A few weeks after releasing Thunderbird 3.0, an overhaul of its open-source e-mail software, Mozilla has issued an early test version of a successor that smooths rough edges and fixes some bugs.
A principal change coming with the first alpha version of Thunderbird 3.1, code-named Lanikai, is the inclusion of the Gecko 1.9.2 browser engine, which is the version used in the present Firefox 3.6. The browser engine can be used in Thunderbird for extensions that do things like show Google Calendar or let people take actions in e-mail that require a Web page.
Several improvements to IMAP.
Several fixes for Smart Folders, message filters, and attachment handling.
Several design improvements and corrections to the interface.
Download Manager is now accessible as a menu item (Tools > Saved Files).
Stability and memory improvements.
The full list includes 147 changes in Thunderbird 3.1a1 so far. Obviously, though, expect more as the alpha matures to beta and eventually final release.
Trying to emulate its Firefox brethren, the Mozilla Messaging group that develops Thunderbird is trying to accelerate the release schedule for the software.