Re: Penny mail
Charging money for sending emails is not viable for various reasons. However, the concept of charging *processing time* is a good one, because it wastes spammers time. See "Hash Cash" for the principle involved.
Tarpitting and Greylisting are available techniques for slowing down, or forcing a spammer to repeat their submission respectively, but I've found that many mail servers are configured not to tolerate these techniques. Cloud email used by legitimate senders in particular thwarts greylisting because each time an email is resent from a cloud service it likely comes from a different IP address to the previous message which means that the recipient mail server thinks it is from a different source.
Biting the hand that feeds IT
