DMARC is Domain-based Message Authentication, Reporting, and Conformance, a policy layer built on SPF and DKIM.
It matters because email is one of the few channels a business can own directly. Strong email fundamentals improve trust, deliverability, segmentation, and long-term lead nurturing.
Example
Example: DMARC tells receiving servers what to do when a message claiming to be from your domain fails SPF or DKIM alignment. It also provides reporting to help monitor abuse.