How to test the remote SMTP connection from your server by using telent.
Before starting you will need to encoded your username and password with base 64 encoder.

BASE64 Encoder websites

https://www.base64encode.org

http://www.freeformatter.com/base64-encoder.html

http://encodertool.com/base64

SMTP Ports: 25, 465, 587

TEST CONNECTION

telnet IP PORT
EHLO >HOSTNAME<
AUTH LOGIN
>Your BASE64 encoded username< 
>Your BASE64 encoded password<

And if you get “235 Authentication successful” then you have a successful connection.