I had to set up a new email for a person yesterday and they use outlook 365 and we had a heck of a time, we were able to set it up on a phone and their laptop that has office 2019 on it. However, their connected outlook 365 kept on failing. Now there are like 20+ of these ghost accounts on the left sidebar and no way to get rid of them because they don't show in managed accounts or in mail accounts. There is no right-click option to remove them either. We tried getting rid of their OST files but when we restarted the PC and relaunched they all came back the ost files.
Any idea on how to get rid of these accounts not connected to anything that is sitting there on the left-hand side. Also, the server admin provided a work around that sometimes office 365 doesn't like IMAP setups and we had to go through the new mail setup but not through the new account setup and it set right up with no issues.