David, thanks for reporting your results. Can you retest please and tell us if this reproduces with a curent beta?
If it reproduces, please run the performance profiler: 1. You must be using Thunderbird 68 or newer - betas from https://www.thunderbird.net/en-US/channel/ or current nightly build from https://archive.mozilla.org/pub/thunderbird/nightly/latest-comm-central/ 2. Install profiler add-on into thunderbird 68 (or newer https://www.thunderbird.net/en-US/channel/ ) - get the add-on file from https://github.com/firefox-devtools/Gecko-Profiler-Addon/blob/master/gecko_profiler.xpi?raw=true and in Tools > add-ons click the gear to install add-on from file 3. Follow instructions at https://profiler.firefox.com/ (videos BASED ON FIREFOX at https://profiler.firefox.com/docs/#/./videos-intro ) 4. Create a profiler URL and post it here. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1012858 Title: "Sending of message failed" dialog needs 100% of one CPU as long as it is open. To manage notifications about this bug go to: https://bugs.launchpad.net/thunderbird/+bug/1012858/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs