Given the maturity of the underlying Mozilla code, Thunderbird is very usable. However, it is considered a Technology Preview, and as such is assumed to have defects.
Scott MacGregor writes: "Thunderbird 0.6 has taken flight! Some of the
more prominent features include a new Windows installer, Pinstripe theme
for Mac OS X, new artwork, improved junk mail controls, new mail
notification in the system dock for Mac OS X, server-wide news filters
and a slew of other new features."
Get your official 0.6 Thunderbird builds:
http://www.mozilla.org/products/thunder ... nload.html
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7) Gecko/20040501