Public key encryption has solved this via signing. What needs to happen is collective marketing to promote some kind of "email 2.0" that requires public keys wi

Public key encryption has solved this via signing. What needs to happen is collective marketing to promote some kind of "email 2.0" that requires public keys with the option to tie them to social media (perhaps the government, but they have a bad track record with technology) . That protocol would return a message saying "your email was not delivered because you didn't sign it with a public key". Others suggest computational tokens as well to prevent mass spam. This might work too. Instead of "trusted" email addresses being passive on the receiver, trusted would mean "don't send a difficult auth token to the sender". Whereas if someone I've never communicated with before emails me, send them a computation that requires the server to do 30 seconds or more of work. Every subsequent message would have an easier token unless I flagged it as spam. Again, if the sender doesnt do the work, they get a "message rejected" failure. No I don't think the blockchain would help here. It might be nice to upload your public key to it, and have a public "reputation score" about accusations of spam for each key, but keys need to be replaceable in the event of compromise and an attacker could replace someone's blockchain profile and there would be nothing anyone could do.