procmail: http://www.procmail.org/
mini faq: http://www.iki.fi/era/procmail/mini-faq.html
pm-tips: http://www.procmail.org/jari/pm-tips.html
quick start: http://www.ii.com/internet/robots/procmail/qs/
proctips: http://www.uwasa.fi/~ts/info/proctips.html