DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email authentication protocol that builds upon SPF and DKIM to provide domain owners with the ability to protect their domain from unauthorized use, commonly known as email spoofing.

Key Components:

• Policy (p): Defines what action to take when emails fail authentication (none, quarantine, reject)
• Subdomain Policy (sp): Policy for subdomains if different from main domain
• Alignment (adkim/aspf): How strictly DKIM and SPF alignment is enforced (relaxed or strict)
• Percentage (pct): Percentage of emails to which the policy applies

How DMARC Works:

1. Email is sent and received by the recipient's mail server
2. The server checks SPF and DKIM authentication
3. DMARC policy is evaluated based on authentication results
4. Action is taken according to the policy (none, quarantine, or reject)
5. Reports are generated and sent to the domain owner