A Microsoft file hosting and synchronization service.
I fixed it!
I went to File -> Office Account. Under User Information I signed out. Had to sign out twice. I singed back in and then removed any connected services that did not automatically come back after signing back in. All that was left was my business one drive and my sites for SharePoint. I then restarted Outlook (because why not). I was then able to go back to an email and attach a linked file.