Mozilla Messaging has launched the third alpha release of Thunderbird 3.0, a major update of the open source e-mail client. The current prerelease series, which is codenamed Shredder, is highly experimental and not intended for production use. The new alpha introduces tons of minor improvements and a handful of significant new features, including some of the first usability enhancements that are part of a major user interface overhaul.

Development on Shredder has been moving forward swiftly. Those of us who have been tracking the project's progress by following the Rumbling Edge bug digest blog are awed by the rate at which bug reports are being resolved. The complete list of fixes and improvements that were made for alpha 3 top 280 items.

The most significant changes in alpha 3 are various performance and usability improvements. The IMAP implementation got a boost in this release, and provides better support for offline usage. The new message view includes some contextually-relevant controls, such as buttons to reply, forward, and delete a message. Small star icons displayed next to the individual e-mail addresses in message headers can be used to quickly add contacts to the addressbook. This feature works in much the same way as the new quick bookmarking feature in Firefox 3.

The user interface changes in alpha 3 are just the beginning, and many more are coming soon. Thunderbird designer Bryan Clark has written several blog entries about user interface improvement ideas and the actual features that are appearing in the nightly builds. He recently described efforts to implement a tabbing system with session restore support. He has also written about some ideas for status bar improvements and subject autocompletion.

Mozilla Messaging got its start last year when it was spun off from the Mozilla Foundation and given $3 million in seed funding. This step was taken to give Thunderbird development more autonomy and so that Mozilla could reduce the scope of its own agenda and focus more closely on the browser ecosystem. The Mozilla Messaging organization, which is now headed by former ActiveState CTO David Ascher, first revealed its strategy for Thunderbird 3 earlier this year.

Mozilla Messaging plans to make Thunderbird an appealing mail option by incrementally improving the application's underlying architecture, refining the user interface to improve workflow and ease of use, and integrating calendaring functionality by leveraging the code of the Lightning extension. The organization also plans to explore other messaging mediums and extend the program so that it can accommodate more of the communication requirements of its users.

The original Thunderbird 3 alpha release, which took flight earlier this year, was the first to include Gecko 1.9, a much-improved version of Mozilla's rendering engine that is also used in Firefox 3.

Integration of the Lightning calendar extension is going to be one of the most important tasks for the Thunderbird developers as they get ready for the 3.0 release. The Calendar QA team is looking for some users to help test Lightning with Thunderbird trunk builds in preparation for beta 1. To participate, follow the instructions on the Mozilla calendar blog and help run some Litmus tests for Lightning.

The alpha 3 release is available for download from the Mozilla Messaging web site. For additional information, check out the release notes and launch announcement.