I’ve added some additional Exchange mailboxes to my account but now I can’t seem to remove them anymore in Outlook as they don’t show up in my account settings or the additional mailboxes list.

Right clicking on a mailbox and choosing “Close <mailbox>” produces the error:

"This group of folders is associated with an e-mail account. To remove the account, click the File Tab, and on the Info tab, click Account Settings. Select the e-mail account, and then click Remove."

As they are not listed there, how can I still close these mailboxes?