Thunderbird is by far the best MUA I've used. I use a Chromebook as my daily workstation and I cannot wait for it to support Linux applications so I can run Thunderbird rather than my current situation (a mix of web-mail and ALPINE).
It requires disabling a fair amount of the benefits of a Chromebook to enable. Yes, I have tried it. Also, the method it uses to display X11 applications is fairly terrible.
