Hooray! As soon as I find the time to delve into the technical details, I’ll be publishing SPF DNS records for all my domains. If this idea catches on, there will be no more Joe-Jobs. Messages whose ‘From’ address is a particular domain will only be accepted when they originated from a machine that is specifically designated as a sender for that domain.
I encourage other webmasters to look into this, here:
http://spf.pobox.com/
This is a very good thing.