http://www.rfc-editor.org/rfc/rfc6577.txt
RFC 6577: Authentication-Results Registration Update for Sender Policy Framework (SPF) Results, M. Kucherawy2012-03-01T23:00:00-00:00This memo updates the registry of authentication method results in Authentication-Results: message header fields, correcting a discontinuity between the original registry creation and the Sender Policy Framework (SPF) specification. [STANDARDS-TRACK]