A free email programs comes with Mac OS X, and it's not a bad one at all. But you shouldn't be satisfied with the default email program at least not until you've checked out the free alternatives. Here are my top free Mac email programs.
PS: Looking for free email, you may also like free email services.
(Updated February 2011)
Mac OS X Mail is a solid, feature-rich and spam-eliminating, but also an extremely nice and easy to use email client.
Mozilla Thunderbird is a fully featured, secure and very functional email client. It lets you handle mail efficiently and with style, and Mozilla Thunderbird filters away junk mail too.
The Opera email client is a slick and flexible interface that will satisfy almost all your email needs, and Opera integrates RSS feeds in this experience as well. Some may find the message editor lacking a bit in power, and the absence of support for encrypted email is unfortunate.
Viêt Hoà Dinh, Dominique Leca & Jean-Marc Denis
Sparrow brings Gmail conversations and labels to the Mac desktop with a deftly slick and decidedly simple interface.
Mulberry is a powerful and incredibly versatile email client available for all the popular platforms. If there is something Mulberry lacks, it is simplicity.
Mailsmith, the email client from the makers of BBEdit, is just as powerful and feature-rich as the text editor.
It's a pity Mailsmith supports POP accounts only, and a — adequately empowering — rich-text editor could be a neat addition, too.
Never underestimate Mozilla! The email component of this open source browser is a solid performer, fully featured and handsomely usable.
Alpine is powerful console email program that makes you use email productively with automation aplenty and nary a distraction.
GNUMail.app is a slick email client with solid support for multiple accounts and powerful filters.