Mozilla Messaging has been hard at work incubating the next major version of the Thunderbird mail client. A new beta release that was made available this week includes some nice user interface improvements and an extremely impressive new system for searching through messages.

Mozilla Messaging was spun off of the Mozilla Foundation in 2007 and established as a subsidiary with $3 million in seed funding. Run by former ActiveState CTO David Ascher, its mandate is to advance Thunderbird and build a new generation of messaging tools based on Mozilla's technology. The Thunderbird 3 roadmap began to coalesce in early 2008 shortly after Mozilla Messaging got pushed out of the nest and the first alpha arrived several months later.

One of the major goals of Thunderbird 3 is to boost usability by simplifying configuration, making commonly-used features more accessible, and providing more flexibility for interacting with messages and other kinds of content. The developers are also overhauling the extension system and delivering important performance improvements in areas like IMAP support. In previous prereleases they introduced contextual controls into the message header view and added support for a tabbed interface.

They have continued experimenting with new user interface concepts in beta 4 with the introduction of an improved search display and support for unified thread viewing. When the user clicks on a closed thread, the preview pane will show summaries of all the messages in the thread. Each summary is accompanied by the name of the poster and the date that the message was sent. This allows users to get an overview of the thread's contents at a glance. The same kind of combined message overview will also be shown when the user employs shift+click or ctrl+click to select multiple messages from the list.

One of the problems with e-mail discussions is that it's sometimes difficult to find a specific message in a thread where the same subject line is used throughout. By providing a short snippet of the email for context, the new thread overview mode in Thunderbird 3 makes it much easier to see the flow of the conversation and identify a specific posting later when you go back to a thread that you have already read.

This feature is a great addition to the mail client, but there are a lot of ways that it could still be improved. It would be useful, for example, if the summaries could be expanded in place to show the whole message. I'd also like an option to be able to have the summaries displayed with indentation to indicate which messages are replies to other messages. It might also be nice to have color coding on the names so it's easier to see who the messages are from at a glance without having to read the names.

The most impressive new feature in this beta release is the revamped search view, which loads in a new tab when the user types a query into Thunderbird's built-in search box. It provides sophisticated interactive filtering features, including a nifty timeline that can be used to narrow your search to a specific year or month. The messages that match the query are shown with excerpts. Users can sort the results by relevance or date and can click a link in the interface to switch to a more conventional inbox-style view with all of the results. The search box itself has gained Awesomebar-like autocompletion that will also make it easier to filter your searches.

The filtering sidebar of the search view will show a list of senders whose messages matched the query. Next to each sender, it will show you the number of matching messages that they sent. When you hover your cursor over one of the names, it will put an overlay on the timeline to show you what portion of matching messages for each month were from that sender. You can click to see only the messages from that sender or you can remove their messages from the result list. Below the senders in the sidebar, there is a folder list that functions basically the same way.

The only major downside of the new search feature is that it doesn't show very many results at once. You have to click a "Show more hits" button to load more. It will incrementally increase the list of visible results, much like the "more" button on Twitter. It would be really nice if additional results could be auto-loaded as the user drags the scrollbar down to the bottom. It would also be useful to have a slider for adjusting the size of the excerpts, kind of like the article length slider in Safari's RSS reader.

The new search feature and unified thread view both reflect the potential for taking advantage of Gecko's capacity for rich presentation to support more intuitive and functional user interface paradigms. The new search feature shows that the Thunderbird developers recognize the power that can be unlocked by using HTML in innovative ways in a desktop mail client. This is hopefully the first step towards moving beyond the conventional trifecta of folder tree, message list, and preview pane that have dominated desktop messaging interfaces.

Mozilla Messaging design expert Bryan Clark wrote a blog entry a few months ago about one of his experiments with rich mail visualization. He shows how CSS transforms can be used to display a message on an isometric cube. Although this example is somewhat frivolous and isn't intended for inclusion in Thunderbird, it's a great demonstration of how emerging Web standards can empower new approaches to presenting mail.

Thunderbird 3 is off to a great start and already has some very nice improvements over previous versions. Although users are increasingly adopting Web-based mail, there are many advantages to using a native desktop client, especially one that can use a built-in HTML rendering engine to deliver the best of both worlds. The key to success for Thunderbird is going to be delivering a top-notch extension system that will allow users to get more value out of the client. Mozilla Messaging has to make third-party developers think of Thunderbird as a messaging platform rather than a mere mail client.

Thunderbird 3 beta 4 is available for download from the Mozilla Messaging website. For additional details, refer to the release notes.

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