4. Adding calendaring functionality
Thunderbird has a calendaring plugin called Lightning that is free to download and use. However you will also need to download a second program, Davmail, which needs to be used inconjunction with Thunderbird/Lightning for Exchange calendaring to work.
Davmail is available for Windows, Mac and Linux and there are setup instructions for Linux and links to external setup information for the other two operating systems on the Davmail page.