Under X, it displays a window on your screen showing you whether or not you have any e-mail.
It beeps when you receive new message, and it can even show you the headers of your first 10 e-mail messages.
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Organize your e-mail before you even open your inbox with filters view it
Thunderbird helps you maintain your privacy view it
How to create an e-mail in Hotmail view it
Instant messaging in Google Wave with the Ping feature view it
Customize your Yahoo email with your own personal touches view it
A video overview of Google's latest, Google Wave view it