[Kwpolska]

The problem with e-mail, and with other forms of communication, is that two parties (or their service providers) need to co-operate. You can run your own e-mail server just fine, but Google, Microsoft and friends might consider you to be a spammer or silently block your e-mail just because.

[indigochill]

What if email was based on a whitelist instead of a blacklist? So you'd only receive email from addresses of people you've already established contact with some other way (maybe using conventional email)? This eliminates spam and if the big providers supported this, it could also enable them to stop blackholing innocent servers (though whether they care is another question).