Remove additional mailboxes from Outlook

Once you add an additional mailbox to Outlook, you might not be able to remove it receiving the message:
"This group of folders is associated with an e-mail account. To remove the account, on the Tools menu, click Account Settings, select the account, and then click Remove."

However, the account isn't listed there and you're unable to remove it. This happens because, annoyingly, while you can give yourself access to a mailbox, you can't actually remove the access as well. To really remove access you need to open ADSIedit and drill down to the user account who's mailbox you're trying to remove in Outlook, go the properties of their object, find the property called "MSExchangeDelegateListLink" and remove your account from it. Restart Outlook and after a couple of minutes the accounts will disappear.