What Is DMARC and Why Is It Important?
Understanding DMARC (Domain-based Message Authentication) and email security
Table of Contents
What Is DMARC?
DMARC (Domain-based Message Authentication) is an email authentication protocol that tells ISPs how to handle emails that fail SPF or DKIM authentication checks. DMARC policies specify whether to accept, quarantine, or reject emails that fail authentication.
DMARC works with SPF and DKIM to provide comprehensive email security. It prevents email spoofing and phishing, improves email deliverability, protects domain reputation, and provides visibility into email authentication.
Check your DMARC records and use our email authentication checker to verify DMARC is properly configured.
Why DMARC Is Important
1. Prevents Spoofing and Phishing
DMARC policies prevent unauthorized senders from using your domain, protecting against email spoofing and phishing attacks.
2. Improves Deliverability
Proper DMARC configuration improves email deliverability by signaling to ISPs that you're a legitimate, security-conscious sender.
3. Protects Domain Reputation
DMARC protects your domain from being used for spam or fraud, maintaining positive domain reputation.
4. Provides Visibility
DMARC reports provide visibility into email authentication, showing who's sending emails from your domain and authentication results.
5. Industry Standard
DMARC is an industry standard expected by ISPs for optimal email security and deliverability.
6. Policy Enforcement
DMARC enables domain owners to enforce policies on how ISPs handle emails that fail authentication.
How DMARC Works
1. DMARC Record Publication
Domain owners publish DMARC policies in DNS as TXT records, specifying how ISPs should handle emails that fail authentication.
2. SPF and DKIM Evaluation
Receiving mail servers evaluate SPF and DKIM authentication results for incoming emails.
3. DMARC Policy Check
If SPF or DKIM fails, servers check the DMARC policy to determine how to handle the email.
4. Policy Enforcement
ISPs enforce DMARC policies: none (accept), quarantine (send to spam), or reject (block).
5. Reporting
DMARC generates reports showing authentication results and email sending activity.
6. Alignment Check
DMARC checks alignment between SPF/DKIM domains and the From domain to ensure proper authentication.
DMARC Policies
DMARC policies specify how ISPs should handle emails that fail authentication:
none (Monitor Only)
Accept emails but monitor authentication results. This is the starting policy for testing DMARC without affecting delivery.
quarantine (Quarantine)
Send emails that fail authentication to spam folders. This provides protection while allowing some delivery.
reject (Reject)
Block emails that fail authentication entirely. This provides maximum protection but requires careful setup.
Policy Progression
Start with 'none' for monitoring, then move to 'quarantine' after verifying authentication, and finally to 'reject' for maximum protection.
DMARC Alignment
DMARC checks alignment between authentication domains and the From domain:
SPF Alignment
SPF alignment checks if the SPF-authenticated domain matches the From domain (strict) or is a subdomain (relaxed).
DKIM Alignment
DKIM alignment checks if the DKIM signature domain matches the From domain (strict) or is a subdomain (relaxed).
Alignment Requirements
For DMARC to pass, either SPF or DKIM must pass AND align with the From domain. Learn more about SPF, DKIM, DMARC alignment.
Alignment Modes
- Strict: Domains must match exactly
- Relaxed: Subdomains are acceptable
Setting Up DMARC
1. Implement SPF and DKIM
First, ensure SPF and DKIM are properly configured.
2. Start with 'none' Policy
Begin with 'none' policy for monitoring: v=DMARC1; p=none; rua=mailto:dmarc@example.com
3. Publish DMARC Record
Publish the DMARC record as a TXT record in DNS at: _dmarc.example.com
4. Monitor Reports
Monitor DMARC reports to understand authentication results and email sending activity.
5. Progress to Quarantine
After verifying authentication, progress to 'quarantine' policy: v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com
6. Finalize with Reject
Once confident in authentication, move to 'reject' policy: v=DMARC1; p=reject; rua=mailto:dmarc@example.com
7. Verify Configuration
Use our DMARC lookup tool and authentication checker to verify DMARC is working correctly.
