Enhanced status code Temporary

SMTP error X.4.4

Unable to route

Updated Jul 1, 2026

The short answer

Unable to route Common cause: No usable route to destination was found

Quick fix

Check recipient-domain DNS and MX records

4 - Temporary. Safe to retry. The message is not lost and most servers retry automatically.
This code is written X.4.4 because the reason is the same whether the failure is temporary (a 4 first digit) or permanent (a 5). Read the first digit of your own bounce to know which applies.

How to fix it

Check recipient-domain DNS and MX records

Related codes

X.4.0 Other or undefined network / routing status X.4.1 No answer from host X.4.2 Bad connection X.4.3 Directory server failure X.4.5 Mail system congestion X.4.6 Routing loop detected
All SMTP error codes
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