Utilize the Exchange Deployment Tools for the entire migration process to streamline the deployment and reduce risk.
Migrate using the Move Mailbox process whenever possible, and resort to the ExMerge process only if migrating between Exchange organizations.
Install the Active Directory Connector on the first Exchange Server in the Site.
Switch the AD domain to Native Mode in advance of the ADC setup and Exchange migration, to ensure proper replication of security groups.
Use the site and server consolidation strategies in Exchange Server 2003 to significantly reduce the number of servers that will need to be supported.
Rely on the ADC Tools to configure the connection agreements, and modify them only if there is a specific reason to do so.
Leave an Exchange 5.5 Server in place only if it is needed to support connectors that are unsupported in Exchange Server 2003.
