Abstract: In a method for authenticating an electronic message to thereby blocking unsolicited messages (“SPAM”), a first server generates a unique message identifier and an associated validation record upon authenticating a sender as one from whom a given recipient has agreed to receive electronic messages. The message identifier is included in the message, as sent to the recipient. The recipient retrieves the message identifier from the message and thereafter requests validation of the message identifier from either the first server, or a second server receiving the validation record and at least a recipient identifier associated with the recipient from the first server. After authenticating the recipient, the first or second server validates the message identifier by checking for the existence of the validation record, and returns an indication of message validation. The message is then accepted or rejected and, perhaps, routed to a folder for subsequent processing, based on the indication.