Variable: mail-mime-unsent-header
mail-mime-unsent-header is a variable defined in rmail.el.gz.
Value
"^Content-Type: message/rfc822 *$"
Documentation
A regexp that matches the header of a MIME body part with a failed message.
Source Code
;; Defined in /usr/src/emacs/lisp/mail/rmail.el.gz
(defvar mail-mime-unsent-header "^Content-Type: message/rfc822 *$"
"A regexp that matches the header of a MIME body part with a failed message.")