How do authentication failures appear in headers or Postmaster Tools?

Authentication failure indicators:

Email headers:

Look for Authentication-Results header

Shows spf=fail, dkim=fail, or dmarc=fail

May show permerror or temperror

Gmail Postmaster Tools:

Authentication section shows pass rates

Declining percentages indicate problems

Split by SPF, DKIM, DMARC

DMARC reports:

Aggregate reports show failure counts

Forensic reports show specific failures

Common failure patterns:

SPF fail: Sending from unauthorized IP

DKIM fail: Key mismatch or signature tampering

DMARC fail: Alignment failure or missing policies

Inspection results stamped on each shipment. Failed inspections documented in the cargo manifest.