Alex,

Is there any chance you started configuring the MTA-STS feature in Xeams but did not finish it all the way? When MTA-STS is configured, Xeams will try to issue an SSL certificate for multiple hosts, and all of them MUST resolve to your public IP. Try the following steps to confirm this theory:

• Using Windows File Explorer or a Terminal if you're on Linux, go to $INSTALL_DIR\config folder
• Look for a file called sslCertHosts.dat.
• This file contains the additional host names that Xeams will try to get an SSL cert for and all of them MUST resolve to your public IP.
• Print the contents of this file and confirm if the host names listed resolve correctly. If not, remove this file, restart Xeams, and try issuing the certificate again.