Exact response pattern
452 4.3.1 Insufficient system storageTemporaryGenericCapacity
What it means
The receiving system lacks temporary storage or queue capacity.
Likely causes
- Disk or queue pressure.
- Provider overload.
Recommended response
- Retry with backoff.
- Avoid opening additional parallel sessions.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.