This article will help you identify what is the reason why you are not able to send or receive emails from your mail server.
There is no difference in the troubleshooting technique on issues with receiving and sending emails.
First I will assume you already know what your servers hostnames are. For example we have as incoming mailserver mail.yourdomain.com and for outgoing mailserver we have smtp.yourdomain.com.
First thing to check is if the host resolves to the proper server IP address.
Open command prompt terminal. If you do not know how to do that please click here HERE.
Then type:

