Your Incoming mail server or POP3 mail settings should be : mail.yourdomain.com
(where yourdomain.com is your actual domain name).
This setting will allow you to check for any email on any POP3 account set up on your domain.
Your Username should be : user@yourdomain.com (where "user" is the username and "yourdomain.com" is your actual domain name)
Note: If your domain name is in the processes of being transferred to the host or is still in propagation, you will need to use your IP address instead of mail.example.com. You can obtain your IP address from your Control Panel