mode-specific paragraph-start

[Tyler Smith <tyler.smith@mail.mcgill.ca>]

Hi,

I want Emacs to recognise ".* wrote:$" as the end of a paragraph, so
that I can autofill email messages and not have the body of a message
get mixed in with the intro i.e., "Tyler wrote:".

I use the following hook to do this (among other things):

(defun my-mail-mode-hook ()
  (auto-fill-mode 1)
  (abbrev-mode 1)
  (fortune-to-signature)
  (setq paragraph-separate (concat paragraph-separate "\\|.* wrote:$"))
  (setq paragraph-start (concat paragraph-start "\\|.* wrote:$"))
  (set-fill-column 70))
(add-hook 'mail-mode-hook 'my-mail-mode-hook)

What I now notice is that my regexp gets added every time I send an
email, so that by the end of the day it's several lines long.
Currently it's: \f\|[ 	]*$\|.* wrote:$\|.* wrote:$

How do I set this variable so that it doesn't continuously grow?

Thanks,

Tyler