If encrypted & signed mail becomes common enough, then I suspect the spam problem goes away. I suspect spammers won't want to sign their mail, and if they do, i

If encrypted & signed mail becomes common enough, then I suspect the spam problem goes away. I suspect spammers won't want to sign their mail, and if they do, it would be trivial to distrust new public keys and maintain a global blacklist of bad established ones. Then almost all encrypted mail can be simply trusted, and spam filtering only has to pick out the occasional real message from the unencrypted dross.