So we are setting up an on premise server. We are relaying email to our Mail Enable server. If I un-check TLS/SSL and dont use a user name or password, mail is sent from 3CX. Fine, that is expected. If I check TLS/SSL, I get a message that the operation was cancelled. I get this with or without authentication. I setup an SMTP relay on the same windows box that runs 3CX and I can get email to relay just fine but when I send an invite, I get the following error. "smtp;554 5.6.1 Body type not supported by Remote Host" My research indicates the SMTP relay server doesn't like the HTML. I see a lot of people having success with Gmail Relay but I really dont want to go that route. I am ready to go out and play in traffic unless someone else has some ideas.