After my email account was moved to Exchange Online, I noticed that my Inbox in MS Outlook client looked different. The All and Unread tabs were replaced with two new tabs: Focused and Other. This was a new feature called Focused Inbox that intelligently was dividing up my Inbox email into these two categories.
After trying it for a few days, I decided I did not need it. To turn it off, go to View → Show Focused Inbox and turn it off.