“User is authenticated but not connected” after changing my Exchange password

When I start Thunderbird (31.2.0 under Ubuntu 14.04), my Outlook 365 account john.doe@example.com accessed over IMAP is completely unreachable (I can't even see the list of folders, even though I have local archives). I see the following message in a D-Bus notification (several times): > The current operation on 'Inbox' did not succeed. The mail server for account john.doe@example.com responded: User is authenticated but not connected. This account has been working for a while. I changed my password during my previous Thunderbird session; after entering the new password, Thunderbird still worked. What does this seemingly nonsensical message “User is authenticated but not connected” mean? How do I get my email?