Exact response pattern
454 4.7.0 Temporary authentication failureTemporaryGenericAuthentication
What it means
SMTP authentication could not be completed temporarily.
Likely causes
- Authentication backend unavailable.
- Temporary TLS or policy issue.
Recommended response
- Retry later.
- Verify credentials only if failures persist.
- Check TLS requirements and SASL logs.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.