How does DMARC work and why is it important for email security?

Table of Contents

• What Is DMARC?
• Why Is DMARC Important?
• Step-by-Step: How DMARC Works
• What Happens If SPF or DKIM Fails?
•  Quick Checklist for Setting Up DMARC
•  Benefits of DMARC for Organizations
• Conclusion
• Frequently Asked Questions (FAQs)

In today’s digital world, email spoofing, phishing, and fraudulent communications remain major cybersecurity challenges. One of the most effective defenses against these attacks is DMARC — Domain-based Message Authentication, Reporting, and Conformance.

This blog explains how DMARC works, why it matters, and how organizations can implement it step by step.

What Is DMARC?

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is an email authentication protocol that helps prevent:

• Email spoofing

• Phishing attacks

• Brand impersonation

DMARC builds on two existing protocols:

• SPF (Sender Policy Framework)

  
  

• DKIM (DomainKeys Identified Mail)

By combining both, DMARC provides a comprehensive approach to verifying whether an email actually came from the domain it claims to represent.

Why Is DMARC Important?

• Reduces the risk of email-based attacks.

• Protects your brand’s reputation.

• Ensures legitimate emails reach the inbox, while fraudulent ones are blocked or quarantined.

Step-by-Step: How DMARC Works

1️⃣ Sender Sends an Email

When someone sends an email from a domain, it carries both SPF and DKIM authentication details.

2️⃣ Mail Server Receives and Evaluates the Email

The recipient’s mail server checks the email for DMARC compliance by looking at:

• SPF validation

• DKIM signature validation

3️⃣ SPF Validation

The mail server confirms if the email’s sending server is authorized using SPF records:

• Checks the DNS for the sender’s SPF record.

• Verifies authorized sending IPs and services.

• Ensures alignment with the domain.

✅ If SPF is authorized → Proceed to DKIM check.
❌ If SPF is unauthorized → DMARC policy is applied.

4️⃣ DKIM Validation

The server checks the DKIM signature for authenticity:

• Uses the DKIM public key published in DNS.

• Validates the digital signature attached to the message.

✅ If DKIM is valid → Proceed to inbox check.
❌ If DKIM is invalid → DMARC policy is applied.

5️⃣ DMARC Policy Decision

Depending on SPF and DKIM results, DMARC applies one of these actions:

• None: Let the message through, but report it.

• Quarantine: Move the message to the spam folder.

• Reject: Block the message entirely.

The policy is defined by the domain owner in the DMARC DNS record.

6️⃣ Reporting

DMARC sends detailed reports back to the domain owner about:

• Emails that passed or failed.

• Sources of unauthorized emails.

• Actions taken by recipient servers.

What Happens If SPF or DKIM Fails?

If either check fails:

• Quarantine the email to spam.

• Reject the email outright.

• Drop the email with no further processing.

The choice depends on the DMARC policy set by the domain administrator.

Quick Checklist for Setting Up DMARC

• ✅ Publish SPF record in DNS.

• ✅ Publish DKIM key in DNS.

• ✅ Set up DMARC policy (none/quarantine/reject).

• ✅ Monitor DMARC reports regularly.

• ✅ Update policies based on ongoing feedback.

Benefits of DMARC for Organizations

• Shields against phishing and spoofing attacks.

• Protects sensitive customer and business data.

• Improves email deliverability rates.

• Provides actionable insights through reporting.

Conclusion

DMARC is essential for any business or organization that sends emails from custom domains. It ensures your communications are trusted while actively defending against cyber threats.

If you manage business emails or handle IT security, setting up DMARC should be a top priority.

FAQs

What is DMARC in email security?

DMARC is a protocol that helps prevent email spoofing and phishing by authenticating emails using SPF and DKIM checks.

Why is DMARC important?

DMARC protects your brand and customers from fraudulent emails, ensuring only legitimate emails get delivered.

How does DMARC work?

DMARC verifies if emails pass SPF and DKIM checks. If not, it applies a specified policy such as reject, quarantine, or none.

What does DMARC stand for?

DMARC stands for Domain-based Message Authentication, Reporting, and Conformance.

What is the difference between SPF, DKIM, and DMARC?

SPF verifies sending IP addresses, DKIM verifies email content with a digital signature, and DMARC enforces policies based on both.

How do I set up DMARC for my domain?

You set up DMARC by publishing a DMARC record in your domain’s DNS with the appropriate policy and reporting addresses.

What is a DMARC policy?

A DMARC policy determines what happens to emails that fail authentication: none, quarantine, or reject.

How does DMARC protect against phishing?

DMARC blocks or flags emails pretending to come from your domain if they fail authentication checks.

What is a DMARC record?

A DMARC record is a DNS entry that contains your DMARC policy, reporting addresses, and configuration settings.

Can DMARC improve email deliverability?

Yes, by ensuring only authenticated emails are delivered, DMARC helps improve trust and deliverability.

What happens if DMARC fails?

If an email fails DMARC checks, it is handled according to the domain’s policy: rejected, quarantined, or allowed but reported.

How do I monitor DMARC reports?

You can monitor DMARC reports using DMARC report analysis tools or services that collect and visualize the reports.

What tools are available for DMARC monitoring?

Popular tools include DMARC Analyzer, Valimail, and Postmark’s DMARC monitoring service.

Is DMARC mandatory for all businesses?

It’s not legally mandatory, but it’s highly recommended for all businesses to protect their email infrastructure.

How often should I review my DMARC reports?

You should review DMARC reports regularly—at least weekly—to identify unauthorized email activity.

What is DMARC alignment?

DMARC alignment ensures that the domain used in the “From” header matches the domain in SPF and DKIM checks.

Can DMARC block legitimate emails?

If configured incorrectly, DMARC may block legitimate emails. Proper setup and monitoring help prevent this.

How do I troubleshoot DMARC issues?

Check SPF and DKIM records, review DMARC reports, and adjust your policy settings as needed.

What is a DMARC quarantine policy?

Quarantine means emails that fail DMARC checks will be sent to the recipient’s spam folder rather than blocked completely.

Can personal email accounts use DMARC?

DMARC is designed for domains, so it doesn’t apply directly to personal accounts unless you control the domain.

Does Gmail use DMARC?

Yes, Gmail and other major email providers use DMARC to protect against spoofed emails.

How do I publish a DMARC record in DNS?

Create a TXT record in your domain’s DNS with the DMARC policy and reporting instructions.

What is an example of a DMARC record?

Example: v=DMARC1; p=reject; rua=mailto:[email protected]

How long does it take for DMARC to work?

DMARC takes effect as soon as the DNS record propagates, usually within a few hours.

What is the default DMARC policy?

There is no default. You must explicitly set a policy: none, quarantine, or reject.

What if I don’t have DKIM set up—can I still use DMARC?

You can, but it’s not recommended. DMARC works best when both SPF and DKIM are configured.

How does DMARC handle forwarded emails?

Forwarded emails can sometimes break DMARC alignment, especially with SPF. DKIM helps reduce these issues.

Can I test my DMARC setup?

Yes, use tools like MXToolbox or DMARC testing services to check your configuration.

What is the difference between p=none, p=quarantine, and p=reject in DMARC?

p=none monitors only, p=quarantine flags emails as spam, and p=reject blocks them outright.

How often should I update my DMARC policy?

Update your policy as your email environment changes or as you increase enforcement from monitoring to quarantine or reject.

What is RUA and RUF in DMARC reports?

RUA refers to aggregate reports; RUF refers to forensic reports. Both provide insight into email authentication results.