Email troubleshooting guides
DMARC and impersonation protection, organized by problem
Diagnose DMARC policy, subdomain policy, reporting, and domain impersonation protection.
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DMARC policy for the visible From subdomain is unexpectedFind the effective DMARC policy for a visible From subdomain. See whether p, sp, np or test mode applies before changing DMARC DNS.
DMARC reports not received: External report destination is not authorizedFind why DMARC aggregate reports are not arriving. Check external reporting authorization in DNS, understand the limits, and verify a safe fix.
Primary sources: Primary technical reference.