Google said it will move gmail.com to a policy of rejecting any messages that don t pass the authentication checks spelled out in the DMARC specification. The move complements similar initiatives from Yahoo and AOL; Yahoo is expected to move its mail services to DMARC on Nov. 2. The premise behind DMARC is that checks email against both the Domain Keys Identified Mail (DKIM) and Sender Policy Framework (SPF) validation systems. If a message satisfies these checks it is sent through to the recipient, otherwise it s quarantined.
Source: https://threatpost.com/google-moving-gmail-to-strict-dmarc-implementation/115125/