QUOTE
Abstract
A practical method for authenticating all incoming email is described. Existing SPF records authenticate some email but the requirement of domain administrators to perfectly maintain their SPF records profoundly limits the utility of SPF. A rapidly compiled and near comprehensive Receiver Generated SPF database will ensure almost universal email authentication. This is achieved by bouncing difficult to classify email along with a request to simply resend the bounce. The domain and sending MTA from the now authenticated resent email will be entered into a single shared Receiver Generated SPF database. All future non-forwarded email from this domain sent via this server will be authenticated after consulting this database.
http://spamfizzle.com/default.aspx/.
