Clutter is a proactive email feature that separates out your mail based on your email reading habits. Clutter has been active by default for Office 365 users since August 15, 2015.
(NOTES: Clutter can only be disabled by visiting outlook.com/owa/state.or.us. You cannot remove the Clutter feature with the desktop application. Also, it is only possible to remove it if you use Internet Explorer, Firefox or Safari. Google Chrome will NOT work for this solution.)
You can use the following steps to disable the Clutter feature:
Open up Outlook Web Access
http://outlook.com/owa/ode.state.or.us
You'll be prompted for your ID\PW
Once logged in – click on the Settings Icon
Then, in the search area – type in Clutter
Under Options, you'll see Clutter
If you click on Clutter you'll see where you can uncheck the box to:
Separate items identified as clutter
Uncheck that box, then click Save