Weeks after the launch of its Firefox 1.0 Web browser, the Mozilla Foundation yesterday released version 1.0 of its Thunderbird email client.

Thunderbird 1.0 is aimed at advanced email users and competes with products such as Microsoft's Outlook Express and Qualcomm's Eudora. The stand-alone open-source email application has been in development since early 2003 and offers features such as a user-trainable junk mail filter and a built-in RSS reader, according to the Mozilla Foundation.

The open-source group also promotes Thunderbird's tight security, which includes not allowing scripts to run by default and not automatically downloading images sent in an email. Also, Thunderbird uses the Mozilla rendering engine to display HTML email messages, not Microsoft's IE engine, making it immune to IE-related bugs.

While downloads of early versions of Thunderbird have already surpassed 1m, the Mozilla Foundation doesn't expect Thunderbird to take off the way Firefox did, a representative for the group says.

The Web browser has been downloaded just over 9m times since November 9, according to the Spread Firefox website.

Thunderbird has its roots in the Netscape Messenger 4.x client and the Mozilla mail and Usenet newsgroup client. Thunderbird development was led by two main engineers supported by volunteers, says Scott MacGregor, one of the engineering leads behind Thunderbird.

The Mozilla open-source project was started in early 1998 by Netscape, which was acquired later that year by AOL. Last year, the people behind Mozilla created a foundation, largely funded by a $2m pledge from AOL, to build, support, and promote Mozilla products.

In the future, the Mozilla Foundation plans to further develop Thunderbird and Firefox. The two stand-alone products essentially succeed the Mozilla Suite, which includes a browser, email client, HTML editor, internet relay chat client and Usenet reader.

Thunderbird 1.0 initially is available only in English. Versions in about a dozen other languages should be available in a week or two, according to MacGregor. Thunderbird is available for Windows, Linux, and Apple's Macintosh OS X operating system.

Thunderbird 1.0 is available as a free download from www.mozilla.org .