I have a fully patched Exchange 2013 server and the latest Thunderbird IMAP-client.
When the user tries to open some subfolders under inbox he gets an error "The current operation on 'subfolder' did not succeed. The mail server for account user@Exchange responed: Server Unavailbale. 15."
Some subfolders work though and subfolders under the subfolder that cant be opened works.
I found this post but no answer to what the user changed to make it work:
https://social.technet.microsoft.com/Forums/office/en-US/2508f50f-6b28-4961-8e6c-5425914d4caa/no-server-unavailable-15-on-exchange-2013?forum=exchangesvrclients
The folder is visible and readable from other clients like Outlook and webmail.