It sounds like the mac client created the folder. Do you have the newest build installed? Older builds created it - the last time i had it created by Outlook Mac, i deleted the folder using my windows computer.
The clutter option appears (in the outlook on the web options) when focused inbox is turned off in the Office 365 accounts, but AFAIK, clutter is no longer supported on the consumer side - nothing should be going into it.
It was indeed created by Outlook on a Mac. From that client, I do not have any option to delete it. In fact, I don't have many options in the Outlook Client (But that's another story)... I don't have this option either in Outlook.com (as shown on the screenshots below). And I do not have the Focused Inbox option turn on.
Well, this isn't created by the Mac Client because it is on my webmail, too. This is typical Microsoft crap. I don't want Focused Inbox. I don't want Archives. I don't want Clutter. I don't want "groups." And I don't want conversations. I want a clean box because I have 76 work-based folders of my own that take priority.
On webmail, there is no "Option" option when you click on the gear, as others have said. There is nothing to turn Clutter off. If you right click in the client and delete, it just reappears a few seconds later. Same with the other folders I mentioned.
Why for @(*@# sakes did they do this? Don't think for us. Just give us a reliable email client, thank you.