After I heard about greylisting, I quickly setup a libmilter implementation for Sendmail on TrekWeb. So far it’s working quite well. The volume of spam I receive has dropped by over 90%. Any spam that gets through must then contend with dspam. I am already running seven different DNS blacklists, but apparently that just wasn’t enough.
sendmail.mc: dnl # DNSBLs -- Seems like an okay place to put these FEATURE(`dnsbl',`dul.dnsbl.sorbs.net')dnl FEATURE(`dnsbl',`sbl-xbl.spamhaus.org')dnl FEATURE(`dnsbl',`list.dsbl.org')dnl FEATURE(`dnsbl',`dynablock.njabl.org')dnl FEATURE(`dnsbl',`dnsbl.njabl.org')dnl FEATURE(`dnsbl',`relays.ordb.org')dnl dnl # I disabled spamcop as it gets many false positives! FEATURE(`dnsbl',`bl.spamcop.net')dnl
Update, April 11th, 2006. Since the beginning of the year, I have found greylisting to have become increasingly ineffective. It still reduces spam fairly effectively, but it’s completely ineffective against a large number of fishing scams, which tend to be sent by actual SMTP implementations and not botnets. Sigh.