This is spamcan, a very powerful anti-spam patch to sendmail.  You can
just get the patch or get the gzip'd tar.  The patch has everything
you need.  I estimate it catches at least 90 percent of the spam sent
to the company I work for.  I've tried the check_mail and check_relay
stuff with 2000 known-spammer ip ranges and domains with domain
validation turned on; it catches nothing compared to regular
expression matching used in spamcan.

Based on user-feedback, a future version of spamcan will impliment
a scoring system.  I anticipate this will help quite a bit.

spamcan-0.96 is released to support sendmail version 8.8.8.

The documentation can be found at http://ftp.kernel.org/pub/software/admin/spamcan

-tim