The present invention provides a method and system for preventing unsolicited bulk email (UBE). Spammers sending UBE typically capitalize on the weakness of SMTP. The present invention affixes a subscriber key value to the local part of an email address. The email and associated key value are sent to a server where the subscriber key value, and subscriber and recipient email addresses are associated and stored into a database. Once stored, the email is sent to the ultimate recipient. A recipient is in possession of a subscriber key value can use this key value to sign an email they intend to send to the original subscriber/sender. Recipient will then send this signed email to a server where the association between the subscriber and the subscriber key value is verified. Once verified the email is sent to the subscriber. In some embodiments, the verification process is not controlled by a server.