This is amazing! as a long time user of Thunderbird on my desktops (along with #Kmail on some of my #KDE machines, I have to be honest ) and K-9 users for years, I can't be more happy to see that partnership happening!
My current email client on Linux and Mac. I used to be a huge #kmail fan on #kde but dumped it years ago due to the addition of underlying frameworks which made it unusable and unreliable. Welcome to the #fediverse