I think that a secure email infrastructure is a good thing to have, in and of itself. By secure, I mean one in which messages get to their destination reliably, i.e. not lost in some spam filter, and one in which a recipient can reliably know where the message came from if they feel the need to track down the sender by other means.
And how is it that OpenPGP and S/MIME do not meet this criteria? Why is it that we also need to break the transport layer to facilitate what you describe above?
a protocol change. Forcing people to relay all email through their ISP's mail system is an operational change.
Forcing people to relay all email through their ISP's mail system is a wet dream of anti-free-speech governments, too. Why should I have to provide non-encrypted information about my email to my ISP just to get it to my friend's mail server? Why on earth do you think that is a legitimate operational change? Having to route telephone calls through the telephone company is an unfortunate fact of infrastructure which we don't currently have with Email. CALEA is a clear demonstration of why this is not necessarily a good thing. Why would you ever want to consider relegating email to these same restrictions?
In a sense, I am suggesting a similar reallocation of resources. Rather than put those resources into filtering spam, I'd suggest that we will get a better result by shifting the resources into mail relaying and managing mail peering agreements. The spam will continue but users will move to using the secure mail architecture and won't see most of it. When the spammers also shift, there will be more tools to track them down or shut them down or simply to rate limit them.
The problem is that currently, most ISPs don't relay mail for other ISPs. Currently, you look up the MX and send to the end-system. What you are proposing, in order to preserve existing mail connectivity under your new system, would require EVERY ISP on the planet to MAIL PEER directly with every other ISP on the planet, OR, a new mail routing protocol with ISPs providing MAIL RELAY for every transit customer. UG-LY!! Owen -- If it wasn't crypto-signed, it probably didn't come from me.