A method is provided for preventing the delivery of unwanted electronic mail messages to a destination client. An original electronic mail message is first received from a source client at a destination server. Next, a reply electronic mail message is sent from the destination server to the source client requesting the source client to complete a registration process to register the source client's electronic mail address with the destination server. The original electronic mail message is only sent from the destination server to the destination client when the source client properly registers the source client's electronic mail address.