Out of Office Assistant is an available feature only if you connect to
Microsoft Exchange Server as your mail server. If you don't use Exchange
Server, you can use Outlook Rules Wizard or one of the third-party automatic
rules processing addins. See http://www.slipstick.com/rules/index.htm and http://www.slipstick.com/addins/index.htm .
If you using outlook to connect to lets say comcast you can go to their page
and your account and set an out of office setting. Check with your provider
if you can do this.