Thunderbird is quite a piece of crap. Apart from the core, everything else is written in javascript and thus it is a single-core web application.

I have decided to just leave it be, and let it hog my computer, because it interface decently with google calendar.

That being said, I can definitely vouch for clients like Claws Mail (a bit ugly, but does its job) and Evolution (super fast, but it's written in C#/Mono)