What I an currently doing to deal with friends' addresses being forged is very simple, easy to implement and over the last year or so has never been fooled. I create a filter for each friend's address when they initially have a spoofing problem and then remove them from the easily fooled friends list.
The filter is dead simple, I just copy the friends From: line from one of their headers into the filter so that not only is the address checked but the user identification they have entered into their mail client is checked. For friends that send mail from a few different programs or places I may have to enter each on its own line.
My From line data looks like this: "Stanley P. Miller"
Firetrust could add the full line checking to the existing tool with very little programming effort.
