Two points. First, Microsoft’s web application for Outlook doesn’t work too well on Safari if you want to set an out-of-office message. (It lies and says that your reply is too long.) Use Firefox, it works great.
Second point, don’t use Mac Mail’s Rules without thinking too hard about it. Between the time I set the message and made it back into my house an hour later, Mac Mail e-mailed replied to every message in my inbox since February.
Oy.