Please do not try to use the more than 5 year old modified versions of DCC software distributed by some Linux packagers. Those versions do not detect bulk mail as well as more recent versions. Installations using those old versions also have problems using the public DCC servers that often make it necessary to add their IP addresses to the blacklist that protects the public DCC servers. Even worse, all known Linux redistributions of DCC software have been changed in ways that break things, including the /var/dcc/libexec/updatedcc shell script that could otherwise be used to fetch, configure, compile, install, and restart a current version.
The license on the free source is in the source as well as dcc-servers.net and Rhyolite Software. The free license is intended to cover individuals and organizations including Internet service providers using DCC to filter their own mail. Organizations selling anti-spam appliances or managed mail services are not eligible for the free license.
The DCC and other man pages describe the features, operating modes, required data files, and other characteristics of the DCC. Also see the DCC FAQ or list of frequently answered questions.
Sendmail must have the
Mail Filter API or Milter enabled.
Some systems such a FreeBSD 4.6 and newer are shipped with
Milter enabled and the library installed by default.
If your system comes with the Milter interface turn on,
then skip to the next step.
Otherwise, the Milter interface must be explicitly enabled
by adding lines like those in
to your sendmail/devtools/Site/site.config.m4 file or equivalent.
Then build sendmail as described in the INSTALL file distributed with sendmail.
You must build
libmilter separately by something like
cd libmilter sh ./Build
After sendmail has been rebuilt if necessary it will need to be restarted. That should be done after the next step after misc/dcc.m4 has been created by the ./configure script.
See the installation considerations in the DCC man page.
Most DCC files are in a "home directory" such as /var/dcc. DCC programs such as cdcc and dccproc are run by end users and should be installed in a directory such as /usr/local/bin. They must also be set-UID to the UID that can change the DCC data files. DCC programs that do not need to be run by end users are installed by default in the libexec subdirectory of the DCC home directory. See the table of ./configure script and makefile parameters. If necessary, set CFLAGS, LDFLAGS, LIBS or other environment variables listed in the table. Omit any parameters you don't really need to change and usually use only:
./configure make install
End users installing only dccproc
can install it in their private
~/bin directories and use private directories for their DCC
In this case, the DCC programs that would otherwise need to be set-UID
need not be.
To build dccproc for an individual user, use something like
./configure --disable-sys-inst --disable-dccm --homedir=$HOME/dccdir --bindir=$HOME/bin make install
The sendmail interface, dccm, must be built with the sendmail source and object tree. By default, the makefiles look for native sendmail libraries (e.g. on FreeBSD), an installed "package" (e.g. on FreeBSD), or a directory named sendmail parallel to the DCC source and object tree. Those who regularly build new versions of sendmail may find it convenient to make a symbolic link there to their current sendmail. Otherwise configure the dccm makefile with
./configure --with-sendmail=/some/where/sendmail make installIf dccm does not build because it cannot find libmilter, check that libmilter was compiled with sendmail in the previous step.
To connect the sendmail Milter interface to dccm,
copy or symbolically link misc/dcc.m4 to
your sendmail/cf/feature directory and
FEATURE(dcc) lines to your sendmail.mc configuration file.
It can be useful to modify sendmail.cf by using
Then rebuild and reinstall your sendmail.cf file, and restart sendmail.
Even if run anonymously, the /var/dcc/map file must contain the IP addresses of DCC servers. If your mail system handles fewer than 100,000 mail messages per day, the installation process generates a serviceable /var/dcc/map file from the included homedir/map.txt file. That file points to the public DCC servers.
If using remote DCC servers such as the public DCC servers, ensure that your firewalls allow outgoing packets to UDP port 6277 on distant systems and incoming responses from UDP port 6277. There is a description one firewall's configuration.
Your MX servers and mail submission clients should be listed in the main whiteclnt file with lines like:
mx ip 10.2.3.4 mx ip 10.5.6.0/28 mxdcc ip 10.5.6.0/28 ok ip 10.7.8.9 submit ip 192.168.1.0/24If those other systems also run DCC clients, use MXDCC instead of MX so that messages will not be reported twice to the DCC network and so have higher target counts, and appear to be unsolicited bulk mail.
Use OK for mail systems that you trust to never send or forward unsolicited bulk mail.
Untrusted SMTP clients such as end users with browsers used as MUAs (mail user agents) should be listed in the whiteclnt file with submit.
Sources of legitimate bulk mail must be recorded in whitelists. Example whiteclnt, whitelist, and common whitelists are among the sample configuration files in the homedir directory. The format of DCC whitelists is described in the DCC man page.
Put suitable values in the DCC configuration file, /var/dcc/dcc_conf for dccm or dccifd. The default client values are usually good for a start and often only DCCM_REJECT_AT needs to be changed when it is time to reject spam.
Optionally create per-user directories for logs and whitelists. See also the CGI scripts in /var/dcc/cgi-bin that allow users to maintain their private whitelists and monitor their individual logs of rejected mail.
It is best to use remote servers until the DCC client, dccm, dccifd, or dccproc, is stable. Then
On Linux or Solaris, consider adding -H to DBCLEAN_ARGS in /var/dcc/conf. See the dbclean man page.
Choose a secret password for your server-ID in your /var/dcc/ids file. This password is used to control your server with the cdcc program. Your server-ID must be unique and can be obtained by contacting Vernon Schryver at email@example.com by email or via a web form.
If you have more than one DCC server, ensure that there are common client-IDs with the same passwords in the /var/dcc/ids files on all of your servers You should define a DNS name like dcc.example.com with A and AAAA records for all of your DCC servers. Then configure your DCC clients to spread their load among your DCC servers with a command like
cdcc "dcc.example.com RTT-1000 ms 32768 secret"where 32768 and secret are the common client-ID and password found in /var/dcc/ids on all of your DCC servers.
Start the server with the system by installing /var/dcc/libexec/rcDCC or an equivalent. If it is used unchanged, rcDCC is best installed with a symbolic link to automate installing updates. The server can be started manually with
The script /var/dcc/libexec/cron-dccd must be used to run dbclean about once a day. An entry like misc/crontab can be put into the crontab file for the user that runs dccd. If you have more than one DCC server, stagger the times at which the cron job is run so that not all of your servers are simultaneously busy cleaning databases.
Install the shutdown script /var/dcc/libexec/rcDCC to shut down the DCC server as the operating system stops. If the DCC server fails to close the database cleanly, the database must be cleaned by the server with it starts. That takes time.
Flooding requires that every server participating in a network of DCC servers have a unique server-ID. Server-IDs can be obtained by contacting Vernon Schryver at firstname.lastname@example.org by email or via a web form.
After you have an official server-ID,
Flooded reports of bulk email contain timestamps that are used for several things including expiring old reports. To accurately detect stale incoming reports, a DCC server needs a clock that is not too inaccurate. For that reason it is good to run an NTP daemon on systems running DCC servers.
Larger sites can use more than one greylist server, with the greylist servers flooding data just like DCC servers.
To configure greylisting:
Client-IDs and matching passwords must be used by clients of greylist servers such as dccm and dccifd. The client-IDs must be in the /var/dcc/map file on the client system. Greylist client-IDs and server-IDs must be in the /var/dcc/ids file on the greylist server. When a system hosts both DCC and greylist servers, it is convenient for clients to use the same client-ID and password for both. It is also convenient for a greylist server and a DCC server on a system to share a common server-ID and password.
The vast majority of installations do not have local DCC servers and can use the greylist server-ID generated automatically in the /var/dcc/ids file.
If the cdcc "info" command does not show the correct greylist server, add it with something like
cdcc "add localhost greylist 32768 secret"The DCC makefile files add a greylist server at localhost or 127.0.0.1 to /var/dcc/map file created for a new DCC installation.
If absolutely necessary, override the greylist embargo, wait, and white values in GREY_DCCD_ARGS in /var/dcc/dcc_conf. Usually simply set GREY_CLIENT_ARGS=on
Sites with more than one greylist server should arrange to flood data among them by adding lines to /var/dcc/grey_flod files in the same format as /var/dcc/flod files. Flooding among greylist servers uses port 6276 by default, and so that port may need to be opened in firewalls.
Install a daily cron job like misc/crontab and /var/dcc/libexec/cron-dccd to clean the database.
Greylisting of local mail systems must be turned off because common mail user agents (MUAs) cannot handle temporary rejections. One way to turn off greylisting of local client is with submit lines in the main whiteclnt file as described above.
An alternative to whitelisting mail submission clients is available with dccm and sendmail by using the misc/hackmc -T script to modify sendmail.cf to trust SMTP clients authenticated with SMTP-TLS or SMTP-AUTH.
The DCC sendmail milter interface dccm should be started before sendmail. That often requires changing an /etc/rc script or configuration file. The script /var/dcc/libexec/rcDCC should be installed, best with a symbolic link. The milter daemon can be started manually with
The general MTA interface dccifd should usually be started before the mail transfer agent or MTA. It should be enabled by setting DCCIFD_ENABLE=on in /var/dcc/dcc_conf. It is also usually necessary to change an /etc/rc script or configuration file to start and stop the daemon with the system. The script /var/dcc/libexec/rcDCC should be installed, best with a symbolic link. The daemon can be started manually with
Dccifd can be used as a Postfix Before-Queue Content filter as described the dccifd documentation.
It is best to only mark mail with X-DCC SMTP headers before changing procmail or dccm to reject mail. Configure dccm with DCCM_LOG_AT in /var/dcc/dcc_conf to log bulk mail with somewhat lower counts.
Some additional mechanisms are available in the DCC client programs. They are often unnecessary when greylisting is used.
When possible, it is almost always better to use dccifd than dccproc. This is certainly true with SpamAssassin. When using SpamAssassin, ensure that the SpamAssassin plugin DCC.pm is up to date. The DCC source includes a copy in the misc directory. Please consider setting dcc_learn_score to report spam to other SpamAssassin with DCC users.
New versions released at the usual place can be installed by running the /var/dcc/libexec/updatedcc script. That script is (re)built by the ./configure script and runs ./configure with parameters and environment variables from the previous installation.
Most of the DCC can be removed by running /var/dcc/libexec/uninstalldcc script. Some logs and configuration files with locally chosen parameters in the home directory are not deleted. Manual changes such as links to /var/dcc/libexec/rcDCC or the installation of the cron job, /var/dcc/libexec/cron-dccd, are not reversed.
There are several installation configuration parameters that can set to suit individual preferences and systems.
|./configure option||env name or |
|used by||default value||use|
|--homedir=HOMEDIR||./configure||/var/dcc/||DCC home directory with most DCC files|
|--bindir=DIR||./configure||/usr/local/bin||directory for DCC user commands including cdcc and dccproc3|
|--libexecdir=DIR||./configure||--homedir/libexec||directory containing most DCC programs|
|--mandir=DIR|| ||./configure||/usr/local/man||directory for man pages3|
|NOMAN1||make||unset||do not install man pages when set3|
|--with-installroot=DIR||./configure||unset||prefix all directory paths to build a binary tarball|
|--with-configsuffix=str||./configure||unset||append str to generated configuration file names|
|--with-uid=UID||./configure||root||user name and set-UID for DCC programs and data|
|DCC_OWN1||make||bin, daemon on OS X, or current||owner or UID of most installed files3|
|DCC_GRP1||make||bin, daemon on OS X, or current||group of most installed files3|
|DCC_MODE1||make||555||mode of most installed programs|
|MANOWN1||make||DCC_OWN or current||owner or UID of installed man pages3|
|MANGRP1||make||DCC_GRP or current||group of installed man pages3|
|--disable-sys-inst||./configure||enabled||disable system installation or chmod, chgrp, and set-UID3|
|--disable-server||./configure||build but do not start||do not build server including dbclean and dccd|
|--disable-dccifd||./configure||build but do not start||do not build program interface|
|--disable-dccm||./configure||build but do not start||do not build sendmail interface|
|--with-sendmail=DIR||./configure||../sendmail or /usr/ports/mail/...||directory containing sendmail milter header files|
|--with-cgi-bin=DIR||./configure||--homedir/cgi-bin||directory for DCC whitelist CGI scripts|
|--with-rundir=DIR||./configure||/var/run/dcc||"run" directory for PIDs and sockets|
|CFLAGS1||make & ./configure||compiler options such as -g or -O2|
|PTHREAD_CFLAGS2||./configure||depends on target||compiler options for compiling dccm and dccifd with pthreads|
|LDFLAGS1||make & ./configure||global linker options|
|PTHREAD_LDFLAGS2||./configure||depends on target||linker options for dccm and dccifd|
|LIBS2||./configure||additional libraries linked with all programs|
|PTHREAD_LIBS2||./configure||depends on target||libraries for dccm and dccifd|
|CC||make & ./configure||cc||C compiler such as "gcc" or "/opt/SUNWspro/SC6.1/bin/cc"|
|DCCD_MAX_FLOODS1||make||32||maximum DCC server flooding peers|
|--with-db-memory=MB||./configure||64||minimum server database buffer size between 32 MBytes and 49152 MBytes|
|--with-max-db-mem=MB||./configure||1920 on 32-bit systems
49152 on 64-bit systems
|maximum server database buffer size|
|--with-max-log-size=KB||./configure||32||maximum dccproc, dccifd, and dccm log file size in KBytes; 0=no limit|
|--disable-IPv6||./configure||enabled; use IPV6 if available||turn off IPv6 support even if available|
|--with-socks[=lib]||./configure||none||location of SOCKS client library|
|--enable-64-bits||./configure||depends on operating system and hardware||enable 64-bits on Solaris and Linux PowerPC|
|--with-make-cmd=pgm||./configure||make or gmake||path to make command|
|--with-DCC-MD5||./configure||local library if available||use MD5 code in DCC source instead of any local library|
|--with-kludge=FILE||./configure||none||include header FILE, best with an absolute path|
|--with-fetch-cmd=pgm||./configure||wget, fetch, curl, or ftp||program used by /var/dcc/libexec/updatedcc, and other utilities to fetch files|
|--with-fetch-cmd-addr=ip||./configure||none||local IP address used by wget, fetch, or curl while fetching files|
|--enable-lang-Dutch||./configure||disabled||enable Dutch dictionary in checksums|
DCC is thought to work on several systems including:
On 64-bit PowerPC systems with more than 4 GBytes, use ./configure --with-64-bits to build a DCC server that can benefit from a full sized database. A 64-bit sendmail milter library will be needed if dccm is used
While building the sendmail milter library, consider using _FFR_USE_POLL to avoid problems with large file descriptors and select().
On 64-bit systems with more than 4 GBytes, use ./configure --with-64-bits to build a DCC server that can benefit from a full sized database. A 64-bit sendmail milter library will be needed if dccm is used
Those system names include trademarks. Please don't abuse them.
Much of the DCC list of frequently asked questions concerns troubleshooting DCC installations. Many of the messages in the archive of the DCC mailing list are also troubleshooting questions and answers.
Dccm and sendmail can be configured to report the checksums of unsolicited bulk mail so that other DCC clients can reject later copies of the same unsolicited bulk mail sent from other sources. Such mechanisms are commonly called spam traps.
Entries in a sendmail access_db can also be rejected or discarded while they are reported to the DCC server by dccm. The script misc/hackmc modifies the output of sendmail .mc files to tell dccm about some undesirable mail. The script accepts one or more .mc files and generates the corresponding slightly modified .cf files. If the access_db entry starts with the string "DCC:", the message is reported by dccm to the DCC server as extremely bulky. Otherwise the message is rejected as usual. The remainder of the the access_db entry after "DCC:" consists of the optional string "DISCARD" followed by an optional SMTP status message. If the string "DISCARD" is present, the message is discarded instead of rejected. This is important to keep senders of unsolicited bulk mail from discovering and removing "spam trap" addresses from their target lists.
For example, a line like the following in an access_db can discard all mail from example.com while reporting it to the DCC server as extremely bulky. Note the quotes (").
example.com DCC: "DISCARD spam"
Spam traps can be configured with option spam-trap-discard and option spam-trap-accept lines in whiteclnt files.
Mail from a spam trap address can be sent to dccproc as described in the dccproc man page
The DCC client and server programs can be built to use the SOCKS protocol. The --with-socks ./configure parameter configures the DCC client library and the DCC server to use common SOCKS network library functions. If the SOCKS library is in a standard place, something like --with-socks=socks should be sufficient. Setting the environment variable DCC_LDFLAGS to something like -L/usr/local/lib is sometimes helpful. Otherwise, using --with-socks without specifying the library name and setting LIBS to the full pathname of the library might work.
DCC client programs including dccproc and dccm that use the DCC client library must be told to use the SOCKS5 protocol with the SOCKS on operation of cdcc. SOCKS5 is required instead of SOCKS4 because DCC clients communicate with DCC servers using UDP.
DCC servers can use SOCKS4 or SOCKS5 when exchanging floods of reports of checksums. Links between individual pairs of peers are configured with the passive and SOCKS flags in the flod file described in the dccd man page. In both cases, the SOCKS library code must be configured, often in the files /etc/socks.conf and /etc/socksd.conf.
When the DCC software is built with SOCKS, IPv6 name resolution is turned off.
The DCC server and client programs have been tested with the DANTE library and server. The DANTE SOCKS implementation is also one of the FreeBSD "ports" or packages.
Note that if a connection fails repeatedly, Dante will disable the rule that failed and will eventually try the underlying connect() call. This fails in almost every SOCKS environment because there is no available route for an ordinary connect(). Dante by default won't re-enable the failing rule. To fix this, change BADROUTE_EXPIRE from the default of 0*60 to 5 in include/config.h in the Dante source and recompile.
This document describes DCC version 1.3.154.