Postfix web site -- http://www.postfix.org

amavisd-new web site -- http://www.ijs.si/software/amavisd/

AMaViS web site -- http://www.amavis.org/

amavis-user mailing list -- http://sourceforge.net/mail/?group_id=6006

Paul Graham's "A Plan for Spam", the paper which introduced Bayesian classification for spam -- http://www.paulgraham.com/spam.html

Microsoft Knowledge Base article listing dangerous file extentions -- http://support.microsoft.com/default.aspx?scid=kb;EN-US;q262631

Naked Ape Consulting's Mail Defender -- http://nakedape.cc/r/mdsam

Sophie web site -- http://www.vanja.com/tools/sophie/

Sophos Anti-Virus web site -- http://www.sophos.com

SpamAssassin web site -- http://spamassassin.apache.org