Likewise. There hasn't been a lot of innovation in the Thunderbird client, but it consistently and mostly stays out of the way. Search is pretty fast and messages go where they're supposed to go.

In ~five years of using it across three machines, I've only had two instances in which a folder got corrupted, and in both cases I was able to repair it and recover the messages.

Also, when I migrated from Windows to Linux, transitioning my email profile was utterly seamless.