rmail-bury in RMAIL

In emacs RMAIL, "b" runs the function "rmail-bury". What this does it bury (that is, remove from the screen) the current Rmail buffer and its summary buffer. This is a "privacy" function, clearing your screen of any mail you may be reading. The easiest way to get back to reading mail after this is "^XbRMAIL".

If, after understanding it's real function, you'd still like to break it, I'd suggest redefining it as the command you probably thought you wanted (to back up one message).

In your .emacs file:

    (setq rmail-mode-hook
       '(lambda ()
          (define-key rmail-mode-map "b" 'rmail-previous-undeleted-message)))