Turn Clutter on or off
You need to turn on Clutter in Outlook Web App, so that you can use it both in Outlook Web App and Outlook.
Sign in to Outlook Web App.
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.
NOTE The Clutter folder remains in Outlook after you turn off the Clutter feature. If you don’t want the folder listed under your Mailbox, move the emails from Clutter to other folders, as appropriate, and then right-click the Clutter folder and choose Delete Folder.
This information originally from: https://support.sf.edu/hc/en-us/articles/205293504-Turn-off-Clutter-in-O...