DMARC Definition

Howard Poston
Aug 08, 2023

What Does DMARC Mean?

Domain-Based Message Authentication, Reporting, and Conformance (DMARC) is an email security protocol designed to protect against phishing attacks. DMARC and its component protocols — the Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) — help to identify if an email originated from the alleged sender.

Why is DMARC Important?

Spoofing is a common technique in phishing attacks. It takes advantage of the fact that many of the fields in an email header are controlled by the software writing the message and are modifiable by an attacker. For example, an attacker can change the alleged email address of the message sender, making it look more believable to the recipient.

One of the key functions of DMARC is to protect against email spoofing attacks. The owner of a particular domain can provide information that is used to verify emails originating from that domain and to identify spoofed emails.

How Does DMARC Work?

DMARC is an optional email security feature, and the owner of a particular domain needs to configure it to take advantage of its protection. This involves:

  • Adding a DMARC policy to the Domain Name Server (DNS) record for the domain and how to handle emails that fail DMARC validation. This policy may include a DKIM public key and/or a list of approved IP addresses for email servers (for use with SPF).
  • Configure approved email servers for the domain to have SPF and/or DKIM configured.

When an email is sent from an authorized server, it will include some information that the recipient can use to verify it, such as:

  • DKIM: If the email server is configured to use DLIM, the email will be digitally signed using the private key that corresponds to the public key in the domain’s DNS record. The recipient can look up the public key and use it to verify the signature, verifying its integrity and authenticity.
  • SPF: With SPF, the domain’s DNS record will include a list of approved IP addresses that can send emails for that domain. The recipient can verify that the IP address of the sender matches the ones included within the DNS record.

If an email passes the test, then it is considered legitimate. Otherwise, the recipient should consult the DMARC policy in the domain’s DNS record to determine what to do with the email. It might accept, reject, quarantine, or report it to the domain owner.

Benefits of DMARC

DMARC provides an additional layer of security for email and helps to protect against email spoofing attacks. If an organization has implemented DMARC, it prevents its domain from being spoofed and has the potential to learn about attempted spoofing attacks due to the optional reporting feature.

The main limitation of DMARC is that it can be difficult to configure correctly. If misconfigured, it can cause legitimate emails to be rejected if they don’t match the DMARC policy.


DMARC builds trust in domains and email by protecting against spoofing attacks and can ensure the integrity of an email’s content (with DKIM). However, it doesn’t encrypt the email or provide any protection against eavesdropping on its content.

Howard Poston

Howard Poston is a copywriter, author, and course developer with experience in cybersecurity and blockchain security, cryptography, and malware analysis. He has an MS in Cyber Operations, a decade of experience in cybersecurity, and over five years of experience as a freelance consultant.

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