1MAILDROP(1) Double Precision, Inc. MAILDROP(1)
2
6 maildrop - mail delivery filter/agent
7
9 maildrop [option...] [-d user] [arg...]
10 maildrop [option...] [filename] [arg...]
12
14 maildrop is a replacement local mail delivery agent that includes a
15 mail filtering language. The system administrator can either replace
16 the existing mail delivery agent with maildrop, or users may run
17 maildrop using the 'forward to program' mechanism of the existing mail
18 delivery agent.
19 maildrop first reads the E-mail message on standard input. Trailing
21 carriage return characters are automatically stripped. An E-mail
22 message consists of header lines, followed by a blank line, followed by
23 the contents of the message.
24 maildrop does not accept an mbox-style From_ line before the first
26 header line. maildrop does not accept leading empty lines before the
27 first non-blank header line. If the message can possibly start with
28 empty lines, and a From_ line, use reformail -f0 to remove any initial
29 empty lines, and replace a From_ line with a proper “Return-Path:”
30 header; then pipe it to maildrop.
31 If the file /etc/maildroprc exists, mail delivery or mail filtering
33 instructions are read from that file. maildrop's delivery/filtering
34 instructions may direct maildrop to save the message in specific
35 mailbox, discard it, return it to sender, or forward it to a different
36 E-mail address.
37 If /etc/maildroprc does not exist, or its mail delivery instructions do
39 not completely dispose of this message, maildrop then reads the mail
40 delivery instructions from $HOME/.mailfilter. If it doesn't exist, or
41 its mail delivery instructions do not completely dispose of the
42 message, maildrop then saves the E-mail message in the default mailbox.
43 maildrop knows how to deliver mail to an standard mailbox files; it
45 also knows how to deliver to maildirs. A maildir is a directory-based
46 mail format used by the Courier[1] and Qmail[2] mail servers. Many
47 other mail servers also know how to read maildirs. When delivering to
48 mailbox files, maildrop will lock the mailbox for the duration of the
49 delivery.
50 This is the general mail delivery behavior. There are minor differences
52 in behavior depending on maildrop delivery mode, which is determined
53 based on how maildrop was started. maildrop uses three different
54 primary operating modes:
55 Manual mode
57 A file containing filtering instructions - filename is specified as
58 an argument to the maildrop command. maildrop reads this filename
59 and follows the instructions in it. Unless the message is
60 explicitly forwarded, bounced, deleted, or delivered to a specific
61 mailbox, it will be delivered to the user's system mailbox.
62 Delivery mode
64 maildrop is the mail server's mail delivery agent. maildrop runs
65 in delivery mode when no filename is specified on the command line.
66 maildrop changes the current directory to the user's home
67 directory, then reads /etc/maildroprc, then $HOME/.mailfilter.
68 Embedded mode
70 maildrop functions as a part of another application. The embedded
71 mode is used by the Courier[1] mail server to integrate mail
72 filtering directly into the process of receiving mail from a remote
73 mail relay, thus rejecting unwanted mail before it is even accepted
74 for local mail delivery. Embedded mode is used when either the -m,
75 or the -M, option is specified, and is described below. See below
76 for a more extensive description of the embedded mode.
77
79 It is safe to install maildrop as a root setuid program. The Courier
80 mail server[1] installs maildrop as a root setuid program by default,
81 in order to be able to use maildrop in embedded mode. If root runs
82 maildrop (or it is setuided to root) the -d option may be used to
83 specify the message's recipient. maildrop immediately resets its
84 userid to the one specified by the -d option. The user's
85 $HOME/.mailfilter is read (if it exists), and the message is delivered
86 to the indicated user.
87 The system administrator can configure maildrop to restrict the -d
89 option for everyone except the mail system itself.
90 If in delivery mode the user's home directory has the sticky bit set,
92 maildrop immediately terminates with an exit code of EX_TEMPFAIL,
93 without doing anything. Mail servers interpret the EX_TEMPFAIL exit
94 code as a request to reschedule the message for another delivery
95 attempt later. Setting the sticky bit allows $HOME/.mailfilter to be
96 edited while temporarily holding all incoming mail.
97 maildrop also terminates with EX_TEMPFAIL if the user's home directory
99 has world write permissions.
100 maildrop immediately terminates with EX_TEMPFAIL if the filename is not
102 owned by the user, or if it has any group or world permissions. This
103 includes read permissions. The permissions on $HOME/.mailfilter may
104 only include read and write privileges to the user.
105 When using the special embedded mode (see below) maildrop immediately
107 terminates with the exit code set to EX_TEMPFAIL if $HOME/.mailfilters
108 is not owned by the user, or if it has any group or world permissions.
109
111 maildrop is heavily optimized and tries to use as little resources as
112 possible. maildrop reads small messages into memory, then filters
113 and/or delivers the message directly from memory. For larger messages,
114 maildrop accesses the message directly from the file. If the standard
115 input is not a file, maildrop writes the message to a temporary file,
116 then accesses the message from the temporary file. The temporary file
117 is automatically removed when the message is delivered.
118
120 -a
121 Makes the Courier Authentication Library usage mandatory, i.e.
122 maildrop will throw a temporary error code if the call to the
123 authlib mechanism fails for some reason, such as authdaemon being
124 inaccessible.
125 Note
127 This setting may already be the default, depending on
128 maildrop's configuration.
129 -A "Header: value"
131 Adds an additional header to the message. Specifying -A "Foo: Bar"
132 effectively adds this header to the message being delivered.
133 The mail transport agent usually adds additional headers when
135 delivering a message to a local mailbox. The way it's usually done
136 is by the mail transport agent sending the message using a pipe to
137 the local delivery agent - such as maildrop - and adding some
138 additional headers in the process. Because maildrop receives the
139 message from a pipe, maildrop must either save the message in
140 memory or write the message into a temporary file.
141 The -A option enables the file containing the message to be
143 provided to maildrop directly, as standard input, and the
144 additional headers specified on the command line. Because the
145 standard input is a file, maildrop will not need a temporary file.
146 Multiple -A options may be specified.
147 -d user
149 Run maildrop in delivery mode for this user ID.
150 The system administrator may optionally restrict the -d option to
152 be available to the mail system only, so it may not be available to
153 you. In all cases, the -d option is allowed if user is the same
154 user who is running maildrop. Also, for the -d option to work at
155 all, maildrop must be executed by root, or maildrop must be a
156 root-owned program with the setuid bit set. Absence of a filename
157 on maildrop's command line implies the -d option for the user
158 running maildrop.
159 If -d is not specified, the first argument following all the
161 options is a name of the file containing filtering instructions.
162 The remaining arguments, if any, are assigned to the variables $1,
163 $2, and so on (see "Environment"[3] and "Variable
164 substitution"[4]).
165 -f address
167 Sets the FROM variable (message envelope sender) to address. The
168 system administrator may optionally disable the -f option for
169 users, so it may not be available to you.
170 -m
172 Run maildrop in embedded mode. It's possible to use both the -m,
173 and the -d options, but it doesn't make much sense to do so. Even
174 if you really wanted to run your message through someone else's
175 .mailfilter, that .mailfilter probably has at least one instruction
176 which is not allowed in the embedded mode.
177 The filename argument to maildrop should be specified. filename is
179 a file that includes filtering instructions to be processed in
180 embedded mode. The -m option is used for debugging filter files
181 which are later placed in $HOME/.mailfilters, and used with the -M
182 option.
183 -M filterfile
185 Run maildrop in a special embedded mode. The -d option is implied
186 when -M is used, and if absent it defaults to the userid running
187 maildrop.
188 All the requirements for the -d option apply. maildrop must either
190 be executed by root, or the maildrop program must be owned by root
191 with the setuid bit set. maildrop immediately gives up root
192 privileges by changing its user ID to the one specified by -d, then
193 reads $HOME/.mailfilters/filterfile. For security reasons the name
194 of the file may not begin with a slash or include periods.
195 maildrop is very paranoid: both $HOME/.mailfilters, and
196 $HOME/.mailfilters/filterfile must be owned by the user, and may
197 not have any group or world permissions.
198 The -M option allows for some friendly cooperation between the user
200 running the application, and the user who provides a filter for the
201 embedded mode. The user running the application can use someone
202 else's canned filter and be assured that the filter is not going to
203 run amok and start sending mail or create files all over the place.
204 The user who provides the filter can be assured that the
205 environment variables are clean, and that there are no surprises.
206 maildrop supports the concept of "default" filter files. If the
208 file specified by the -M option cannot be found in
209 $HOME/.mailfilters, maildrop will try to open
210 $HOME/.mailfilters/filterfileprefix-default. filterfileprefix is
211 the initial part of filterfile up until the last '-' character in
212 filterfile.
213 If $HOME/.mailfilters/filterfileprefix-default does not exist, and
215 there are any other dashes left in filterfileprefix, maildrop
216 removes the last dash and everything following it, then tries
217 again.
218 As a last resort maildrop tries to open $HOME/.mailfilters/default.
220 For example, if the parameter to the -M option is
222 mailfilter-lists-maildrop, maildrop will try to open the following
223 files, in order:
224 Note that maildrop looks for -default files ONLY if -M is used.
226 -D uuu/ggg
228 This option is reserved for use by the version of maildrop that
229 comes integrated with the Courier mail server[1].
230 -V level
232 Initialize the VERBOSE variable to level. Because maildrop parses
233 the entire file before running it, this option is used to produce
234 debugging output in the parsing phase. Otherwise, if filename has
235 syntax errors, then no debugging output is possible because the
236 VERBOSE variable is not yet set.
237 -V is ignored when maildrop runs in delivery mode.
239 -w N
241 The -w N option places a warning message into the maildir if the
242 maildir has a quota setting, and after the message was successfully
243 delivered the maildir was at least N percent full.
244 -W filename
246 Copy the warning message from filename, or from /etc/quotawarnmsg
247 if this option is not specified, with the addition of the "Date:"
248 and "Message-Id:" headers. The warning is repeated every 24 hours
249 (at least), until the maildir drops below N percent full.
250 -t socket
252 This option is available if maildrop is compiled with optional
253 Dovecot authentication support. socket specifies the location of
254 Dovecot master authentication socket, for example
255 /var/run/dovecot/auth-master.
256
258 If a filename is not specified on the command line, or if the -d option
259 is used, maildrop will run in delivery mode. In delivery mode, maildrop
260 changes to the home directory of the user specified by the -d option
261 (or the user who is running maildrop if the -d option was not given)
262 and reads $HOME/.mailfilter for filtering instructions.
263 $HOME/.mailfilter must be owned by the user, and have no group or
264 global permissions (maildrop terminates if it does).
265 If $HOME/.mailfilter does not exist, maildrop will simply deliver the
267 message to the user's mailbox.
268 If the file /etc/maildroprc exists, maildrop reads filtering
270 instructions from this file first, before reading $HOME/.mailfilter.
271 This allows the system administrator to provide global filtering
272 instructions for all users.
273 Note
275 /etc/maildroprc is read only in delivery mode.
276
278 The -d option can also specify a name of a virtual account or mailbox.
279 See the makeuserdb(1) manual page in the Courier Authentication
280 library's documentation for more information.
281
283 The embedded mode is used when maildrop's filtering abilities are
284 desired, but no actual mail delivery is needed. In embedded mode
285 maildrop is executed by another application, and is passed the ‐m or
286 the ‐M option.[5] maildrop reads the message, then runs the filtering
287 rules specified in filename.
288 filename may contain any filtering instructions EXCEPT the following:
290 ` ... `
292 Text strings delimited by back-tick characters (run shell command)
293 are not allowed.
294 cc[6]
296 The cc command is not allowed in embedded mode.
297 dotlock[7]
299 The dotlock command is not allowed in embedded mode.
300 flock[8]
302 The flock command is not allowed in embedded mode.
303 gdbmopen[9]
305 In embedded mode, GDBM databases may be opened only for reading.
306 log[10]
308 The log command is not allowed in embedded mode.
309 logfile[10]
311 The logfile command is not allowed in embedded mode.
312 system[11]
314 The system command is not allowed in embedded mode.
315 to[12]
317 The to command is not allowed in embedded mode.
318 xfilter[13]
320 The xfilter command is not allowed in embedded mode.
321 Normally when the filename does not explicitly delivers a message,
323 maildrop will deliver the message to the user's default mailbox. This
324 is also disabled in embedded mode.
325 The filename may communicate with the parent application by using the
327 echo[14] statement and the EXITCODE environment variable.
328 /etc/maildroprcs
330 If maildrop encounters an include[15] statement where the filename
331 starts with /etc/maildroprcs/, the normal restrictions for the embedded
332 mode are suspended while executing the filter file in the
333 /etc/maildroprcs directory. The restrictions are also suspended for any
334 additional filter files that are included from /etc/maildroprcs. The
335 restrictions resume once maildrop finishes executing the file from
336 /etc/maildroprcs.
337 This allows the system administrator to have a controlled environment
339 for running external commands (via the backticks, the system[11] or the
340 xfilter[13] commands).
341 The name of the file may not contain any periods (so that a creative
343 individual can't write include
344 "/etc/maildroprcs/../../home/user/recipe").
345 Before executing the commands in the /etc/maildroprcs file, maildrop
347 automatically resets the following variables to their initial values:
348 DEFAULT, HOME, LOCKEXT, LOCKSLEEP, LOCKTIMEOUT, LOCKREFRESH, LOGNAME,
349 PATH, SENDMAIL, and SHELL. Please note that the previous values of
350 these variables (if they were changed) will NOT be restored once
351 maildrop finishes executing the commands from /etc/maildroprcs.
352
354 maildrop has a watchdog timer that attempts to abort runaway filtering.
355 If filtering is not complete within a predefined time interval (defined
356 by the system administrator, usually five minutes), maildrop
357 terminates.
358
360 /etc/passwd
361 Sets user's home directory, and related variables. If NIS/YP is
362 install, that will be used as well.
363 /etc/maildroprc
365 Global filtering instructions for delivery mode.
366 /var/mail
368 System mailbox (actual directory defined by the system
369 administrator).
370 /usr/lib/sendmail
372 Program to forward mail (exact program defined by the system
373 administrator).
374 $HOME/.mailfilter
376 Filtering instructions in delivery mode.
377 $HOME/.mailfilters
379 Directory containing files used in special embedded mode.
380
382 lockmail(1)[16], maildropfilter(7)[17], makedat(1)[18],
383 maildropgdbm(7)[9], maildropex(7)[19], reformail(1)[20],
384 makemime(1)[21], reformime(1)[22], egrep(1), grep(1), , courier(8)[23],
385 sendmail(8), http://www.qmail.org.
386
388 Sam Varshavchik
389 Author
390
392 1. Courier
393 http://www.courier-mta.org
394 2. Qmail
396 http://www.qmail.org
397 3. "Environment"
399 http://www.courier-mta.org/maildrop/maildropfilter.html#environment
400 4. "Variable substitution"
402 http://www.courier-mta.org/maildrop/maildropfilter.html#varsubst
403 5. is passed the ‐m or the ‐M option.
405 http://www.courier-mta.org/maildrop/#options
406 6. cc
408 http://www.courier-mta.org/maildrop/maildropfilter.html#cc
409 7. dotlock
411 http://www.courier-mta.org/maildrop/maildropfilter.html#dotlock
412 8. flock
414 http://www.courier-mta.org/maildrop/maildropfilter.html#flock
415 9. gdbmopen
417 http://www.courier-mta.org/maildrop/maildropgdbm.html
418 10. log
420 http://www.courier-mta.org/maildrop/maildropfilter.html#log
421 11. system
423 http://www.courier-mta.org/maildrop/maildropfilter.html#system
424 12. to
426 http://www.courier-mta.org/maildrop/maildropfilter.html#to
427 13. xfilter
429 http://www.courier-mta.org/maildrop/maildropfilter.html#xfilter
430 14. echo
432 http://www.courier-mta.org/maildrop/maildropfilter.html#echo
433 15. include
435 http://www.courier-mta.org/maildrop/maildropfilter.html#include
436 16. lockmail(1)
438 http://www.courier-mta.org/maildrop/lockmail.html
439 17. maildropfilter(7)
441 http://www.courier-mta.org/maildrop/maildropfilter.html
442 18. makedat(1)
444 http://www.courier-mta.org/maildrop/makedat.html
445 19. maildropex(7)
447 http://www.courier-mta.org/maildrop/maildropex.html
448 20. reformail(1)
450 http://www.courier-mta.org/maildrop/reformail.html
451 21. makemime(1)
453 http://www.courier-mta.org/maildrop/makemime.html
454 22. reformime(1)
456 http://www.courier-mta.org/maildrop/reformime.html
457 23. courier(8)
459 http://www.courier-mta.org/maildrop/courier.html
460Courier Mail Server 02/16/2018 MAILDROP(1)