message-alter-recipients-function

message-alter-recipients-function is a variable defined in `message.el'.
Its value is

nil

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

Documentation:
Function called to allow alteration of reply header structures.
It is called in `message-get-reply-headers' for each recipient.
The function is called with one parameter, a cons cell ...

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.1 of Emacs.