#1 Verify From: header accurately

[Mike DeGraw-Bertsch]

One of the most commonly-faked lines--and hardest to
verify--in spam is the From: header. spamNX needs to
reliably verify the From: header of all external email.

VRFYing addresses, and potentially caching the results
in a database, is an attractive but likely unworkable
solution, as not all servers allow VRFY, and other
problems.

Simple heuristics should be employed when checking the
address--looking for fake internal address, all number
addresses from Juno, ...