DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email security protocol that helps protect domains from email spoofing and phishing attacks. It allows domain owners to specify policies for how receiving mail servers should handle emails that fail authentication checks using SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). DMARC also provides a way for email providers to report back to the domain owner about suspicious or failed messages. By implementing DMARC, organizations can reduce the risk of fraudulent emails being sent from their domains, improving email trust and security.