May be it is related to https://bugzilla.redhat.com/show_bug.cgi?id=1441601#c8 ? Are patches from there in ubuntu?
** Bug watch added: Red Hat Bugzilla #1441601 https://bugzilla.redhat.com/show_bug.cgi?id=1441601 -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to thunderbird in Ubuntu. https://bugs.launchpad.net/bugs/1691333 Title: upgrade to 52.1.1 breaks smtp starttls on 16.04 and 17.04 Status in thunderbird package in Ubuntu: New Bug description: after todays update to 52.1.1 while sending message using smtp server with STARTTLS and auth thunderbird reports unknown error: Ошибка отправления сообщения. Отправка сообщения с использованием Сервера исходящей почты (SMTP) «XXXX» не удалась по неизвестной причине Previous version (45.8.0) works OK. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/1691333/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp
