(defvar my-mh-screen-saved nil
  "Set to non-nil when mh-e window configuration shown.")
(defvar my-normal-screen nil "Normal window configuration.")
(defvar my-mh-screen nil "mh-e window configuration.")

(defun my-mh-rmail (&optional arg)
  "Toggle between mh-e and normal screen configurations.
With non-nil or prefix argument, inc mailbox as well when going into mail."
  (interactive "P")			; user callable function, P=prefix arg
  (setq my-mh-screen-saved		; save state
        (cond
         ;; Bring up mh-e screen if arg or normal window configuration.
         ;; If arg or +inbox buffer doesn't exist, run mh-rmail.
         ((or arg (null my-mh-screen-saved))
          (setq my-normal-screen (current-window-configuration))
          (if (or arg (null (get-buffer "+inbox")))
              (mh-rmail)
            (set-window-configuration my-mh-screen))
          t)				; set my-mh-screen-saved to t
         ;; Otherwise, save mh-e screen and restore normal screen.
         (t
          (setq my-mh-screen (current-window-configuration))
          (set-window-configuration my-normal-screen)
          nil))))			; set my-mh-screen-saved to nil

(global-set-key "\C-x\r" 'my-mh-rmail)	; call with C-x RET