This article applies to:
You have moved a mailbox from Exchange on-premise to Exchange Online in Office 365 but you need to roll it back.
A typical scenario is when it turns out that you have an older 3rd party application which needs to access the content of the mailbox, but the application itself is not Office 365 compatible.
If your Exchange organization is in hybrid mode it is quite easy to bring the mailbox back.
In Exchange Online admin center, under migration select the plus sign to create a new migration job and select Migrate from Exchange Online
Select the mailbox or mailboxes you want to migrate from Office 365 to your local Exchange Server.
Select the Exchange proxy server which will handle the migration job
Give the migration job a name and fill in options as shown.
Select to automatically start and complete the migration job.
Your migration job will show up in the migration job list.
Since we have chosen to automatically complete the job, as soon as the mailbox content is synchronized your mailbox will be switched to the old Exchange on-premise environment.