Joel on Software: One-cent email.

"Here's what I'd like to see: a system that delivers an email for one cent. Nobody has to use it, but if you want to get your messages through, you pay one cent and the system delivers it for you. Every spam filtering system on earth can safely whitelist all email that comes from the one cent server, because no spammer can afford the penny times the 19 million messages they send. I would use it for all my email. You could even give 3/4s of a cent to the recipient as a credit to use for sending their own mail, keeping the 1/4 cent to pay for the servers."