What Is DMARC? — Domain-Based Email Authentication Explained (2025)
If SPF and DKIM are the locks on your email doors, DMARC is the security policy that tells servers what to do when those locks fail. DMARC — Domain-based Message Authentication, Reporting, and Conformance — ensures mailbox providers only trust messages that truly come from you.
1️⃣ Why DMARC Exists
Email was never designed with identity verification in mind. Anyone can claim to send from any domain. DMARC closes that loophole by requiring two checks — SPF and DKIM — to align with the visible “From” address. If neither matches, the recipient can reject, quarantine, or deliver with warning.
Example DMARC Record:
_dmarc.mailtested.com TXT
"v=DMARC1; p=quarantine; rua=mailto:[email protected]; aspf=s; adkim=s"2️⃣ How DMARC Works in Practice
- Recipient mail server receives your message.
- It validates SPF (sending IP) and DKIM (digital signature).
- If either one aligns with your “From” domain — DMARC passes.
- If both fail, the DMARC policy defines what happens next: none, quarantine, or reject.
3️⃣ The Three DMARC Policy Levels
- p=none — monitor only, no enforcement.
- p=quarantine — suspect emails go to spam.
- p=reject — unauthenticated messages are blocked completely.
Start with p=none to collect reports without risking delivery.
Once SPF and DKIM consistently pass, move to p=quarantine, then p=reject for full protection.
4️⃣ Reporting and Monitoring
DMARC adds two optional tags — rua and ruf — for aggregate and forensic reports.
These reports show which IPs are sending mail on your behalf and which ones fail authentication.
They’re invaluable for detecting spoofing or third-party misuse of your brand.
5️⃣ Common DMARC Configuration Mistakes
- Publishing DMARC without working SPF/DKIM records.
- Setting
p=rejecttoo early and blocking legitimate traffic. - Incorrect syntax (missing semicolons or quotes).
- Using wrong reporting mailbox (needs to accept external reports).
Always validate your DNS syntax and alignment before enforcing strict policies. The MailTested DMARC Checker will flag common issues automatically.
6️⃣ How DMARC Improves Deliverability
While DMARC’s purpose is security, it directly boosts inbox placement. Mailbox providers reward authenticated domains with better reputation scores. When your messages consistently pass SPF, DKIM, and DMARC, they’re treated as high-trust senders.
✅ Final Thoughts
DMARC isn’t optional anymore — it’s the global standard for brand-safe email delivery. Once implemented, it protects your customers, your reputation, and your bottom line. Combine SPF, DKIM, and DMARC with regular testing through MailTested to ensure every message lands safely in the inbox.