How to Switch to Native Mode
Because Exchange 2003 is structured to take advantage of Active Directory functionality, there are some limitations when Exchange 2003 coexists in the same organization with Exchange 5.5. When Exchange 2003 servers coexist with Exchange 5.5, your organization must run in mixed mode.
Running in mixed mode limits the functionality of Exchange 2003. Therefore, after migrating from Exchange 5.5 to Exchange 2003, it is recommended that you switch from mixed mode to native mode.
Before You Begin
Before you switch to Native mode consider the following:
After you switch your Exchange 2003 organization from mixed mode to native mode, you cannot switch the organization back to mixed mode. Before you switch to Native Mode be certain that your Exchange 2003 organization will not have to interoperate with Exchange 5.5 in the future.
You must remove all Exchange 5.5 servers from the organization before you can switch to native mode. See How to Remove Exchange 5.5 Servers from Your Exchange 2003 Organization.
You must remove the Site Replication Service before you can switch to native mode. See How to Remove Exchange SRS.
To switch to native mode
Start Exchange System Manager: Click Start, point to All Programs, point to Microsoft Exchange, and then click System Manager.
In the console tree, right-click the organization that you want to switch to native mode, and then click Properties.
In <Organization Name> Properties, under Change operation mode, click Change Mode.
In the <Organization Name> Properties dialog box, the Change Mode button is unavailable if any Exchange 5.5 servers are present or SRS exists in the organization.
In the warning dialog box, click Yes if you are sure that you want to permanently switch to native mode. Click Apply to accept your new Exchange mode.
To take full advantage of Exchange native mode, you must restart the Microsoft Exchange Information Store service on all of the Exchange servers in your organization. You do not need to restart all of the Microsoft Exchange Information Store services simultaneously, but you must restart the service on each server for the server to take advantage of all Exchange native mode features. Restart the service on your servers after the change to native mode has been replicated to your local Windows domain controller. See How to Restart the Microsoft Exchange Information Store Service.
To determine whether the changes have been replicated to your local domain controller, see How to Determine if You Are Running Exchange in Mixed or Native Mode.
For More Information
For more information, see Planning to Move from Exchange 5.5 to Exchange 2003.