An updated internet-draft is available from the IETF. This draft is a work item of the Authentication, Authorization and Accounting Working Group of the IETF.
Abstract: «Increased diversity and abuse of access, across the open Internet, mandates additional accountability for sending SMTP clients, in the absence of prior, direct arrangement with receiving SMTP servers. One means for enabling this is by registration with third-party services that vouch for the policies and accountability of SMTP clients accessing SMTP servers. This specification defines a means for an SMTP client to list third-party services that are prepared to vouch for it, and a means for an SMTP server, or its intermediary, to query vouching services.»