BTW I've followed the instructions therein to log the events and you can see below the results:
2019-08-08 21:30:15.478000 UTC - [5220:Main Thread]: I/SMTP SMTP Connecting to: xxx.xxx.xxx.xx:110 2019-08-08 21:30:15.525000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:15.525000 UTC - [5220:Main Thread]: I/SMTP SMTP Response: +OK Hello there. 2019-08-08 21:30:15.525000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 14 2019-08-08 21:30:16.500000 UTC - [5220:Main Thread]: I/SMTP SMTP Send: QUIT 2019-08-08 21:30:16.500000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:16.519000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:16.519000 UTC - [5220:Main Thread]: I/SMTP SMTP Response: +OK Better luck next time. 2019-08-08 21:30:16.519000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 11 2019-08-08 21:30:16.530000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 12 2019-08-08 21:30:16.530000 UTC - [5220:Main Thread]: I/SMTP SMTP connection error quitting 80004004, ignoring 2019-08-08 21:30:17.789000 UTC - [5220:Main Thread]: I/SMTP SMTP Connecting to: xxx.xxx.xxx.xx:110 2019-08-08 21:30:17.839000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:17.839000 UTC - [5220:Main Thread]: I/SMTP SMTP Response: +OK Hello there. 2019-08-08 21:30:17.839000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 14 2019-08-08 21:30:18.812000 UTC - [5220:Main Thread]: I/SMTP SMTP Send: QUIT 2019-08-08 21:30:18.812000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:18.832000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:18.832000 UTC - [5220:Main Thread]: I/SMTP SMTP Response: +OK Better luck next time. 2019-08-08 21:30:18.832000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 11 2019-08-08 21:30:18.842000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 12 2019-08-08 21:30:18.842000 UTC - [5220:Main Thread]: I/SMTP SMTP connection error quitting 80004004, ignoring 2019-08-08 21:30:19.852000 UTC - [5220:Main Thread]: I/SMTP SMTP Connecting to: xxx.xxx.xxx.xx:110 2019-08-08 21:30:19.912000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:19.912000 UTC - [5220:Main Thread]: I/SMTP SMTP Response: +OK Hello there. 2019-08-08 21:30:19.912000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 14 2019-08-08 21:30:20.944000 UTC - [5220:Main Thread]: I/SMTP SMTP Send: QUIT 2019-08-08 21:30:20.944000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:20.964000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 0 2019-08-08 21:30:20.964000 UTC - [5220:Main Thread]: I/SMTP SMTP Response: +OK Better luck next time. 2019-08-08 21:30:20.964000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 11 2019-08-08 21:30:20.974000 UTC - [5220:Main Thread]: I/SMTP SMTP entering state: 12 2019-08-08 21:30:20.974000 UTC - [5220:Main Thread]: I/SMTP SMTP connection error quitting 80004004, ignoring -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1215882 Title: Emails are silently discarded on 554 reply to STARTTLS To manage notifications about this bug go to: https://bugs.launchpad.net/thunderbird/+bug/1215882/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs