DMARC (Domain-based Message Authentication, Reporting & Conformance)

Definition: DMARC is an email authentication protocol that provides instructions to email servers on how to handle unauthenticated emails from a domain. DMARC builds upon SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) by setting specific rules for verifying sender identity and ensuring email legitimacy. When an email is received, DMARC helps verify that it comes from a trusted sender by checking SPF and DKIM authentication results. If an email fails authentication, DMARC directs the receiving server to either deliver, quarantine, or reject the message based on the sender’s DMARC policy.

The main purpose of DMARC is to prevent email spoofing, phishing, and domain impersonation by ensuring that only authenticated emails reach the inbox. DMARC allows domain owners to set policies to safeguard their domain and provides detailed reports on authentication activity, making it easier to identify and stop unauthorized emails. By enforcing authentication, DMARC helps organizations protect their brand reputation, reduce spam and phishing risks, and improve email deliverability by signaling to email providers that their emails are legitimate.

How DMARC Works:

1. Policy Setup: The domain owner sets a DMARC policy, typically as “none,” “quarantine,” or “reject.” The policy determines how unauthenticated emails should be handled.
2. Email Verification: When an email is received, the receiving server checks the SPF and DKIM records to confirm if the sender is authorized and that the email is untampered.
3. Action Based on Policy: If the email fails both SPF and DKIM checks, DMARC enforces the policy to either allow, quarantine, or reject the email.
4. Reporting: DMARC sends daily reports to the domain owner, detailing authentication results and highlighting potential threats or unauthorized use of the domain.

Analogy: DMARC is like giving instructions to the post office and your friend on what to do if they get a letter that might be fake. It tells them, “If you get a letter that doesn’t have the right mailman (SPF) or the special sticker (DKIM), you should throw it away or tell me about it.

So, SPF, DKIM, and DMARC work together to make sure that emails are really from the person they say they are, just like the special stamps and stickers make sure the letter is really from you.