Other places to check that you didn't mention would be Address Book using Google Contacts and the possibility that you configured some other account to use that Gmail SMTP server, which is probably still available in Outgoing Server (SMTP) settings, at the bottom of the list of accounts in the Account Settings tab.

Thank you.

I did find the email in contacts and deleted it.

I did delete the outgoing SMTP setting for that particular gmail account - but I do have four other gmail accounts that I use and do not want to delete.

Would these have any bearing on the gmail account I want gone?

(I have in the past successfully deleted gmail accounts, including the SMTP setting, and have not had any conflicts retaining the other gmail accounts.)

Merely having the SMTP settings stored there shouldn't be a problem. It's only if Thunderbird was trying to use those settings to send mail (i.e. if you had an active account configured to use them) that they could cause the problem. I was mentioning that just in case. I believe it was having the Google Contacts still in your Address Book that was causing the problem.

If only it was solved by removing the offending gmail account in Contacts. Alas. The problem is still there.

I do use Google SMTP settings for other gmail accounts to send email.

Are you saying that is a problem?

If you're using the SMTP settings of the deleted account in any other account, then yes, that would be another cause of the problem, but that should be easy to fix by using the right outgoing server settings for each account, not the outgoing server settings of an account that no longer exists…

I am not sure how to fix since 1) I don't remember what the SMTP settings were for the deleted account (but likely the same as the others - the default for gmail; 2) all of the other gmail accounts use the same SMTP setting. And they work.

Would you have a suggestion as to where to find the "right outgoing server setting" for each account, when it appears that the setting is correct?

Ie I'm using Google's default port: 465

Thanks!

It seems 465 is the only option:

587 (TLS): Recommended for securely sending emails. Requires the use of Transport Layer Security (TLS) encryption. 465 (SSL): Used for SMTP connections encrypted with Secure Sockets Layer (SSL). Note that this port is considered less modern than TLS but is still supported. 25: Typically used for SMTP without encryption (not recommended for secure email sending).

No, it's only trying to use the username of the deleted account that would cause the problem. The other settings will of course have to be the same for any account using the same outgoing server. Is trying to authenticate with that server as if you were trying to use it from the deleted account (i.e. with the username of that account) that this might be causing the problem.

Well, as I mentioned in my 2nd reply - I deleted that SMTP in account settings for that email. There is *nothing* at. all. referencing this gmail account. And still getting the popup. ugh.

Someone with a similar problem mentioned in another thread that removing OAuth entries related to the old account from Settings > Privacy & Security > Saved Passwords solved the problem. I don't understand why those entries would cause the problem by themselves if there are no more references to the account elsewhere in Thunderbird, and most cases of this problem I've seen could be successfully solved by figuring where was Thunderbird still making use of the old account, but you may want to check that if you hadn't already.

Thank you so much for taking the time.

I neglected to mention in my initial post - I had removed the reference in saved passwords also.

Completely flummoxed and pretty much resigned to seeing this popup. I have been trying to resolve for a few months.

Of course, if another possible solution occurs to you, I would definitely give it a try!