Thunderbird was working fine receiving and sending emails until yesterday afternoon. I have 10 email accounts installed that are on 5 different servers, all set to IMAP. Suddenly I cannot send any email as I get the SMTP timeout error every time. Running TB 52.1.1 (64bit) on Ubuntu 16.04. I checked the SMTP settings and none have changed. Whatever it is, it is not a server problem, but a Thunderbird problem as far as I can see. Any help much appreciated as I have a backlog of emails to send!