We run Exchange 2003 on Server 2003. Our clients are mostly XP machines running Outlook 2007. We recently added a couple of Windows 7 systems, and are running Outlook 2007 on them. Occasionally our users will receive a message that Outlook is attempting to connect to Exchange, BUT instead of specifying the Exchange server, the message specifies one of our domain controllers. Exchange doesn't live on those DCs, so of course the system freezes up momentarily.