Journaling is an option that allows you to record all inbound and outbound email communications to support a company’s email retention and/or archival protocols. Journaling allows you to more easily comply with state or federal (or your country’s) records retention laws, as well as your company’s internal records retention strategy.
If journaling is enabled, can MigrationWiz migrate all the data in the journaling mailbox?
It is supported, but with the caveat that for those users with journaling enabled, you would need to purchase an additional separate mailbox migration license or User Migration Bundle license (for example, purchase a license for the journaling mailbox, as well as a license for the mailbox of the actual user).
Exchange journaling inspects all messages that pass through the Hub transport. If a message matches the criteria specified in journaling rules, a journal report is created and delivered to the journaling mailbox.
Journaling rules defined at the Destination will not be triggered when migrating mailbox data via Exchange Web Services (EWS), therefore it is not necessary to disable journaling during migration.
Microsoft TechNet article providing a detailed overview of journaling in Exchange Online.
Microsoft TechNet article providing a comprehensive summary of journaling options for Exchange.