alt Hacker NewsIf snail mail cost $0.001 per recipient people would be getting much, much more junkmail. Likewise, if e-mail cost as much as even bulk snail mail, there'd be much less spam.
Some sort of payment scheme is really the best, most durable option. The problem of mailing-lists and personal correspondence could be solved by an exclusion mechanism where the recipient effectively whitelists senders, explicitly or implicitly (e.g. whitelist a replying-sender automatically if a recipient initiates a conversation).
The problem with a payment scheme is that spammers (who make money by spamming) will happily pay as a cost of doing business (or negotiate discounts/deals), but Joe User might just look at the cost and say, "you know what, maybe I'll send this as SMS instead of E-mail."
So the end result will be more spam and fewer legit E-mails.