A nice idea, but how exactly does it work? Who collects the charges? If your answer is, "your ISP collects the charges when you send mail" ok, so if I email you, then you assume that my ISP charged me for it?? So all I have to do is find an ISP in russia that will wave the charges in exchage for a flat fee. Well guess what, the spammers are already in russia! If your answer is, "the ISP that recieved the mail will collect the charges" then I can't wait to hear the protocol you've come up with that Ketchikan University in BFE alaska is going to use to charge joe_shmoe@taiwan.com. Is the payment made in dollars?

Also keep in mind (from the linked article) most emails are sent from botnets. What that means is, your computer gets hacked and the spammers use your computer to send the spam. So I'd like to see how your system stops spammers from hacking your computer or your grandma's computer and running up charges that you and your grandma have to pay.

It really is a difficult problem guys. I was talking to a coworker yesterday about my idea (posted above) and he shot a bunch of holes in it. For starters, under my system the spammers would DOS people by claiming that they had sent spam, thus reducing the level of trust in the whole system.

It's a seriously difficult problem.