Migrating mailboxes from Exchange 5.5 to Exchange Server 2007 directly is not supported. Using native tools, administrators will have to perform this kind of migration as a two-step process which includes: Migrating from Exchange 5.5 to Exchange 2003 Migrating from Exchange 2003 to Exchange 2007Typically, there will be two scenarios: Scenario 1: Exchange 5.5 and Exchange 2003 are in same Organization; Exchange 2007 is in a different Organization Here is the brief description of typical steps and related information: - In Exchange 2003 / 5.5 Organization 1. Exchange Server 2003 Migration Wizard doesn’t allow migration from an Exchange 5.5 in the same organization. 2. You should verify that Active Directory Connector is installed on Exchange 5.5 machine and replication service is configured with correct credentials and with correct port. You can do this by going to Start > Programs > Microsoft Exchange > Active Directory Connector. Change to port for Exchange Server to 389 if it is set to something else. 3. You can wait for replication or you can select replicate now in Active Directory Connector (especially if Exchange 2003 in newly configured in this organization). 4. Once you can see all the users with mailbox information in Exchange 2003 machine, you are ready for migration to Exchange 2007.- In E2007 Organization 1. Verify that there is a trust between these two organizations. 2. You need to have Administrative privileges in the other organization. 3. You cannot do Cross-Org migration using the GUI wizard. You have to use Exchange Power-Shell. 4. Open Exchange Power Shell and enter $s=get-Credential. Enter the Administrator account and password of the other organization. This credential information would be saved in variable “s”. 5. Then to transfer a mailbox, you can use the following commandMove-Mailbox -identity <username> -sourceForestGlobalCatalog <e2k3server> -targetDatabase <Target MBD > -sourceForestCredential $s -NTAccountOU Users. 6. If this command gives some error, verify that Exchange information store service and Exchange System Attendant Service is running.Scenario 2: Exchange 5.5 is one organization; Exchange 2003 and Exchange 2007 are in a different Organization. Verify that there is a trust between these two organizations. This one is easier and it can be done using GUI wizards. - In Exchange 5.5 Organization 1. In Exchange 5.5, you should go to Exchange Administrator Console and verify that the port for LDAP is set to 389 in Protocols.- In Exchange 2003 and Exchange 2007 Organization 1. On Exchange 2003, run the Migration Wizard. Move the selected user mailboxes to Exchange 2003 server using Migration Wizard. 2. On Exchange 2007, run the Migration Wizard to move mailboxes to Exchange 2007.Conclusion 1. Users with moved mailboxes will still use OldOrg\UserName to login and check their emails as their login credentials are still in the previous organization. 2. Users will appear as disabled users in Exchange 2007 machines.Note: ISV tools are available to help in this kind of migration, including 'Quest Migration Manager for Exchange' that can aid in Exchange 5.5 to Exchange 2007 migrations and archiving tools such as 'CommVault QiNetix' that can archive Exchange 5.5 content and restore to Exchange 2007. Other tools might be available too. This blog posts covers what can be done with native Microsoft Exchange tools only.