From what a book I'm reading, MS Outlook Inside-Out, says-here's what's
happening. A client-side rule (such as with the Out of Office Assistant)
processes the automatic response only once per messages received from the
same email account. To have a reply sent to every message you receive, you
must setup a server-side rule, which means you save the rule to an Exchange
Server. It is then processed for each message that arrives.
Hope this bit of info helps.
