1MIMEDEFANG-FILTER(5) File Formats Manual MIMEDEFANG-FILTER(5)
2
6 mimedefang-filter - Configuration file for MIMEDefang mail filter.
7
10 mimedefang-filter is a Perl fragment that controls how mimedefang.pl
11 disposes of various parts of a MIME message. In addition, it contains
12 some global variable settings that affect the operation of mimede‐
13 fang.pl.
14
17 Incoming messages are scanned as follows:
18 1) A temporary working directory is created. It is made the current
21 working directory and the e-mail message is split into parts in this
22 directory. Each part is represented internally as an instance of
23 MIME::Entity.
24 2) If the file /etc/mail/mimedefang-filter.pl defines a Perl function
27 called filter_begin, it is called with a single argument consisting of
28 a MIME::Entity representing the parsed e-mail message. Any return
29 value is ignored.
30 3) For each leaf part of the mail message, filter is called with four
33 arguments: entity, a MIME::Entity object; fname, the suggested filename
34 taken from the MIME Content-Disposition header; ext, the file exten‐
35 sion, and type, the MIME Content-Type value. For each non-leaf part of
36 the mail message, filter_multipart is called with the same four argu‐
37 ments as filter. A non-leaf part of a message is a part that contains
38 nested parts. Such a part has no useful body, but you should still
39 perform filename checks to check for viruses that use malformed MIME to
40 masquerade as non-leaf parts (like message/rfc822). In general, any
41 action you perform in filter_multipart applies to the part itself and
42 any contained parts.
43 Note that both filter and filter_multipart are optional. If you do not
46 define them, a default function that simply accepts each part is used.
47 4) After all parts have been processed, the function filter_end is
50 called if it has been defined. It is passed a single argument consist‐
51 ing of the (possibly modified) MIME::Entity object representing the
52 message about to be delivered. Within filter_end, you can call func‐
53 tions that modify the message headers body.
54 5) After filter_end returns, the function filter_wrapup is called if it
57 has been defined. It is passed a single argument consisting of the
58 (possibly modified) MIME::Entity object representing the message about
59 to be delivered, including any modifications made in filter_end.
60 Within filter_wrapup, you can not call functions that modify the mes‐
61 sage body, but you can still add or modify message headers.
62
65 mimedefang.pl examines each part of the MIME message and chooses a dis‐
66 position for that part. (A disposition is selected by calling one of
67 the following functions from filter and then immediately returning.)
68 Available dispositions are:
69 action_accept
72 The part is passed through unchanged. If no disposition func‐
73 tion is returned, this is the default.
74 action_accept_with_warning
77 The part is passed through unchanged, but a warning is added to
78 the mail message.
79 action_drop
82 The part is deleted without any notification to the recipients.
83 action_drop_with_warning
86 The part is deleted and a warning is added to the mail message.
87 action_replace_with_warning
90 The part is deleted and instead replaced with a text message.
91 action_quarantine
94 The part is deleted and a warning is added to the mail message.
95 In addition, a copy of the part is saved on the mail server in
96 the directory /var/spool/MD-Quarantine and a notification is
97 sent to the MIMEDefang administrator.
98 action_bounce
101 The entire e-mail message is rejected and an error returned to
102 the sender. The intended recipients are not notified. Note
103 that in spite of the name, MIMEDefang does not generate and e-
104 mail a failure notification. Rather, it causes the SMTP server
105 to return a 5XX SMTP failure code.
106 action_discard
109 The entire e-mail message is discarded silently. Neither the
110 sender nor the intended recipients are notified.
111
114 You can define a function called filter_relay in your filter. This
115 lets you reject SMTP connection attempts early on in the SMTP dialog,
116 rather than waiting until the whole message has been sent. Note that
117 for this check to take place, you must use the -r flag with mimedefang.
118 filter_relay is passed six arguments: $hostip is the IP address of the
121 relay host (for example, "127.0.0.1"), $hostname is the host name if
122 known (for example, "localhost.localdomain"). If the host name could
123 not be determined, $hostname is $hostip enclosed in square brackets.
124 (That is, ("$hostname" eq "[$hostip]") will be true.)
125 The remaining four arguments to filter_relay are $port, $myip, $myport
128 and $qid, which contain the client's TCP port, the Sendmail daemon's
129 listening IP address, the Sendmail daemon's listening port, and the
130 Sendmail Queue-ID, respectively. Note that the Queue-ID may not yet be
131 available at this stage (for example, Postfix does not allocate a
132 queue-ID this early.) If the Queue-ID is not available, the string NO‐
133 QUEUE is passed instead.
134 filter_relay must return a two-element list: ($code, $msg). $msg spec‐
137 ifies the text message to use for the SMTP reply, but because of limi‐
138 tations in the Milter API, this message is for documentation purposes
139 only---you cannot set the text of the SMTP message returned to the SMTP
140 client from filter_relay.
141 $code is a literal string, and can have one of the following values:
143 'REJECT'
146 if the connection should be rejected.
147 'CONTINUE'
150 if the connection should be accepted.
151 'TEMPFAIL'
154 if a temporary failure code should be returned.
155 'DISCARD'
158 if the message should be accepted and silently discarded.
159 'ACCEPT_AND_NO_MORE_FILTERING'
162 if the connection should be accepted and no further filtering
163 done.
164 Earlier versions of MIMEDefang used -1 for TEMPFAIL, 0 for REJECT and 1
167 for CONTINUE. These values still work, but are deprecated.
168 In the case of REJECT or TEMPFAIL, $msg specifies the text part of the
171 SMTP reply. $msg must not contain newlines.
172 For example, if you wish to reject connection attempts from any machine
175 in the spammer.com domain, you could use this function:
176 sub filter_relay {
178 my ($ip, $name) = @_;
179 if ($name =~ /spammer\.com$/) {
180 return ('REJECT', "Sorry; spammer.com is blacklisted");
181 }
182 return ('CONTINUE', "ok");
183 }
184
187 You can define a function called filter_helo in your filter. This lets
188 you reject connections after the HELO/EHLO SMTP command. Note that for
189 this function to be called, you must use the -H flag with mimedefang.
190 filter_helo is passed seven arguments: $ip and $name are the IP address
193 and name of the sending relay, as in filter_relay. The third argument,
194 $helo, is the argument supplied in the HELO/EHLO command.
195 The remaining four arguments to filter_helo are $port, $myip, $myport
198 and $qid, which contain the client's TCP port, the Sendmail daemon's
199 listening IP address, the Sendmail daemon's listening port, and the
200 Sendmail Queue-ID, respectively. Note that the Queue-ID may not yet be
201 available at this stage (for example, Postfix does not allocate a
202 queue-ID this early.) If the Queue-ID is not available, the string NO‐
203 QUEUE is passed instead.
204 filter_helo must return a two-to-five element list: ($code, $msg,
207 $smtp_code, $smtp_dsn, $delay). $code is a return code, with the same
208 meaning as the $code return from filter_relay. $msg specifies the text
209 message to use for the SMTP reply. If $smtp_code and $smtp_dsn are
210 supplied, they become the SMTP numerical reply code and the enhanced
211 status delivery code (DSN code). If they are not supplied, sensible
212 defaults are used. $delay specifies a delay in seconds; the C milter
213 code will sleep for $delay seconds before returning the reply to Send‐
214 mail. $delay defaults to zero.
215 (Note that the delay is implemented in the Milter C code; if you spec‐
217 ify a delay of 30 seconds, that doesn't mean a Perl worker is tied up
218 for the duration of the delay. The delay only costs one Milter
219 thread.)
220
223 You can define a function called filter_sender in your filter. This
224 lets you reject messages from certain senders, rather than waiting un‐
225 til the whole message has been sent. Note that for this check to take
226 place, you must use the -s flag with mimedefang.
227 filter_sender is passed four arguments: $sender is the envelope e-mail
230 address of the sender (for example, "<dfs@roaringpenguin.com>"). The
231 address may or may not be surrounded by angle brackets. $ip and $name
232 are the IP address and host name of the SMTP relay. Finally, $helo is
233 the argument to the SMTP "HELO" command.
234 Inside filter_sender, you can access any ESMTP arguments (such as
237 "SIZE=12345") in the array @ESMTPArgs. Each ESMTP argument occupies
238 one array element.
239 filter_sender must return a two-to-five element list, with the same
242 meaning as the return value from filter_helo.
243 For example, if you wish to reject messages from spammer@badguy.com,
246 you could use this function:
247 sub filter_sender {
249 my ($sender, $ip, $hostname, $helo) = @_;
250 if ($sender =~ /^<?spammer\@badguy\.com>?$/i) {
251 return ('REJECT', 'Sorry; spammer@badguy.com is blacklisted.');
252 }
253 return ('CONTINUE', "ok");
254 }
255 As another example, some spammers identify their own machine as your
258 machine in the SMTP "HELO" command. This function rejects a machine
259 claiming to be in the "roaringpenguin.com" domain unless it really is a
260 Roaring Penguin machine:
261 sub filter_sender {
263 my($sender, $ip, $hostname, $helo) = @_;
264 if ($helo =~ /roaringpenguin.com/i) {
265 if ($ip ne "127.0.0.1" and
266 $ip ne "216.191.236.23" and
267 $ip ne "216.191.236.30") {
268 return('REJECT', "Go away... $ip is not in roaringpenguin.com");
269 }
270 }
271 return ('CONTINUE', "ok");
272 }
273 As a third example, you may wish to prevent spoofs by requiring SMTP
276 authentication when email is sent from some email addresses. This func‐
277 tion rejects mail from "king@example.com", unless the connecting user
278 properly authenticated as "elvisp". Note that this needs access to the
279 %SendmailMacros global, that is not available in filter_sender until
280 after a call to read_commands_file.
281 sub filter_sender {
283 my($sender, $ip, $hostname, $helo) = @_;
284 read_commands_file();
285 ### notice: This assumes The King uses authentication without realm!
286 if ($sender =~ /^<?king\@example\.com>?$/i and
287 $SendmailMacros{auth_authen} ne "elvisp") {
288 return('REJECT', "Faking mail from the king is not allowed.");
289 }
290 return ('CONTINUE', "ok");
291 }
292
296 You can define a function called filter_recipient in your filter. This
297 lets you reject messages to certain recipients, rather than waiting un‐
298 til the whole message has been sent. Note that for this check to take
299 place, you must use the -t flag with mimedefang.
300 filter_recipient is passed nine arguments: $recipient is the envelope
303 address of the recipient and $sender is the envelope e-mail address of
304 the sender (for example, "<dfs@roaringpenguin.com>"). The addresses
305 may or may not be surrounded by angle brackets. $ip and $name are the
306 IP address and host name of the SMTP relay. $first is the envelope ad‐
307 dress of the first recipient for this message, and $helo is the argu‐
308 ment to the SMTP "HELO" command. The last three arguments,
309 $rcpt_mailer, $rcpt_host and $rcpt_addr are the Sendmail mailer, host
310 and address triple for the recipient address. For example, for local
311 recipients, $rcpt_mailer is likely to be "local", while for remote re‐
312 cipients, it is likely to be "esmtp".
313 Inside filter_recipient, you can access any ESMTP arguments (such as
316 "NOTIFY=never") in the array @ESMTPArgs. Each ESMTP argument occupies
317 one array element.
318 filter_recipient must return a two-to-five element list whose interpre‐
321 tation is the same as for filter_sender. Note, however, that if fil‐
322 ter_recipient returns 'DISCARD', then the entire message for all recip‐
323 ients is discarded. (It doesn't really make sense, but that's how Mil‐
324 ter works.)
325 For example, if you wish to reject messages from spammer@badguy.com,
328 unless they are to postmaster@mydomain.com, you could use this func‐
329 tion:
330 sub filter_recipient {
332 my ($recipient, $sender, $ip, $hostname, $first, $helo,
333 $rcpt_mailer, $rcpt_host, $rcpt_addr) = @_;
334 if ($sender =~ /^<?spammer\@badguy\.com>?$/i) {
335 if ($recipient =~ /^<?postmaster\@mydomain\.com>?$/i) {
336 return ('CONTINUE', "ok");
337 }
338 return ('REJECT', 'Sorry; spammer@badguy.com is blacklisted.');
339 }
340 return ('CONTINUE', "ok");
341 }
342
345 Just before a worker begins processing messages, mimedefang.pl calls
346 the functions filter_initialize (if it is defined) with no arguments.
347 By the time filter_initialize is called, all the other initialization
348 (such as setting up syslog facility and priority) has been done.
349 If you are not using an embedded Perl interpreter, then performing an
351 action inside filter_initialize is practically the same as performing
352 it directly in the filter file, outside any function definition. How‐
353 ever, if you are using an embedded Perl interpreter, then anything you
354 call directly from outside a function definition is executed once only
355 in the parent process. Anything in filter_initialize is executed once
356 per worker. If you use any code that opens a descriptor (for example,
357 a connection to a database server), you must run that code inside fil‐
358 ter_initialize and not directly from the filter, because the multi‐
359 plexor closes all open descriptors when it activates a new worker.
360 From within filter_initialize a configuration file could be loaded by
361 calling read_config. read_config accepts a configuration file path and
362 it can be used to overwrite global variables. Configuration file for‐
363 mat is pure Perl code.
364 When a worker is about to exit, mimedefang.pl calls the function fil‐
366 ter_cleanup (if it is defined) with no arguments. This function can do
367 whatever cleanup you like, such as closing file descriptors and clean‐
368 ing up long-lived worker resources. The return value from fil‐
369 ter_cleanup becomes the worker's exit status. (You should therefore
370 ensure that filter_cleanup returns an integer suitable for a process
371 exit status.)
372 If filter_cleanup takes longer than 10 seconds to run, the worker is
375 sent a SIGTERM signal. If that doesn't kill it (because you're catch‐
376 ing signals, perhaps), then a further 10 seconds later, the worker is
377 sent a SIGKILL signal.
378
381 If you define a function called filter_create_parser taking no argu‐
382 ments, then mimedefang.pl will call it to create a MIME::Parser object
383 for parsing mail messages.
384 Filter_create_parser is expected to return a MIME::Parser object (or an
386 instance of a class derived from MIME::Parser).
387 You can use filter_create_parser to change the behavior of the
389 MIME::Parser used by mimedefang.pl.
390 If you do not define a filter_create_parser function, then a built-in
392 version equivalent to this is used:
393 sub filter_create_parser () {
395 my $parser = MIME::Parser->new();
396 $parser->extract_nested_messages(1);
397 $parser->extract_uuencode(1);
398 $parser->output_to_core(0);
399 $parser->tmp_to_core(0);
400 return $parser;
401 }
402
404 The man page for mimedefang-protocol(7) lists commands that are passed
405 to workers in server mode (see "SERVER COMMANDS".) You can define a
406 function called filter_unknown_cmd to extend the set of commands your
407 filter can handle.
408 If you define filter_unknown_cmd, it is passed the unknown command as a
410 single argument. It should return a list of values as follows: The
411 first element of the list must be either "ok" or "error:" (with the
412 colon.) The remaining arguments are percent-encoded. All the result‐
413 ing pieces are joined together with a single space between them, and
414 the resulting string passed back as the reply to the multiplexor.
415 For example, the following function will make your filter reply to a
417 "PING" command with "PONG":
418 sub filter_unknown_cmd ($) {
420 my($cmd) = @_;
421 if ($cmd eq "PING") {
422 return("ok", "PONG");
423 }
424 return("error:", "Unknown command");
425 }
426 You can test this filter by typing the following as root:
428 md-mx-ctrl PING
430 The response should be:
432 ok PONG
434 If you extend the set of commands using filter_unknown_cmd, you should
436 make all your commands start with an upper-case letter to avoid clashes
437 with future built-in commands.
438
441 A very common mail setup is to have a MIMEDefang machine act as an SMTP
442 proxy, accepting and scanning mail and then relaying it to the real
443 mail server. Unfortunately, this means that the MIMEDefang machine
444 cannot know if a local address is valid or not, and will forward all
445 mail for the appropriate domains. If a mail comes in for an unknown
446 user, the MIMEDefang machine will be forced to generate a bounce mes‐
447 sage when it tries to relay the mail.
448 It's often desirable to have the MIMEDefang host reply with a "User un‐
451 known" SMTP response directly. While this can be done by copying the
452 list of local users to the MIMEDefang machine, MIMEDefang has a built-
453 in function called md_check_against_smtp_server for querying another
454 relay host:
455 md_check_against_smtp_server($sender, $recip, $helo, $server, $port)
458 This
459 function connects to the SMTP server $server and pretends to
460 send mail from $sender to $recip. The return value is always a
461 two-element array. If the RCPT TO: command succeeds, the return
462 value is ("CONTINUE", "OK"). If the RCPT fails with a permanent
463 failure, the return value is ("REJECT", $msg), where $msg is the
464 message from the SMTP server. Any temporary failures, connec‐
465 tion errors, etc. result in a return value of ("TEMPFAIL",
466 $msg).
467 The optional argument $port specifies the TCP port to connect
469 to. If it is not supplied, then the default SMTP port of 25 is
470 used.
471 If the server offers STARTTLS support, TLS step-up is attempted.
473 If TLS step-up fails, the check will fall-back to using clear
474 text and log the failure
475 Suppose the machine filter.domain.tld is filtering mail destined for
478 the real mail server mail.domain.tld. You could have a filter_recipi‐
479 ent function like this:
480 sub filter_recipient
482 {
483 my($recip, $sender, $ip, $host, $first, $helo,
484 $rcpt_mailer, $rcpt_host, $rcpt_addr) = @_;
485 return md_check_against_smtp_server($sender, $recip,
486 "filter.domain.tld",
487 "mail.domain.tld");
488 }
489 For each RCPT TO: command, MIMEDefang opens an SMTP connection to
491 mail.domain.tld and checks if the command would succeed.
492 Please note that you should only use md_check_against_smtp_server if
495 your mail server responds with a failure code for nonexistent users at
496 the RCPT TO: level. Also, this function may impose too much overhead
497 if you receive a lot of e-mail, and it will generate lots of useless
498 log entries on the real mail server (because of all the RCPT TO:
499 probes.) It may also significantly increase the load on the real mail
500 server.
501
504 The following Perl global variables should be set in mimedefang-filter:
505 $AdminAddress
508 The e-mail address of the MIMEDefang administrator.
509 $DaemonAddress
512 The e-mail address from which MIMEDefang-originated notifica‐
513 tions come.
514 $AddWarningsInline
517 If this variable is set to 0, then all MIMEDefang warnings (such
518 as created by action_quarantine or action_drop_with_warning) are
519 collected together and added in a separate MIME part called
520 WARNING.TXT. If the variable is set to 1, then the warnings are
521 added directly in the first text/plain and text/html parts of
522 the message. If the message does not contain any text/plain or
523 text/html parts, then a WARNING.TXT MIME part is added as be‐
524 fore.
525 $MaxMIMEParts
528 A message containing many MIME parts can cause MIME::Tools to
529 consume large amounts of memory and bring your system to its
530 knees. If you set $MaxMIMEParts to a positive number, then MIME
531 parsing is terminated for messages with more than that many
532 parts, and the message is bounced. In this case, none of your
533 filter functions is called.
534 By default, $MaxMIMEParts is set to -1, meaning there is no
536 limit on the number of parts in a message. Note that in order
537 to use this variable, you must install the Roaring Penguin
538 patched version of MIME::Tools, version 5.411a-RP-Patched-02 or
539 newer.
540 $Stupidity{"NoMultipleInlines"}
543 Set this to 1 if your e-mail is too stupid to display multiple
544 MIME parts in-line. In this case, a nasty hack causes the first
545 part of the original message to appear as an attachment if warn‐
546 ing are issued. Mail clients that are not this stupid are Net‐
547 scape Communicator and Pine. On the other hand, Microsoft Ex‐
548 change and Microsoft Outlook are indeed this stupid. Perhaps
549 users of those clients should switch.
550 The following global variables may optionally be set. If they
552 are not set, sensible defaults are used:
553 $AddApparentlyToForSpamAssassin
556 By default, MIMEDefang tries to pass SpamAssassin a message that
557 looks exactly like one it would receive via procmail. This
558 means adding a Received: header, adding a Message-ID header if
559 necessary, and adding a Return-Path: header. If you set $AddAp‐
560 parentlyToForSpamAssassin to 1, then MIMEDefang also adds an Ap‐
561 parently-To: header with all the envelope recipients before
562 passing the message to SpamAssassin. This lets SpamAssassin de‐
563 tect possibly whitelisted recipient addresses.
564 The default value for $AddApparentlyToForSpamAssassin is 0.
566 $SyslogFacility
569 This specifies the logging facility used by mimedefang.pl. By
570 default, it is set to "mail", but you can set it to other possi‐
571 bilites. See the openlog(3) man page for details. You should
572 name facilities as all-lowercase without the leading "LOG_".
573 That is, use "local3", not "LOG_LOCAL3".
574 $WarningLocation (default 0)
577 If set to 0 (the default), non-inline warnings are placed first.
578 If you want the warning at the end of the e-mail, set $Warn‐
579 ingLocation to -1.
580 $DaemonName (default "MIMEDefang")
583 The full name used when MIMEDefang sends out notifications.
584 $AdminName (default "MIMEDefang Administrator")
587 The full name of the MIMEDefang administrator.
588 $SALocalTestsOnly (default 1)
591 If set to 1, SpamAssassin calls will use only local tests. This
592 is the default and recommended setting. This disables Received,
593 RBL and Razor tests in an all or nothing fashion. To use Razor
594 this MUST be set to 0. You can add 'skip_rbl_checks 1' to your
595 SpamAssassin config file if you need to.
596 $NotifySenderSubject (default "MIMEDefang Notification")
599 The subject used when e-mail is sent out by action_no‐
600 tify_sender(). If you set this, you should set it each time you
601 call action_notify_sender() to ensure consistency.
602 $NotifyAdministratorSubject (default "MIMEDefang Notification")
604 The subject used when e-mail is sent out by action_notify_admin‐
605 istrator(). If you set this, you should set it each time you
606 call action_notify_administrator() to ensure consistency.
607 $QuarantineSubject (default "MIMEDefang Quarantine Report")
610 The subject used when a quarantine notice is sent to the admin‐
611 istrator. If you set this, you should set it each time you call
612 action_quarantine() or action_quarantine_entire_message().
613 $NotifyNoPreamble (default 0)
616 Normally, notifications sent by action_notify_sender() have a
617 preamble warning about message modifications. If you do not
618 want this, set $NotifyNoPreamble to 1.
619 $CSSHost (default 127.0.0.1:7777:local)
622 Host and port for the Symantec CarrierScan Server virus scanner.
623 This takes the form ip_addr:port:local_or_nonlocal. The ip_addr
624 and port are the host and port on which CarrierScan Server is
625 listening. If you want to scan local files, append :local to
626 force the use of the AVSCANLOCAL command. If the CarrierScan
627 Server is on another host, append :nonlocal to force the file
628 contents to be sent to the scanner over the socket.
629 $SophieSock (default /var/spool/MIMEDefang/sophie)
632 Socket used for Sophie daemon calls within message_con‐
633 tains_virus_sophie and entity_contains_virus_sophie unless a
634 socket is provided by the calling routine.
635 $ClamdSock (default /var/spool/MIMEDefang/clamd.sock)
638 Socket used for clamd daemon calls within message_con‐
639 tains_virus_clamd and entity_contains_virus_clamd unless a
640 socket is provided by the calling routine.
641 $TrophieSock (default /var/spool/MIMEDefang/trophie)
644 Socket used for Trophie daemon calls within message_con‐
645 tains_virus_trophie and entity_contains_virus_trophie unless a
646 socket is provided by the calling routine.
647
651 The heart of mimedefang-filter is the filter procedure. See the exam‐
652 ples that came with MIMEDefang to learn to write a filter. The filter
653 is called with the following arguments:
654 $entity
657 The MIME::Entity object. (See the MIME::tools Perl module docu‐
658 mentation.)
659 $fname The suggested attachment filename, or "" if none was supplied.
662 $ext The file extension (all characters from the rightmost period to
665 the end of the filename.)
666 $type The MIME type (for example, "text/plain".)
669 The filename is derived as follows:
672 o First, if the Content-Disposition header has a "filename" field,
675 it is used.
676 o Otherwise, if the Content-Type header has a "name" field, it is
679 used.
680 o Otherwise, the Content-Description header value is used.
683 Note that the truly paranoid will check all three fields for matches.
686 The functions re_match and re_match_ext perform regular expression
687 matches on all three of the fields named above, and return 1 if any
688 field matches. See the sample filters for details. The calling se‐
689 quence is:
690 re_match($entity, "regexp")
692 re_match_ext($entity, "regexp")
693 re_match returns true if any of the fields matches the regexp without
695 regard to case. re_match_ext returns true if the extension in any
696 field matches. An extension is defined as the last dot in a name and
697 all remaining characters.
698 A third function called re_match_in_zip_directory will look inside zip
701 files and return true if any of the file names inside the zip archive
702 match the regular expression. Call it like this:
703 my $bh = $entity->bodyhandle();
705 my $path = (defined($bh)) ? $bh->path() : undef;
706 if (defined($path) and re_match_in_zip_directory($path, "regexp")) {
707 # Take action...
708 }
709 You should not call re_match_in_zip_directory unless you know that the
711 entity is a zip file attachment.
712 Another function called re_match_in_rar_directory will look inside rar
715 files and return true if any of the file names inside the rar archive
716 match the regular expression. The function is very similar to
717 re_match_in_zip_directory but the unrar binary is required and must be
718 specified in $Features{"unrar"}.
719 Another function called re_match_in_7z_directory will look inside 7zip
722 files and return true if any of the file names inside the 7zip archive
723 match the regular expression. The function is very similar to
724 re_match_in_zip_directory but the 7z binary is required and must be
725 specified in $Features{"7zip"}.
726
729 The following global variables are set by mimedefang.pl and are avail‐
730 able for use in your filter. All of these variables are always avail‐
731 able to filter_begin, filter, filter_multipart and filter_end. In ad‐
732 dition, some of them are available in filter_relay, filter_sender or
733 filter_recipient. If this is the case, it will be noted below.
734 %Features
737 This hash lets you determine at run-time whether certain func‐
738 tionality is available. This hash is available at all times as‐
739 suming the detect_and_load_perl_modules() function has been
740 called. The defined features are:
741 $Features{"SpamAssassin"} is 1 if SpamAssassin 1.6 or better is
743 installed; 0 otherwise.
744 $Features{"HTML::Parser"} is 1 if HTML::Parser is installed; 0
746 otherwise.
747 $Features{"Virus:FPROTD"} is currently always 0. Set it to 1 in
749 your filter file if you have F-Risk's FPROTD scanner earlier
750 than version 6.
751 $Features{"Virus:FPROTD6"} is currently always 0. Set it to 1
753 in your filter file if you have version 6 of F-Risk's FPROTD
754 scanner.
755 $Features{"Virus:SymantecCSS"} is currently always 0. Set it to
757 1 in your filter file if you have the Symantec CarrierScan
758 Server virus scanner.
759 $Features{"Virus:NAI"} is the full path to NAI uvscan if it is
761 installed; 0 if it is not.
762 $Features{"Virus:BDC"} is the full path to Bitdefender bdc if it
764 is installed; 0 if it is not.
765 $Features{"Virus:NVCC"} is the full path to Norman Virus Control
767 nvcc if it is installed; 0 if it is not.
768 $Features{"Virus:HBEDV"} is the full path to H+BEDV AntiVir if
770 it is installed; 0 if it is not.
771 $Features{"Virus:VEXIRA"} is the full path to Central Command
773 Vexira if it is installed; 0 if it is not.
774 $Features{"Virus:SOPHOS"} is the full path to Sophos sweep if it
776 is installed; 0 if it is not.
777 $Features{"Virus:SAVSCAN"} is the full path to Sophos savscan if
779 it is installed; 0 if it is not.
780 $Features{"Virus:CLAMAV"} is the full path to Clam AV clamscan
782 if it is installed; 0 if it is not.
783 $Features{"Virus:AVP"} is the full path to AVP AvpLinux if it is
785 installed; 0 if it is not.
786 $Features{"Virus:AVP5"} is the full path to Kaspersky "ave‐
788 client" if it is installed; 0 if it is not.
789 $Features{"Virus:CSAV"} is the full path to Command csav if it
791 is installed; 0 if it is not.
792 $Features{"Virus:FSAV"} is the full path to F-Secure fsav if it
794 is installed; 0 if it is not.
795 $Features{"Virus:FPROT"} is the full path to F-Risk f-prot if it
797 is installed; 0 if it is not.
798 $Features{"Virus:FPSCAN"} is the full path to F-Risk fpscan if
800 it is installed; 0 if it is not.
801 $Features{"Virus:SOPHIE"} is the full path to Sophie if it is
803 installed; 0 if it is not.
804 $Features{"Virus:CLAMD"} is the full path to clamd if it is in‐
806 stalled; 0 if it is not.
807 $Features{"Virus:CLAMDSCAN"} is the full path to clamdscan if it
809 is installed; 0 if it is not.
810 $Features{"Virus:TROPHIE"} is the full path to Trophie if it is
812 installed; 0 if it is not.
813 $Features{"Virus:NOD32"} is the full path to ESET NOD32 nod32cli
815 if it is installed; 0 if it is not.
816 $Features{"Path:RSPAMC"} is the full path to rspamc(1) if it is
818 installed (deprecated); 0 if it is not.
819 NOTE: Perl-module based features such as SpamAssassin are deter‐
821 mined at runtime and may change as these are added and removed.
822 Most Virus features are predetermined at the time of configura‐
823 tion and do not adapt to runtime availability unless changed by
824 the filter rules.
825 $CWD This variable holds the working directory for the current mes‐
828 sage. During filter processing, mimedefang.pl chdir's into this
829 directory before calling any of the filter_ functions. Note
830 that this variable is set correctly in filter_sender and fil‐
831 ter_recipient, but not in filter_relay.
832 $SuspiciousCharsInHeaders
835 If this variable is true, then mimedefang has discovered suspi‐
836 cious characters in message headers. This might be an exploit
837 for bugs in MIME-parsing routines in some badly-written mail
838 user agents (e.g. Microsoft Outlook.) You should always drop
839 such messages.
840 $SuspiciousCharsInBody
843 If this variable is true, then mimedefang has discovered suspi‐
844 cious characters in the message body. This might be an exploit
845 for bugs in MIME-parsing routines in some badly-written mail
846 user agents (e.g. Microsoft Outlook.) You should always drop
847 such messages.
848 $RelayHostname
851 The host name of the relay. This is the name of the host that
852 is attempting to send e-mail to your host. May be "undef" if
853 the host name could not be determined. This variable is avail‐
854 able in filter_relay, filter_sender and filter_recipient in ad‐
855 dition to the body filtering functions.
856 $RelayAddr
859 The IP address of the sending relay (as a string consisting of
860 four dot-separated decimal numbers.) One potential use of $Re‐
861 layAddr is to limit mailing to certain lists to people within
862 your organization. This variable is available in filter_relay,
863 filter_sender and filter_recipient in addition to the body fil‐
864 tering functions.
865 $Helo The argument given to the SMTP "HELO" command. This variable is
868 available in filter_sender and filter_recipient, but not in fil‐
869 ter_relay.
870 $Subject
873 The contents of the "Subject:" header.
874 $Sender
877 The sender of the e-mail. This variable is set in filter_sender
878 and filter_recipient in addition to the body filtering func‐
879 tions.
880 @Recipients
883 A list of the recipients. In filter_recipient, it is set to the
884 single recipient currently under consideration. Or, after call‐
885 ing read_commands_file within filter_recipient, the current re‐
886 cipient under consideration is in the final position of the ar‐
887 ray, at $Recipients[-1], while any previous (and accepted) re‐
888 cipients are at the beginning of the array, that is, in @Recipi‐
889 ents[0 .. $#Recipients-1].
890 $MessageID
894 The contents of the "Message-ID:" header if one is present.
895 Otherwise, contains the string "NOQUEUE".
896 $QueueID
899 The Sendmail queue identifier if it could be determined. This
900 variable is set correctly in filter_relay, filter_helo, fil‐
901 ter_sender and filter_recipient. Note, however, that Postfix
902 may not allocate a queue ID until filter_recipient time. If a
903 Queue-ID has not yet been allocated, $QueueID is set to "NO‐
904 QUEUE".
905 $MsgID Set to $QueueID if the queue ID could be determined; otherwise,
908 set to $MessageID. This identifier should be used in logging,
909 because it matches the identifier used by Sendmail to log mes‐
910 sages. Note that this variable is set correctly in fil‐
911 ter_sender and filter_recipient, but it is not available in fil‐
912 ter_relay.
913 $VirusScannerMessages
916 Each time a virus-scanning function is called, messages (if any)
917 from the virus scanner are accumulated in this variable. You
918 can use it in filter_end to formulate a notification (if you
919 wish.)
920 $VirusName
923 If a virus-scanning function found a virus, this variable will
924 hold the virus name (if it could be determined.)
925 $SASpamTester
928 If defined, this is the configured Mail::SpamAssassin object
929 used for mail tests. It may be initialized with a call to
930 spam_assassin_init which also returns it.
931 %SendmailMacros
934 This hash contains the values of some Sendmail macros. The hash
935 elements exist only for macros defined by Sendmail. See the
936 Sendmail documentation for the meanings of the macros.
937 By default, mimedefang passes the values of the following
939 macros: ${daemon_name}, ${daemon_port}, ${if_name}, ${if_addr},
940 $j, $_, $i, ${tls_version}, ${cipher}, ${cipher_bits},
941 ${cert_subject}, ${cert_issuer}, ${auth_type}, ${auth_authen},
942 ${auth_ssf}, ${auth_author}, ${mail_mailer}, ${mail_host} and
943 ${mail_addr}. In addition, ${client_port} is set to the
944 client's TCP port.
945 If any macro is not set or not passed to milter, it will be un‐
947 available. To access the value of a macro, use:
948 $SendmailMacros{"macro_name"}
951 Do not place curly brackets around the macro name. This vari‐
954 able is available in filter_sender and filter_recipient after a
955 call to read_commands_file.
956 @SenderESMTPArgs
959 This array contains all the ESMTP arguments supplied in the MAIL
960 FROM: command. For example:
961 sub print_sender_esmtp_args {
963 foreach (@SenderESMTPArgs) {
964 print STDERR "Sender ESMTP arg: $_0;
965 }
966 }
967 %RecipientESMTPArgs
970 This hash contains all the ESMTP arguments supplied in each RCPT
971 TO: command. For example:
972 sub print_recip_esmtp_args {
974 foreach my $recip (@Recipients) {
975 foreach(@{$RecipientESMTPArgs{$recip}}) {
976 print STDERR "Recip ESMTP arg for $recip: $_0;
977 }
978 }
979 }
980 %RecipientMailers
983 This hash contains the Sendmail "mailer-host-address" triple for
984 each recipient. Here's an example of how to use it:
985 sub print_mailer_info {
987 my($recip, $mailer, $host, $addr);
988 foreach $recip (@Recipients) {
989 $mailer = ${RecipientMailers{$recip}}[0];
990 $host = ${RecipientMailers{$recip}}[1];
991 $addr = ${RecipientMailers{$recip}}[2];
992 print STDERR "$recip: mailer=$mailer, host=$host, addr=$addr\n";
993 }
994 }
995 In filter_recipient, this variable by default only contains in‐
997 formation on the recipient currently under investigation. Infor‐
998 mation on all recipients is available after calling read_com‐
999 mands_file.
1000
1003 When the filter procedure decides how to dispose of a part, it should
1004 call one or more action_ subroutines. The action subroutines are:
1005 action_accept()
1008 Accept the part.
1009 action_rebuild()
1012 Rebuild the mail body, even if mimedefang thinks no changes were
1013 made. Normally, mimedefang does not alter a message if no
1014 changes were made. action_rebuild may be used if you make
1015 changes to entities directly (by manipulating the MIME::Head,
1016 for example.) Unless you call action_rebuild, mimedefang will
1017 be unaware of the changes. Note that all the built-in action...
1018 routines that change a message implicitly call action_rebuild.
1019 action_add_header($hdr, $val)
1022 Add a header to the message. This can be used in filter_begin
1023 or filter_end. The $hdr component is the header name without
1024 the colon, and the $val is the header value. For example, to
1025 add the header:
1026 X-MyHeader: A nice piece of text
1028 use:
1030 action_add_header("X-MyHeader", "A nice piece of text");
1032 action_change_header($hdr, $val, $index)
1035 Changes an existing header in the message. This can be used in
1036 filter_begin or filter_end. The $hdr parameter is the header
1037 name without the colon, and $val is the header value. If the
1038 header does not exist, then a header with the given name and
1039 value is added.
1040 The $index parameter is optional; it defaults to 1. If you sup‐
1042 ply it, then the $index'th occurrence of the header is changed,
1043 if there is more than one header with the same name. (This is
1044 common with the Received: header, for example.)
1045 action_insert_header($hdr, $val, $index)
1048 Add a header to the message int the specified position $index.
1049 A position of 0 specifies that the header should be prepended
1050 before existing headers. This can be used in filter_begin or
1051 filter_end. The $hdr component is the header name without the
1052 colon, and the $val is the header value.
1053 action_delete_header($hdr, $index)
1056 Deletes an existing header in the message. This can be used in
1057 filter_begin or filter_end. The $hdr parameter is the header
1058 name without the colon.
1059 The $index parameter is optional; it defaults to 1. If you sup‐
1061 ply it, then the $index'th occurrence of the header is deleted,
1062 if there is more than one header with the same name.
1063 action_delete_all_headers($hdr)
1066 Deletes all headers with the specified name. This can be used
1067 in filter_begin or filter_end. The $hdr parameter is the header
1068 name without the colon.
1069 action_drop()
1072 Drop the part. If called from filter_multipart, drops all con‐
1073 tained parts also.
1074 action_drop_with_warning($msg)
1077 Drop the part, but add the warning $msg to the e-mail message.
1078 If called from filter_multipart, drops all contained parts also.
1079 action_accept_with_warning($msg)
1082 Accept the part, but add the warning $msg to the e-mail message.
1083 action_replace_with_warning($msg)
1086 Drop the part and replace it with a text part $msg. If called
1087 from filter_multipart, drops all contained parts also.
1088 action_replace_with_url($entity, $doc_root, $base_url, $msg, [$cd_data,
1091 $salt])
1092 Drop the part, but save it in a unique location under $doc_root.
1093 The part is replaced with the text message $msg. The string
1094 "_URL_" in $msg is replaced with $base_url/something, that can
1095 be used to retrieve the message.
1096 You should not use this function in filter_multipart.
1098 This action is intended for stripping large parts out of the
1100 message and replacing them to a link on a Web server. Here's
1101 how you would use it in filter():
1102 $size = (stat($entity->bodyhandle->path))[7];
1104 if ($size > 1000000) {
1105 return action_replace_with_url($entity,
1106 "/home/httpd/html/mail_parts",
1107 "http://mailserver.company.com/mail_parts",
1108 "The attachment was larger than 1,000,000 bytes.\n" .
1109 "It was removed, but may be accessed at this URL:\n\n" .
1110 "\t_URL_\n");
1111 }
1112 This example moves attachments greater than 1,000,000 bytes into
1114 /home/httpd/html/mail_parts and replaces them with a link. The
1115 directory should be accessible via a Web server at
1116 http://mailserver.company.com/mail_parts.
1117 The generated name is created by performing a SHA1 hash of the
1119 part and adding the extension to the ASCII-HEX representation of
1120 the hash. If many different e-mails are sent containing an
1121 identical large part, only one copy of the part is stored, re‐
1122 gardless of the number of senders or recipients.
1123 For privacy reasons, you must turn off Web server indexing in
1125 the directory in which you place mail parts, or anyone will be
1126 able to read them. If indexing is disabled, an attacker would
1127 have to guess the SHA1 hash of a part in order to read it.
1128 Optionally, a fifth argument can supply data to be saved into a
1130 hidden dot filename based on the generated name. This data can
1131 then be read in on the fly by a CGI script or mod_perl module
1132 before serving the file to a web client, and used to add infor‐
1133 mation to the response, such as Content-Disposition data.
1134 A sixth optional argument, $salt, is mixed in to the SHA1 hash.
1136 This salt can be any string and should be kept confidential.
1137 The salt is designed to prevent people from guessing whether or
1138 not a particular attachment has been received on your server by
1139 altering the SHA1 hash calculation.
1140 action_defang($entity, $name, $fname, $type)
1143 Accept the part, but change its name to $name, its suggested
1144 filename to $fname and its MIME type to $type. If $name or
1145 $fname are "", then mimedefang.pl generates generic names. Do
1146 not use this action in filter_multipart.
1147 If you use action_defang, you must define a subroutine called
1149 defang_warning in your filter. This routine takes two argu‐
1150 ments: $oldfname (the original name of an attachment) and $fname
1151 (the defanged version.) It should return a message telling the
1152 user what happened. For example:
1153 sub defang_warning {
1155 my($oldfname, $fname) = @_;
1156 return "The attachment '$oldfname' was renamed to '$fname'\n";
1157 }
1158 action_external_filter($entity, $cmd)
1162 Run an external UNIX command $cmd. This command must read the
1163 part from the file ./FILTERINPUT and leave the result in ./FIL‐
1164 TEROUTPUT. If the command executes successfully, returns 1,
1165 otherwise 0. You can test the return value and call another ac‐
1166 tion_ if the filter failed. Do not use this action in fil‐
1167 ter_multipart.
1168 action_quarantine($entity, $msg)
1171 Drop and quarantine the part, but add the warning $msg to the e-
1172 mail message.
1173 action_quarantine_entire_message($msg)
1176 Quarantines the entire message in a quarantine directory on the
1177 mail server, but does not otherwise affect disposition of the
1178 message. If "$msg" is non-empty, it is included in any adminis‐
1179 trator notification.
1180 action_sm_quarantine($reason)
1183 Quarantines a message in the Sendmail mail queue using the new
1184 QUARANTINE facility of Sendmail 8.13. Consult the Sendmail doc‐
1185 umentation for details about this facility. If you use ac‐
1186 tion_sm_quarantine with a version of Sendmail that lacks the
1187 QUARANTINE facility, mimedefang will log an error message and
1188 not quarantine the message.
1189 action_bounce($reply, $code, $dsn)
1192 Reject the entire e-mail message with an SMTP failure code, and
1193 the one-line error message $reply. If the optional $code and
1194 $dsn arguments are supplied, they specify the numerical SMTP re‐
1195 ply code and the extended status code (DSN code). If the codes
1196 you supply do not make sense for a bounce, they are replaced
1197 with "554" and "5.7.1" respectively.
1198 action_bounce merely makes a note that the message is to be
1200 bounced; remaining parts are still processed. If action_bounce
1201 is called for more than one part, the mail is bounced with the
1202 message in the final call to action_bounce. You can profitably
1203 call action_quarantine followed by action_bounce if you want to
1204 keep a copy of the offending part. Note that the message is not
1205 bounced immediately; rather, remaining parts are processed and
1206 the message is bounced after all parts have been processed.
1207 Note that despite its name, action_bounce does not generate a
1209 "bounce message". It merely rejects the message with an SMTP
1210 failure code.
1211 WARNING: action_bounce() may cause the sending relay to generate
1213 spurious bounce messages if the sender address is faked. This
1214 is a particular problem with viruses. However, we believe that
1215 on balance, it's better to bounce a virus than to silently dis‐
1216 card it. It's almost never a good idea to hide a problem.
1217 action_tempfail($msg, $code, $dsn)
1220 Cause an SMTP "temporary failure" code to be returned, so the
1221 sending mail relay requeues the message and tries again later.
1222 The message $msg is included with the temporary failure code.
1223 If the optional $code and $dsn arguments are supplied, they
1224 specify the numerical SMTP reply code and the extended status
1225 code (DSN code). If the codes you supply do not make sense for
1226 a temporary failure, they are replaced with "450" and "4.7.1"
1227 respectively.
1228 action_discard()
1231 Silently discard the message, notifying nobody. You can prof‐
1232 itably call action_quarantine followed by action_discard if you
1233 want to keep a copy of the offending part. Note that the mes‐
1234 sage is not discarded immediately; rather, remaining parts are
1235 processed and the message is discarded after all parts have been
1236 processed.
1237 action_notify_sender($message)
1240 This action sends an e-mail back to the original sender with the
1241 indicated message. You may call another action after this one.
1242 If action_notify_sender is called more than once, the messages
1243 are accumulated into a single e-mail message -- at most one no‐
1244 tification message is sent per incoming message. The message
1245 should be terminated with a newline.
1246 The notification is delivered in deferred mode; you should run a
1248 client-queue runner if you are using Sendmail 8.12.
1249 NOTE: Viruses often fake the sender address. For that reason,
1251 if a virus-scanner has detected a virus, action_notify_sender is
1252 disabled and will simply log an error message if you try to use
1253 it.
1254 action_notify_administrator($message)
1257 This action e-mails the MIMEDefang administrator the supplied
1258 message. You may call another action after this one; action_no‐
1259 tify_administrator does not affect mail processing. If ac‐
1260 tion_notify_administrator is called more than once, the messages
1261 are accumulated into a single e-mail message -- at most one no‐
1262 tification message is sent per incoming message. The message
1263 should be terminated with a newline.
1264 The notification is delivered in deferred mode; you should run a
1266 client-queue runner if you are using Sendmail 8.12.
1267 append_text_boilerplate($entity, $boilerplate, $all)
1270 This action should only be called from filter_end. It appends
1271 the text "\n$boilerplate\n" to the first text/plain part (if
1272 $all is 0) or to all text/plain parts (if $all is 1).
1273 append_html_boilerplate($entity, $boilerplate, $all)
1276 This action should only be called from filter_end. It adds the
1277 text "\n$boilerplate\n" to the first text/html part (if $all is
1278 0) or to all text/html parts (if $all is 1). This function
1279 tries to be smart about inserting the boilerplate; it uses
1280 HTML::Parser to detect closing tags and inserts the boilerplate
1281 before the </body> tag if there is one, or before the </html>
1282 tag if there is no </body>. If there is no </body> or </html>
1283 tag, it appends the boilerplate to the end of the part.
1284 Do not use append_html_boilerplate unless you have installed the
1286 HTML::Parser Perl module.
1287 Here is an example illustrating how to use the boilerplate func‐
1289 tions:
1290 sub filter_end {
1292 my($entity) = @_;
1293 append_text_boilerplate($entity,
1294 "Lame text disclaimer", 0);
1295 append_html_boilerplate($entity,
1296 "<em>Lame</em> HTML disclaimer", 0);
1297 }
1298 action_add_part($entity, $type, $encoding, $data, $fname, $disposition
1301 [, $offset])
1302 This action should only be called from the filter_end routine.
1303 It adds a new part to the message, converting the original mes‐
1304 sage to mutipart if necessary. The function returns the part so
1305 that additional mime attributes may be set on it. Here's an ex‐
1306 ample:
1307 sub filter_end {
1309 my($entity) = @_;
1310 action_add_part($entity, "text/plain", "-suggest",
1312 "This e-mail does not represent" .
1313 "the official policy of FuBar, Inc.\n",
1314 "disclaimer.txt", "inline");
1315 }
1316 The $entity parameter must be the argument passed in to fil‐
1318 ter_end. The $offset parameter is optional; if omitted, it de‐
1319 faults to -1, which adds the new part at the end. See the
1320 MIME::Entity man page and the add_part member function for the
1321 meaning of $offset.
1322 Note that action_add_part tries to be more intelligent than sim‐
1324 ply calling $entity->add_part. The decision process is as fol‐
1325 lows:
1326 o If the top-level entity is multipart/mixed, then the part is
1329 simply added.
1330 o Otherwise, a new top-level multipart/mixed container is gener‐
1333 ated, and the original top-level entity is made the first part
1334 of the multipart/mixed container. The new part is then added to
1335 the multipart/mixed container.
1336 action_add_entity($entity [, $offset])
1339 This is similar to action_add_part but takes a pre-built
1340 MIME::Entity object rather than constructing one based on $type,
1341 $encoding, $data, $fname and $disposition arguments.
1342
1345 mimedefang.pl includes some useful functions you can call from your
1346 filter:
1347 detect_and_load_perl_modules()
1350 Unless you really know what you're doing, this function must be
1351 called first thing in your filter file. It causes mimedefang.pl
1352 to detect and load Perl modules such as Mail::SpamAssassin,
1353 Net::DNS, etc., and to populate the %Features hash.
1354 send_quarantine_notifications()
1357 This function should be called from filter_end. If any parts
1358 were quarantined, a quarantine notification is sent to the
1359 MIMEDefang administrator. Please note that if you do not call
1360 send_quarantine_notifications, then no quarantine notifications
1361 are sent.
1362 get_quarantine_dir()
1365 This function returns the full path name of the quarantine di‐
1366 rectory. If you have not yet quarantined any parts of the mes‐
1367 sage, a quarantine directory is created and its pathname re‐
1368 turned.
1369 change_sender($sender)
1372 This function changes the envelope sender to $sender. It can
1373 only be called from filter_begin or any later function. Please
1374 note that this function is only supported with Sendmail/Milter
1375 8.14.0 or newer. It has no effect if you're running older ver‐
1376 sions.
1377 add_recipient($recip)
1380 This function adds $recip to the list of envelope recipients. A
1381 copy of the message (after any modifications by MIMEDefang) will
1382 be sent to $recip in addition to the original recipients. Note
1383 that add_recipient does not modify the @Recipients array; it
1384 just makes a note to Sendmail to add the recipient.
1385 delete_recipient($recip)
1388 This function deletes $recip from the list of recipients. That
1389 person will not receive a copy of the mail. $recip should ex‐
1390 actly match an entry in the @Recipients array for delete_recipi‐
1391 ent() to work. Note that delete_recipient does not modify the
1392 @Recipients array; it just makes a note to Sendmail to delete
1393 the recipient.
1394 resend_message($recip1, $recip2, ...)
1396 or
1397 resend_message(@recips)
1399 This function immediately resends the original, unmodified mail
1400 message to each of the named recipients. The sender's address
1401 is preserved. Be very careful when using this function, because
1402 it resends the original message, which may contain undesired at‐
1403 tachments. Also, you should not call this function from fil‐
1404 ter(), because it resends the message each time it is called.
1405 This may result in multiple copies being sent if you are not
1406 careful. Call from filter_begin() or filter_end() to be safe.
1407 The function returns true on success, or false if it fails.
1409 Note that the resend_message function delivers the mail in de‐
1411 ferred mode (using Sendmail's "-odd" flag.) You must run a
1412 client-submission queue processor if you use Sendmail 8.12. We
1413 recommend executing this command as part of the Sendmail startup
1414 sequence:
1415 sendmail -Ac -q5m
1417 remove_redundant_html_parts($entity)
1420 This function should only be called from filter_end. It removes
1421 redundant HTML parts from the message. It works by deleting any
1422 part of type text/html from the message if (1) it is a sub-part
1423 of a multipart/alternative part, and (2) there is another part
1424 of type text/plain under the multipart/alternative part.
1425 replace_entire_message($entity)
1428 This function can only be called from filter_end. It replaces
1429 the entire message with $entity, a MIME::Entity object that you
1430 have constructed. You can use any of the MIME::Tools functions
1431 to construct the entity.
1432 read_commands_file()
1435 This function should only be called from filter_sender and fil‐
1436 ter_recipient. This will read the COMMANDS file (as described in
1437 mimedefang-protocol(7)), and will fill or update the following
1438 global variables: $Sender, @Recipients, %RecipientMailers, $Re‐
1439 layAddr, $RealRelayAddr, $RelayHostname, $RealRelayHostname,
1440 $QueueID, $Helo, %SendmailMacros.
1441 If you do not call read_commands_file, then the only information
1443 available in filter_sender and filter_recipient is that which is
1444 passed as an argument to the function.
1445 stream_by_domain()
1448 Do not use this function unless you have Sendmail 8.12 and lo‐
1449 cally- submitted e-mail is submitted using SMTP.
1450 This function should only be called at the very beginning of
1452 filter_begin(), like this:
1453 sub filter_begin {
1455 if (stream_by_domain()) {
1456 return;
1457 }
1458 # Rest of filter_begin
1459 }
1460 stream_by_domain() looks at all the recipients of the message,
1462 and if they belong to the same domain (e.g., joe@domain.com,
1463 jane@domain.com and sue@domain.com), it returns 0 and sets the
1464 global variable $Domain to the domain (domain.com in this exam‐
1465 ple.)
1466 If users are in different domains, stream_by_domain() resends
1468 the message (once to each domain) and returns 1 For example, if
1469 the original recipients are joe@abc.net, jane@xyz.net and
1470 sue@abc.net, the original message is resent twice: One copy to
1471 joe@abc.net and sue@abc.net, and another copy to jane@xyz.net.
1472 Also, any subsequent scanning is canceled (filter() and fil‐
1473 ter_end() will not be called for the original message) and the
1474 message is silently discarded.
1475 If you have Sendmail 8.12, then locally-submitted messages are
1477 sent via SMTP, and MIMEDefang will be called for each resent
1478 message. It is possible to set up Sendmail 8.12 so locally-sub‐
1479 mitted messages are delivered directly; in this case,
1480 stream_by_domain will not work.
1481 Using stream_by_domain allows you to customize your filter rules
1483 for each domain. If you use the function as described above,
1484 you can do this in your filter routine:
1485 sub filter {
1487 my($entity, $fname, $ext, $type) = @_;
1488 if ($Domain eq "abc.com") {
1489 # Filter actions for abc.com
1490 } elsif ($Domain eq "xyz.com") {
1491 # Filter actions for xyz.com
1492 } else {
1493 # Default filter actions
1494 }
1495 }
1496 You cannot rely on $Domain being set unless you have called
1498 stream_by_domain().
1499 stream_by_recipient()
1502 Do not use this function unless you have Sendmail 8.12 and lo‐
1503 cally- submitted e-mail is submitted using SMTP.
1504 This function should only be called at the very beginning of
1506 filter_begin(), like this:
1507 sub filter_begin {
1509 if (stream_by_recipient()) {
1510 return;
1511 }
1512 # Rest of filter_begin
1513 }
1514 If there is more than one recipient, stream_by_recipient() re‐
1516 sends the message once to each recipient. That way, you can
1517 customize your filter rules on a per-recipient basis. This may
1518 increase the load on your mail server considerably.
1519 Also, a "recipient" is determined before alias expansion. So
1521 "all@mydomain.com" is considered a single recipient, even if
1522 Sendmail delivers to a list.
1523 If you have Sendmail 8.12, then locally-submitted messages are
1525 sent via SMTP, and MIMEDefang will be called for each resent
1526 message. It is possible to set up Sendmail 8.12 so locally-sub‐
1527 mitted messages are delivered directly; in this case,
1528 stream_by_recipient() will not work.
1529 stream_by_recipient() allows you to customize your filter rules
1531 for each recipient in a manner similar to stream_by_domain().
1532
1535 md_graphdefang_log_enable($facility, $enum_recips)
1536 Enables the md_graphdefang_log function (described next). The
1537 function logs to syslog using the specified facility. If you
1538 omit $facility, it defaults to 'mail'. If you do not call
1539 md_graphdefang_log_enable in your filter, then any calls to
1540 md_graphdefang_log simply do nothing.
1541 If you supply $enum_recips as 1, then a line of logging is out‐
1543 put for each recipient of a mail message. If it is zero, then
1544 only a single line is output for each message. If you omit
1545 $enum_recips, it defaults to 1.
1546 md_graphdefang_log($event, $v1, $v2)
1549 Logs an event with up to two optional additional parameters.
1550 The log message has a specific format useful for graphing tools;
1551 the message looks like this:
1552 MDLOG,msgid,event,v1,v2,sender,recipient,subj
1554 "MDLOG" is literal text. "msgid" is the Sendmail queue identi‐
1556 fier. "event" is the event name, and "v1" and "v2" are the ad‐
1557 ditional parameters. "sender" is the sender's e-mail address.
1558 "recipient" is the recipient's e-mail address, and "subj" is the
1559 message subject. If a message has more than one recipient,
1560 md_graphdefang_log may log an event message for each recipient,
1561 depending on how you called md_graphdefang_log_enable.
1562 Note that md_graphdefang_log should not be used in filter_relay,
1564 filter_sender or filter_recipient. The global variables it re‐
1565 lies on are not valid in that context.
1566 If you want to log general text strings, do not use md_graphde‐
1568 fang_log. Instead, use md_syslog (described next).
1569 md_syslog($level, $msg)
1572 Logs the message $msg to syslog, using level $level. The level
1573 is a literal string, and should be one of 'err', 'debug', 'warn‐
1574 ing', ´emerg', 'crit', 'notice' or 'info'. (See syslog(3) for
1575 details.)
1576 Note that md_syslog does not perform %-subsitutions like sys‐
1578 log(3) does. Depending on your Perl installation, md_syslog
1579 boils down to a call to Unix::Syslog::syslog or Sys::Sys‐
1580 log::syslog. See the Unix::Syslog or Sys::Syslog man pages for
1581 more details.
1582 md_openlog($tag, $facility)
1585 Sets the tag used in syslog messages to $tag, and sends the logs
1586 to the $facility facility. If you do not call md_openlog before
1587 you call md_syslog, then it is called implicitly with $tag set
1588 to mimedefang.pl and $facility set to mail.
1589
1592 mimedefang.pl includes the following functions for looking up IP ad‐
1593 dresses in DNS-based real-time blacklists. Note that the "re‐
1594 lay_is_blacklisted" functions are deprecated and may be removed in a
1595 future release. Instead, you should use the module Net::DNSBL::Client
1596 from CPAN.
1597 relay_is_blacklisted($relay, $domain)
1600 This checks a DNS-based real-time spam blacklist, and returns
1601 true if the relay host is blacklisted, or false otherwise. (In
1602 fact, the return value is whatever the blacklist returns as a
1603 resolved hostname, such as "127.0.0.4")
1604 Note that relay_is_blacklisted uses the built-in gethostbyname
1606 function; this is usually quite inefficient and does not permit
1607 you to set a timeout on the lookup. Instead, we recommend using
1608 one of the other DNS lookup function described in this section.
1609 (Note, though, that the other functions require the Perl
1610 Net::DNS module, whereas relay_is_blacklisted does not.)
1611 Here's an example of how to use relay_is_blacklisted:
1613 if (relay_is_blacklisted($RelayAddr, "rbl.spamhaus.org")) {
1615 action_add_header("X-Blacklist-Warning",
1616 "Relay $RelayAddr is blacklisted by Spamhaus");
1617 }
1618 relay_is_blacklisted_multi($relay, $timeout, $answers_wanted, [$do‐
1621 main1, $domain2, ...], $res)
1622 This function is similar to relay_is_blacklisted, except that it
1623 takes a timeout argument (specified in seconds) and an array of
1624 domains to check. The function checks all domains in parallel,
1625 and is guaranteed to return in $timeout seconds. (Actually, it
1626 may take up to one second longer.)
1627 The parameters are:
1629 $relay -- the IP address you want to look up
1631 $timeout -- a timeout in seconds after which the function should
1633 return
1634 $answers_wanted -- the maximum number of positive answers you
1636 care about. For example, if you're looking up an address in 10
1637 different RBLs, but are going to bounce it if it is on four or
1638 more, you can set $answers_wanted to 4, and the function returns
1639 as soon as four "hits" are discovered. If you set $an‐
1640 swers_wanted to zero, then the function does not return early.
1641 [$domain1, $domain2, ...] -- a reference to an array of strings,
1643 where each string is an RBL domain.
1644 $res -- a Net::DNS::Resolver object. This argument is optional;
1646 if you do not supply it, then relay_is_blacklisted_multi con‐
1647 structs its own resolver.
1648 The return value is a reference to a hash; the keys of the hash
1650 are the original domains, and the corresponding values are ei‐
1651 ther SERVFAIL, NXDOMAIN, or a list of IP addresses in dotted-
1652 quad notation.
1653 Here's an example:
1655 $ans = relay_is_blacklisted_multi($RelayAddr, 8, 0,
1657 ["sbl.spamhaus.org", "relays.ordb.org"]);
1658 foreach $domain (keys(%$ans)) {
1660 $r = $ans->{$domain};
1661 if (ref($r) eq "ARRAY") {
1662 # It's an array -- it IS listed in RBL
1663 print STDERR "Lookup in $domain yields [ ";
1664 foreach $addr (@$r) {
1665 print STDERR $addr . " ";
1666 }
1667 print STDERR "]\n";
1668 } else {
1669 # It is NOT listed in RBL
1670 print STDERR "Lookup in $domain yields "
1671 . $ans->{$domain} . "\n";
1672 }
1673 }
1674 You should compare each of $ans->{$domain} to "SERVFAIL" and
1676 "NXDOMAIN" to see if the relay is not listed. Any other return
1677 value will be an array of IP addresses indicating that the relay
1678 is listed.
1679 Any lookup that does not succeed within $timeout seconds has the
1681 corresponding return value set to SERVFAIL.
1682 relay_is_blacklisted_multi_list($relay, $timeout, $answers_wanted,
1685 [$domain1, $domain2, ...], $res)
1686 This function is similar to relay_is_blacklisted_multi except
1687 that the return value is simply an array of RBL domains in which
1688 the relay was listed.
1689 relay_is_blacklisted_multi_count($relay, $timeout, $answers_wanted,
1692 [$domain1, $domain2, ...], $res)
1693 This function is similar to relay_is_blacklisted_multi except
1694 that the return value is an integer specifying the number of do‐
1695 mains on which the relay was blacklisted.
1696 md_get_bogus_mx_hosts($domain)
1699 This function looks up all the MX records for the specified do‐
1701 main (or A records if there are no MX records) and returns a
1702 list of "bogus" IP addresses found amongst the records. A "bo‐
1703 gus" IP address is an IP address in a private network
1704 (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), the loopback net‐
1705 work (127.0.0.0/8), local-link for auto-DHCP (169.254.0.0/16),
1706 IPv4 multicast (224.0.0.0/4) or reserved (240.0.0.0/4).
1707 Here's how you might use the function in filter_sender:
1710 sub filter_sender {
1712 my ($sender, $ip, $hostname, $helo) = @_;
1713 if ($sender =~ /@([^>]+)/) {
1714 my $domain = $1;
1715 my @bogushosts = md_get_bogus_mx_hosts($domain);
1716 if (scalar(@bogushosts)) {
1717 return('REJECT', "Domain $domain contains bogus MX record(s) " .
1718 join(', ', @bogushosts));
1719 }
1720 }
1721 return ('CONTINUE', 'ok');
1722 }
1723
1726 mimedefang.pl includes some "test" functions:
1727 md_version()
1730 returns the version of MIMEDefang as a string (for example,
1731 "3.4.1").
1732 message_rejected()
1735 Returns true if any of action_tempfail, action_bounce or ac‐
1736 tion_discard have been called for this message; returns false
1737 otherwise.
1738 If you have the Mail::SpamAssassin Perl module installed (see
1741 https://spamassassin.apache.org) you may call any of the spam_assas‐
1742 sin_* functions. They should only be called from filter_begin or fil‐
1743 ter_end because they operate on the entire message at once. Most func‐
1744 tions use an optionally provided config file. If no config file is
1745 provided, mimedefang.pl will look for one of four default SpamAssassin
1746 preference files. The first of the following found will be used:
1747 o /etc/mail/sa-mimedefang.cf
1750 o /etc/mail/spamassassin/sa-mimedefang.cf
1752 o /etc/mail/spamassassin/local.cf
1754 o /etc/mail/spamassassin.cf
1756 Important Note: MIMEDefang does not permit SpamAssassin to modify mes‐
1759 sages. If you want to tag spam messages with special headers or alter
1760 the subject line, you must use MIMEDefang functions to do it. Setting
1761 SpamAssassin configuration options to alter messages will not work.
1762 spam_assassin_is_spam([ $config_file ])
1765 Determine if the current message is SPAM/UCE as determined by
1766 SpamAssassin. Compares the score of the message against the
1767 threshold score (see below) and returns true if it is. Uses
1768 spam_assassin_check below.
1769 spam_assassin_check([ $config_file ])
1772 This function returns a four-element list of the form ($hits,
1773 $required, $tests, $report). $hits is the "score" given to the
1774 message by SpamAssassin (higher score means more likely SPAM).
1775 $required is the number of hits required before SpamAssassin
1776 concludes that the message is SPAM. $tests is a comma-separated
1777 list of SpamAssassin test names, and $report is text detailing
1778 which tests triggered and their point score. This gives you in‐
1779 sight into why SpamAssassin concluded that the message is SPAM.
1780 Uses spam_assassin_status below.
1781 spam_assassin_status([ $config_file ])
1784 This function returns a Mail::SpamAssasin::PerMsgStatus object.
1785 Read the SpamAssassin documentation for details about this ob‐
1786 ject. You are responsible for calling the finish method when
1787 you are done with it. Uses spam_assassin_init and spam_assas‐
1788 sin_mail below.
1789 spam_assassin_init([ $config_file ])
1792 This function returns the new global Mail::SpamAssassin object
1793 with the specified or default config (outlined above). If the
1794 global object is already defined, returns it -- does not change
1795 config files! The object can be used to perform other SpamAs‐
1796 sassin related functions.
1797 spam_assassin_mail()
1800 This function returns a Mail::SpamAssassin::NoMailAudit object
1801 with the current email message contained in it. It may be used
1802 to perform other SpamAssassin related functions.
1803 rspamd_check([ $uri ]) *experimental*
1806 This function returns a six-element list of the form ($hits,
1807 $required, $tests, $report, $action, $is_spam). $hits is the
1808 "score" given to the message by Rspamd (higher score means more
1809 likely SPAM). $required is the number of hits required before
1810 Rspamd concludes that the message is SPAM. $tests is a list of
1811 Rspamd test names, and $report is text detailing which tests
1812 triggered and their point score. If JSON and LWP modules are
1813 present $report will be a json string; $action is the action
1814 that rspamd(8) wants to apply and $is_spam is a boolean value
1815 (true/false) that determines if the message is spam or not.
1816 This gives you insight into why Rspamd concluded that the mes‐
1817 sage is SPAM.
1818 md_copy_orig_msg_to_work_dir()
1821 Normally, virus-scanners are passed only the unpacked, decoded
1822 parts of a MIME message. If you want to pass the original, un‐
1823 decoded message in as well, call md_copy_orig_msg_to_work_dir
1824 prior to calling message_contains_virus.
1825 md_copy_orig_msg_to_work_dir_as_mbox_file()
1828 Normally, virus-scanners are passed only the unpacked, decoded
1829 parts of a MIME message. If you want to pass the original, un‐
1830 decoded message in as a UNIX-style "mbox" file, call
1831 md_copy_orig_msg_to_work_dir_as_mbox_file prior to calling mes‐
1832 sage_contains_virus. The only difference between this function
1833 and md_copy_orig_msg_to_work_dir is that this function prepends
1834 a "From_" line to make the message look like a UNIX-style mbox
1835 file. This is required for some virus scanners (such as Clam
1836 AntiVirus) to recognize the file as an e-mail message.
1837 message_contains_virus()
1840 This function runs every installed virus-scanner and returns the
1841 scanner results. The function should be called in list context;
1842 the return value is a three-element list ($code, $category, $ac‐
1843 tion).
1844 $code is the actual return code from the virus scanner.
1846 $category is a string categorizing the return code:
1848 "ok" - no viruses detected.
1850 "not-installed" - indicated virus scanner is not installed.
1852 "cannot-execute" - for some reason, the scanner could not be ex‐
1854 ecuted.
1855 "virus" - a virus was found.
1857 "suspicious" - a "suspicious" file was found.
1859 "interrupted" - scanning was interrupted.
1861 "swerr" - an internal scanner software error occurred.
1863 $action is a string containing the recommended action:
1865 "ok" - allow the message through unmolested.
1867 "quarantine" - a virus was detected; quarantine it.
1869 "tempfail" - something went wrong; tempfail the message.
1871 message_contains_virus_trend()
1875 message_contains_virus_nai()
1877 message_contains_virus_bdc()
1879 message_contains_virus_nvcc()
1881 message_contains_virus_csav()
1883 message_contains_virus_fsav()
1885 message_contains_virus_hbedv()
1887 message_contains_virus_vexira()
1889 message_contains_virus_sophos()
1891 message_contains_virus_clamav()
1893 message_contains_virus_clamdscan()
1895 message_contains_virus_avp()
1897 message_contains_virus_avp5()
1899 message_contains_virus_fprot()
1901 message_contains_virus_fpscan()
1903 message_contains_virus_fprotd()
1905 message_contains_virus_fprotd_v6()
1907 message_contains_virus_nod32()
1909 These functions should be called in list context. They use the
1911 indicated anti-virus software to scan the message for viruses.
1912 These functions are intended for use in filter_begin() to make
1913 an initial scan of the e-mail message.
1914 The supported virus scanners are:
1916 nai NAI "uvscan" - http://www.nai.com/
1918 Bitdefender "bdc" - http://www.bitdefender.com/
1920 csav Command Anti-Virus - http://www.commandsoftware.com/
1922 fsav F-Secure Anti-Virus - http://www.f-secure.com/
1924 hbedv H+BEDV "AntiVir" - http://www.hbedv.com/
1926 vexira Vexira "Vexira" - http://www.centralcommand.com/
1928 sophos Sophos AntiVirus - http://www.sophos.com/
1930 avp Kaspersky AVP and aveclient (AVP5) - http://www.avp.ru/
1932 clamav Clam AntiVirus - https://www.clamav.net/
1934 f-prot F-RISK F-PROT - http://www.f-prot.com/
1936 nod32cli
1938 ESET NOD32 - http://www.eset.com/
1939 message_contains_virus_carrier_scan([$host])
1942 Connects to the specified host:port:local_or_nonlocal (default
1943 $CSSHost), where the Symantec CarrierScan Server daemon is ex‐
1944 pected to be listening. Return values are the same as the other
1945 message_contains_virus functions.
1946 message_contains_virus_sophie([$sophie_sock])
1949 Connects to the specified socket (default $SophieSock), where
1950 the Sophie daemon is expected to be listening. Return values
1951 are the same as the other message_contains_virus functions.
1952 message_contains_virus_clamd([$clamd_sock])
1955 Connects to the specified socket (default $ClamdSock), where the
1956 clamd daemon is expected to be listening. Return values are the
1957 same as the other message_contains_virus functions.
1958 message_contains_virus_trophie([$trophie_sock])
1961 Connects to the specified socket (default $TrophieSock), where
1962 the Trophie daemon is expected to be listening. Return values
1963 are the same as the other message_contains_virus functions.
1964 entity_contains_virus($entity)
1967 This function runs the specified MIME::Entity through every in‐
1969 stalled virus-scanner and returns the scanner results. The re‐
1970 turn values are the same as for message_contains_virus().
1971 entity_contains_virus_trend($entity)
1974 entity_contains_virus_nai($entity)
1976 entity_contains_virus_bdc($entity)
1978 entity_contains_virus_nvcc($entity)
1980 entity_contains_virus_csav($entity)
1982 entity_contains_virus_fsav($entity)
1984 entity_contains_virus_hbedv($entity)
1986 entity_contains_virus_sophos($entity)
1988 entity_contains_virus_clamav($entity)
1990 entity_contains_virus_clamdscan($entity)
1992 entity_contains_virus_avp($entity)
1994 entity_contains_virus_avp5($entity)
1996 entity_contains_virus_fprot($entity)
1998 entity_contains_virus_fpscan($entity)
2000 entity_contains_virus_fprotd($entity)
2002 entity_contains_virus_fprotd_v6($entity)
2004 entity_contains_virus_nod32($entity)
2006 These functions, meant to be called from filter(), are similar
2007 to the message_contains_virus functions except they scan only
2008 the current part. They should be called from list context, and
2009 their return values are as described for the message_con‐
2010 tains_virus functions.
2011 entity_contains_virus_carrier_scan($entity[, $host])
2014 Connects to the specified host:port:local_or_nonlocal (default
2015 $CSSHost), where the Symantec CarrierScan Server daemon is ex‐
2016 pected to be listening. Return values are the same as the other
2017 entity_contains_virus functions.
2018 entity_contains_virus_sophie($entity[, $sophie_sock])
2021 Connects to the specified socket (default $SophieSock), where
2022 the Sophie daemon is expected to be listening. Return values
2023 are the same as the other entity_contains_virus functions.
2024 entity_contains_virus_trophie($entity[, $trophie_sock])
2027 Connects to the specified socket (default $TrophieSock), where
2028 the Trophie daemon is expected to be listening. Return values
2029 are the same as the other entity_contains_virus functions.
2030 entity_contains_virus_clamd($entity[, $clamd_sock])
2033 Connects to the specified socket (default $ClamdSock), where the
2034 clamd daemon is expected to be listening. Return values are the
2035 same as the other entity_contains_virus functions.
2036
2039 This section illustrates the flow of messages through MIMEDefang.
2040 1. INITIAL CONNECTION
2043 If you invoked mimedefang with the -r option and have defined a
2044 filter_relay routine, it is called.
2045 2. SMTP HELO COMMAND
2048 The HELO string is stored internally, but no filter functions
2049 are called.
2050 3. SMTP MAIL FROM: COMMAND
2053 If you invoked mimedefang with the -s option and have defined a
2054 filter_sender routine, it is called.
2055 4. SMTP RCPT TO: COMMAND
2058 If you invoked mimedefang with the -t option and have defined a
2059 filter_recipient routine, it is called.
2060 5. END OF SMTP DATA
2063 filter_begin is called. For each MIME part, filter is called.
2064 Then filter_end is called.
2065
2068 Most organizations have more than one machine handling internet e-mail.
2069 If the primary machine is down, mail is routed to a secondary (or ter‐
2070 tiary, etc.) MX server, which stores the mail until the primary MX host
2071 comes back up. Mail is then relayed to the primary MX host.
2072 Relaying from a secondary to a primary MX host has the unfortunate side
2075 effect of losing the original relay's IP address information. MIMEDe‐
2076 fang allows you to preserve this information. One way around the prob‐
2077 lem is to run MIMEDefang on all the secondary MX hosts and use the same
2078 filter. However, you may not have control over the secondary MX hosts.
2079 If you can persuade the owners of the secondary MX hosts to run MIMEDe‐
2080 fang with a simple filter that only preserves relay information and
2081 does no other scanning, your primary MX host can obtain relay informa‐
2082 tion and make decisions using $RelayAddr and $RelayHostname.
2083 When you configure MIMEDefang, supply the "--with-ipheader" argument to
2086 the ./configure script. When you install MIMEDefang, a file called
2087 /etc/mail/mimedefang-ip-key will be created which contains a randomly-
2088 generated header name. Copy this file to all of your mail relays. It
2089 is important that all of your MX hosts have the same key. The key
2090 should be kept confidential, but it's not disastrous if it leaks out.
2091 On your secondary MX hosts, add this line to filter_end:
2094 add_ip_validation_header();
2096 Note: You should only add the validation header to mail destined for
2099 one of your other MX hosts! Otherwise, the validation header will leak
2100 out.
2101 When the secondary MX hosts relay to the primary MX host, $RelayAddr
2104 and $RelayHostname will be set based on the IP validation header. If
2105 MIMEDefang notices this header, it sets the global variable $WasResent
2106 to 1. Since you don't want to trust the header unless it was set by
2107 one of your secondary MX hosts, you should put this code in filter_be‐
2108 gin:
2109 if ($WasResent) {
2111 if ($RealRelayAddr ne "ip.of.secondary.mx" and
2112 $RealRelayAddr ne "ip.of.tertiary.mx") {
2113 $RelayAddr = $RealRelayAddr;
2114 $RelayHostname = $RealRelayHostname;
2115 }
2116 }
2117 This resets the relay address and hostname to the actual relay address
2119 and hostname, unless the message is coming from one of your other MX
2120 hosts.
2121 On the primary MX host, you should add this in filter_begin:
2124 delete_ip_validation_header();
2126 This prevents the validation header from leaking out to recipients.
2129 Note: The IP validation header works only in message-oriented func‐
2132 tions. It (obviously) has no effect on filter_relay, filter_sender and
2133 filter_recipient, because no header information is available yet. You
2134 must take this into account when writing your filter; you must defer
2135 relay-based decisions to the message filter for mail arriving from your
2136 other MX hosts.
2137
2140 The following list describes the lifetime of global variables (thanks
2141 to Tony Nugent for providing this documentation.)
2142 If you set a global variable:
2144 Outside a subroutine in your filter file
2147 It is available to all functions, all the time.
2148 In filter_relay, filter_sender or filter_recipient
2151 Not guaranteed to be available to any other function, not even
2152 from one filter_recipient call to the next, when receiving a
2153 multi-recipient email message.
2154 In filter_begin
2157 Available to filter_begin, filter and filter_end
2158 In filter
2161 Available to filter and filter_end
2162 In filter_end
2165 Available within filter_end
2166 The "built-in" globals like $Subject, $Sender, etc. are always avail‐
2169 able to filter_begin, filter and filter_end. Some are available to fil‐
2170 ter_relay, filter_sender or filter_recipient, but you should check the
2171 documentation of the variable above for details.
2172
2175 There are four basic groups of filtering functions:
2176 1 filter_relay
2179 2 filter_sender
2182 3 filter_recipient
2185 4 filter_begin, filter, filter_multipart, filter_end
2188 In general, for a given mail message, these groups of functions may be
2191 called in completely different Perl processes. Thus, there is no way
2192 to maintain state inside Perl between groups of functions. That is,
2193 you cannot set a variable in filter_relay and expect it to be available
2194 in filter_sender, because the filter_sender invocation might take place
2195 in a completely different process.
2196 For a given mail message, it is always the case that filter_begin, fil‐
2199 ter, filter_multipart and filter_end are called in the same Perl
2200 process. Therefore, you can use global variables to carry state among
2201 those functions. You should be very careful to initialize such vari‐
2202 ables in filter_begin to ensure no data leaks from one message to an‐
2203 other.
2204 Also for a given mail message, the $CWD global variable holds the mes‐
2207 sage spool directory, and the current working directory is set to $CWD.
2208 Therefore, you can store state in files inside $CWD. If filter_sender
2209 stores data in a file inside $CWD, then filter_recipient can retrieve
2210 that data.
2211 Since filter_relay is called directly after a mail connection is estab‐
2214 lished, there is no message context yet, no per-message mimedefang
2215 spool directory, and the $CWD global is not set. Therefore, it is not
2216 possible to share information from filter_relay to one of the other
2217 filter functions. The only thing that filter_relay has in common with
2218 the other functions are the values in the globals $RelayAddr, and $Re‐
2219 layHostname. These could be used to access per-remote-host information
2220 in some database.
2221 Inside $CWD, we reserve filenames beginning with upper-case letters for
2224 internal MIMEDefang use. If you want to create files to store state,
2225 name them beginning with a lower-case letter to avoid clashes with fu‐
2226 ture releases of MIMEDefang.
2227
2230 If you have Sendmail 8.13 or later, and have compiled it with the SOCK‐
2231 ETMAP option, then you can use a special map type that communicates
2232 over a socket with another program (rather than looking up a key in a
2233 Berkeley database, for example.)
2234 mimedefang-multiplexor implements the Sendmail SOCKETMAP protocol if
2237 you supply the -N option. In that case, you can define a function
2238 called filter_map to implement map lookups. filter_map takes two argu‐
2239 ments: $mapname is the name of the Sendmail map (as given in the K
2240 sendmail configuration directive), and $key is the key to be looked up.
2241 filter_map must return a two-element list: ($code, $val) $code can be
2244 one of:
2245 OK The lookup was successful. In this case, $val must be the re‐
2248 sult of the lookup
2249 NOTFOUND
2252 The lookup was unsuccessful -- the key was not found. In this
2253 case, $val should be the empty string.
2254 TEMP There was a temporary failure of some kind. $val can be an ex‐
2257 planatory error message.
2258 TIMEOUT
2261 There was a timeout of some kind. $val can be an explanatory
2262 error message.
2263 PERM There was a permanent failure. This is not the same as an un‐
2266 successful lookup; it should be used only to indicate a serious
2267 misconfiguration. As before, $val can be an explanatory error
2268 message.
2269 Consider this small example. Here is a minimal Sendmail configuration
2272 file:
2273 V10/Berkeley
2275 Kmysock socket unix:/var/spool/MIMEDefang/map.sock
2276 kothersock socket unix:/var/spool/MIMEDefang/map.sock
2277 If mimedefang-multiplexor is invoked with the arguments -N
2280 unix:/var/spool/MIMEDefang/map.sock, and the filter defines filter_map
2281 as follows:
2282 sub filter_map ($$) {
2284 my($mapname, $key) = @_;
2285 my $ans;
2286 if($mapname ne "mysock") {
2287 return("PERM", "Unknown map $mapname");
2288 }
2289 $ans = reverse($key);
2290 return ("OK", $ans);
2291 }
2292 Then in Sendmail's testing mode, we see the following:
2294 > /map mysock testing123
2296 map_lookup: mysock (testing123) returns 321gnitset (0)
2297 > /map othersock foo
2298 map_lookup: othersock (foo) no match (69)
2299 (The return code of 69 means EX_UNAVAILABLE or Service Unavailable)
2302 A real-world example could do map lookups in an LDAP directory or SQL
2305 database, or perform other kinds of processing. You can even implement
2306 standard Sendmail maps like virtusertable, mailertable, access_db, etc.
2307 using SOCKETMAP.
2308
2311 If you supply the -X option to mimedefang-multiplexor, then every so
2312 often, a "tick" request is sent to a free worker. If your filter de‐
2313 fines a function called filter_tick, then this function is called with
2314 a single argument: the tick type. If you run multiple parallel ticks,
2315 then each tick has a type ranging from 0 to n-1, where n is the number
2316 of parallel ticks. If you're only running one tick request, then the
2317 argument to filter_tick is always 0.
2318 You can use this facility to run periodic tasks from within MIMEDefang.
2320 Note, however, that you have no control over which worker is picked to
2321 run filter_tick. Also, at most one filter_tick call with a particular
2322 "type" argument will be active at any time, and if there are no free
2323 workers when a tick would occur, the tick is skipped.
2324
2327 The following virus scanners are supported by MIMEDefang:
2328 o Symantec CarrierScan Server (http://www.symantec.com/re‐
2331 gion/can/eng/product/scs/)
2332 o Trend Micro vscan (http://www.antivirus.com/)
2335 o Sophos Sweep (http://www.sophos.com/products/antivirus/savu‐
2338 nix.html)
2339 o H+BEDV AntiVir (http://www.hbedv.com/)
2342 o Central Command Vexira (http://www.centralcommand.com/)
2345 o NAI uvscan (http://www.nai.com)
2348 o Bitdefender bdc (http://www.bitdefender.com)
2351 o Norman Virus Control (NVCC) (http://www.norman.no/)
2354 o Command csav (http://www.commandsoftware.com)
2357 o F-Secure fsav (http://www.f-secure.com)
2360 o The clamscan and clamdscan command-line scanners and the clamd
2363 daemon from Clam AntiVirus (https://www.clamav.net/)
2364 o Kaspersky Anti-Virus (AVP) (http://www.kaspersky.com/)
2367 o F-Risk F-Prot (http://www.f-prot.com/)
2370 o F-Risk F-Prot v6 (http://www.f-prot.com/)
2373 o F-Risk FPROTD (daemonized version of F-Prot)
2377 o Symantec CarrierScan Server (http://www.symantec.ca/re‐
2380 gion/can/eng/product/scs/buymenu.html)
2381 o Sophie (http://www.vanja.com/tools/sophie/), which uses the lib‐
2384 savi library from Sophos, is supported in daemon-scanning mode.
2385 o Trophie (http://www.vanja.com/tools/trophie/), which uses the
2388 libvsapi library from Trend Micro, is supported in daemon-scan‐
2389 ning mode.
2390 o ESET NOD32 (http://www.eset.com/)
2393
2396 mimedefang was written by Dianne Skoll <dfs@roaringpenguin.com>. The
2397 mimedefang home page is https://www.mimedefang.org/.
2398
2401 mimedefang(8), mimedefang.pl(8), Mail::MIMEDefang(3)
24024th Berkeley Distribution 8 February 2005 MIMEDEFANG-FILTER(5)