Outlook 365 Issues

The Folder Pane shows two email addresses. The email tab in Account settings only shows two email addresses, one of which is not included in the Folder Pane. The missing email address is my main email.

If I try to add an email account, I am asked  "who are you?" If I use my main email address I am told it does not exist (it does, and is successfully used to log into my Microsoft account).