Test STARTTLS SMTP Connection

Run the following command to connect

openssl s_client -connect {server}:{port} -starttls smtp

Then find out what authentication is supported. It should now show "AUTH LOGIN" now that you have an encrypted connection:

ehlo {domain.com}

If you see "AUTH LOGIN" in the list then do the following:

AUTH LOGIN

Then base64 encode your username and password. Put the results of the username on the first line and press enter. Then the results of the password and press enter. You should then see a message to indicate if the authentication passed or failed.