DMARC subdomain diagnostics

Check the effective DMARC policy for a subdomain

A visible From address such as news.example.com can inherit policy from a parent domain. Before changing DMARC, identify the exact policy owner and whether p, sp, np or test mode changes the effective result.

Problem description

Mail from your subdomain is rejected or handled differently after a DMARC change:

DMARC policy for the visible From subdomain is unexpected.

Check the effective DMARC policy free

How an effective policy is selected

Direct record: _dmarc.subdomain.example.com supplies the policy when valid.
Inherited policy: a parent DMARC record can supply sp= for an existing subdomain or fall back to p=.
Non-existent domain: a valid np= can apply when DNS confirms that the requested subdomain does not exist.
Test mode: t=y lowers effective enforcement, so the declared and effective policies can differ.

Use the result safely

Enter the domain in the visible From address, not a guessed return-path or provider hostname.
Check whether the reported policy is direct or inherited and preserve intended parent-domain behavior.
Verify legitimate senders pass aligned SPF or DKIM before tightening p, sp or np.
Confirm a fresh message with the receiving provider after a DNS change.

The check reports current public DNS policy only. It does not independently verify a message's SPF/DKIM alignment, historical policy or inbox placement. Technical reference: RFC 9989 DMARC.