Is your usage IMAP-centered ? Then I can only recommend Trojita (http://trojita.flaska.net/ http://trojita.flaska.net/). There are a few quirks here and there,

Is your usage IMAP-centered ? Then I can only recommend Trojita (http://trojita.flaska.net/ http://trojita.flaska.net/). There are a few quirks here and there, but it's pretty much the one application that is started when my computer starts and closed only when it is shut down. Its smart usage of IMAP makes it extremely efficient (doesn't download all of your emails just to display one, doesn't download the entirety of a single mail just to display its subject, ...). The only downside is that your usage has to be pretty close to IMAP for trojita to work best for you.