Recently I had an issue where some old Exchange Mailboxes that I had full access to had been deactivated or I had removed my full access permissions, but they were not being removed from my folder view in outlook. I found that to resolve the issue if I went to the properties of the account that was still appearing in my navigation pane using ADSI Edit or doing a Get-ADuser -Identity
-Properties MsExchDelegateListLink
the output would show my account still listed as a delegate. to remove my account and any other account in that property I did a set-aduser -Identity -Clear MsExchDelegateListLink
Closed and re-opened Outlook and a few minutes later the accounts were removed from my folder view.
Thanks to this Blog post for pointing me in the correct direction
http://social.technet.microsoft.com/Forums/office/en-US/87637d40-3801-4282-9df1-e519759aee07/cannot-remove-additional-mailbox
