that's part of why sending the response to the return-path address is
better - it's more likely to reach someone who can actually make use
of the response.
But they are not always the most useful target.
Consider an original message which has a From: PHB and CC: HR, and where
the recipient is the only address listed in To:. It is reasonable for an
out-of-office notification to go to the From: and CC: parties, since this
message is specifically intended for the recipient (given the other people
in the distribution, it would be a damn good idea to send it to all of
them). It is not entirely logical to send the message to the secretary
mailbox in the reverse-path. The secretary doesn't care.
It's never appropriate to send vacation notices to the entire list
of mailboxes in the To/CC.
Imagine the case of exactly this thread, where several people are
on the To/CC line, and the ietf-822(_at_)ietf(_dot_)org mailing list is also
on the To/CC line. If a vacation program did a reply-all, the
vacation notice would go to the ietf-822 mailing list.
-d