amavisd-new: www.ijs.si/software/amavisd
Maia Mailguard: www.renaissoft.com/maia
SpamAssassin: www.spamassassin.org
Clam Antivirus: www.clamav.net
Vipul's Razor: razor.sourceforge.net
Pyzor: pyzor.sourceforge.net
The Distributed Checksum Clearinghouse: www.rhyolite.com/anti-spam/dcc
Sender Policy Framework: spf.pobox.com
