Try the following steps:

• Stop Xeams
• Assuming you are on Windows, go to C:\Xeams\config and open AppConfig.xml in any editor such as Notepad. If you are on Linux, this file will be in /opt/Xeams/config folder.
• Remove the lines containing following parameters:
  
  
  • sslCertificateFileName
  • sslCertificatePassword
  • sslCertKeystoreType
    
    
• Save the file
• Delete/rename C:\Xeams\config\synametrics.cert file so it is not found at runtime
• Restart Xeams

The above steps will make your Xeams download a self-signed certificate again from Synametrics website.

NOTE: It is not a good idea to run a self-signed certificate on an email server. That is because it is up to the sender's email server to ignore or reject this certificate. Some email servers may not like this and may decide not to use STARTTLS or in the worst case scenario, not send the message at all.