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.
Virus scanners do this (some even in their default configurations, it
seems), and it's really annoying.
Yeah, I have seen this behavior on the main IETF list a time or two.
Autoreplies sent to Cc: or To:
fields is never a good idea because the software cannot know the
semantics of the addresses.