Just like the main domain in your account, add-on domains can have their own email account. Since add-on domains don't have a separate control panel to manage their sites, email accounts must be added through the main control panel.
how to add an email account for an add-on domain:
Login to 'cPanel' with the URL: yourdomainname.com/cpanel
Click 'Mail'.
Enter the email username you want to use for the email account and click the drop down icon to select the addon domain name.
Enter the desired password.
Click 'Create Account'.
