DMARC which stands for Domain-based Message Authentication, Reporting, and Conformance is an email security protocol. When enabled, your email domain is protected from spoofing by hackers. DMARC sets up an authentication test for recipient mail-relays to test if the email sent from your domain is authentic and legitimate. During these authentication checks, each message is analyzed by the receiving email system to determine whether the message is authentic and from your register mail relays. Failing this authentication test will result in that email message being quarantined or rejected (set in the DNS record).
DMARC is the gatekeeper we all need to protect our brand and our clients from impersonation attacks coming from our company’s domain name.
Source: MXToolbox
Additional Reading: DMARC Inching It’s Way Onto Australian Govt Domains