I.e. something that works very well, doesn't require user intervention, that kills spam before being downloaded to the client, and is easy to setup on almost any OS or any POP or IMAP server.
In other words, something like SpamAssasin on the server but something that's so trivial to setup that users don't have to think about it.
Perhaps there will be such an uprising by users that ISPs will be forced to implement something like SA on their servers.
E-mail is going to become unusable for most people unless something changes so that spam and viruses and trojans and worms aren't so much of a problem. My wife almost never uses her e-mail, but she got 46+ copies of the latest Win worm on her account yesterday. (She uses MacOS 8.6 so Spam Assassin isn't an option.) Either some sort of trust mechanism is going to have to be made trivial for users or something like SA on servers is going to have to become ubiquitous or e-mail is going to become unusable. It's also affecting the whole internet infrastructure, so something needs to be done.
Some institution like CERT or W3C or similar should be working on solving this spam/worm/virus/trojan problem, I think.
Cheers,
Scott.