I think you might be confused between an email client and email service. Mail.app is what is known as an email client. It allows you to retrieve and manipulate email from POP and IMAP email servers. .Mac serves email in either POP or IMAP form, which Mail.app can access. AOL has its own proprietary email connection technique. They supply both ends of this relationship with AOL mail servers and the AOL mail client. Mail.app is free, but it does not include an email account. There are many ways to get one, from your ISP or from a third party for a variety of prices with a variety of features.