Not sure what you mean… Is it that you're using Unified Folders and would expect the account to appear under the unified Inbox? Do you have other mail accounts in Thunderbird? Do you see the "phantom" account in the folder pane if you choose View > Folders > All Folders?

Anyway, the place to look for any account and manage it would be the Account Settings rather than the folder pane.

He means when using burger>New Account>Existing email entering the details and clicking [Done] this error message comes up and the new email account is not added. Deleting the Thunderbird data solves this, but that is NOT an option as that also deletes address books and current IMAP settings (including which emails have been read). When we were trying to add the new account, Thunderbird tried automagically to use the wrong server. When we entered the correct server we started to get the error message. Clearly there is a config error regarding the IMAP (incoming) server which total deletion removes (typical Windows fix: reset everything regardless of the collateral damage). How can we just remove the incorrect IMAP server setting and enter the correct one?

I am setting up TB from nothing onto a MacBook already configured with email accounts.

At the first account I try to set up - a Gmail.com one, I get this error.

I expect TB and Apple Mail to co-exist. Mail and Spark co-exist, Mail and TB used to co-exist a whiles ago. And before pointing out that there is a valid reason for the error, my developer playbook says that one must allow for simple users, and if you cannot engineer around them, point out politely why the error occurred and what to do to reconfigure something "Sorry we cannot mess with an existing incoming IMAP config in case we break something". Now I have to go and check up on the settings in Mail and use my brain. Such hard work.

A

There are very few, if any, developers here. We are users trying on a volunteer basis to help each other.

The place to change account settings is where David indicated. Do you know how to access account settings?

Do you have more than one account using the same incoming server?

When I last used Apple’s e-mail service, it worked fine in Thunderbird.

Who provides your e-mail service? Some volunteers here often look up settings for the people they are helping.