Exact response pattern
550 5.4.4 Unable to routePermanentGenericRouting
What it means
The receiving system cannot determine a delivery route.
Likely causes
- Broken transport map.
- Invalid relay domain.
- Missing route.
Recommended response
- Check transport maps, relay domains and MX resolution.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.