A DMARC (Domain-based Message Authentication, Reporting, and Conformance) record is a DNS (Domain Name System) record that helps protect email domains from unauthorized use and email spoofing. DMARC builds upon the authentication mechanisms provided by SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) to provide more robust email authentication and reporting capabilities.

DMARC allows domain owners to specify a policy for how receiving mail servers should handle emails that claim to be from their domain. It enables domain owners to instruct receiving mail servers to take specific actions, such as reject, quarantine, or deliver the email based on the results of SPF and DKIM authentication checks.

Here’s a brief overview of how DMARC works:

1. The domain owner publishes a DMARC record in their DNS, specifying their desired DMARC policy. The DMARC record includes information such as the email address where reports should be sent and the desired policy mode (none, quarantine, or reject).
2. When an email claiming to be from the domain is received by a recipient’s mail server, the server performs SPF and DKIM checks to authenticate the email.
3. The recipient’s mail server then checks for the presence of a DMARC record for the sender’s domain. If a DMARC record exists, the server uses the specified policy to determine how to handle the email based on the results of SPF and DKIM authentication checks.
4. Depending on the DMARC policy specified, the email can be:
   • None: The recipient’s mail server does not take any specific action and continues with its normal email handling process. However, DMARC reports are sent to the email address specified in the DMARC record.
   • Quarantine: The email is treated with suspicion, and the recipient’s mail server may choose to place it in the recipient’s spam or quarantine folder.
   • Reject: The email is rejected outright, and the recipient’s mail server does not deliver it to the recipient’s inbox.

DMARC also provides detailed reporting capabilities, allowing domain owners to receive reports on email authentication failures and successes. These reports provide valuable insights into how emails from their domain are being handled and help identify potential sources of abuse or unauthorized use.

Implementing DMARC involves creating a DMARC record and adding it to the DNS of the domain. The record specifies the desired policy mode, reporting email address, and other optional parameters. DMARC policies can be gradually enforced by starting with a monitoring-only mode (none) and gradually moving to quarantine or reject modes once the domain owner has analyzed the reports and verified the authentication setup.

By implementing DMARC, domain owners can improve email deliverability, protect their brand reputation, and combat email spoofing and phishing attacks that abuse their domain.