What is DMARC & How Does it Work?

Protect your inbox with sophisticated email authentication protocols

Emails are a ubiquitous means of communication. However, with the rise of cyber threats like phishing, spoofing, and other sophisticated crimes, protecting your email from malicious attacks has become paramount.

DMARC is an email security protocol designed to combat these threats and bolster the integrity of your inbox.

What is DMARC?

DMARC, which stands for Domain-based Message Authentication, Reporting, and Conformance, was developed to combat phishing attacks, spoofing, and domain abuse, which are prevalent cyber threats in today's digital landscape.

The primary goal of DMARC is to verify the authenticity of an email's sender and protect recipients from fraudulent emails sent under the guise of trusted domains.

By leveraging existing authentication methods, such as SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) {DKIM glossary article link once published}, DMARC provides an additional layer of security to your email infrastructure.

What are the Benefits of DMARC?

  • DMARC enhances the existing SPF and DKIM authentication methods, providing a robust email validation mechanism.
  • By preventing cyber criminals from impersonating your email domain, DMARC safeguards your brand's reputation. Recipients can trust that emails from your domain are legitimate, improving customer confidence.
  • DMARC's ability to block fraudulent emails directly reduces the problem of phishing attacks to an extent, protecting users from falling victim to scams.
  • It generates detailed reports on email authentication results, allowing domain owners to analyze potential threats and take appropriate action.
  • Custom policies that suit your organization's security needs. You can start with a "none" policy for monitoring and gradually move to "quarantine" and "reject" as your confidence in the authentication system grows.

How Does DMARC Work?

DMARC operates on the principle of domain alignment, which ensures that the domain in the email's "From" address aligns with that used in SPF and DKIM authentication. This DMARC alignment prevents cybercriminals from impersonating legitimate domains and deceiving recipients.

  1. SPF Authentication: SPF allows domain owners to define authorized sending sources for their emails. When an email is received, the recipient's mail server checks if the sending IP address is listed in the SPF record of the domain mentioned in the "From" address. If the alignment is successful, the email is considered genuine.
  2. DKIM Authentication: DKIM {DKIM article once published} adds a digital signature to outgoing emails, verifying their integrity and authenticity. The recipient's mail server can verify the DKIM signature using the public key published in the domain's DNS records.
  3. DMARC Policy: DMARC ties SPF and DKIM together, specifying how the recipient's mail server should handle emails that fail authentication checks. Domain owners can set up three DMARC policies:
    • None: The domain owner is only interested in monitoring email authentication, not acting based on the results.
    • Quarantine: Suspicious emails that fail SPF or DKIM checks get sent to the recipient's spam or quarantine folder.
    • Reject: Emails that fail authentication get rejected outright, reducing the likelihood of phishing attacks.

What Does a DMARC Record Look Like?

A DMARC record is a DNS (Domain Name System) record that informs email receivers how to handle emails from your domain. It is a text-based record added to your domain's DNS settings. A typical DMARC record comprises the following components:

v=DMARC1; p=reject; rua=mailto:reports@example.com; ruf=mailto:forensicsexample.com; pct=100;

  • v: Version of the DMARC protocol. The current version is "DMARC1."
  • p: The DMARC policy for your domain indicates the preferred action when an email fails authentication.
  • rua: The email address to which the aggregate DMARC reports will deliver.
  • ruf: The email address to which the forensic DMARC reports will deliver.
  • pct: The percentage of emails that should be subject to the DMARC policy. A value of "100" means all emails; "none" means no emails.

DMARC Best Practices and Tools

Implementing DMARC requires careful planning and adherence to best practices to achieve optimal results. Here are some essential DMARC best practices to keep in mind:

  1. Monitor Email Authentication: Start with a "none" policy to monitor email authentication results without taking any action. Analyze the reports and fine-tune SPF and DKIM configurations.
  2. Gradual Policy Enforcement: Once confident in your SPF and DKIM configurations, move to a "quarantine" policy to divert suspicious emails to spam or quarantine folders. Eventually, progress to a "reject" policy for maximum protection.
  3. Monitor DMARC Reports Regularly: Pay close attention to the DMARC reports, as they offer insights into authentication failures and possible threats. Regular monitoring allows you to stay proactive against potential attacks.
  4. Configure SPF and DKIM Correctly: Ensure that your SPF and DKIM records are correct, covering all legitimate sending sources and using robust encryption methods for DKIM keys.
  5. Implement DNSSEC: DNSSEC (Domain Name System Security Extensions) enhances the security of your DNS records, making them less susceptible to tampering or spoofing.
  6. Use DMARC Reporting Tools: Several DMARC reporting tools can provide an in-depth analysis of your email authentication status. These tools can help you track your progress and identify areas for improvement.

Last, but not the least, keep track of the latest DMARC developments and best practices.


Q: Does DMARC eliminate all email threats?

No. While DMARC significantly reduces email threats like phishing and spoofing, it may not address all types of email-related cyber threats. Additional email security measures should complement DMARC.

Q: Is DMARC implementation complex?

The complexity of DMARC implementation depends on your email infrastructure and existing authentication configurations. Proper planning and gradual policy enforcement can simplify the process.

Q: Can DMARC reject legitimate emails?

DMARC's "reject" policy can potentially lead to the rejection of legitimate emails if they fail SPF or DKIM checks. Careful monitoring and fine-tuning of SPF and DKIM configurations can minimize false positives.

Q: Is DMARC suitable for small businesses?

Yes, DMARC is beneficial for businesses of all sizes. Smaller organizations can start with monitoring policies and gradually progress to more robust enforcement.

Q: Are there any DMARC tools available for free?

Several DMARC reporting and analysis tools offer free versions with limited features. These tools can be a good starting point for organizations on a budget.