Exact response pattern
251 User not local; will forwardSuccessGenericRouting
What it means
The receiving server accepted the recipient and will forward the message.
Likely causes
- The recipient is hosted elsewhere but forwarding is configured.
Recommended response
- No action is normally required.
- Verify forwarding behavior if delivery is delayed.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.