4.4.316: destination server refused the connection

What it means

Exchange Online returns this when it sends to a server outside Microsoft 365 and cannot open an SMTP connection because the remote end refuses it (socket error 10061, connection refused). The code is temporary, so the service keeps the message and retries; if the refusal lasts, it ends as a 4.4.7 expiry. Microsoft notes that the problem almost always lies with the receiving server or its network, and that the error includes the IP address of the server that refused, which tells you whose server it is.

Common causes

• The receiving mail server is down, or its SMTP service is not listening on port 25.
• A firewall in front of the receiving server is rejecting connections from Microsoft 365.
• The MX record points to an address that does not run a mail server.

How to fix it

1. 01Read the IP address in the report to identify which server refused the connection.
2. 02Contact the recipient's organization or its mail provider and give them that address and the time of the attempts.
3. 03The destination admin should check that the server accepts connections on port 25 from Microsoft 365 and that the MX record points to it.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

• Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com

Further reading

• MX lookup