Your mailbox has been temporarily moved on Microsoft Exchange server.

Scenario:

You've switched to Office 365. You've connected Outlook to the Office 365 servers, but now Outlook is complaining: "Your mailbox has been temporarily moved on the Microsoft Exchange server. A temporary mailbox exists, but might not have all your previous data..."

The Problem:

You likely didn't delete and create a new Outlook profile using the Control Panel's Mail (Microsoft Outllok 2016) icon.

If you create the new profile using the Mail (32 bit) icon, you will get the above error every time you open up Outlook.

The Solution
Create a new Outlook profile using the Control Panel's Mail (Microsoft Outllok 2016) icon, not the Mail (32 bit) icon.