Gmail DMARC policy rejection

Fix Gmail 550 5.7.40 DMARC policy required

Gmail can report a policy requirement when a sending domain has no applicable DMARC policy. Confirm the current policy through a bounded RFC 9989 DNS tree walk before publishing or changing a record.

Problem description

Gmail rejects mail from your domain with the following error message:

Gmail rejected: 550 5.7.40 DMARC policy is required for this sender.

Check the DMARC policy free

What the check distinguishes

Missing policy: the full bounded tree walk found no applicable DMARC record.
Invalid policy: a candidate record exists but cannot be applied safely.
Temporary DNS result: policy absence is unknown, so the checker does not recommend publishing over an unverified state.
Valid policy: public DNS has a policy, but that alone does not prove a particular message is aligned.

Safe policy workflow

Confirm every legitimate sender and its aligned SPF or DKIM configuration.
Publish a valid monitoring policy first when the domain has no policy.
Use reports and fresh message headers to verify legitimate traffic before moving to enforcement.
Select p=quarantine or p=reject only after verified alignment; neither is a universal repair for a delivery problem.

Technical reference: RFC 9989 DMARC.