The concept behind Microsoft's Clutter folder was that your email would learn which emails are important to your based on your actions with reading, or not reading, emails that come to your inbox.  Microsoft has begun moving away from the Clutter concept and has been moving toward a 'Focused Inbox' and Other instead.  If you see messages going to Clutter that should be in your inbox or inbox messages that should go to clutter, please see Microsoft's instructions at the link below for how to take those actions.



https://support.office.com/en-us/article/Use-Clutter-to-sort-low-priority-messages-in-Outlook-7b50c5db-7704-4e55-8a1b-dfc7bf1eafa0


By the way, similar functionality is available for 'Focused Inbox' and 'Other' and junk email as well.