History Of Filtering


procmail - traditional UNIX mail filter

Identify spam senders and delete on sight; later, match patterns in "disguised" spam messages, especially in the headers

Very hard to configure, for most people

DNS Blacklists: Paul Vixie's MAPS RBL

Identify spam sources by IP, and route them down the plughole

Third parties set up new DNS blacklists later

Not quite so reliable anymore; many false positives