First, go to your account settings, they should be under Edit or Options in the menu:
Once you're in your account settings, add a new account from the actions menu at the bottom:
Enter your name, email address, and the password to the account, then hit continue:
On the next screen, click on the Manual Config button:
You will need to add your domain to the username, so that the username is your full email account.
Make sure the Incoming and Outgoing mail servers are set to mail.domain.com where your domain is the second part of your email address after the @ symbol
When you click the "Done" button, you will get a security warning:
Simply click on the confirm security exception. When you send mail for the first time, you will get this notice again. Confirm security exception again when that happens.
