DMARC Compliance

What is DMARC?

DMARC is a protocol for authenticating that an email sent from an organization's domain is a legitimate message and not fraudulent. The illegitimate use of an organization's domain is a common technique in impersonation attacks, where cyber criminals pose as a trusted source inside an organization and to trick recipients of the email into divulging sensitive information or transferring money to fraudulent accounts. 

What is DMARC Compliance?

DMARC compliance refers to email that is sent in compliance with specifications of the Domain-based Message Authentication, Reporting and Conformance protocol. The DMARC protocol leverages two established authentication standards, Sender Policy Framework (SPF)  and the DomainKeys Identified Mail (DKIM), to enable mail servers to determine whether an inbound message from a specific domain is legitimate or not.

DMARC essentially ensures that email is properly authenticating against DKIM and SPF standards, and enables sending organizations to post policies to their DNS record about how to handle messages that don’t authenticate. DMARC also enables receiving mail senders to send aggregate and forensic reports back to senders, providing greater visibility into what messages are not authenticating, and why.

While DMARC compliance is highly effective at stopping an impersonation attack based on illegitimate use of an actual domain, it does nothing to address email spoofing  that uses look-alike domains, display name spoofing, newly registered domains or reply-to mismatches. That's why, when seeking solutions that can help to prevent an email data breachmore organizations today look for multilayered defenses against email fraud.

The Importance of Achieving DMARC Compliance

Achieving DMARC compliance helps a domain owner reduce direct domain spoofing, strengthen email authentication, and give receiving mail servers clearer instructions on how to handle suspicious messages. A properly aligned DMARC policy  also improves visibility through DMARC reports, making it easier to:

• Identify unauthorized senders

• Investigate DMARC failures

• Separate legitimate email from abuse.

It also supports email deliverability. As mailbox providers place more weight on authenticated mail, being DMARC compliant helps an email sender improve inbox placement and reduce the risk of messages being filtered or rejected.

DMARC Compliance Checklist

DMARC is increasingly becoming an operational requirement, not just a best practice. Beyond stronger email authentication, DMARC compliance now supports major sender requirements, trust signals, and broader anti-phishing efforts.

1. PCI-DSS recommendations

DMARC is recognized as a strong supporting control for organizations working toward PCI-DSS -aligned email security practices. As anti-phishing expectations increase, implementing DMARC helps reduce impersonation risk and supports stronger protection for regulated communications.

2. Google and Yahoo sender requirements

For bulk senders, DMARC compliance is now especially important. Major mailbox providers like Google and Yahoo have introduced stricter authentication expectations, making it more important for domains that send high volumes of mail to publish a valid DMARC record and send authenticated, DMARC-compliant messages.

3. Gmail’s blue verified checkmark

For domains that have achieved DMARC compliance and also meet BIMI requirements, Gmail may display a verified brand checkmark next to messages. This can help reinforce trust in the sender, improve brand recognition, and make legitimate email easier for recipients to identify.

How to Meet DMARC Compliance and Requirements

Achieving DMARC compliance is usually a phased process, not a one-time change. The safest approach is to start with proper authentication and visibility, then tighten enforcement as you confirm that legitimate mail is aligned and protected.

1. Configure SPF and DKIM first

Before implementing DMARC, make sure your legitimate sending sources are already authenticating correctly with SPF and/or DKIM. This includes publishing a valid SPF record and confirming that each approved email sender is set up to pass authentication.

2. Publish your DMARC record

Next, create and publish your DMARC record in DNS. This is the core of DMARC implementation, since it tells receiving systems how to process mail that fails authentication checks.

3. Start with a monitoring policy

When you first implement DMARC, begin with a monitoring policy such as p=none. This allows you to collect DMARC reports without affecting legitimate email while you validate your sources and review alignment.

4. Review reports and identify failures

Use DMARC monitoring to review each DMARC report and see which systems are sending mail on your behalf. This helps you spot unauthorized sources, understand DMARC failures, and correct issues before moving to stricter policy settings.

5. Validate your record and setup

Use a DMARC record checker to confirm that your record syntax is correct and publicly available. This extra validation step helps ensure your DMARC setup is working as expected and that your domain is moving toward being DMARC compliant.

6. Move toward enforcement

Once all approved senders are authenticating and aligned correctly, move from monitoring to stronger DMARC enforcement, such as quarantine or reject. This final step helps your mail server and other receiving systems better block spoofed mail while preserving delivery for legitimate messages.

Try Our SPF, DKIM, and DMARC Checker 

Best Practices to Stay DMARC Compliant

Maintaining DMARC compliance requires more than publishing a record once. To keep your protection effective over time, organizations should regularly review and strengthen the controls that support authenticated email.

• Move toward enforcement: Once your approved senders are properly aligned, move from monitoring to a stronger DMARC policy such as quarantine or reject to better block spoofed mail.

• Protect subdomains: Review whether subdomains are sending mail and make sure they are covered by the right policy so they are not left exposed.

• Validate third-party senders: Any external platform sending on your behalf should be properly authorized and configured to pass SPF checks  and/or DKIM checks.

• Monitor reports consistently: Review DMARC reports on an ongoing basis to catch unauthorized senders, misconfigurations, and issues that could affect email delivery.

• Update records as your environment changes: New vendors, cloud services, or sending tools can create gaps if your SPF, DKIM, and DMARC configurations are not kept current.

Following these practices can help you maintain stronger email authentication, preserve deliverability, and reduce the risk of domain abuse over time.

Achieving DMARC compliance with Mimecast

To provide organizations with a wider set of tools for email security and information protection, Mimecast offers an all-in-one subscription service for email security, archiving and continuity. Mimecast's SaaS-based offering provides a multilayered approach to email security and a suite of solutions that help reduce the cost and complexity of managing business email.

Mimecast helps to ensure DMARC compliance through the Mimecast Secure Email Gateway. Combining threat intelligence and sophisticated protection engines, Secure Email Gateway performs DNS authentication to check on SPF, DKIM and DMARC compliance. Combined with Mimecast DMARC Analyzer, Mimecast provides visibility that helps to detect and block unauthorized use of an organization's domains to prevent spoofing and impersonation attacks.

Additional solutions to combat email attacks

In addition to helping organizations with DMARC compliance, Mimecast provides comprehensive defenses against other kinds of advanced threats with tools to protect against malicious URLs, weaponized attachments, social engineering and threats from malicious insiders. Additionally, Mimecast provides secure messaging services that enable employees to securely send sensitive information and large files up to 2 GB from their email inbox. Mimecast also offers tools for content control and data loss prevention that can help to identify and block potential leaks, both inadvertent and malicious.