Help with procmail spam filtering

[scott at ehrlichtronics.com (Scott Ehrlich)]

I am trying to set up some more procmail recipies, this time to handle
spam filtering.   I've scoured the web and received some great insights,
but nothing yet specific to my needs, presenting in a way I can
confidentally understand.

What I'm looking to filter out (at least start with):

- Return-Path and/or From: field are from forged usernames of my domain

- Return-Path and/or From: field differ from sending host in Received
lines (there could be some cases of legit mail, and I'll handle those
cases later)

- Received line does not have a valid reverse dns (though there are a few
lists I'm on that show 'unknown' for the reverse that are valid)


Thanks for any help.   I'll keep lookin'

Scott