When attempting to diagnose an email issue, there is a whole range of potential problems. These could be very simple or extremely complicated, however most commonly, the issue will be connectivity related. This means there is trouble with you connecting to the mail server, not that the server is offline. Here is a link to a free third-party service, which you can run to check if the issue is with your local computer.
If you can log in successfully, this means that your email server is working as it should and the issue is most likely your connectivity to the mail server. If this is the case, check to see if your firewall or network security features aren't blocking access to the cPanel mail server.
Please get in touch with our support team if you require further assistance.