Exact response pattern
451 4.3.0 Temporary local problem - please try laterTemporaryGenericServer
What it means
The receiver encountered a temporary internal processing problem.
Likely causes
- Filtering service failure.
- Storage or database problem.
- Temporary configuration issue.
Recommended response
- Retry later.
- Do not change content based on a single occurrence.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.