Further info about Autodiscover that follows my article "Exchange Autodiscover".
When installing a Client Access Server in your Exchange organization a Service Connection Point (SCP) is created in Active Directory. Domain joined clients will always search Active Directory for this SCP and will configure your Outlook profile according the information found in this SCP.
There are situations where you don't want this to happen, for example when you have an internal Exchange Server 2007 or Exchange Server 2010 deployment, but you want to use an external (hosted) Exchange Server 2007/2010. If you have this situation, you don't want to have the internal information interfere with the external Exchange Autodiscover configuration.
You can set a registry key to disable the internal SCP checking to accomplish this. Open the registry editor and navigate to the following key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\12.0\Outlook (or 14.0 if you use Outlook 2010)
Create a new key Autodiscover
Create a DWORD (32-bit) ExcludeScpLookup
Give it a value 1 if you don't want to use the internal SCP
Give it a value 0 if you do want to use the internal SCP