DCC and SpamAssassin

Vernon Schryver vjs@rhyolite.com
Thu Nov 10 02:07:52 UTC 2011

For the last 18 months, the DCC source has included a new version of
the SpamAssassin DCC plugin.  As far as I know, it is completely upward
compatible.  Besides a general clean up of the Perl source and a bunch
of changes that should make DCC.pm faster and more robust, it includes
a mechanism that reports message detected as spam by SpamAssassin to DCC
with target counts of 'many'.

Two or three months ago a DCC installation started using that mechanism
on its incoming 750K messages/day.  The effect is to increase DCC
target counts for messages considered spam by SpamAssassin to 'many'.
That should have little effect on DCC installations that set DCC
thresholds to values below 1000.  750K messages/day is too few to
support certain conclusions, but judging from the DCC server graphs,
it has noticable effects on the majority of other DCC installatios
that use the DCC.pm default synonym of 9999999 for 'many'.

That increased target count of 'many' can not only help other DCC
installations, but also sites using the mechanism with the default
DCC.pm threshold of 999999.  For example, a message from an SMTP
client (mail sender) at an IP address in a DNS blacklist (DNSBLs)
can get a DCC target count of 'many'.  A later copy received via
an address not in a DNSBL can trigger a SpamAssassin+DCC rule.

To try the mechanism, make a copy of your current DCC.pm file and
install the DCC.pm file in your SpamAssassin installation from the
misc directory of your DCC build/installation tree.  (I would use
a symbolic link.)  If you have used /var/dcc/libexec/updatedcc,
look in /var/dcc/build/dcc/misc/DCC.pm
At worst, check the current DCC source tree at

Then set the DCC.pm parameter dcc_learn_score to whatever you use
for the global SpamAssassin threshold or perhaps a little more.
Depending on your SpamAssassin installation, you might then need
to restart an SA deamon.

Vernon Schryver    vjs@rhyolite.com

More information about the DCC mailing list

Contact vjs@rhyolite.com by mail or use the form.