The message-reply function pops up a message buffer that’s a
reply to the message in the current buffer.
Message uses the normal methods to determine where replies are to go
(see Responses), but you can change the behavior to suit your needs
by fiddling with the message-reply-to-function variable.
If you want the replies to go to the Sender instead of the
From, you could do something like this:
(setq message-reply-to-function
(lambda ()
(cond ((equal (mail-fetch-field "from") "somebody")
(list (cons 'To (mail-fetch-field "sender"))))
(t
nil))))
This function will be called narrowed to the head of the article that is being replied to.
As you can see, this function should return a list. In this case, it
returns ((To . "Whom")) if it has an opinion as to what the To
header should be. If it does not, it should just return nil, and
the normal methods for determining the To header will be used.
Each list element should be a cons, where the CAR should be the
name of a header (e.g., CC) and the CDR should be the header
value (e.g., ‘larsi@ifi.uio.no’). All these headers will be
inserted into the head of the outgoing mail.