After sorting out account configuration issues very recently with Thunderbird, and having it work perfectly with 21.04, the program now is erratic when sending mail. I am unable to quit Thunderbird with either the top left menu Quit command or the keyboard chord command. Sometimes after invoking the Quit command from the Menu, nothing will happen for several seconds and then the computer will just do a restart (as if it were reading my mind). If the computer does not restart after giving a quit command, I have to manually select restart from Settings, in order for the mail program to be no longer active.

I do not mind restarting the computer when the mail program refuses to quit. I do not mind when the computer just automatically restarts after a ineffective Quit command. I do think that neither of these things is a normal way of operating Thunderbird, which has worked well for me, before 21.10.

If this is something that will be addressed by whoever it is that does these things, then I am content to just restart when the mail program locks up. Otherwise, I may need a fix.