How to turn the 'Clutter' feature off in Office 365
Sign in to Outlook Web App with your email address and Office 365 password..
At the top left corner of the page, select the App launcher icon, and then select Mail.
On the top right corner of the page, go to Settings > Options > Mail > Automatic processing > Clutter.
Choose Separate items identified as Clutter, then Save .
You can turn Clutter off anytime by selecting Don't separate items identified as Clutter.
Please note that this will stop any new emails going into the Clutter folder, but will not revert the changes made. You should move all the Clutter folder contents back to your inbox, and then delete the Clutter folder manually.