Coexistence

As you proceed with your Exchange 2007 upgrade, you will almost certainly have a period of time during which your Exchange 2007 servers will be required to coexist with legacy Exchange. During this time, there are several points you should consider:

• If you have multiple routing group connectors with legacy Exchange routing groups, especially so that there are multiple paths between a legacy Exchange routing group and the Exchange 2007 routing group, you must disable the propagation of link state routing. Link state routing is not used by Exchange 2007, but the presence of multiple paths can cause message routing loops in the legacy Exchange servers. The Exchange 2007 documentation contains instructions on performing this task under the topic "How to Suppress Link State Updates."

• Legacy Exchange servers use the X-EXCH50 SMTP extension to pass Exchange-specific properties with message data within the organization. While Exchange 2007 no longer uses this connection, any routing group connectors created with legacy routing groups in the organization are automatically configured to support this extension. If you have a multiple-forest configuration where Exchange 2007 and legacy Exchange servers are communicating but in separate forests, you will need to enable this extension manually. The Exchange 2007 documentation contains instructions on performing this task under the topic "Configuring Cross-Forest Connectors."

• The Edge role can be used as a smarthost for an Exchange 2003 organization without requiring the Active Directory preparation steps. However, because Edge cannot synchronize with a legacy Exchange organization, you lose much of the advanced functionality that it offers.

• The UM role cannot offers services for recipients whose mailboxes are on legacy Exchange servers.