Based on the calendar, which shows if you're out of office, the server should
be able to auto reply an out of office notice to sender.  Of course this
option can be configured.  Many times when the calendar reminds me of an out
of office appointment or out of office all day event, I don't always remember
to turn out of office assitant on.  So when an email comes in,
Outlook/exchange can see that according to my calendar, I'm currently out of
the office, then auto replies with a generic out of office notice.  It should
be simple enough to implement. 8*)