 | expression2
1035 This is the bitwise or operator. Its result is a 32 bit integer,
1038 which is a bitwise-or combination of the left hand side and the
1039 right hand side.
1040 & - bitwise and
1042 expression1 & expression2
1043 This is the bitwise and operator. Its result is a 32 bit integer,
1046 which is a bitwise-and combination of the left hand side and the
1047 right hand side.
1048 +, -, *, / - numerical operations
1050 expression1 + expression2
1051 expression1 - expression2
1053 expression1 * expression2
1055 expression1 / expression2
1057 These are numerical, floating point, operators.
1061 =~ /pattern/:options - pattern match against string
1063 expression =~ /pattern/:option
1064 The left hand side of the =~ operator can be any expression. The
1067 right hand side is always a pattern specification. The result of
1068 the operator is the weighted match of the pattern against
1069 expression (if the options do not specify weighted scoring, the
1070 result is simply 1 if the pattern was found, 0 if not).
1071 See "Patterns[14]" for more information.
1073 /pattern/:options - pattern match against message
1075 /pattern/:option
1076 The result of this operator is the weighted match of the pattern
1079 against the current message (if the options do not specify weighted
1080 scoring, the result is simply 1 if the pattern was found, 0 if
1081 not).
1082 See "Patterns[14]" for more information.
1084 !, ~ - logical/bitwise not operator.
1086 ! expression
1087 ~ expression
1089 The result of the ! operator is a logical opposite of its right
1092 hand side expression. If the right hand side expression evaluated
1093 to a logical true, the result is a logical false. If it evaluated
1094 to a logical false, the result is a logical true.
1095 maildrop uses the following concept of true/false: an empty text
1097 literal, or a text literal that consists of the single character
1098 "0" is a logical false value. Anything else is a logical true
1099 value.
1100 The result of the ~ operator is a bitwise complement of its right
1102 hand side expression. The right hand side expression is evaluated
1103 as a 32 bit integer, and the result of this operator is a bitwise
1104 complement of the result.
1105 escape(string) - escape special characters in a string.
1107 escape(expression)
1108 The escape function returns its sole argument with every occurrence
1111 of a special character prefixed by a backslash. A special character
1112 is any of the following characters:
1113 |!$()[]\+*?.&;`'-~<>^{}"
1115 This can used when matching pattern sections[15], and then taking
1118 one section and matching it again. For example:
1119 if ( /^From:\s*(.*)/ )
1121 {
1122 MATCH1=escape($MATCH1)
1123 if ( /^Subject:.*$MATCH1/ )
1124 {
1125 ...
1126 }
1127 }
1128 This example checks if the contents of the From: header can also be
1131 found in the Subject: header. If the escape function were not used,
1132 then any special characters in the From: header that are also used
1133 in regular expressions, such as * or +, would introduce
1134 unpredictable behavior, most likely a syntax error.
1135 The reason why this list of special characters also includes
1137 characters not used in maildrop's regular expressions is to allow
1138 maildrop's variables to be used on the command line of a shell
1139 command executed by the xfilter command, backtick characters, or to
1140 or cc commands.
1141 Although using data from an external data source is dangerous, and
1143 it may result in inadvertent exploits, using the escape function
1144 should hopefully result in fewer surprises.
1145 gdbmopen, gdbmclose, gdbmfetch, gdbmstore - GDBM support in maildrop
1147 These functions provide support for GDBM database files. See
1148 maildropgdbm(5)[16] for more information.
1149 Note
1151 The system administrator can disable GDBM support in maildrop,
1152 so these commands may not be available to you.
1153 getaddr(string) - extract RFC 2822 addresses from a header.
1155 if ( /^From:\s*(.*)/ )
1156 {
1157 ADDR=getaddr($MATCH1)
1158 }
1159 This function is usually applied to a header that contains RFC
1162 2822[17] addresses. It extracts the actual addresses from the
1163 header, without any comments or extraneous punctuation. Each
1164 address is followed by a newline character. For example, if string
1165 contains:
1166 joe@domain.com (Joe Brown), "Alex Smith" <alex@domain.com>, tom@domain.com
1168 The result of the getaddr function is the following string:
1171 joe@domain.com<NL>alex@domain.com<NL>tom@domain.com<NL>
1173 Note
1176 Because getaddr() interprets RFC 2822[18] loosely, it is not
1177 necessary to strip off the "To:" or the "Cc:" header from the
1178 string, before feeding it to getaddr(). For example, the
1179 following snippet of code takes all addresses in the message,
1180 and concatenates them into a single string, separated by
1181 spaces:
1182 ADDRLIST=""
1184 foreach /^(To|Cc): .*/
1185 {
1186 foreach (getaddr $MATCH) =~ /.+/
1187 {
1188 ADDRLIST="$ADDRLIST $MATCH"
1189 }
1190 }
1191 Note
1194 In certain rare situations, RFC 2822[18] allows spaces to be
1195 included in E-mail addresses, so this example is just
1196 educational.
1197 hasaddr(string) - Search for an address.
1199 if ( hasaddr(string) )
1200 {
1201 ...
1202 }
1203 "string" is of the form user@domain. The hasaddr function returns 1
1206 if this address is included in any To:, Cc:,Resent-To:, or
1207 Resent-Cc:, header in the message, otherwise this function returns
1208 0.
1209 This is more than just a simple text search. Each header is parsed
1211 according to RFC822. Addresses found in the header are extracted,
1212 ignoring all comments and names. The remaining addresses are
1213 checked, and if "string" is one of them, hasaddr returns 1,
1214 otherwise it returns 0.
1215 The comparison is case-insensitive. This actually violates RFC822
1217 (and several others) a little bit, because the user part of the
1218 address may be (but is not required to be) case sensitive.
1219 length (string) - length of a string
1221 if (length(string) > 80)
1222 {
1223 ...
1224 }
1225 The length function returns the number of characters in string.
1228 lookup (expr, 'filename', 'options') - read file for patterns
1230 if (lookup(expr, file, "option"))
1231 {
1232 ...
1233 }
1234 expr is any expression. filename is a name of a file containing a
1237 list of patterns. Note that filename is relative to the current
1238 directory, which is the home directory of the user when maildrop
1239 runs in delivery mode, or embedded mode. maildrop then reads the
1240 file. Blank lines will be ignored, as well as any lines that begin
1241 with the # character (comments).
1242 Leading whitespace (but not trailing whitespace, take care) is
1244 removed, and the remaining contents of each line are interpreted as
1245 a pattern which is matched against expr. As soon as the match is
1246 found, lookup returns "1". If no match is found after reading the
1247 entire file, lookup returns "0". For example:
1248 if ( /^To:\s*(.*)/ && lookup( $MATCH1, "badto.dat" ))
1250 {
1251 exit
1252 }
1253 The file badto.dat contains the following two lines:
1256 friend@public
1258 ^[^@]*$
1259 If a message has a To: header that contains the text
1262 "friend@public", or does not contain at least one @ character, then
1263 the message will be silently dropped on the floor ( maildrop will
1264 terminate without delivering the message anywhere).
1265 options are the pattern matching options to use. The only supported
1267 option is "D" (the rest are meaningless, in this case).
1268 Note
1270 Be careful with discarding messages like that. Pattern matching
1271 can be tricky, and a slight miscalculation can cause mail to be
1272 unintentionally discarded. It is much desirable to first
1273 deliver message to a separate folder or mailbox, and once the
1274 filter is verified to work correctly, change it so the messages
1275 are discarded completely.
1276 substr(string,start [,count]) - return substring
1278 foo=substr($foo, 1, 10)
1279 The substr function extracts characters from string beginning with
1282 character #start. If count is specified, at most count characters
1283 starting at position start are kept, any excess is trimmed.
1284 time - return current time
1286 foo=time
1287 The time function returns the current time, in seconds, since
1290 January 1, 1970. This function is useful when using GDBM files. See
1291 maildropex(7)[19] for an example of using the time function.
1292 tolower(string) - Convert string to lowercase.
1294 foo=tolower(string)
1295 This function returns the string with all uppercase characters
1298 replaced by lowercase characters.
1299 toupper(string) - Convert string to uppercase.
1301 foo=toupper(string)
1302 This function returns the string with all lowercase characters
1305 replaced by uppercase characters.
1306 Statements
1308 The filter file is read by maildrop ($HOME/.mailfilter or another
1309 file), and it contains filtering statements, one per line. The
1310 filtering language used by maildrop has a loosely - defined grammatical
1311 structure.
1312 Statements are listed one per line. Multiple statements may be listed
1314 on the same line by separating them with semicolons. To continue a long
1315 statement on the next line, terminate the line with a backslash
1316 character.
1317
1319 If getaddr() or hasaddr() functions are used on broken headers, the
1320 results are unpredictable.
1321 hasaddr() is completely case insensitive. This actually violates a few
1323 RFCs, because the userid portion of the address could be
1324 case-sensitive, but it's not in too many cases, so there.
1325
1327 lockmail(1)[20], maildrop(1)[21], maildropgdbm(5)[16],
1328 maildirquota(8)[4], reformail(1)[22], egrep(1), sendmail(8).
1329
1331 Sam Varshavchik
1332 Author
1333
1335 1. Courier mail server
1336 http://www.courier-mta.org/
1337 2. dot-courier(5)
1339 http://www.courier-mta.org/maildrop/dot-courier.html
1340 3. value of the -M option
1342 http://www.courier-mta.org/maildrop/maildrop.html#moption
1343 4. maildirquota(8)
1345 http://www.courier-mta.org/maildrop/maildirquota.html
1346 5. system
1348 http://www.courier-mta.org/maildrop/#system
1349 6. xfilter
1351 http://www.courier-mta.org/maildrop/#xfilter
1352 7. PCRE
1354 http://www.pcre.org
1355 8. See the to statement
1357 http://www.courier-mta.org/maildrop/#to
1358 9. flock statement
1360 http://www.courier-mta.org/maildrop/#flock
1361 10. embedded mode
1363 http://www.courier-mta.org/maildrop/maildrop.html#embedded
1364 11. dotlock statement
1366 http://www.courier-mta.org/maildrop/#dotlock
1367 12. cc
1369 http://www.courier-mta.org/maildrop/#cc
1370 13. evaluates to a logical true
1372 http://www.courier-mta.org/maildrop/#if
1373 14. Patterns
1375 http://www.courier-mta.org/maildrop/#patterns
1376 15. matching pattern sections
1378 http://www.courier-mta.org/maildrop/#patmatch
1379 16. maildropgdbm(5)
1381 http://www.courier-mta.org/maildrop/maildropgdbm.html
1382 17. RFC 2822
1384 http://www.rfc-editor.org/rfc/rfc2822.txt
1385 18. RFC 2822
1387 http://www.rfc-editor.org/rfc/rfc822.txt
1388 19. maildropex(7)
1390 http://www.courier-mta.org/maildrop/maildropex.html
1391 20. lockmail(1)
1393 http://www.courier-mta.org/maildrop/lockmail.html
1394 21. maildrop(1)
1396 http://www.courier-mta.org/maildrop/maildrop.html
1397 22. reformail(1)
1399 http://www.courier-mta.org/maildrop/reformail.html
1400Courier Mail Server 07/24/2017 MAILDROPFILTER(7)