Exact response pattern
554 5.4.0 Error: too many hopsPermanentGenericRouting
What it means
The transaction failed because the route is invalid, often due to a loop.
Likely causes
- Routing loop.
- Misconfigured forwarding.
Recommended response
- Inspect headers and route configuration.
- Correct the loop before resending.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.