Onlamp.com has a hot-to article focused on using Procmail on FreeBSD. "Two of the programs mentioned at this site are spam bouncer and junkfilter, both of which are in
the FreeBSD ports collection. This makes their installation painless. You'll find, though, it will take some trial
and error on your part to tweak any spam filter to suit your needs. Also, no spam filter can be 100% accurate,
as there will always be legitimate users that have email accounts with blocked domains and spammers are
always trying to find new ways to bypass spam filters."
January 14, 2002