Exact response pattern
550 5.2.2 Mailbox fullPermanentGenericQuota
What it means
The receiver treats the over-quota mailbox as a permanent failure.
Likely causes
- Recipient storage exhausted for an extended period.
Recommended response
- Stop repeated delivery attempts.
- Use a defined suppression policy for persistent quota failures.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.