I was not aware Thunderbird had a message that told you your settings were out of date. Are you sure this was not some setting generated by your antivirus program? So now instead of trying to fix your accounts, we are trying to set them up anew without the original error message or anything to indicate what the original error message was about or what the problem is. If you wanted to make a difficult job harder, you have achieved that. Almost every instance I have even seen of this sort of error on setting up a new account where the settings are for a major provider that Thunderbird would have detected from it's [https://autoconfig.thunderbird.net/v1.1/yahoo.co.uk database ]and then could not connect to was a direct result of a failed antivirus product, the remainder were VPN related as they do not play well with email. Start your OS started in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. Instructions for each operating system: [https://support.microsoft.com/en-us/windows/start-your-pc-in-safe-mode-in-windows-92c27cff-db89-8644-1ce4-b3e5e56fe234 Windows 10/11], [https://support.microsoft.com/en-us/windows/windows-startup-settings-including-safe-mode-7f31dcea-6427-0ba0-ec1b-729a56321cd3 Windows 8], [https://support.microsoft.com/en-us/windows/advanced-startup-options-including-safe-mode-b90e7808-80b5-a291-d4b8-1a1af602b617#start-computer-safe-mode=windows-7 Windows 7], [http://support.apple.com/kb/ht1564 OSX] Now try and add your mail account to Thunderbird. Note that a wired internet connection is required for at least Windows safe mode with networking. So plug your laptop in to the router before you try. WiFi will not be available. This process should load windows without your antivirus, without your VPN and without any of the normal startup programs, many of which can cause connectivity issues.