exim can use "your message" instead of "the message".
"^ *---+ +Original message follows +---+ *$\\|"
"^ *---+ +Your message follows +---+ *$\\|"
"^|? *---+ +Message text follows: +---+ *|?$\\|"
- "^ *---+ +This is a copy of the message, including all the headers.*---+ *$")
+ "^ *---+ +This is a copy of \\w+ message, including all the headers.*---+ *$")
"A regexp that matches the separator before the text of a failed message.")
(defvar mail-mime-unsent-header "^Content-Type: message/rfc822 *$"