Is Earthlink your isp? I don't see anywhere on their
home page a hosting site for webmail style applications, like, for example, Hotmail, Yahoo mail, or G mail.
If Earthlink is simply your ISP, you should be able to use any email client (like Outlook Express - part of Windows) to connect to the server and download emails, which will be scanned by default by Avast.
Perhaps you better tell us what operating system you use, and how you connect to the internet?
(The operating system should appear when the system is starting up, and is likely to be something like Windows XP, or Windows Vista. Please advise.)