(goto-char (point-min))
;; Quote parts.
(while (re-search-forward
- "<#/?!*\\(multipart\\|part\\|external\\|mml\\)" nil t)
+ "<#!*/?\\(multipart\\|part\\|external\\|mml\\)" nil t)
;; Insert ! after the #.
(goto-char (+ (match-beginning 0) 2))
(insert "!")))))