Sender Email Address Verification Using Reachback

"Reachback" provides a unique new approach to the spam suppression problem. Unlike competing approaches, reachback uses existing email distribution systems but does not use DNS. It is robust against in-transit modifications to the standard From headers and mail forwarding, and can identify email sources down to the granularity of individual users. Reachback has the option to use single secret keys and public/private key pairs. It can be deployed site wide and can be incrementally deployed by individual users to add immediate value through automated white listing.

According to the technology of this patent application, information is added to each email message to provide access to a source of validation information that produces evidence (which cannot be forged) of the true source of the email address.  This new method (and associated infrastructure) is referred to as "Reachback".  A Reachback system computes validation information about each sent email message and the original message is augmented with a special "Reachback" header that includes a URL identifying a Reachback server. The Reachback server publishes the validation information that verifies the email message and that specifically verifies the identity of the true sender of the email message.  The combination of the Reachback server, its internet IP address, and the validation information allows a recipient of the email message to reliably infer a connection from the email to the Reachback URL, then to the Reachback sever, and finally to the email sender. 

Implementing Reachback requires the use of three components in addition to the normal email transfer architecture. These components are (1) an HTTP server (which typically already exists within email architecture servers), (2) a sender-side proxy that inserts the Reachback URL into the email message, and (3) a receiver side validator that validates the email message and the identity of its sender. Positioning of the proxy and the validator within the email architecture is flexible, as described in the patent application. 

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