If you are performing a multi-stage migration, you should remove or disable the Exchange mailboxes of users who have already been migrated so that new messages are delivered to the GroupWise mailboxes and not the Exchange mailboxes. However, do not remove or disable the Exchange mailboxes until all migrated users have had time to receive their notification messages that provide their GroupWise usernames, passwords, and server information.
If some users to not receive their notification messages and you configured the Migration Utility to send copies to the Administrator user, the needed information can be retrieved from the Administrator mailbox. Users’ usernames and passwords are also available in the CSV used by the Migration Utility, as described in Section 3.2.2, Creating the Exchange Data File.
After all users have been migrated from each Exchange server, you can shut down Exchange and use the server for other purposes as needed.