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.
IncrediMail is not only easy to use with its helpful assistants and simple configuration, it can also make your start with email a funny and exciting experience -- exciting in a positive sense as IncrediMail should give you little to worry about.
Starfish Family Mail is an easy to use and fun email client that protects kids (and anybody else) by allowing only specific contacts and by stripping HTML. Unfortunately, its authentication is weak.
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.)
AOL's email service is particularly simple and easy to use, and it can be a lot of fun, too.
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.
Mozilla Thunderbird is a fully featured, secure and very functional email client and RSS feed reader. It lets you handle mail efficiently and with style, and Mozilla Thunderbird filters away junk mail too.
7. Pegasus Mail
Pegasus Mail is not the email client that is the easiest to use, and it is not the neatest either. But is is highly secure, powerful, and most importantly it comes with the best help documents I've seen to make it attractive even for beginners.