With the introduction of the rewritten mail send there has been a huge uptick in the number of folk having issues sending mail from Thunderbird. The changes have also brought with them a new way of logging the sending of mail in Thunderbird to provide diagnostic information.
Logging is now done using the error console (Ctrl+Shift+J) in the
developer tools, but for this to occur you need to enable logging using
the config editor. Modify/set the preference
All using the linked config editor instructions
Now open the Error Console and clear any existing entries by clicking on the trash icon.Send a mail, debug logs should show up in the Console tab looking something like what is shown below.
If you have been asked to supply a log, or are seeking support somewhere with failures in sending then the following will provide a text file with the log in it.
Right click the console/log window and select all from the menu.
Right click again and select the rather oddly named "copy message"
Open windows notepad.(Windows key+R type notepad and press enter)
Save the file to your documents and either copy and paste or upload the file to provide the log to others. Be aware that the From and To addresses in the email are in the log you are sharing.
This part will certainly not work in versions after 91.
Again using the config editor set the preference mailnews.smtp.jsmodule to false. This will invoke the old mail sending code that has been replaced and already removed from Thunderbird from V93 onwards. This will allow the diagnosis of the problems to ensure it is the new send code that is at issue. It will also allow a few months of using the old code while bugs are fixed. Please file bug in bugzilla if you identify a bug in the new code.