The beta, which came out in early December, is a developer preview release being made available for the Thunderbird testing community. For users, the beta includes a new message tagging feature as well as new ways to browse through messages. For developers, the beta includes improvements to the extensions system.
The new tags feature replaces the existing label feature, with a nice addition—the ability to create custom tags. In addition, we could also mark messages with a star, which is another column that can be sorted in the message view.
The new "message toast" element has also been retooled to provide a little more detail about new messages.
We liked the new navigation elements. We could add buttons to the main menu that allowed us to click sequentially through the message list, as well as navigate through previously read messages using a forward and back button.
A few new elements have been added to folder organization as well, such as the ability to designate some folders as favorites. We could then change folder views between the main folder list, a recent folder list, an unread folder list and a favorites folder list.
Changes to the extensions system include enhanced security and easier localization. In addition, developers can now create extensions that save custom data in the mail database as well as add columns to the message list.
The final version of Thunderbird 2.0 should come out in the first quarter of 2007. Testers can find out more about this developer preview release here.