DMARC

DMARC (Domain-based Message Authentication, Reporting and Conformance) is a technical specification, created by a group of organizations to help reduce the potential for email-based abuse, such as spam, email spoofing and phishing e-mails, by solving some long-standing operational, deployment, and reporting issues related to email authentication protocols.

DMARC build on top of Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM), which provide mechanisms to validate the authenticity of emails, but do not provide any standardization for enforcement. DMARC provides that enforcement mechanism.

Enabling DMARC for your outgoing mail

This is discussed here.

Enable or disable DMARC reporting

To enable or disable the sending of DMARC reports (to alert supposed senders to the use and misuse of their domain) you can toggle Configuration->SMTP->SMTP checks->Enable reporting to DMARC domains.

You will need to restart the Incoming MTA to apply this change.

Purging unsent reports

Occasionally a domain will be configured with an unreachable DMARC reporting address. In this case, you can purging unsent DMARC reports with:

cd /tmp/dmarc_reports && find . -mtime +15 -delete