Exact response pattern
550 5.4.6 Routing loop detectedPermanentGenericRouting
What it means
The message is looping between mail systems.
Likely causes
- Incorrect MX or smart-host routing.
- Mutual relays.
Recommended response
- Inspect Received headers.
- Correct transport maps and connector scopes.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.