So in the interest of balance I have to say thunderbird is a excellent program. I use it as my daily driver in work and for personal use.
It has so many features that puts me, the user, in control that I totally take them for granted until I have to use outlook for something.
I use it in a multinational, I used it with exchange and now with office 365. People can complain away but there are many like me who rely on it every single day and it has a real, positive impact on our work lives every single day.
Some days are just email client and Web browser, and without thunderbird and Firefox working for me as the user...... I dunno, work would be a lot more frustrating I guess. MASSIVE thanks to all the contributors to thunderbird!