Here is the patent reference.
Method and system for filtering electronic messages
Abstract
The present invention provides a system and method for filtering
unsolicited electronic commercial messages. A system and method
according to the present invention for screening out unsolicited
commercial messages comprises the steps of receiving a message from a
sender, sending a challenge back to the sender, receiving a response to
the challenge, and determining if the response is a proper response.
Inventors: Cobb; Christopher Alan (500 Beale St. Apt.120, San
Francisco, CA 94105) Appl. No.: 921950 Filed: August 26, 1997
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/search-adv.htm&r=4&f=G&l=50&d=PTXT&p=1&p=1&S1=6,199,102&OS=+6,199,102&RS=6,199,102
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