According to the release notes, the e-mail client provides several new features. First among them are the tabs familiar to Firefox users that allow opening multiple mail messages side by side. The tabs are stored when quitting Thunderbird and are restored when reopening.

The developers around David Ascher also whittled at the search function. Search results can now be filtered by more attributes and even using the timeline tool. Thunderbird also indexes received mails in advance to get to the search results more quickly.

Important messages can be archived by pressing the A key to file them in the new Archive folder system. The new Add-ons Manager allows extensions to be installed directly from Thunderbird, although Thunderbird 2 extensions might not quite work in Thunderbird 3 and it might be best to test them individually for new add-on versions.

The new mail account setup is helpful in that it tries to detect automatically the IMAP and POP3 settings, sparing you from having to do costly searches on the major free mail provider websites. It's enough just to enter the name, e-mail address and password, and Thunderbird theoretically takes care of the rest.

Developers furthermore simplified the address book and improved and upgraded the integrated spam filter. If you forget to include an attachment, Thunderbird will remind you to do so, provided you defined a keyword such as "attached" or "included" and include it in the message.

An integrated migration assistant helps users upgrade from Thunderbird 2 to 3 and offers some choices for settings. However, developers suggest backing up profiles, because the upgrade might overwrite the previous version. The e-mail files are usually stored in the $HOME/.mozilla-thunderbird directory. Because the directory can get quite large, enough free space should be provided on the hard drive.

The release does have some known issues. For example, some Thunderbird 2 users may not be able to log in to their SMTP server because the secure authentication fails. Switching back and forth between Thunderbird 3 and an older release may also not update passwords properly because of where they're now stored.

You can download Thunderbird 3 right away, but it might make more sense to wait until the individual distros provide it, for a better integration into the desktop.