I have been looking at ways to get autodiscovery working within Outlook 2010 when a mailbox is stored on Exchange 2003. We have both Exchange 2003 and Exchange 2010. The mailboxes on Exchange 2010 work fine with autodiscover when using Outlook 2007 or Outlook 2010. However, if the mailbox is on Exchange 2003, Outlook 2010 does not work while Outlook 2007 does. Any reason as to why or any advice?