This week I switched email hosting providers for the first time in 20 years, and was surprised that Thunderbird STILL does not have a way for deactivating accounts so that a mail check (via Get Messages) is not issued for closed accounts. MailWasherPro has a very simple checkbox for each account to exclude or "Include account in mail check". Such a check box could easily be implemented on the Server Settings page for each account. Otherwise Thunderbird keeps trying to log in to a non-existing account then producing error messages.
Instead I had to go through the extremely tedious way of moving email from the closed account, to Local Folders folder, by folder. Some messages wouldn't move, I don't know why not. I have used Thunderbird for a very long time, prior to that Eudora, all up 3 decades or more, so there were a lot of folders and emails.