Patent ID: RE41411

Claim:
A method for filtering electronic messages, the method comprising: receiving an electronic message from a sender, the electronic message including an address field containing a sender's address; comparing the sender's address to a list of accepted senders; applying a heuristic to the sender's address to determine if the sender's address is formatted according to a message standard of a messaging medium of transmission through which the electronic message is received in order to make a determination of whether the sender's address is valid or invalid; analyzing the electronic message to determine whether the electronic message includes a first token that indicates that the electronic message is a reply to a first challenge message; and sending a prompt second challenge message back to the sender if the sender's address is valid and if the sender's address is not contained in the list of accepted senders and if the electronic message does not include the first token , wherein the second challenge message includes a prompt is designed to be answered by a person and not a machine and wherein the second challenge message further includes a second token .