How to open the next message in the currently selected mailbox in mail.app When viewing a message in a separate window in Apple Mail (Mountain Lion), how can I open the next message in the list with a keyboard shortcut?
I found navigating email in a thread incredibly frustrating especially for long email that have hundreds of lines of quoted text, and was trying to find the answer to this.

So here goes:


first highlight an email in a thread: click next to the title, the email borders should be highlighted
use the right/left arrow buttons to go to the next/previous email in this thread