I'm split on the issue.
The majority of the email traffic currently out there is spam.
a "pay per email" system would cut down on the network load side of spam.
On the other hand, there's the question of implementation. For it to work, every internet provider in the world has to subscribe to it.
Then there's the question of who gets the money. Certainly not Bill Gates.
Also, what do we do to prevent spammers from following DDOS hackers and using (thanks to Bill Gates and crew) trojan horses and worms (as they've already started doing) to set up mail servers on innocent third parties and sending uncommanded emails. Even at 1 cent/email, if someone sets up a spamserver zombie, folks could be getting $60,000 email bills. The spam remains; the problem complicates itself.
There's also the worrisome problem that once we start charging, some MBA is gonna figure out that, original problem be damned, we've got a revenue source here. Why not make it $1/email?