Clutter is an email filtering option available to Office 365 students. It is similar to an anti-spam filter as it moves less important email (based on your reading habits) into a 'Clutter' folder where they can be ignored or reviewed later. Most of the mail going into the folder should be bulk mail (advertisements) and messages from mailing lists. However, you will want to periodically check the Clutter folder as it may move legitimate email into this folder.
Individuals can choose to disable Clutter if desired. To disable Clutter log into OWA, click on the Gear (top right corner), Options, Automatic Processing, Clutter and select Don't separate items identified as Clutter then click Save.
If you are using OWA and need to mark messages as "not clutter", either right click on the message and choose 'Mark as not clutter' or just drag it to the Inbox. If Exchange is missing messages you want marked as clutter, right click and choose 'Mark as clutter' or drag it to the Clutter folder. In Outlook and other clients, you’ll need to drag a message to the clutter folder to mark it as clutter or drag it to the Inbox to mark it not clutter.
Users can drag messages they deem suitable to the Clutter folder to "train" the tool to spot similar email in the future. The tool gets smarter over time, learning from your prior actions with similar messages.
Once Clutter is enabled in OWA, it appears in other clients linked to that Exchange account, including Outlook on both Windows and OS X desktops and notebooks, and the iPhone and Android OWA apps.
Note: If you have rules moving messages, Clutter is applied after server-side rules are applied and items touched by rules won't be filtered by clutter.