The Exchange Migrator is licensed based on the total number of mailboxes in the Office 365 subscription. The application checks the number of mailboxes in the Office 365 subscription via remote PowerShell when setting up the connections to Office 365. A common misconception is that it is licensed by the number of mailboxes you are trying to import or export. Since it is based on the number of mailboxes in the subscription, you can import multiple PSTs files in the same mailbox, or export the same mailbox multiple times, without exceeding the license counts. Additionally you can install the Exchange Migrator on multiple migration workstations using the same key.
Updated: April 16, 2016