mail-unsent-separator

mail-unsent-separator is a variable defined in `rmail.el'.
Its value is

"^ *---+ +Unsent message follows +---+ *$\\|^ *---+ +Returned message +---+ *$\\|^ *---+ *Returned mail follows *---+ *$\\|^Start of returned message$\\|^---+ Below this line is a copy of the message.$\\|^ *---+ +Original message +---+ *$\\|^ *--+ +begin message +--+ *$\\|^ *---+ +Original message follows +---+ *$\\|^ *---+ +Your message follows +---+ *$\\|^|? *---+ +Message text follows: +---+ *|?$\\|^ *---+ +This is a copy of \\w+ message, including all the headers.*---+ *$"

Documentation:
A regexp that matches the separator before the text of a failed message.