Along with the Firefox 11.0 release yesterday, Mozilla has released version 11.0 of its Thunderbird E-mail client, for Mac OS X, Linux, and Windows. The new version includes user interface improvements, and several bug fixes. It also fixes eight security flaws, five of which Mozilla rates as Critical. More details are available in the Release Notes.
You can get the new version via the built-in update mechanism (Help / Check for Updates), or you can download versions for all platforms, in more than 50 languages.