Methods of preventing spam email in an email system include determining whether a sender of email to a receiver of email has paid a required setup price or cost to become a registered sender of email to the receiver. If it is determined that the sender has not paid the required setup cost, then the receiver can reject the sender's email to thereby eliminate the receipt of unwanted spam messages. In order to qualify as a registered sender, the sender undergoes a qualification scheme wherein it pays the required cost, which may be for example monetary or computationally related, and is assigned an encrypted key by the receiver which allows the sender to send to the receiver email authenticated using the unique key associated with the sender and receiver. The receiver has the option of accepting or rejecting email from a sender in this fashion and can change the required setup cost or requirement at any time to ensure that the sender does not try to corrupt the email system once registered.