I've been using Thunderbird in office for a couple months now, never had any problems. Today, nobody is able to send or receive messages. After selecting "get all new messages," the following error message pops up: "The current operation on 'Inbox' did not succeed. The mail server for account <my email address> responded: Unable to open mailbox." When trying to send a message, the following error appears: "An error occurred while sending mail. The mail server responded: Unexpected failure, please try later. Please check the message and try again"