Variable: mail-header-separator
mail-header-separator is a customizable variable defined in
sendmail.el.gz.
Value
"--text follows this line--"
Documentation
Line used to separate headers from text in messages being composed.
Probably introduced at or before Emacs version 17.
Source Code
;; Defined in /usr/src/emacs/lisp/mail/sendmail.el.gz
;;;###autoload
(defcustom mail-header-separator "--text follows this line--"
"Line used to separate headers from text in messages being composed."
:type 'string)