Scenario: Exchange 2010 to 2016 migration. Error moving mailboxes either from ECP or Exchange Powershell.
Error: MigrationTransientException: MapiExceptionMdbOffline: Unable to get mailbox information.
This error could be cause by several issue. One could be that the destination mailbox database or archive database has mailbox size limits that are lower than the size of the mailbox/archive being moved.
Make sure that the destination database does not have restrictive limits. If necessary, navigate to severs –> databases and amplify the mailbox size limit on both the mailbox database and archive database.