DMARC (Domain-based Message Authentication, Reporting, and Conformance) ​

Email fraud poses a significant threat. Daily, cybercriminals attempt to impersonate legitimate companies by sending fraudulent emails to customers and employees. These communications often appear genuine but are intended to extract sensitive information or deploy malware.

This is where DMARC plays a crucial role.

DMARC functions as the policy enforcer for email authentication. While SPF and DKIM assist in verifying the origin and signature of an email, DMARC instructs receiving servers on how to manage messages that fail these authentication checks. Furthermore, it provides visibility into all entities sending emails from your domain, including both legitimate and malicious sources.

Implementing DMARC is essential for individuals and organizations dedicated to protecting their brand and improving email deliverability. Many avoid this implementation due to perceived complexity, which can lead to unnecessary email security and deliverability challenges.

What is DMARC? ​

DMARC, or Domain-based Message Authentication, Reporting & Conformance, is a protocol designed to enhance email security by working with SPF and DKIM. It empowers domain owners to dictate how email receivers should handle unauthenticated messages that appear to originate from their domain.

The primary functions of DMARC include:

1. Authenticating incoming emails through SPF and DKIM.
2. Providing instructions to receiving servers on actions to take when an email fails authentication.
3. Generating reports for the domain owner regarding attempts to send emails using their domain.

These rules are established within a specific DNS record known as a TXT record, which is formatted as follows:

v=DMARC1; p=none; rua=mailto:reports@yourdomain.com

Let's break down this syntax:

• v=DMARC1: Specifies the version of DMARC being used (currently only version 1 exists).
• p=none: Sets the policy for handling emails that fail DMARC checks. Options include:
  • none: Take no action (monitoring mode) but still send reports
  • quarantine: Treat the message with suspicion (typically sending it to the spam folder)
  • reject: Block the message completely
• rua=mailto:reports@yourdomain.com: Specifies the email address where aggregate reports should be sent. These reports provide data about all messages claiming to be from your domain.

How Does DMARC Work? ​

It operates by verifying the alignment between the visible "From" domain and the domains authenticated through SPF and/or DKIM. Here's a breakdown of the process that occurs each time an email is received:

1. Lookup: The recipient checks for a DMARC record in the sender's DNS (_dmarc.example.com).

2. Alignment Check: The system confirms whether the domain in the "From" address matches the domains authenticated by SPF and/or DKIM.

3. Authentication Check: It evaluates if the email successfully passes either SPF or DKIM, ensuring that the authenticated method aligns with the "From" domain.

4. Policy Evaluation: Depending on your DMARC policy (none, quarantine, or reject), the recipient determines the appropriate action:

   • Accept the message (none)
   • Redirect it to spam (quarantine)
   • Completely block it (reject)

5. Reporting: If configured, the receiving server will send reports (aggregate and/or forensic) back to the domain owner.

For instance, if an attempt is made to spoof invoice@example.com without the sending server being included in your SPF or without a valid DKIM signature, and your policy is set to p=reject, the email will be blocked.

Why is DMARC Important? ​

DMARC is essential for protecting your domain from impersonation, phishing, and email spoofing. Without it, malicious actors can forge your domain in the "From" address, sending fraudulent emails that seem legitimate. While SPF and DKIM validate specific technical aspects, they do not ensure alignment with the domain visible to users, creating a vulnerability. DMARC addresses this by enforcing domain alignment, ensuring the visible sender matches authenticated sources and allowing domain owners to control actions for messages that fail this check.

In addition to security, DMARC offers operational benefits. It fosters trust with email providers and recipients, enhancing deliverability and reducing the chances of emails being marked as spam. DMARC reports provide valuable insights into how your domain is utilized, showing who sends emails on your behalf and their authentication success. Given that phishing is a primary attack vector, DMARC is essential. It is a critical component of any email security and brand protection strategy, and many inbox providers now require it for high-volume senders or those wishing to display brand logos via BIMI.

Frequently Asked Questions About DMARC ​

Do I need DMARC if I already have SPF and DKIM? ​

Yes. SPF and DKIM handle the technical authentication, but DMARC adds policy enforcement and reporting. Without DMARC, unauthorized emails might still appear to come from your domain, and you won't have insight into who is abusing it.

Will implementing DMARC affect my email deliverability? ​

When done properly, DMARC improves deliverability by proving to email providers that your emails are genuine. However, if set too strictly without alignment or monitoring, it can cause legitimate emails to be rejected. It's best to begin with a "none" policy and gradually move to "quarantine" or "reject."

Is DMARC hard to set up? ​

It can look intimidating, but many email platforms offer help or automated tools to guide setup. Start with a monitoring-only mode to observe your domain's traffic and then enforce stronger policies once you're confident.

How do I monitor DMARC activity? ​

DMARC sends regular XML reports to the email address you specify in your DNS record. These reports can be difficult to read manually, so most organizations use DMARC report analyzers or dashboards to track and interpret the data.

Related Concepts ​

• SPF (Sender Policy Framework)
• DKIM (DomainKeys Identified Mail)
• Email Authentication
• Email Spoofing