Variable: message-extra-wide-headers
message-extra-wide-headers is a customizable variable defined in
message.el.gz.
Value
nil
Documentation
If non-nil, a list of additional address headers.
These are used when composing a wide reply.
Source Code
;; Defined in /usr/src/emacs/lisp/gnus/message.el.gz
(defcustom message-extra-wide-headers nil
"If non-nil, a list of additional address headers.
These are used when composing a wide reply."
:group 'message-sending
:type '(repeat string))