Enhanced SMTP status code · RFC 3463 · IANA
5.4.6 Routing loop detected
The message was forwarded too many times, because of wrong routing or a forwarding loop.
- Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1). The registry says this code is only useful as a temporary failure.
Also seen as:
4.4.6 - Subject: X.4 · Network and routing
Network and routing status (DNS included); under the control of the destination's or an intermediate server's administrator.
How 5.4.6 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Gmail
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554 5.4.6
Message exceeded 50 hops, this may indicate an email loop.
The message went through more than 50 servers, a sign of a forwarding loop. Check automatic forwarding.
Microsoft 365 / Exchange Online
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5.4.6
Routing loop detected
A configuration error created a mail loop; Exchange breaks it after 20 iterations.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026