On 2001-11-08, Matt Armstrong <matt+dated+1007876070.52bd2b@lickey.com>
wrote:
> Of course, if point is already at the sweet spot, message-bol should
> then go to the real beginning of line.

This does what you want (I'm not sure if I duplicated some functionality
with message-point-in-header-p, maybe some more experienced gnus hacker
can tell me):

(defun message-point-in-header-p ()
  (let* ((point-in-header (point))
         (body-begin (progn
                       (message-goto-body)
                       (point))))
    (prog1
        (< point-in-header body-begin)
      (goto-char point-in-header))))  ; saves the save-excursion overhead

(defun message-beginning-of-line (&optional n)
  (interactive "p")
  (let ((cur-point (point)))
    (beginning-of-line n)
    (when (message-point-in-header-p)
      (let ((to-point  (save-excursion
                         (end-of-line)
                         (re-search-backward "^[^:]*: " nil t)
                         (match-end 0))))
      (unless (= cur-point to-point)
        (goto-char to-point))))))
      

(define-key message-mode-map "\C-a" 'message-beginning-of-line)

Have fun,
-- 
Andreas Fuchs, <asf@acm.org>, asf@jabber.at, antifuchs