Your Exchange server is probably set not to allow out of office responses to
the Internet.

The settings are in Advanced properties of Internet Message Formats

It's probably a good idea not to allow automated messages of any kind to be
sent to the Internet, they can cause message loops, they tell spammmers the
address is valid and they annoy people whose email address has been spoofed
by a virus.

assistant from within either outlook or outlook web access, the out of
office reply is only sent for internal emails - external mail just gets
arrives as normal with no out of office reply. Any body any ideas?