When you're just getting started less is more. An overload of features can easily result in a bad email experience. Ease of use and a good help system can help introduce novice users to electronic mail painlessly. But you also need to look for strong security so you can make mistakes (and you should!), and good export functionality so you can switch easily when you need a more powerful program.
3. Windows Mail
If you have Windows, you have Windows Mail, and of all the programs to begin your email life with, Windows Mail is not the worst. Its looks are a bit more serious than IncrediMail's, but that doesn't mean you can't have a lot of fun with it. (In versions of Windows prior to Vista, the included email program was called Outlook Express, a client very similar to Windows Mail.)
Eudora comes with a long list of powerful features, and sometimes it can be a bit difficult to find the more exotic ones, but for the most part its straight-forward interface that has grown over the years is consistent and surprisingly easy to use. And Eudora certainly has all the potential and all the features to accommodate to your growing needs.