Question : Outlook cannot connect to Exchange 2007 during a DC reboot

When I reboot one of my three domain controllers, all Outlook clients lose their connection to our Exchange 2007 server.  This only happens on one of the DC's.  The DC is question is running Windows Server 2008 Enterprise.  The other two DC are running Windows Server 2003 Standard. All three DC's are also configured as DNS servers The Exchange 2007 server is using one of the W2K3 servers ans the Configuration Domain Controller and has all three DC's listed as DNS servers.

Any suggestions as to why the Outlook 2007 clients lose connection to Exchange 2007 when this specific DC is rebooted?

Answer : Outlook cannot connect to Exchange 2007 during a DC reboot

I think this will explain why .. http://www.computerperformance.co.uk/exchange2003/exchange2003_global_catalog.htm#Why_does_Exchange_2003_need_Global_Catalog_Servers_
Exchange needs a GC.  You could make one of your other DCs a GC.