Although the Clutter folder is a ‘system’ folder (in Outlook/Exchange parlance) it can actually be deleted by the user within Outlook. However this doesn’t actually remove the folder from the server and mail is still directed into it but the user can’t see it… Classic Microsoft…
The quick fix is to log in to OWA as the user, locate the Clutter folder, right-click, Permissions, add the user and assign Owner rights…