If we had a good way to send and receive money through the Internet then it might make sense to charge a fee to accept an incoming email. One would have a whitelist of senders who get automatic refunds. Everyone else will be spending realmoney to send you email.
I think that you might be on to something with the fee in the sense that you could apply a solicitation surcharge to unapproved senders. It would only work if it was guaranteed to get your response, otherwise it's not worth it.
What about a separate email address (or even domain) for premium email? You could set the fee to receive an email (and adjust it to restrict flow to what you can handle), and refund people who don't get a response from you within x period of time. Certain senders could be excluded from paying. The senders could even choose how much to pay (These emails were sent without payment. Those were.)
You then publish only that address on your site/blog/whatever, and give your personal address to friends and family.
This idea needs a lot of digging into to really see if it's viable but I like the concept. The potential downside is that the government might like the idea of email tax.
A tiny "postage" fee might also solve spam.