You will need the server settings for your e-mail address. Go to EarthLink Server Settings to get these settings.
Open Mail from the Dock or Applications folder.
In the Add Account section:
In the Incoming Mail Server window, add the incoming Mail Server details.
In Incoming mail security, select password under Authentication. Check SSL. Click continue.
In the Outgoing Mail Server window, click the arrow in the drop-down menu and select Edit Server List. Use smtpauth.earthlink.net
Click on Continue.
Now you will get a window for Outgoing Mail Security. Select password in Authentication. Check SSL. Click continue.
You will now get an account summary of the new account to be created. Click on create.
Your account is created. You're now ready to send and receive e-mails on your Mac OS X 10.8.5.