ISC Networking Help System - Why does Exchange Out of Office reply to everything (or Why isn't OOF like Pobox Classic Vacation)?

By default, Exchange Out of Office will respond to any message that you receive. You may wish to utilize a different setting, i.e. only respond to your contacts, or use OOF rules. Information about configuring OOF rules can be found at:

http://support.microsoft.com/?kbid=290846