A system and method for determining whether an e-mail originates from a sender authorized by an address provider to send the e-mail to an intended recipient's e-mail address. The e-mail identifies an address provider from which the intended recipient's e-mail address was obtained. The e-mail is delivered...http://www.google.de/patents/US8126971?utm_source=gb-gplus-sharePatent US8126971 - E-mail authentication
