Yesterday, at work, I was adding a group mailbox that I believed that I had access to, to my outlook 2010 client. For some reason only Microsoft knows about, this forces a restart of the outlook client.
It turned out that I didn’t have the permissions required to this shared mailbox, and when I started outlook it kept asking for username and password for that mailbox.
When I clicked “cancel”, outlook stopped responding for a long time, so navigating to the menu where I could remove the account again took an eternity.
The quick way to remove the account from outlook is, surprisingly, to use the control panel. There is a “Mail” function there. It takes you to the same mail account management dialog as from whithin outlook, only difference being that because outlook is closed, it doesn’t try to open the mailboxes, so I could remove the shared mailbox until I got the permission for it today.