http://www.mozilla.org/Thunderbird 1.0 is Mozilla’s next generation e-mail client. Thunderbird makes emailing safer, faster, and easier than ever before with the industry’s best implementations of features such as intelligent spam filters, saved search folders, builtin RSS support, privacy protection and much more.
Software that is Mozilla this year ends up being netscape next year. So in a sence it is sort of beta. However I've yet to have any real problem with any of their software.
Give it a try, I think you'll like it.
It is highly configurable, and easy to work with. Best of all its free of course.
