The SMTP server does not support the STARTTLS extension.

[Tom Lee]

I am using Exchange 2016 and the 3CX is set using custom.
It was working last week. Over the weekend it does not work.
We did change the SSL on the Exchange server. Do we need to restart the SMTP on the 3CX?

 

[Tom Lee]

Find the issue! Somehow the command changing the SSL on the connectors was not run.