If you are using EAC it will use New-MigrationBatch cmdlet and New-MigrationBatch cmdlet uses a system migration mailbox “Migration.8f3e7716-2011-43e4-96b1-aba62d229136” to keep the metadata. This issue occurs even though the mailbox database that hosts the Migration mailbox is neither the source or target mailbox database. The transactions logs that are generated may be very large, depending on the size of mailboxes that are moved, and could lead to disk space issues.
So Microsoft given the solution , while moving mailboxes around databases if you think it will be a problem to generate transaction logs on the database where Migration System Mailbox is (Due to large metadata), than you should consider the following options.
- Turn on Circular Logging for the database where Migration System Mailbox is. (Circular logging is evil don’t do it if you have important mailboxes on that database, lol).
- Go back to your Exchange 2010 days and use New-MoveRequest to move mailboxes.
- Move the transaction log path to a very large volume for the database where Migration System Mailbox is.