Variable: message-send-hook
message-send-hook is a customizable variable defined in message.el.gz.
Value
(smail:widen)
Documentation
Hook run before sending messages.
This hook is run quite early when sending.
Probably introduced at or before Emacs version 27.1.
Source Code
;; Defined in /usr/src/emacs/lisp/gnus/message.el.gz
(defcustom message-send-hook nil
"Hook run before sending messages.
This hook is run quite early when sending."
:group 'message-various
:options '(ispell-message)
:link '(custom-manual "(message)Various Message Variables")
:type 'hook)