In order for Outlook 2007/2010 to access the Out of Office Assistant, Outlook must connect to the server’s autodiscover service. Out of Office Assistant will encounter an error if the domain does not have an autodiscover CNAME record.
Contact your local IT administrators and have them add the following:
Exchange 2007 – autodiscover.yourdomain.com (redirects to) autodiscover.elephantoutlook.com
Exchange 2010 – autodiscover.yourdomain.com (redirects to) autodiscover.us.elephantoutlook.com
Once the CNAME record is created Outlook’s out of office assistant will work as expected.