Abstract: A method and system for filtering spam is disclosed. The present invention is directed at filtering spam. Generally, whenever a message is first received from an unapproved sender, a confirmation request email is sent to the sender's email address requesting the sender to confirm its existence and identity. Spammers typically don't receive, and can't handle reply emails. Therefore, until the unapproved sender replies to the confirmation request email, electronic messages received by the unapproved sender are treated as spam. An inclusion list of senders is maintained by the spam filter that includes a list of approved senders. Electronic messages from approved senders are not treated as spam, and are immediately delivered to the user. Generally, a database of valid source addresses for a user is maintained either on the user's computing device or on a mail server, depending upon the specific application.