Looks like work on the 2.0 version of the Mozilla Thunderbird email client is progressing well. Mozilla just announced that the Alpha version is available for testing:

Mozilla Corp. on Thursday gave users a first look at the next version of its Thunderbird e-mail client by releasing an alpha of v. 2.0.

Thunderbird 2.0 Alpha 1, which can be downloaded in Windows, Linux, and Mac OS X editions, is suitable for developers only, Mozilla said on its Web site, although there are no actual barriers that block others from trying the software.

“[It] is being made available for testing purposes only,” Mozilla stated on the site. “Current users of Mozilla Thunderbird 1.5.0.x should not use Thunderbird 2 Alpha 1.”

I’ve been playing around with the Firefox 2.0 beta and have been enjoying it immensely, particularly the built-in spell checking, so I’m looking forward to the new Thunderbird client.