message-cross-post-note-function

message-cross-post-note-function is a variable defined in `message.el'.
Its value is

message-cross-post-insert-note

• This variable may be risky if used as a file-local variable.

Documentation:
Function to use to insert note about Crosspost or Followup-To.
The function will be called with four arguments. The function should not only
insert a note, but also ensure old notes are deleted. See the documentation
for `message-cross-post-insert-note'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.