Step 1: Launce Apple Mail
Step 2: From the Top Menu select Mail > Add Account as shown below:
Step 3: Select the account type by scrolling to the bottom of the account list and select "Add another Account as shown below.
Step 4: Enter in your credentials as shown below.
Step 5: After Apple Mail has tried to configure the mailbox it will allow manual config as shown below. Set your incoming and outgoing mail servers to your email server Domain Name, Then click Sign in to Continue as shown below.
Step 6: Now you will be able to access your web mail, Please note this may take some time to download all your emails address book and calendar.