If your Exchange organization is in native mode, where all servers are running Exchange 2000 Server or later, this division between administrative groups and routing groups enables you to create routing groups that span administrative groups and move servers between routing groups that exist in different administrative groups. This functionality also allows you to separate routing and administrative functions. For example, you can administer servers in two central administrative groups, placing servers from each administrative group in different routing groups, based on your network topology and usage requirements. However, the functionality of routing groups in a mixed-mode environment, where some servers are running Exchange Server 2003 or Exchange 2000 Server while others are running Exchange Server 5.5, is different than in native mode. In mixed mode, you: Cannot have a routing group that spans multiple administrative groups. Cannot move servers between routing groups that exist in different administrative groups.