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author Peter Gervai <grin@grin.hu>
date Tue, 10 Mar 2009 13:49:58 +0100
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1 .\" Copyright (c) 2008 by Rhyolite Software, LLC
2 .\"
3 .\" This agreement is not applicable to any entity which sells anti-spam
4 .\" solutions to others or provides an anti-spam solution as part of a
5 .\" security solution sold to other entities, or to a private network
6 .\" which employs the DCC or uses data provided by operation of the DCC
7 .\" but does not provide corresponding data to other users.
8 .\"
9 .\" Permission to use, copy, modify, and distribute this software without
10 .\" changes for any purpose with or without fee is hereby granted, provided
11 .\" that the above copyright notice and this permission notice appear in all
12 .\" copies and any distributed versions or copies are either unchanged
13 .\" or not called anything similar to "DCC" or "Distributed Checksum
14 .\" Clearinghouse".
15 .\"
16 .\" Parties not eligible to receive a license under this agreement can
17 .\" obtain a commercial license to use DCC by contacting Rhyolite Software
18 .\" at sales@rhyolite.com.
19 .\"
20 .\" A commercial license would be for Distributed Checksum and Reputation
21 .\" Clearinghouse software. That software includes additional features. This
22 .\" free license for Distributed ChecksumClearinghouse Software does not in any
23 .\" way grant permision to use Distributed Checksum and Reputation Clearinghouse
24 .\" software
25 .\"
26 .\" THE SOFTWARE IS PROVIDED "AS IS" AND RHYOLITE SOFTWARE, LLC DISCLAIMS ALL
27 .\" WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
28 .\" OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL RHYOLITE SOFTWARE, LLC
29 .\" BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
30 .\" OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
31 .\" WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
32 .\" ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
33 .\" SOFTWARE.
34 .\"
35 .\" Rhyolite Software DCC 1.3.103-1.120 $Revision$
36 .\"
37 .Dd February 26, 2009
38 .ds volume-ds-DCC Distributed Checksum Clearinghouse
39 .Dt dccproc 8 DCC
40 .Os " "
41 .Sh NAME
42 .Nm dccproc
43 .Nd Distributed Checksum Clearinghouse Procmail Interface
44 .Sh SYNOPSIS
45 .Nm dccproc
46 .Bk -words
47 .Op Fl VdAQCHER
48 .Op Fl h Ar homedir
49 .Op Fl m Ar map
50 .Op Fl w Ar whiteclnt
51 .Op Fl T Ar tmpdir
52 .Op Fl a Ar IP-address
53 .Op Fl f Ar env_from
54 .Op Fl t Ar targets
55 .Op Fl x Ar exitcode
56 .br
57 .Oo
58 .Fl c Xo
59 .Sm off
60 .Ar type,
61 .Op Ar log-thold,
62 .Ar rej-thold
63 .Sm on
64 .Xc
65 .Oc
66 .Oo
67 .Fl g Xo
68 .Sm off
69 .Op Ar not-
70 .Ar type
71 .Sm on
72 .Xc
73 .Oc
74 .Op Fl S Ar header
75 .br
76 .Op Fl i Ar infile
77 .Op Fl o Ar outfile
78 .Op Fl l Ar logdir
79 .Op Fl B Ar dnsbl-option
80 .Op Fl L Ar ltype,facility.level
81 .Ek
82 .Sh DESCRIPTION
83 .Nm Dccproc
84 copies a complete SMTP message from standard input or a file
85 to standard output or another file.
86 As it copies the message,
87 it computes the DCC checksums for the message,
88 reports them to a DCC server, and adds
89 a header line to the message.
90 Another program such as
91 .Xr procmail 1
92 can use the added header line to filter mail.
93 Dccproc does not support any thresholds of its own,
94 because equivalent effects can be achieved with regular expressions
95 and you can apply dccproc several times using different DCC servers
96 and then score mail based what all of the DCC servers say.
97 .Pp
98 Error messages are sent to stderr as well as the system log.
99 Connect stderr and stdout to the same file to see errors in context,
100 but direct stderr to /dev/null to keep DCC error messages out of the mail.
101 The
102 .Fl i
103 option can also be used to separate the error messages.
104 .Pp
105 .Nm Dccproc
106 sends reports of checksums related to mail received by DCC clients
107 and queries about the total number of reports of particular checksums.
108 A DCC server receives no
109 mail, address, headers, or other information,
110 but only cryptographically secure checksums of such information.
111 A DCC server cannot determine the text or other information that corresponds
112 to the checksums it receives.
113 It only acts as a clearinghouse of counts of checksums computed by clients.
114 .Pp
115 For the sake of privacy for even the checksums of private mail,
116 the checksums of senders of purely internal mail or other
117 mail that is known to not be unsolicited bulk can be listed in a whitelist
118 to not be reported to the DCC server.
119 .Pp
120 When
121 .Xr sendmail 8
122 is used,
123 .Xr dccm 8
124 is a better DCC interface.
125 .Xr Dccifd 8
126 is more efficient than
127 .Nm
128 because it is a daemon, but that has costs in complexity.
129 See
130 .Xr dccsight 8
131 for a way to use previously computed checksums.
132 .Ss OPTIONS
133 The following options are available:
134 .Bl -tag -width 3n
135 .It Fl V
136 displays the version of the DCC
137 .Xr procmail 1
138 interface.
139 .It Fl d
140 enables debugging output from the DCC client software.
141 Additional
142 .Fl d
143 options increase the number of messages.
144 One causes error messages to be sent to STDERR as well as the system log.
145 .It Fl A
146 adds to existing X-DCC headers (if any)
147 of the brand of the current server
148 instead of
149 replacing existing headers.
150 .It Fl Q
151 only queries the DCC server about the checksums of messages
152 instead of reporting and then querying.
153 This is useful when
154 .Nm
155 is used to filter mail that has already been reported to a DCC
156 server by another DCC client such as
157 .Xr dccm 8 .
158 No single mail message should be reported to a DCC
159 server more than once per recipient.
160 .Pp
161 It is better to use
162 .Em MXDCC
163 lines in the
164 .Fl w Ar whiteclnt
165 file for your MX mail servers that use DCC than
166 .Fl Q
167 .It Fl C
168 outputs only the X-DCC header
169 and the checksums for the message.
170 .It Fl H
171 outputs only the X-DCC header.
172 .It Fl E
173 adds lines to the start of the log file turned on with
174 .Fl l
175 and
176 .Fl c
177 describing what might have been the envelope of the message.
178 The information for the inferred envelope comes from arguments including
179 .Fl a
180 and headers in the message when
181 .Fl R
182 is used.
183 No lines are generated for which no information is available,
184 such as the envelope recipient.
185 .It Fl R
186 says the first Received lines have the standard
187 "helo\ (name\ [address])..."
188 format and the address is that of the SMTP client
189 that would otherwise be provided with
190 .Fl a .
191 The
192 .Fl a
193 option should be used
194 if the local SMTP server adds a Received line with some other format
195 or does not add a Received line.
196 Received headers specifying IP addresses marked
197 .Em MX
198 or
199 .Em MXDCC
200 in the
201 .Fl w Ar whiteclnt
202 file are skipped.
203 .It Fl h Ar homedir
204 overrides the default DCC home directory,
205 .Pa @prefix@ .
206 .It Fl m Ar map
207 specifies a name or path of the memory mapped parameter file instead
208 of the default
209 .Pa map
210 in the DCC home directory.
211 It should be created with the
212 .Ic new map
213 operation of the
214 .Xr cdcc 8
215 command.
216 .It Fl w Ar whiteclnt
217 specifies an optional file containing SMTP client IP addresses and
218 SMTP headers
219 of mail that do not need X-DCC headers and whose checksums should not
220 be reported to the DCC server.
221 It can also contain checksums of spam.
222 If the pathname is not absolute, it is relative to the DCC home directory.
223 Thus, individual users with private whitelists usually specify them
224 with absolute paths.
225 Common whitelists shared by users must be in the DCC home directory or
226 one of its subdirectories and owned by the set-UID user of
227 .Nm dccproc .
228 It is useful to
229 .Ar include
230 a common or system-wide whitelist in private lists.
231 .Pp
232 Because the contents of the
233 .Ar whiteclnt
234 file are used frequently, a companion file is automatically
235 created and maintained.
236 It has the same pathname but with an added suffix of
237 .Ar .dccw .
238 It contains a memory mapped hash table of the main file.
239 .Pp
240 .Ar Option
241 lines can be used to modify many aspects of
242 .Nm
243 filtering,
244 as described in the main
245 .Xr dcc 8
246 man page.
247 For example, an
248 .Ar option spam-trap-accept
249 line turns off DCC filtering and reports the message as spam.
250 .It Fl T Ar tmpdir
251 changes the default directory for temporary files from the system default.
252 The system default is
253 .Pa /tmp .
254 .It Fl a Ar IP-address
255 specifies the IP address (not the host name) of
256 the immediately previous SMTP client.
257 It is often not available.
258 .Fl a Ar 0.0.0.0
259 is ignored.
260 .Fl a .
261 The
262 .Fl a
263 option should be used
264 instead of
265 .Fl R
266 if the local SMTP server adds a Received line with some other format
267 or does not add a Received line.
268 .It Fl f Ar env_from
269 specifies the RFC\ 821 envelope "Mail\ From" value with which the
270 message arrived.
271 It is often not available.
272 If
273 .Fl f
274 is not present, the contents of the first Return-Path: or UNIX style
275 From_ header is used.
276 The
277 .Ar env_from
278 string is often but need not be bracketed with "<>".
279 .It Fl t Ar targets
280 specifies the number of addressees of the message if other than 1.
281 The string
282 .Ar many
283 instead of a number asserts that there were too many addressees
284 and that the message is unsolicited bulk email.
285 .It Fl x Ar exitcode
286 specifies the code or status with which
287 .Nm
288 exits if the
289 .Fl c
290 thresholds are reached or the
291 .Fl w Ar whiteclnt
292 file blacklists the message.
293 .Pp
294 The default value is EX_NOUSER.
295 EX_NOUSER is 67 on many systems.
296 Use 0 to always exit successfully.
297 .It Fl c Xo
298 .Sm off
299 .Ar type,
300 .Op Ar log-thold,
301 .Ar rej-thold
302 .Sm on
303 .Xc
304 sets logging and "spam" thresholds for checksum
305 .Ar type .
306 The checksum types are
307 .Ar IP ,
308 .Ar env_From ,
309 .Ar From ,
310 .Ar Message-ID ,
311 .Ar substitute ,
312 .Ar Received ,
313 .Ar Body ,
314 .Ar Fuz1 ,
315 .Ar Fuz2 ,
316 .Ar rep-total ,
317 and
318 .Ar rep .
319 The first six,
320 .Ar IP
321 through
322 .Ar substitute ,
323 have no effect except when a local DCC server configured with
324 .Fl K
325 is used.
326 The
327 .Ar substitute
328 thresholds apply to the first substitute heading encountered in the mail
329 message.
330 The string
331 .Ar ALL
332 sets thresholds for all types, but is unlikely to be useful except for
333 setting logging thresholds.
334 The string
335 .Ar CMN
336 specifies the commonly used checksums
337 .Ar Body ,
338 .Ar Fuz1 ,
339 and
340 .Ar Fuz2 .
341 .Ar Rej-thold
342 and
343 .Ar log-thold
344 must be numbers, the string
345 .Ar NEVER ,
346 or the string
347 .Ar MANY
348 indicating millions of targets.
349 Counts from the DCC server as large as the threshold for any single type
350 are taken as sufficient evidence
351 that the message should be logged or rejected.
352 .Pp
353 .Ar Log-thold
354 is the threshold at which messages are logged.
355 It can be handy to log messages at a lower threshold to find
356 solicited bulk mail sources such as mailing lists.
357 If no logging threshold is set,
358 only rejected mail and messages with complicated combinations of white
359 and blacklisting are logged.
360 Messages that reach at least one of their rejection thresholds are
361 logged regardless of logging thresholds.
362 .Pp
363 .Ar Rej-thold
364 is the threshold at which messages are considered "bulk,"
365 and so should be rejected or discarded if not whitelisted.
366 .Pp
367 DCC Reputation thresholds in the commercial version
368 of the DCC are controlled by thresholds on checksum types
369 .Ar rep
370 and
371 .Ar rep-total .
372 Messages from an IP address that the DCC database says has sent
373 more than
374 .Fl t Ar rep-total,log-thold
375 messages are logged.
376 A DCC Reputation is computed for messages received
377 from IP addresses that
378 have sent more than
379 .Fl t Ar rep-total,log-thold
380 messages.
381 The DCC Reputation of an IP address is the percentage of its messages
382 that have been detected as bulk
383 or having at least 10 recipients.
384 The defaults are equivalent to
385 .Fl t Ar rep,never
386 and
387 .Fl t Ar rep-total,never,20 .
388 .Pp
389 Bad DCC Reputations do not reject mail unless enabled by an
390 .Ar option DCC-rep-on
391 line in a
392 .Pa whiteclnt
393 file.
394 .Pp
395 The checksums of locally whitelisted messages are not checked with
396 the DCC server and so only the number of targets of the current copy of
397 a whitelisted message are compared against the thresholds.
398 .Pp
399 The default is
400 .Ar ALL,NEVER ,
401 so that nothing is discarded, rejected, or logged.
402 A common choice is
403 .Ar CMN,25,50
404 to reject or discard
405 mail with common bodies except as overridden by
406 the whitelist of the DCC server, the sendmail
407 .Em ${dcc_isspam}
408 and
409 .Em ${dcc_notspam}
410 macros, and
411 .Fl g ,
412 and
413 .Fl w .
414 .It Fl g Xo
415 .Sm off
416 .Op Ar not-
417 .Ar type
418 .Sm on
419 .Xc
420 indicates that whitelisted,
421 .Ar OK
422 or
423 .Ar OK2 ,
424 counts from the DCC server for a type of checksum are to be believed.
425 They should be ignored if prefixed with
426 .Ar not- .
427 .Ar Type
428 is one of the same set of strings as for
429 .Fl c .
430 Only
431 .Ar IP ,
432 .Ar env_From ,
433 and
434 .Ar From
435 are likely choices.
436 By default all three are honored,
437 and hence the need for
438 .Ar not- .
439 .It Fl S Ar hdr
440 adds to the list of substitute or locally chosen headers that
441 are checked with the
442 .Fl w Ar whiteclnt
443 file and sent to the DCC server.
444 The checksum of the last header of type
445 .Ar hdr
446 found in the message is checked.
447 As many as 6 different substitute headers can be specified, but only
448 the checksum of the first of the 6 will be sent to the DCC server.
449 .It Fl i Ar infile
450 specifies an input file for the entire message
451 instead of standard input.
452 If not absolute, the pathname is interpreted relative to the
453 directory in which
454 .Nm
455 was started.
456 .It Fl o Ar outfile
457 specifies an output file for the entire message including headers
458 instead of standard output.
459 If not absolute, the pathname is interpreted relative to the
460 directory in which
461 .Nm
462 was started.
463 .It Fl l Ar logdir
464 specifies a directory for copies of messages whose
465 checksum target counts exceed
466 .Fl c
467 thresholds.
468 The format of each file is affected by
469 .Fl E .
470 .Pp
471 See the FILES section below concerning the contents of the files.
472 See also the
473 .Ar option log-subdirectory-{day,hour,minute}
474 lines in
475 .Pa whiteclnt
476 files described in
477 .Xr dcc 8 .
478 .Pp
479 The directory is relative to the DCC home directory if it is not absolute
480 .It Fl B Ar dnsbl-option
481 enables DNS blacklist checks of the SMTP client IP address, SMTP envelope
482 Mail_From sender domain name, and of host names in URLs in the message body.
483 Body URL blacklisting has too many false positives to use on
484 abuse mailboxes.
485 It is less effective than greylisting with
486 .Xr dccm 8
487 or
488 .Xr dccifd 8
489 but can be useful in situations where
490 greylisting cannot be used.
491 .Pp
492 .Ar Dnsbl-option
493 is either one of the
494 .Fl B Ar set:option
495 forms or
496 .Bd -literal -compact -offset 4n
497 .Fl B Xo
498 .Sm off
499 .Ar domain Oo Ar ,IPaddr
500 .Op Ar /xx Op Ar ,bltype Oc
501 .Sm on
502 .Xc
503 .Ed
504 .Ar Domain
505 is a DNS blacklist domain such as example.com
506 that will be searched.
507 .Ar IPaddr Ns Op Ar /xxx
508 is the string "any"
509 an IP address in the DNS blacklist
510 that indicates that the mail message
511 should be rejected,
512 or a CIDR block covering results from the DNS blacklist.
513 "127.0.0.2" is assumed if
514 .Ar IPaddr
515 is absent.
516 IPv6 addresses can be specified with the usual colon (:) notation.
517 Names can be used instead of numeric addresses.
518 The type of DNS blacklist
519 is specified by
520 .Ar bltype
521 as
522 .Ar name ,
523 .Ar IPv4 ,
524 or
525 .Ar IPv6 .
526 Given an envelope sender domain name or a domain name in a URL of
527 spam.domain.org
528 and a blacklist of type
529 .Ar name ,
530 spam.domain.org.example.com will be tried.
531 Blacklist types of
532 .Ar IPv4
533 and
534 .Ar IPv6
535 require that the domain name in a URL sender address
536 be resolved into an IPv4 or IPv6
537 address.
538 The address is then written as a reversed string of decimal
539 octets to check the DNS blacklist, as in 2.0.0.127.example.com,
540 .Pp
541 More than one blacklist can be specified and blacklists can be grouped.
542 All searching within a group is stopped at the first positive result.
543 .Pp
544 Unlike
545 .Xr dccm 8
546 and
547 .Xr dccifd 8 ,
548 no
549 .Ar option\ DNSBL-on
550 line is required in the
551 .Pa whiteclnt
552 file.
553 A
554 .Fl B
555 argument is sufficient to show that DNSBL filtering is wanted by the
556 .Nm
557 user.
558 .Bl -tag -width 3n
559 .It Fl B Ar set:no-client
560 says that SMTP client IP addresses and reverse DNS domain names should
561 not be checked in the following blacklists.
562 .br
563 .Fl B Ar set:client
564 restores the default for the following blacklists.
565 .It Fl B Ar set:no-mail_host
566 says that SMTP envelope Mail_From sender domain names should
567 not be checked in the following blacklists.
568 .Fl B Ar set:mail_host
569 restores the default.
570 .It Fl B Ar set:no-URL
571 says that URLs in the message body should not be checked in the
572 in the following blacklists.
573 .Fl B Ar set:URL
574 restores the default.
575 .It Fl B Ar set:no-MX
576 says MX servers of sender Mail_From domain names and host names in URLs
577 should not be checked in the following blacklists.
578 .br
579 .Fl B Ar set:MX
580 restores the default.
581 .It Fl B Ar set:no-NS
582 says DNS servers of sender Mail_From domain names and host names in URLs
583 should not be checked in the following blacklists.
584 .Fl B Ar set:NS
585 restores the default.
586 .It Fl B Ar set:defaults
587 is equivalent to all of
588 .Fl B Ar set:no-temp-fail
589 .Fl B Ar set:client
590 .br
591 .Fl B Ar set:mail_host
592 .Fl B Ar set:URL
593 .Fl B Ar set:MX
594 and
595 .Fl B Ar set:NS
596 .It Fl B Ar set:group=X
597 adds later DNS blacklists specified with
598 .Bd -literal -compact -offset 4n
599 .Fl B Xo
600 .Sm off
601 .Ar domain Oo Ar ,IPaddr
602 .Op Ar /xx Op Ar ,bltype Oc
603 .Sm on
604 .Xc
605 .Ed
606 to group 1, 2, or 3.
607 .It Fl B Ar set:debug=X
608 sets the DNS blacklist logging level
609 .It Fl B Ar set:msg-secs=S
610 limits
611 .Nm
612 to
613 .Ar S
614 seconds total for checking all DNS blacklists.
615 The default is 25.
616 .It Fl B Ar set:URL-secs=S
617 limits
618 .Nm
619 to at most
620 .Ar S
621 seconds resolving and checking any single URL.
622 The default is 11.
623 Some spam contains dozens of URLs and that
624 some "spamvertised" URLs contain host names that need minutes to
625 resolve.
626 Busy mail systems cannot afford to spend minutes checking each incoming
627 mail message.
628 .El
629 .It Fl L Ar ltype,facility.level
630 specifies how messages should be logged.
631 .Ar Ltype
632 must be
633 .Ar error ,
634 .Ar info ,
635 or
636 .Ar off
637 to indicate which of the two types of messages are being controlled or
638 to turn off all
639 .Xr syslog 3
640 messages from
641 .Nm .
642 .Ar Level
643 must be a
644 .Xr syslog 3
645 level among
646 .Ar EMERG ,
647 .Ar ALERT ,
648 .Ar CRIT , ERR ,
649 .Ar WARNING ,
650 .Ar NOTICE ,
651 .Ar INFO ,
652 and
653 .Ar DEBUG .
654 .Ar Facility
655 must be among
656 .Ar AUTH ,
657 .Ar AUTHPRIV ,
658 .Ar CRON ,
659 .Ar DAEMON ,
660 .Ar FTP ,
661 .Ar KERN ,
662 .Ar LPR ,
663 .Ar MAIL ,
664 .Ar NEWS ,
665 .Ar USER ,
666 .Ar UUCP ,
667 and
668 .Ar LOCAL0
669 through
670 .Ar LOCAL7 .
671 The default is equivalent to
672 .Dl Fl L Ar info,MAIL.NOTICE Fl L Ar error,MAIL.ERR
673 .El
674 .Pp
675 .Nm
676 exits with 0 on success and with the
677 .Fl x
678 value if the
679 .Fl c
680 thresholds are reached or the
681 .Fl w Ar whiteclnt
682 file blacklists the message.
683 If at all possible,
684 the input mail message is output to standard output or the
685 .Fl o Ar outfile
686 despite errors.
687 If possible, error messages are put into the system log instead of
688 being mixed with the output mail message.
689 The exit status is zero for errors so that the mail message
690 will not be rejected.
691 .Pp
692 If
693 .Nm
694 is run more than 500 times in fewer than 5000 seconds,
695 .Nm
696 tries to start
697 .Xr Dccifd 8 .
698 The attempt is made at most once per hour.
699 Dccifd is significantly more efficient than
700 .Nm .
701 With luck, mechanisms such as SpamAssassin will notice when dccifd is
702 running and switch to dccifd.
703 .Sh FILES
704 .Bl -tag -width whiteclnt -compact
705 .It Pa @prefix@
706 DCC home directory in which other files are found.
707 .It Pa map
708 memory mapped file in the DCC home directory
709 of information concerning DCC servers.
710 .It Pa whiteclnt
711 contains the client whitelist in
712 the format described in
713 .Xr dcc 8 .
714 .It Pa whiteclnt.dccw
715 is a memory mapped hash table corresponding to the
716 .Pa whiteclnt
717 file.
718 .It Pa tmpdir
719 contains temporary files created and deleted as
720 .Nm
721 processes the message.
722 .It Pa logdir
723 is an optional directory specified with
724 .Fl l
725 and containing marked mail.
726 Each file in the directory contains one message, at least one of whose
727 checksums reached one of its
728 .Fl c
729 thresholds.
730 The entire body of the SMTP message including its header
731 is followed by the checksums for the message.
732 .El
733 .Sh EXAMPLES
734 The following
735 .Xr procmailrc 5
736 rule adds an X-DCC header to passing mail
737 .Bd -literal -offset 4n
738 :0 f
739 | /usr/local/bin/dccproc -ERw whiteclnt
740 .Ed
741 .Pp
742 This
743 .Xr procmailrc 5
744 recipe rejects mail with total counts of 10 or larger for
745 the commonly used checksums:
746 .Bd -literal -offset 4n
747 :0 fW
748 | /usr/local/bin/dccproc -ERw whiteclnt -ccmn,10
749 :0 e
750 {
751 EXITCODE=67
752 :0
753 /dev/null
754 }
755 .Ed
756 .Sh SEE ALSO
757 .Xr cdcc 8 ,
758 .Xr dcc 8 ,
759 .Xr dbclean 8 ,
760 .Xr dccd 8 ,
761 .Xr dblist 8 ,
762 .Xr dccifd 8 ,
763 .Xr dccm 8 ,
764 .Xr dccsight 8 ,
765 .Xr mail 1 ,
766 .Xr procmail 1 .
767 .Sh HISTORY
768 Distributed Checksum Clearinghouses are based on an idea of Paul Vixie.
769 Implementation of
770 .Nm
771 was started at Rhyolite Software in 2000.
772 This document describes version 1.3.103.
773 .Sh BUGS
774 .Nm
775 uses
776 .Fl c
777 where
778 .Xr dccm 8
779 uses
780 .Fl t .