Mozilla Messaging pushed the stable release of Thunderbird 3 out of the nest on Tuesday, and there's a lot to like in case you haven't been following the beta development of this Outlook alternative. The long-overdue Thunderbird 3 is available for Windows, Mac, and Linux, and it introduces several hefty new features and some long-needed improvements, including an overhauled search and message indexing, tab support, and a revamped setup wizard that's designed to make new account setup quick and painless.

One feature that isn't included is the calendaring add-on, Lightning. Originally, Mozilla had planned to bake the extension into the program, but decided back in February 2009 to change course and leave it up to users to download. Although Thunderbird natively comes with Microsoft Exchange support, there's no calendar and therefore no meeting support in the default Thunderbird installation. Along with Lightning, there's an essential Google Calendar add-on for Lightning that gives Google users calendar support in Lightning. Currently, the only version of Lightning that works in Thunderbird 3 is the nightly build, available here.

Even without Lightning, Thunderbird makes for an excellent desktop-based e-mail client. Beyond Outlook replacement, it also makes a savvy offline or local-storage tool for the various Web mail providers. Gmail integration has existed in Thunderbird for a while, but improvements in version 3 include better recognition and integration of Gmail's special folders. These include Sent and Trash, and the non-English versions of Gmail. The All Mail option in Gmail defaults in Thunderbird to the Archives folder.

Thunderbird 3's new search results pane. (Credit: Screenshot by Seth Rosenblatt/CNET)

Undeniably, the killer feature in Thunderbird 3 is the search. The most obvious competitor, Microsoft Outlook, doesn't offer anything that comes close to the level of granular control that Mozilla has given Thunderbird users. The new search bar is dominant at the top of the interface, and is set by default to search all messages. When you search, a new tab will open with your results organized as shown in the screenshot above. Filters based on e-mail addresses, folders, and tags appear on the left, while the majority of the window is given over to displaying summaries of the e-mails that meet your criteria. There's also a timeline bar graph at the top of the results. Click it, and then mouse over any of the subcategories to see how they occurred over time.

You can change the search box to one of several filters, including Subject, From, Recipient, To, CC, and Message Body. Frustratingly, you can't filter by Tag. You can also save any of these filtered searches as a virtual folder. Editors' note: The previous two paragraphs have been rewritten for clarity.

The new search bar drops down with options, but also can do predictive on-the-fly queries similar to the URL bar in Firefox 3. (Credit: Screenshot by Seth Rosenblatt/CNET)

There is one drawback to the search: the first time it indexes your messages, you're potentially in for a long, long wait. In testing, this depended entirely on the number of messages in your folders. High volume accounts, whether locally archived or all on a server, should probably set their indexing to run overnight. After the first indexing, each new e-mail is added as it comes in.

E-mails open by default into new tabs, making the e-mail reading experience far more similar to the Web-browsing one. This can be toggled under the Advanced section of the Options, under the Reading and Display tab. The hot keys for the e-mail tabs have been mapped the same as in Firefox, so middle-click an e-mail to open it in a new tab but retain your focus on the current tab. The CTRL+Tab hot key combo will cycle through your tabs, and there's an open tab button on the right side of the tab bar to help manage your tabs.

There's a new activity manager that records all interactions between your e-mail provider and Thunderbird, making it easier to track down errors when you send or receive mail. There's also an entirely new system for archiving messages based on Gmail's "archive and forget it" method. The new version offers the traditional multiple-folder-based solution, as well as the new dumping-ground style, which can be activated via the "A" hot key. Thunderbird 3 supports Firefox personas, too, further reinforcing their shared architecture.

Thunderbird 3 beta 4 introduces tighter folder integration for Gmail users. (Credit: Screenshot by Seth Rosenblatt/CNET)

Other changes include major code improvements. The setup wizard now looks to for additional information on how to configure the account. This changes how new Web mail accounts are created. Mozilla has said that only the domain name from your e-mail address gets sent to Mozilla's servers, and that the entire process falls under the Mozilla's privacy policy. Nevertheless, it's a move that's likely to cause some concern among privacy advocates.

The compact header mode has been deleted, which is sure to annoy those who like using Thunderbird on smaller-form computers like Netbooks. Windows users should see Thunderbird results appearing in federated searches in Windows Vista and Windows 7, while Mac users will find Growl notification support for new e-mails, integration with Spotlight and the Mac OS X address book, and support for The full changelog for Thunderbird 3 can be read here.

Thunderbird 3 rates as a top-notch e-mail client, and it's definitely the best freeware one around. It will require some fidgeting to get it to be usable in a corporate environment, but it's far more scalable to user needs than anything else currently available.