Michael Boyle finds Mail frustrating 
to get around in.
He asks:
Why oh Why can’t Apple Mail allow me to navigate with the arrow keys the way NetNewsWire does? The relationship between the feeds pane and each feed’s posts in NNW is so fast and intuitive; whereas there seems to be no relationship between the mailboxes pane and the message panes in Apple Mail.
I am happy to admit that driving NetNewsWire with the keyboard alone is a pleasure.
However, it can also be done in Mail, even if the process is not quite as intuitive.
If you are keyboard-only kind of person, see an earlier Hawk Wings post “Moving around Mail.app using the keyboard“.