you go to account setting and use the account actions button. This will delete the currently selected account in the list above it.

Thank you for answering,

This is the screen I think you are talking about. But I don't see an Account Actions button there. Is this something new in the current Thunderbird version?

Magda

Stay in the left sidebar after clicking 'account settings' and scroll down.

Wow, that's very arcane. I guess it needs to be so people don't delete their accounts accidentally , but WOW! Anyway, it worked. Thank you