UPDATED – Security White Paper 2017-001_v1_2 – DMARC — Defeating E-Mail Abuse Wednesday, January 11, 2017 10:13:00 AM CET DMARC is a mechanism to define a coherent e-mail policy that can effectively be used by both the sender and the receiver of the e-mail messages. The senders can list the authentication mechanisms they have put in place, and the receivers are informed what the sender suggests them to do, if the authentication fails on any message thatclaims to originate from them.