DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a tool that helps protect email domains from being used for spam or phishing. But how it’s enforced can vary. Here’s a simple explanation of some things to consider when enforcing DMARC policies.

Even if an email passes the DMARC check, the receiver can still choose to reject or quarantine (treat as suspicious) the email. This is because DMARC doesn’t tell the receiver whether the email is good or bad, it just verifies that the email really did come from the domain it says it came from. So, receivers should still use other tools to help spot spam or phishing emails.

Similarly, even if an email fails the DMARC check, the receiver can still choose to accept the email. But if they do this, they should try not to increase the chance of accepting spam or phishing emails. One way to do this is to add a special note to the email (called an Authentication-Results header field) that says the email failed the DMARC check.

Reporting DMARC Actions

Receivers only need to report when they reject or quarantine an email because of the DMARC policy. They don’t need to report when they reject or quarantine an email for other reasons. This is to prevent spammers from learning too much about how the receiver handles emails.

Balancing DMARC with Other Policies

The final decision about what to do with an email is always up to the receiver. They might decide to prioritize DMARC over other policies, like SPF (Sender Policy Framework). But this means they have to accept and process the whole email, which could be a risk.

If a DMARC policy is found for an email, receivers usually ignore any instructions from other authentication mechanisms. But they can choose to do otherwise.

Handling ‘None’ Policies and Reporting Instructions

If a DMARC policy of ‘none’ is found, this shouldn’t change how the receiver normally handles emails. A ‘none’ policy means the sender isn’t asking the receiver to do anything special with their emails.

Receivers should also follow the reporting instructions in the DMARC policy, even if there aren’t any instructions for DKIM (DomainKeys Identified Mail) or SPF reporting. These reports help the sender understand how their DMARC policy is working.

Remember, this is a simplified explanation. In reality, enforcing DMARC policies involves a lot of complex decisions and processes. But hopefully, this gives you a basic understanding of some of the things to consider.

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