When you go through the trouble of reinventing email to provide proper security, you should also solve the spam problem as part of the protocol.
It would be great if the recipient could specify the amount of proof of work required for example. Or ask for a certain amount of bitcoin in exchange for accepting promotional material. Or a mail attribute that indicates it's a newsletter. Lots of interesting possibilities.
> you should also solve the spam problem as part of the protocol.
I disagree. Different problems sometimes require mutually exclusive solutions.
In fact, receiving lots of unsolicited mail provides some plausible deniability. So a spam free-for-all might actually be a useful part of the new network.
Or you know, renders the system completely worthless because no one can sort through that much spam.
Which also makes it completely trivial to DDoS into oblivion. And the problem gets worse then that: the more anonymous it is, the less it's possible to stop someone from spamming.
Though I suppose you could attack this problem from the email address side: make it computationally expensive to general an email address, to make address-hopping as a spammer more difficult.
Maybe a new system could instigate whitelisting from the ground up, with a built in "contact request" protocol (which may be required anyway to exchange keys).
We've got very used to email's totally open mailboxes, and it seems to me that the cost may well outweigh the benefit.
