Mozilla has released its first alpha version of Thunderbird 3.3, an update to the e-mail software code-named Miramar that drops support for PowerPC-based Mac. Miramar is available for Windows, Mac, and Linux.

The new software includes the Gecko browser engine used in Firefox, and with version 3.3, Thunderbird moves to the Gecko 2.0 engine that's the core of the upcoming Firefox 4. Firefox 4 is dropping support for Macs using PowerPC processors, too, to ease the arrival of new features such as a more secure and crash-proof plug-in design.

Apple announced its intention to drop PowerPC chips in June 2005 and released only an Intel version of its current operating system Mac OS X 10.6, aka Snow Leopard. But older machines inevitably linger in the real world. For those customers, software companies often maintain older versions of their software for a time.

According to the Miramar release notes published yesterday, one aspect of Thunderbird 3.3 is "support for Mac 32/64 bit Universal builds (Miramar Alpha 1 will no longer support PowerPC on Mac)."

Also coming: the new software also gets updated interfaces for managing add-ons and extensions, the ability to show the size of files being downloads, user interface improvements on Windows Vista and Windows 7, and many stability and performance improvements.

The current version of Thunderbird is 3.1.6. Mozilla is still debating whether to release Thunderbird 3.2, which would include an earlier version of the Gecko browser engine.

Firefox is the better known and more widely used software from Mozilla, but the Thunderbird group is working to make its software more useful. In particular, there's a long list of Thunderbird experiments designed to bring fresh ideas to the software. Those ideas include Thunderbird Sync, to synchronize user information across versions of the software installed on different machines' Contacts for Thunderbird to ingest contact data from Web services such as Facebook' data miners to extract useful information such as package shipping numbers from e-mail' and Thunderbird Air to revamp the user interface for small Netbook screens.

In addition, according to notes from a planning meeting yesterday, Thunderbird programmers are working on a feature to emulate Gmail's conversation view, which compresses back-and-forth e-mail discussions into a single item.