Forum Discussion
Hybrid Exchange change of SMTP relay connector
Whenever I setup a connector for this purpose on an Exchange 2016 Server, I always set the security tab options as follows;
I would definitely double and triple check your firewall rules too. Do you definitely have the Exchange Online IP's all allowed for the Exchange 2016 server?
Check the Exchange 2016 box for any particular settings or limitations that may be causing the connection issue, such as IP restrictions or authentication settings.
In addition, confirm that DNS resolution and network connection from the Exchange 2016 machine to Office 365 are working properly.
Finally, check any recent modifications or additions to the Exchange 2016 setup that may affect SMTP relay services operation.
If the problem persists, it may be helpful to engage with Exchange professionals or Microsoft support for more troubleshooting and solutions.