http://www.rfc-editor.org/rfc/rfc7601.txt
RFC 7601: Message Header Field for Indicating Message Authentication Status, M. Kucherawy2015-08-01T23:00:00-00:00This document specifies a message header field called Authentication- Results for use with electronic mail messages to indicate the results of message authentication efforts. Any receiver-side software, such as mail filters or Mail User Agents (MUAs), can use this header field to relay that information in a convenient and meaningful way to users or to make sorting and filtering decisions.