More information needed. Are you indicating you have more than one account and want the names of both to be your name? This has nothing to do with sending messages and is to allow Thunderbird to know one from the other. if your issue is other than this, please post more info. Thank you.

No. TB started creating these new account names on its own after I had been troubleshooting another issue. Don't know if that's related but I just want to get back into my original, single account with the original username (my email). When I start up TB now I end up in one of these phantom accounts. It otherwise looks like mine but it's not the original. Apparently the original exists because it won't let me correct it to that name but how do I get to it and eliminate these ghosts?

If the phantom accounts are listed in left pane of main screen, rugit click, select 'settings' and then scroll down slightly to 'account actions' where you can delete it.

Wow! Not only did that solve the problem of the extraneous account, it solved my main problem described elsewhere which was that after switching to OAuth2 I could not log in to Thunderbird. I've been battling this for days without success despite many helpful suggestions from forums. No idea why this did that but I don't care.

Thank you!

Now we'll see whether it sticks and whether I can find a way to get back all my old messages/folders. I thought they would be preserved when I reinstalled TB per some suggestion. They're apparently gone and I'm devestated. Turns out my cloud backup account that is supposed to save everything instead for some reason decides that certain directories are not user data and doesn't bother with them. Apparently includes my folders. I'll look around but...

Dang.