<p><pre><code> U.S. Patent No.7,406,501
System and method for instant messaging using an e-mail
protocol
Abstract
Systems and methods allowing an instant messaging user to exchange messages with an e-mail user.
To the instant messaging user, the experience is a seamless exchange of instant messages; to the
e-mail user, the experience is a seamless exchange of e-mail messages. Conversion of an instant
message to an e-mail message includes insertion of a token into the e-mail message, and conversion
of an e-mail message to an instant message includes validating a token extracted from the e-mail
message.
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It looks like GMail is also infringing that patent.