Getting started with backing up Exchange Online includes completing the Office 365 guided setup—which helps you perform some of the required setup tasks—adding the mailboxes that you want to back up, and performing a test backup and restore.
Important: If possible, perform the getting started process in a test environment. After you perform a test backup and restore, you can move the system into production.
Verify that your environment meets the system requirements for Exchange Online.
What to Do Next
To back up all Active Directory users, add the Active Directory group to the Exchange Online app.
To back up public folders, add the public folders to the Exchange Online app.
To back up group mailboxes, atleast one licensed user must be added to the list of owners.
For security reasons, consider replacing the global administrator role with the Exchange administrator role.