What you're seeing is Gmail requiring a stronger form of authentication than merely sending a username and password:

https://support.google.com/mail/answer/7126229

The real question here is why you haven't seen this until now if you've been using Thunderbird with Gmail before…

It is only recently that the message comes up. I have been using Thunderbird for a long time now. The mystery to me is why the message keeps coming up when I am already logged in and can receive messages etc.

When I do try and enter my details I get an error as per the attached image.

Thanks

Guess I must be missing something here then, but the image you posted has a "Next" button in it to proceed, doesn't look like an error message to me…

Hi David I have attached another snapshot of the message that comes up after I press next. It says "Google - 400 That's an error. The server cannot process the request because it is malformed. It should not be retried. That's all we know." I can't do anything else with it but exit from it. And then the message pops up again. I don't know why after all these years Google is asking me to sign in. I would like to disable the message for the Google sign in on my home computer using Windows 10. I do not use Thunderbird on my mobile phone - it's not necessary.

Ahh! That's new to me, first time I hear of that. Something you may try is going to your Google (not Gmail) account settings and check your Security settings there. Thunderbird should appear in the list of connections to third-party apps and services. Maybe you can see something there that sheds some light on this. Deleting that connection and re-authorising Thunderbird again would be an option to consider…

I am not sure whether the following links are related to your problem or not: https://support.mozilla.org/en-US/kb/automatic-conversion-google-mail-accounts-oauth20 https://support.mozilla.org/en-US/kb/thunderbird-and-gmail

Quote: "Cookies and javascript must be enabled for the OAuth 2.0 setup process to work."

Perhaps you can enable cookies and javascript, and then try to sign in with Google again.

Hello Yu5tiqX9og Thank you for providing the solution. I changed the cookie settings. I already had the authentication method set to OAuth2.

Great and good to know, but I'm confused now. That's not something new. You must have had those settings enabled if it worked before… Did you disable them at some point afterwards maybe?

Hello DavidGG I tried to sync my android calendar with Thunderbird at some stage so during that time it's possible I changed a setting but cannot recall doing so. I still cannot sync my android calendar with Thunderbird so I just gave up.

OK, I see what it is that I was missing:

receiving and sending mail will work with cookies rejected. But rejecting all cookies or removing the exception has the disadvantage that when the OAuth token for Gmail access expires at some date in the future, the OAuth dialog will show up and fail again until you accept the required cookies.

So someone might disable those settings, not knowing or remembering why they might be necessary, and then not see the effect of having disabled them until much later, when he/she no longer remembers he/she had disabled them…

I'll keep that in mind for the next time the same happens to someone, which I'm pretty sure now it eventually will… :)