This guide assumes you've already setup your e-mail accounts through cPanel if you haven't please login to your cPanel account and select the "E-Mail Accounts" option.
1. Once you open up the Mail client you will be prompted with a "Welcome to Mail" window asking you to fill out your name, e-mail and password. Fill it out according to the e-mail account you setup.
2. In the following dialog it will ask you to configure your "Incoming Mail Server". I would recommend you select either "POP" or "IMAP" for the account type. Inside the "Incoming Mail Server" input box you will be putting "mail.yourdomain.com" (replace "yourdomain.com" with your actual domain).
3. You will now be asked to setup your "Outgoing Mail Server". This is the same as the previous dialog except you'll need to check "Use Authentication".
If everything was successful you should be presented with the Mail client ready for use. If you have trouble at this point please contact support with any error(s) you're receiving.