Abstract: Effective aspects of stamping outbound e-mail are combined with a registration system for e-mail senders. A mail sender participates by registering From: line information with a trusted third-party repository known as a stamp authority. When the sender sends an e-mail message, a hash of the From: line is compared against the From: line information for the sender stored in the repository. If the result is a match, the e-mail is allowed to be sent, subject to any other restrictions imposed by the stamping process. If there is not a match, then the e-mail is prevented from being stamped.