Enhanced SMTP status code · RFC 3463 · IANA
4.4.2 Bad connection
The connection opened, but the transaction could not finish because of a timeout or a poor link.
- Class: Temporary failure
Class 4: a persistent transient failure. The message was fine, but a passing condition delayed or stopped delivery; a later attempt may succeed (RFC 3463 §3.1). The sending server retries on its own for a while. The registry says this code is only useful as a temporary failure.
- 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.
- Associated basic codes (IANA registry)
How 4.4.2 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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451 4.4.2
Timeout - closing connection.
The connection stayed idle too long and Gmail closed it. The sending server retries; if it repeats, check the network and the sending server.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026