Junk folder name conflict
Junk mail folder called 'Junk Email' on Outlook for Mac (v15.26.1), but called 'Junk' on web browser version causing a synchronisation issue with the follow error message being received:
"One or more folders in your mailbox have name conflicts with others or system reserved names.
Folders with these names can't be downloaded by your IMAP e-mail program.
Please connect to your mailbox using your Web browser and rename those folders. Once renamed, those folders will be displayed in your IMAP e-mail application correctly."