On the other hand, I gave thunderbird a try after switching to linux and found their UI so bad that it was harming usability. After the app had finished taking up the screen with various controls, settings and the list of messages, there was a tiny window left over to read the email itself, and it seemed like the threading of messages was basically broken. It wasn't that it looked old exactly that bothered me (although it did), but that I was buried in a mountain of jank from the start.

I quickly found a new client, but not one I love. If thunderbird does get a UI overhaul I'd give them another chance, and it sounds like they're moving towards a UI that I at the very least would prefer.