421.4.4.2 connection dropped exchange

Question

Good afternoon

I appreciate that you can help with this problem, I have an Exchange 2019 server installed locally, the problem I have is specifically with some domains, most of them work fine, however occasionally it happens to me with some domains that the emails stay in the sending queue generating this message:

421.4.4.2 Broken Connection Exchange

The error occurs in certain domains when an email is sent to more than one recipient, however, if you delete the email queue and send the email to the affected domain again, leaving only one recipient, the email goes out without a problem.

Please could you help me with what validations I can do to determine the cause.

Thank you so much

Answer 1

Hi @Camilo Quintero ，

Thanks for posting in our Q&A forum.

The error message you’re seeing, “421.4.4.2 Broken Connection Exchange,” indicates that there is a problem with the connection between your server and the recipient’s server.

Based on the information you’ve provided, it seems that the issue occurs when an email is sent to more than one recipient. One possible solution is to create a new send connector for the affected domains and set ForceHELO to true. You may also need to restart the Microsoft Exchange Transport service. You can also try enabling TLS 1.2 on your server if it isn’t already enabled.

If the issue persists, you may want to check if your server’s Public IP is listed in any blacklist DNS, which could cause delays in message delivery.

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