Your scheme would keep the email out of the mailbox and out of the client -- I like it. But it still generates traffic to my network.
Well, it springs from an idea that works for me (as a user) without being particularly good for the network. As I currently implement it, using different email addresses, the spam I'm avoiding ends up sitting on my ISP's mail server waiting to bounce. I was thinking that widespread use of keys would eventually act as a deterrent to spam - knowing that email to even a valid "public" key is going to be filtered through an extremely selective spam filter ought to discourage people. On further consideration, this may be a little naive of me.
Andrew. -- Andrew Shore.