Looks like Thunderbird still needs to connect to Google for some reason, which in turn is causing Google to ask you to authorise Thunderbird to do that. You need to figure what could be causing Thunderbird to still want to connect to Google after having deleted the account: * Are you sure the account was really deleted from Thunderbird and it does no longer appear in the accounts list on the left of the account settings window? * Were you using this account in Thunderbird for other Google services, i.e. Contacts or Calendar? * Google allows non-Gmail accounts to use Gmail outgoing (SMTP) server (with some caveats). Check the outgoing (SMTP) server settings of your other accounts to see whether any of them is configured to use Gmail SMTP server.