[leccine]

How about a PKI system were one or more authorities can sign keys and the email server admins can approve public keys based on its combined score coming from the authorities. Authorities could be universities, engineering organizations and other non-profit entities.

[mpyne]

So now people have to register identities and can't use anonymous email addresses. And it wouldn't fix the issue anyways since spammers would just use botnets of legit sender addresses.

[leccine]

You are mixing up registration with registration with real data. You could still register an email address with arbitrary details and after a while you could establish a score that would grant your non-spam status. What you are confused with is that in this system there is no disposable email address. That is actually a valid concern but I don't use those so i really don't care.