Exchange 2000 organizations operating in native mode are more administratively flexible than those operating in mixed mode. You can switch to native mode once you've completed your migration to Exchange 2000 and no longer need to support older versions.
Before you switch to native mode, all of the system folders from all sites must replicate to Exchange 2000 servers and all Connection Agreements and Site Replication Services must be removed. Once you're sure you're ready, follow these steps to make the switch to native mode:
Your Exchange organization is now in native mode. As with many things in network administration, actually making a change is faster and easier than all of the preparation it takes to be ready to make the change.
Note: Once you switch to native mode in Exchange 2000, you can't go back, so make sure you're ready before you make the switch.