@morrow without logs this will be hard to track down. can you ask your administrator to open up a support case for this?
The complete mailbox added to the Folder list can be removed from Outlook. This can be done by navigating in Outlook to: Tools > Email Accounts > Remove or display existing accounts > Next Here, select Zarafa client and click Change.... A new window will be opened. Click the tab Advanced, select the name of the user of which the mailbox should be removed and click the Delete button. When you select OK and Finish you will leave the window and Outlook will be available again.