Mozilla unveiled the final version of its open-source Thunderbird 2 email client on Thursday, improving how users can organize and label their messages.

Users can now add customized tags to messages, a feature that has proven popular with other blog and photo-sharing sites, Mozilla said. The tagging function replaces static labels that users can assign to messages in older versions of the client. Also new is a feature to sort through email by history, similar to what a user can do in a web browser.

Thunderbird 2's search box will start displaying results as soon as the user begins typing, and specific searches can be stored in folders, Mozilla said. The client can also access other web-based email services, such as Gmail and .Mac.

Notification has also been refined. New messages now generate a notice that lists the subject and the sender of new messages in the lower right corner of the screen, then fades after a few seconds.

On the security side, Thunderbird 2 will block remote images in email messages. The junk mail filter can learn about spam messages in order to block similar ones, a feature that is used in combination with the spam filters of the web mail provider, Mozilla said.

Thunderbird 2 is a free client that's available for Mac OS X, Windows and Linux systems in over 30 languages.

Mozilla also disclosed information on Thunderbird 3, which is due to ship in early 2008. Mozilla plans to enhance the user interface plus incorporate other platform improvements that will take advantage of the Gecko 1.9 rendering engine.