dccm(8) Distributed Checksum Clearinghouse dccm(8)NAMEdccm — Distributed Checksum Clearinghouse Milter Interface
SYNOPSISdccm [-VdbxANPQ] [-G on | off | noIP | IPmask/xx] [-h homedir] [-I user]
[-p protocol:filename | protocol:port@host] [-m map]
[-w whiteclnt] [-U userdirs] [-a IGNORE | REJECT | DISCARD]
[-t type,[log-thold,]rej-thold] [-g [not-]type] [-S header]
[-l logdir] [-R rundir] [-r rejection-msg] [-j maxjobs]
[-B dnsbl-option] [-L ltype,facility.level]
DESCRIPTIONdccm is a daemon built with the sendmail milter interface intended to
connect sendmail(8) to DCC servers. When built with the milter filter
machinery and configured to talk to dccm in the sendmail.cf file, send‐
mail passes all email to dccm which in turn reports related checksums to
the nearest DCC server. dccm then adds an X-DCC SMTP header line to the
message. Sendmail is told to reject the message if it is unsolicited
bulk mail.
Dccm sends reports of checksums related to mail received by DCC clients
and queries about the total number of reports of particular checksums. A
DCC server receives no mail, address, headers, or other information, but
only cryptographically secure checksums of such information. A DCC
server cannot determine the text or other information that corresponds to
the checksums it receives. Its only acts as a clearinghouse of counts
for checksums computed by clients. For complete privacy as far as the
DCC is concerned, the checksums of purely internal mail or other mail
that is known to not be unsolicited bulk can be listed in a whitelist to
not be reported to the DCC server.
Since the checksums of messages that are whitelisted locally by the
/usr/local/dcc/whiteclnt file are not reported to the DCC server, dccm
knows nothing about the total recipient counts for their checksums and so
cannot add X-DCC header lines to such messages. Sendmail does not tell
dccm about messages that are not received by sendmail via SMTP, including
messages submitted locally and received via UUCP, and so they also do not
receive X-DCC header lines.
Enable the daemon and put its parameters in the /usr/local/dcc/conf file
and start the daemon with the /usr/local/dcc/libexec/start-dccm or
/usr/local/dcc/libexec/rcDCC scripts.
The list of servers that dccm contacts is in the memory mapped file
/usr/local/dcc/map shared by local DCC clients. The file is maintained
with cdcc(8).
OPTIONS
The following options are available:
-V displays the version of dccm. Two or more -V options show the
options with which it was built.
-d enables debugging output from the DCC client software. Additional
-d options increase the number of messages. A single -d logs
aborted SMTP transactions including those from some "dictionary
attacks."
-b causes the daemon to not detach itself from the controlling tty and
put itself into the background.
-x causes the daemon to try "extra hard" to contact a DCC server.
Since it is usually more important to deliver mail than to report
its checksums, dccm normally does not delay too long while trying to
contact a DCC server. It will not try again for several seconds
after a failure. With -x, it will always try to contact the DCC
server and it will tell the MTA to answer the DATA command with a
4yz temporary failure.
-A adds to existing X-DCC headers in the message instead of replacing
existing headers of the brand of the current server.
-N neither adds, deletes, nor replaces existing X-DCC headers in the
message. Each mail message is logged, rejected, and otherwise han‐
dled the same.
-P The SpamAsassin DCC.pm plugin should watch for "bulk" in X-DCC SMTP
header fields, but historically has looked for counts of "many".
However, there are situations when dccm knows that a mail message is
extremely bulky and probably spam. For example, mail from a sender
that is blacklisted in whiteclnt gets an X-DCC header that includes
bulk. To acommodate that bug in SpamAssassin, by default whenever
dccm generates an X-DCC header containing "bulk", it also forces the
Body count to "many". -P turns off that kludge and the Body con‐
tains the count from the DCC server.
-Q only queries the DCC server about the checksums of messages instead
of reporting. This is useful when dccm is used to filter mail that
has already been reported to a DCC server by another DCC client. No
single mail message should be reported to a DCC server more than
once per recipient, because each report will increase the apparent
"bulkness" of the message.
It is better to use MXDCC lines in the global
/usr/local/dcc/whiteclnt file for your MX mail servers that use DCC
than to use -Q with dccm.
Do not use -Q except on mail that you know has been reported to a
DCC server. DCC depends on reports of all except known private mail
and works only because almost no DCC installations use -Q.
-G on | off | noIP | IPmask/xx
controls greylisting. At least one working greylist server must be
listed in the /usr/local/dcc/map file. If more than one is named,
they must "flood" or change checksums and they must use the same -G
parameters. See dccd(8). Usually all dccm or dccifd DCC client
processes use the same -G parameters.
IPmask/xx and noIP remove part or all of the IP address from the
greylist triple.
-h homedir
overrides the default DCC home directory, /usr/local/dcc.
-I user
specifies the UID and GID of the process.
-p protocol:filename | protocol:port@host
specifies the protocol and address by which sendmail will contact
dccm. The default is a UNIX domain socket in the "run" directory,
/var/run/dcc/dccm. (See also -R) This protocol and address must
match the value in sendmail.cf. This mechanism can be used to con‐
nect dccm on one computer to sendmail on another computer when a
port and host name or IP address are used.
-m map
specifies a name or path of the memory mapped parameter file instead
of the default /usr/local/dcc/map. It should be created with the
cdcc(8) command.
-w whiteclnt
specifies an optional file containing filtering parameters as well
as SMTP client IP addresses, SMTP envelope values, and header values
of mail that is spam or is not spam and does not need a X-DCC
header, and whose checksums should not be reported to the DCC
server.
If the pathname whiteclnt is not absolute, it is relative to the DCC
home directory.
The format of the dccm whiteclnt file is the same as the
/usr/local/dcc/whitelist files used by dbclean(8) and the whiteclnt
file used by dccproc(8). See dcc(8) for a description of DCC white
and blacklists. Because the contents of the whiteclnt file are used
frequently, a companion file is automatically created and main‐
tained. It has the same pathname but with an added suffix of .dccw
and contains a memory mapped hash table of the main file.
A whitelist entry ("OK") or two or more semi-whitelistings ("OK2")
for one of the message's checksums prevents all of the message's
checksums from being reported to the DCC server and the addition of
a X-DCC header line by dccm. A whitelist entry for a checksum also
prevents rejecting or discarding the message based on DCC recipient
counts as specified by -a and -t. Otherwise, one or more checksums
with blacklisting entries ("MANY") cause all of the message's check‐
sums to be reported to the server with an addressee count of "MANY".
If the message has a single recipient, an env_To whiteclnt entry of
"OK" for the checksum of its recipient address acts like any other
whiteclnt entry of "OK." When the SMTP message has more than one
recipient, the effects can be complicated. When a message has sev‐
eral recipients with some but not all listed in the whiteclnt file,
dccm tries comply with the wishes of the users who want filtering as
well as those who don't by silently not delivering the message to
those who want filtering (i.e. are not whitelisted) and delivering
the message to users who don't want filtering.
-U userdirs
enables per-user whiteclnt files and log directories. Each target
of a message can have a directory of log files named
usedirs/${dcc_userdir}/log where ${dcc_userdir} is the sendmail.cf
macro described below. If ${dcc_userdir} is not set,
userdirs/${rcpt_mailer}/${rcpt_addr}/log is used. The most likely
value of mailer is local. Appropriate values for both
${rcpt_mailer} and ${rcpt_addr} can be seen by examining env_To
lines in -l logdir files. If it is not absolute, userdirs is rela‐
tive to the DCC home directory. The directory containing the log
files must be named log and it must be writable by the dccm process.
Each log directory must exist or logging for the corresponding is
silently disabled. The files created in the log directory are owned
by the UID of the dccm process, but they have group and other read
and write permissions copied from the corresponding log directory.
To ensure the privacy of mail, it may be good to make the directo‐
ries readable only by owner and group, and to use a cron script that
changes the owner of each file to match the grandparent addr direc‐
tory.
There can also be a per-user whitelist file named
userdirs/addr/whiteclnt for each addressee addr. Any checksum that
is not white- or blacklisted by an individual addressee's per-user
whiteclnt file is checked in the main /usr/local/dcc/whiteclnt
file. A missing per-addressee whiteclnt file is the same as an
empty file. Relative paths for files included in per-addressee
files are resolved in the DCC home directory. The whiteclnt files
and the addr directories containing them must be writable by the
dccm process.
Option lines in per-user whiteclnt files can be used to modify many
aspects of dccm filtering, as described in the main dcc man page.
For example, an option dcc-off line turns off DCC filtering for
individual mailboxes.
-a IGNORE | REJECT | DISCARD
specifies the action taken when DCC server counts or -t thresholds
say that a message is unsolicited and bulk. IGNORE causes the mes‐
sage to be unaffected except for adding the X-DCC header line to the
message. This turns off all filtering except greylisting.
Spam can also be REJECTed or accepted and silently DISCARDed without
being delivered to local mailboxes. The default is REJECT.
Mail forwarded via IP addresses marked MX or MXDCC in the main
/usr/local/dcc/whiteclnt file is treated as if -a DISCARD were spec‐
ified. This prevents "bouncing" spam.
Determinations that mail is or is not spam from sendmail via
${dcc_isspam} or ${dcc_notspam} macros override -a. The effects of
the -w whiteclnt are not affected by -a.
-t type,[log-thold,]rej-thold
sets logging and "spam" thresholds for checksum type. The checksum
types are IP, env_From, From, Message-ID, substitute, Received,
Body, Fuz1, Fuz2, rep-total, and rep. The first six, IP through
substitute, have no effect except when a local DCC server configured
with -K is used. The substitute thresholds apply to the first sub‐
stitute heading encountered in the mail message. The string ALL
sets thresholds for all types, but is unlikely to be useful except
for setting logging thresholds. The string CMN specifies the com‐
monly used checksums Body, Fuz1, and Fuz2. Rej-thold and log-thold
must be numbers, the string NEVER, or the string MANY indicating
millions of targets. Counts from the DCC server as large as the
threshold for any single type are taken as sufficient evidence that
the message should be logged or rejected.
Log-thold is the threshold at which messages are logged. It can be
handy to log messages at a lower threshold to find solicited bulk
mail sources such as mailing lists. If no logging threshold is set,
only rejected mail and messages with complicated combinations of
white and blacklisting are logged. Messages that reach at least one
of their rejection thresholds are logged regardless of logging
thresholds.
Rej-thold is the threshold at which messages are considered "bulk,"
and so should be rejected or discarded if not whitelisted.
DCC Reputation thresholds in the commercial version of DCC are con‐
trolled by thresholds on checksum types rep and rep-total. The DCC
Reputations of IP addresses that the DCC database says have sent
more than rep-total,log-thold are computed and messages from those
addresses are logged. Messages from IP addresses with DCC Reputa‐
tions of at least the rep,rej-thold rejection threshold can be
rejected. The DCC Reputation of an IP address is the percentage of
its messages known to have been sent to at least 10 recipients. The
defaults are equivalent to rep,never and rep-total,never,20.
Bulk DCC Reputations do not reject mail unless enabled by an
option DCC-rep-on line a whiteclnt file.
The checksums of locally whitelisted messages are not checked with
the DCC server and so only the number of targets of the current copy
of a whitelisted message are compared against the thresholds.
The default is ALL,NEVER, so that nothing is discarded, rejected, or
logged. A common choice is CMN,25,50 to reject or discard mail with
common bodies except as overridden by the whitelist of the DCC
server, the sendmail ${dcc_isspam} and ${dcc_notspam} macros, and
-g, and -w.
-g [not-]type
indicates that whitelisted, OK or OK2, counts from the DCC server
for a type of checksum are to be believed. They should be ignored
if prefixed with not-. Type is one of the same set of strings as
for -t. Only IP, env_From, and From are likely choices. By default
all three are honored, and hence the need for not-.
-S hdr
adds to the list of substitute or locally chosen headers that are
checked with the -w whiteclnt file and sent to the DCC server. The
checksum of the last header of type hdr found in the message is
checked. Hdr can be HELO to specify the SMTP envelope HELO value.
Hdr can also be mail_host to specify the host name from the
Mail_from value in the SMTP envelope. As many as 8 different sub‐
stitute headers can be specified, but only the checksum of the first
will be sent to the DCC server.
-l logdir
specifies a directory in which files containing copies of messages
processed by dccm are kept. They can be copied to per-user directo‐
ries specified with -U. Information about other recipients of a
message is deleted from the per-user copies.
See the FILES section below concerning the contents of the files.
See also the option log-subdirectory-{day,hour,minute} lines in
whiteclnt files described in dcc(8).
The directory is relative to the DCC home directory if it is not
absolute
-R rundir
specifies the "run" directory where the UNIX domain socket and file
containing the daemon's process ID are stored. The default value is
/var/run/dcc .
-r rejection-msg
specifies the rejection message for unsolicited bulk mail or for
mail temporarily blocked by greylisting when -G is specified. The
first -r rejection-msg replaces the default bulk mail rejection mes‐
sage, "5.7.1 550 mail %ID from %CIP rejected by DCC". The second
replaces "4.2.1 452 mail %ID from %CIP temporary greylist embar‐
goed". The third -r rejection-msg replaces the default SMTP rejec‐
tion message "5.7.1 550 %ID bad reputation; see http://commercial-
dcc.rhyolite.com/cgi-bin/reps.cgi?tgt=%CIP" for mail with bulk DCC
Reputations. If rejection-msg is the zero-length string, the -r
setting is counted but the corresponding default message is not
changed.
Rejection-msg can contain specific information about the mail mes‐
sage. The following strings starting with % are replaced with the
corresponding values:
%ID message ID such as the unique part of log file name or
sendmail queue ID
%CIP SMTP client IP address
%BTYPE type of DNS blacklist hit, such as "SMTP client",
"mail_host", or "URL NS"
%BTGT IP address or name declared bad by DNS blacklist
%BPROBE domain name found in DNS blacklist such as
4.3.2.10.example.com
%BRESULT value of the %BPROBE domain name found in DNS black‐
list
A common alternate for the bulk mail rejection message is "4.7.1 451
Access denied by DCC" to tell the sending mail system to continue
trying. Use a 4yz response with caution, because it is likely to
delay for days a delivery failure message for false positives. If
the rejection message does not start with an RFC 1893 status code
and RFC 2821 reply code, 5.7.1 and 550 or 4.2.1 and 452 are used.
See also -B set:rej-msg to set the status message for mail rejected
by DNS blacklists.
-j maxjobs
limits the number of simultaneous requests that will be processed.
The default value is the maximum number that seems to be possible
given system limits on open files, select() bit masks, and so forth.
Start dccm with -d and see the starting message in the system log to
see the limit.
-B dnsbl-option
enables DNS white- and blacklist checks of the SMTP client IP
address, SMTP envelope Mail_From sender domain name, and of host
names in URLs in the message body. Body URL blacklisting has too
many false positives to use on abuse mailboxes. It is less effec‐
tive than greylisting with dccm(8) or dccifd(8) but can be useful in
situations where greylisting cannot be used. It can be combined
with greylisting.
Dnsbl-option is either one of the -B set:option forms or
-B domain[any[,bltype]]
-B domain[,IPaddr[/xx[&IPmask][,bltype]]]
-B domain[,IPaddrLO[-IPaddrHI[&IPmask][,bltype]]]
Domain is a DNS blacklist domain such as example.com that will be
searched. The strings any, IPaddr, IPaddr/xx, or IPaddrLO-IPaddrHI,
specifies which IP addresses found in the DNS blacklist after apply‐
ing the optional IP address mask IPmask say that mail messages
should be rejected or accepted with -B set:white. "127.0.0.2" is
assumed if no address(es) are specified. IPv6 addresses can be
specified with the usual colon (:) notation. Host names can be used
instead of numeric addresses. The type of DNS blacklist is speci‐
fied by bltype as name, all-names, IPv4, or IPv6. Given an envelope
sender domain name or a domain name in a URL of spam.domain.org and
a blacklist of type name, spam.domain.org.example.com will be looked
up. The names spam.domain.org.example.com, domain.org.example.com,
and org.example.com will be looked up in blacklists of type
all-names. Use name with DNS blacklists that use wildcards for
speed but all-names for other DNS name blacklists. Blacklist types
of IPv4 and IPv6 require that the domain name in a URL sender
address be resolved into an IPv4 or IPv6 address. The resolved
address from the mail message is then written as a reversed string
of decimal octets to check the DNS blacklist, as in
2.0.0.127.example.com.
A domain of "." and type of name can be used to blacklist domain
names with specified addresses. This can be useful to detect URLs
with domain names listed in a Response Policy Zone (RPZ). For exam‐
ple, the following can be used to reject mail containing URLs listed
by a response policy zone that maps evil domain names to 224.0.0.0
with an informative status message:
'-Bset:rej-msg=5.7.1 550 %ID %BTYPE \
http://example.com/query/dbl?domain=%BTGT'
-B.,224.0.0.0,name
More than one blacklist can be specified and blacklists can be
grouped with -B set:group=X. All searching within a group of black‐
lists is stopped at the first positive result.
Unlike dccproc(8), positive results are ignored by dccm after being
logged unless an option DNSBL-on or option DNSBLx-on line appears a
whiteclnt file.
-B set:no-client
implies that SMTP client IP addresses and reverse DNS domain
names should not be checked in the following blacklists.
-B set:client restores the default for the following black‐
lists.
-B set:no-mail_host
implies that SMTP envelope Mail_From sender domain names should
not be checked in the following blacklists. -B set:mail_host
restores the default.
-B set:no-URL
says that URLs in the message body should not be checked in the
in the following blacklists. -B set:URL restores the default.
-B set:no-MX
says MX servers of sender Mail_From domain names and host names
in URLs should not be checked in the following blacklists.
-B set:MX restores the default.
-B set:no-NS
says DNS servers of sender Mail_From domain names and host
names in URLs should not be checked in the following black‐
lists. -B set:NS restores the default.
-B set:white
says the DNS list is a whitelist of names or IP addresses.
-B set:black restores the default. DNS whitelist usually also
need -B set:no-mail_host, -B set:no-URL, -B set:no-MX,
-B set:no-NS, and -B set:no-mail_host.
-B set:defaults
is equivalent to all of -B set:black -B set:client
-B set:mail_host -B set:URL -B set:MX and -B set:NS
-B set:group=X
adds following DNS blacklists specified with -B domain[...] to
group 1, 2, 3, or 4.
-B set:debug=X
sets the DNS blacklist logging level
-B set:msg-secs=S
limits dccm to S seconds total for checking all DNS blacklists.
The default is 25.
-B set:URL-secs=S
limits dccm to at most S seconds resolving and checking any
single URL or IP address. The default is 11. Some spam con‐
tains dozens of URLs and some "spamvertised" URLs contain host
names that need minutes to resolve. Busy mail systems cannot
afford to spend minutes checking each incoming mail message.
-B set:rej-msg="rejection message"
sets the SMTP rejection message for the following blacklists.
Rejection-msg must be in the same format as for -r. If
rejection message is null, the default is restored. The
default DNS blacklist rejection message is the first message
set with -r.
-B set:max_helpers=X
sets maximum number of helper processes to X. In order to use
typical single-threaded DNS resolver libraries, dccm uses
fleets of helper processes. It is rarely a good idea to change
the default, which is the same as the maximum number of simul‐
taneous jobs set with -j.
-B set:progpath=/usr/local/dcc/libexec/dns-helper
changes the path to the helper program.
-L ltype,facility.level
specifies how messages should be logged. Ltype must be error, info,
or off to indicate which of the two types of messages are being con‐
trolled or to turn off all syslog(3) messages from dccm. Level must
be a syslog(3) level among EMERG, ALERT, CRIT, ERR, WARNING, NOTICE,
INFO, and DEBUG. Facility must be among AUTH, AUTHPRIV, CRON,
DAEMON, FTP, KERN, LPR, MAIL, NEWS, USER, UUCP, and LOCAL0 through
LOCAL7. The default is equivalent to
-L info,MAIL.NOTICE -L error,MAIL.ERR
dccm normally sends counts of mail rejected and so forth the to system
log at midnight. The SIGUSR1 signal sends an immediate report to the
system log. They will be repeated every 24 hours instead of at midnight.
SENDMAIL MACROS
Sendmail can affect dccm with the values of some sendmail.cf macros.
These macro names must be added to the Milter.macros option statements in
sendmail.cf as in the example "Feature" file dcc.m4.
${dcc_isspam} causes a mail message to be reported to the DCC server as
having been addressed to "MANY" recipients. The
${dcc_isspam} macro is ignored if the ${dcc_notspam} macro
is set to a non-null string
If the value of the ${dcc_isspam} is null, dccm uses SMTP
rejection messages controlled by -a and -r. If the value
of the ${dcc_isspam} macro starts with "DISCARD", the mail
message is silently discarded as with -a DISCARD. If value
of the macro not null and does not start with "DISCARD",
it is used as the SMTP error message given to the SMTP
client trying to send the rejected message. The message
starts with an optional SMTP error type and number fol‐
lowed by text.
The -a option does not effect messages marked spam with
${dcc_isspam}. When the ${dcc_isspam} macro is set, the
message is rejected or discarded despite local or DCC
database whitelist entries. The local whitelist does con‐
trol whether the message's checksums will be reported to
the DCC server and an X-DCC SMTP header line will be
added.
${dcc_notspam}
causes a message not be considered unsolicited bulk
despite evidence to the contrary. It also prevents dccm
from reporting the checksums of the message to the DCC
server and from adding an X-DCC header line.
When the macro is set by the sendmail.cf rules,
${dcc_notspam} macros overrides DCC threshlds that say the
message should be rejected as well as the effects of the
${dcc_isspam} macro.
${dcc_mail_host}
specifies the name of the SMTP client that is sending the
message. This macro is usually the same as the mail_host
macro. They can differ when a sendmail "smart relay" is
involved. The ${dcc_mail_host} macro does not work if
FEATURE(delay_checks) is used, and so dccm falls back on
mail_host.
${dcc_userdir}
is the per-user whitelist and log directory for a recipi‐
ent. If the macro is not set in sendmail.cf,
$&{rcpt_mailer}/$&{rcpt_addr} is assumed, but with the
recipient address converted to lower case. Whatever value
is used, the directory name after the last slash (/) char‐
acter is converted to lower case. Any value containing
the string "/../" is ignored.
This macro also does not work if FEATURE(delay_checks) is
used.
The following two lines in a sendmail mc file have the
same effect as not defining the ${dcc_userdir} macro, pro‐
vided FEATURE(dcc) is also used and the sendmail
cf/feature directory has a symbolic link to the
/usr/local/dcc/build/dcc/misc/dcc.m4 file.
SLocal_check_rcpt
R$* $: $1 $(macro {dcc_userdir} $@ $&{rcpt_mailer}/$&{rcpt_addr} $))
FILES
/usr/local/dcc
is the DCC home directory.
/usr/local/dcc/libexec/start-dccm
is a script used by /usr/local/dcc/libexec/rcDCC to start
dccm.
dcc_conf contains parameters used by the scripts to start DCC daemons
and cron jobs.
logdir is an optional directory specified with -l and containing
marked mail. Each file in the directory contains one message,
at least one of whose checksums reached its -t thresholds or
that is interesting for some other reason. Each file starts
with lines containing the date when the message was received,
the IP address of the SMTP client, and SMTP envelope values.
Those lines are followed by the body of the SMTP message
including its header as it was received by sendmail and with‐
out any new or changed header lines. Only approximately the
first 32 KBytes of the body are recorded unless modified by
./configure --with-max-log-size=xx The checksums for the mes‐
sage follow the body. They are followed by lines indicating
that the ${dcc_isspam} or ${dcc_notspam} sendmail.cf macros
were set or one of the checksums is white- or blacklisted by
the -w whiteclnt file. Each file ends with the X-DCC header
line added to the message and the disposition of the message
including SMTP status message if appropriate.
map is the memory mapped file of information concerning DCC
servers in the DCC home directory. See -m.
whiteclnt contains the client whitelist in the format described in
dcc(8). See -w.
whiteclnt.dccw
is a memory mapped hash table of the /usr/local/dcc/whiteclnt
file.
/var/run/dcc/dccm.pid
directory contains daemon's process ID. The string “dccm” is
replaced by the file name containing the daemon to facilitate
running multiple daemons, probably connected to remote
instances of sendmail using TCP/IP instead of a UNIX domain
socket. See also -R.
/var/run/dcc/dccm
is the default UNIX domain socket used by the sendmail milter
interface. See also -R.
sendmail.cf
is the sendmail(8) control file.
/usr/local/dcc/build/dcc/misc/dcc.m4
sendmail mc file that should have a symbolic link in the send‐
mail cf/feature directory so that FEATURE(dcc) can be used in
a sendmail mc file.
EXAMPLES
Dccm should be started before sendmail with something like the script
/usr/local/dcc/libexec/start-dccm. It looks for common DCC parameters in
the /usr/local/dcc/dcc_conf file.
Those numbers should modified to fit local conditions. It might be wise
to replace the "100" numbers with much larger values or with "MANY" until
a few weeks of monitoring the log directory show that sources of mailing
lists are in the server's whitelist file (see dccd(8)) or the local
/usr/local/dcc/whiteclnt file.
It is usually necessary to regularly delete old log files with a script
like /usr/local/dcc/libexec/cron-dccd.
On systems unlike modern FreeBSD and other UNIX-like systems which
include sendmail milter support, sendmail must be built with the milter
interface, such as by creating a devtools/Site/site.config.m4 or similar
file containing something like the following lines:
APPENDDEF(`conf_sendmail_ENVDEF', `-D_FFR_MILTER=1')
APPENDDEF(`conf_libmilter_ENVDEF', `-D_FFR_MILTER=1')
Appropriate lines invoking the milter interface must be added to
sendmail.cf. That can be done by putting a symbolic link to the the
misc/dcc.m4 file in the DCC source to the sendmail cf/feature directory
and adding the line
FEATURE(dcc)
to the local .mc file.
Note that dccm should not be used with the Postfix milter mechanism.
Instead use dccifd(8) as a before-queue filter as described in that man
page.
SEE ALSOcdcc(8), dbclean(8), dcc(8), dccd(8), dblist(8), dccifd(8), dccproc(8),
dccsight(8), sendmail(8).
HISTORY
Distributed Checksum Clearinghouses are based on an idea of Paul Vixie.
Implementation of dccm was started at Rhyolite Software in 2000. This
document describes version 1.3.158.
BUGSdccm uses -t where dccproc(8) uses -c.
Systems without setrlimit(2) and getrlimit(2) RLIMIT_NOFILE can have
problems with the default limit on the number of simultaneous jobs, the
value of -j. Every job requires four open files. These problems are
usually seen with errors messages that say something like
dccm[24448]: DCC: accept() returned invalid socket
A fix is to use a smaller value for -j or to allow dccm to open more
files. Sendmail version 8.13 and later can be told to poll() instead of
select with SM_CONF_POLL. Some older versions of sendmail knew about
FFR_USE_POLL. One of the following lines in your devtools/Site/site.con‐
fig.m4 file can help:
APPENDDEF(`conf_libmilter_ENVDEF', `-DSM_CONF_POLL')
APPENDDEF(`conf_libmilter_ENVDEF', `-DFFR_USE_POLL')
On many systems with sendmail 8.11.3 and preceding, a bug in the sendmail
milter mechanism causes dccm to die with a core file when given a signal.
April 03, 2015
