The
message-followup command pops up a message buffer
that's a followup to the message in the current buffer.
Message
uses the normal methods to determine where followups are to go,
but you can change the behavior to suit your needs by fiddling
with the message-followup-to-function. It is used in
the same way as message-reply-to-function (see
Reply).
The
message-use-followup-to variable says what to do
about Followup-To headers. If it is
use, always use the value. If it is ask
(which is the default), ask whether to use the value. If it is
t, use the value unless it is
‘poster’. If
it is nil, don't use the value.