How to Clean Up Inactive Mailboxes Before Migration?
One effective way to streamline your Office 365 Tenant to Tenant Migration is by identifying and removing stale or unused mailboxes. This not only reduces costs but also simplifies the migration scope.
Using Office 365 Manual Mailbox Migration, run reports with PowerShell (Get-MailboxStatistics) to identify inactive users based on last logon time. Archive or export mailboxes that are inactive and determine which accounts should be excluded from the migration project.
For users with files in OneDrive, apply the same logic to Cross Tenant OneDrive Migration by using storage reports from the Microsoft 365 Admin Center. Files can be transferred to team storage or reassigned before decommissioning inactive users.