Most common causes
- SPF failed or passed on an identity that was not aligned with the visible From domain
- DKIM failed or signed with a domain that was not aligned
- Forwarding or message modification broke the only aligned authentication path
- The domain moved to p=reject before every legitimate sender was correctly authenticated
What to verify next
- Run DMARC Alignment Lab with the real From, envelope and DKIM identities
- Inspect Authentication-Results from the failed message
- Inventory third-party senders that use the affected From domain
- Correct authentication and alignment rather than weakening policy without evidence
Best diagnostic path
Live analysis
Mail Failure Doctor
Classify the complete rejection and preserve provider-specific diagnostic context.
Open analysis → Live analysisDMARC Alignment Lab
Compare visible From, envelope sender and DKIM identities without reducing the result to a pass/fail label.
Open analysis → Live analysisEmail Infrastructure Digital Twin
Map the domain’s public mail infrastructure and provider relationships before remediation.
Open analysis →Why the exact message matters
The same status family can be triggered by different conditions, and providers frequently add diagnostic text that narrows the issue. Use the complete rejection text rather than treating the numeric code as a complete diagnosis.
Provider reference
For the provider-defined meaning and current requirements, review Microsoft Exchange Online NDR reference.