While I love using em client, I find it a bit slow compared to other programs when reading and filing mail. The best way for me to speed up is to not use the mouse and be able to do everything with the keyboard.
What I don’t like with the keyboard shortcuts is the usage of control modifiers. When reading and filing mail the entire keyboard is available, so why not use n for next unread message or a for archive. Think Vi instead of Emacs (for those who have used both).
Filing is cumbersome because you need to use the mouse. (using the keyboard with the move to function does not work very well). Being able to use the keyboard and filtering the list of folders would be nice.
On the other hand since searching works so well in em client it may make more sense to have one archive folder (like the SPAM folder) with a single button command to file the read email to the archive.