The first thing you need to do in order to configure your Mail Enable POP Account with Apple's Mail.app is open Mail.app and go to the Mail menu, then choose Preferences.

After you open up the preferences make sure you are on the Accounts section of the Preferences.  Click the + sign in the bottom left.

In the next screen you will fill out the basic information, such as Name and Email Address.

On the next screen we will fill out the Incoming server settings.  Choose POP from the dropdown and give it a description so you know what account this is.  Make sure you replace example.com with your organization's domain name.  (Your username will always be your full email address)

On the next screen we will fill out the Outgoing server settings.  Again, make sure you replace example.com with your domain name.  Also make sure Use Authentication is checked.

Hit continue and that's it!  Your new email account has been set up.