There was also a push in the 90s to make a kind of "postage stamp" where the cost of sending an email was CPU, which would have had the same effect of prohibiti

There was also a push in the 90s to make a kind of "postage stamp" where the cost of sending an email was CPU, which would have had the same effect of prohibiting spam by making email too expensive to spam with. ISTR the guy who came up with that idea (or one of the guys) has had an interesting series of projects since. Can't remember much beyond that, though.