Exchange, Office 365 backup and migration Licensing

• Backup and migration Licensing are based on the total number of source mailboxes that will be migrated / backed up. Each migrated / backed up mailbox consumes one license.
• A single license is consumed for each source mailbox (SMTP address) matched when you start a migration. Once the license has been consumed (assigned to a mailbox), reassigning it to another source mailbox is no longer possible. Mailboxes are counted by the licensing system only once.
• Source mailboxes that have already been counted by the licensing system can be migrated as many times as you want. There is no risk that the same source mailbox will use more than one license when you restart the migration.

Public Folders Backup and Migration

• Note that the Public folder backup and migration takes 20 licenses out of the total license purchased. This number is fixed and doesn't depend on the actual number of public folders that are being backed up or migrated or their size

Using the same mailbox on multiple machines

• Once a license is consumed to migrate a specific source mailbox, attempting to migrate the same mailbox by using another instance of the program (installed on a different computer) will not consume another license.