Update 08/15/2019 14:05 PM 14 days
Between the hours of 4am - 930am Eastern, Outlook users would have seen a autodiscover prompt for an account not tied to their organization (firstname.lastname@example.org) in error. The autodiscover prompt was a result of us testing public folders for our 2016 environment and that account was one of our demo public folders. Although no users could see or open the public folder, autodiscover detected it as an available mailbox and begun to prompt users about allowing Outlook to try and connect to the public folder.
The public folder was disabled and we will investigate this further into the off hours