Windows Live Mail
is a desktop program with some great new ways to manage your email. It's part of Windows Live Essentials, a free download that also includes Messenger, Photo Gallery, Movie Maker, and other software that helps you do more with Windows 7.
With Windows Live Mail, you can read and reply to your email even when you're offline. When you're back online, new email messages will download to your PC, and any messages in your outbox will be sent.