Enhanced SMTP status code · RFC 3463 · IANA
4.4.317 Cannot connect to remote server [Message=UntrustedRoot]
The recipient's server sends its TLS certificate without the full chain, and Exchange Online cannot verify it. Configure the full chain on the server.
- 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.
- 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 4.4.317 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Microsoft 365 / Exchange Online
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450 4.4.317
Cannot connect to remote server [Message=UntrustedRoot]
The recipient's server sends its TLS certificate without the full chain, and Exchange Online cannot verify it. Configure the full chain on the server. Check with SMTP server check.
What you can check here
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026