How Does Office 365 Provide Mailbox-Level Backups?

Well, it doesn’t! “Microsoft doesn’t give you direct access to the mailbox databases. Instead, they give you deleted item retention, plus you can use single-item retention and various types of holds.” Here is a link to more details about this:

There is no Office 365 feature or capability that protects against a logical corruption in the Mailbox. As well, you can’t use New-MailboxExportRequest or the EAC to export the contents of Office 365 mailboxes to PST files.

If Mailbox-Level backup is an absolute requirement for particular Mailboxes (let’s say CEO’s mailbox), probably those mailboxes shouldn’t move to Office 365.

So plan accordingly your integration with Office 365!