Mozilla's Thunderbird has come into its own with version 2 for Windows, Mac, and in a portable edition. Starring features and innovations that take aim at both Web e-mail clients and industry standards such as Microsoft's Outlook, open-source Thunderbird offers the best of both worlds.
Back and forward buttons, like the ones you have in your Web browser, let you jump through messages in the order that you viewed them. Keep your e-mails organized with tags, even across dozens of message folders. Configuration is as simple as entering your e-mail address and password. Search results can be saved, and Thunderbird has Firefox's extension capability, allowing for user-designed tweaks that greatly enhance the program, including Lightning, which provides calendaring features.
Even when weighed down by multiple folders and RSS feeds, the program loads fast, and the basic feature set remains intact: good junk mail filters, HTML support, multiple identities, and POP, IMAP, and Microsoft Exchange server support. Security features include S/MIME, digital signing, message encryption, and a built-in phishing detector. Flexible, powerful, and lightweight, Thunderbird 2 is an appropriate companion application to Firefox in every way.