I have re-installed Windows 10 recently and re-imported my Thunderbird profile and since then I am unable to send messages with Thunderbird. None of my 12+ e-mail accounts allow me to send messages, but receiving messages work fine. I've done all the steps listed on your website, including disabling my antivirus completely, but nothing works. However, I did notice something crucial, which is that '''running Thunderbird in "Troubleshoot Mode" does fix the problem''' of not being able to send messages. And yes, I have tried to make the changes of disabling all add-ons and resetting toolbars/controls permanent, but that did not fix the problem. The only thing that works is restarting the browser in Troubleshoot mode. '''The issue is obviously not with my mail servers or it wouldn't work in Troubleshoot mode.''' Any help would be appreciated.