What is your operating system? What version of Thunderbird?

(Are you saying you cannot even set up your Gmail account? Or that your already-set up account can't log on? I wrote the below before re-reading your post and had in mind the latter scenario, although the parts about removing cookies and passwords are still relevant. Please let me know if I'm off-base.)

First of all, uninstalling/reinstalling Thunderbird almost never solves this kind of problem. That's because all of your specific email account information is stored in your Profile, which isn't touched by a reinstall.

In your case, you should first confirm that your Gmail settings are correct. My working settings are:

Incoming Server Type: IMAP Mail Server Incoming Server Name: imap.gmail.com Port: 993 User Name: <my email address> Connection Security: SSL/TLS Authentication method: OAuth2

SMTP Server Name: smtp.gmail.com Port: 465 Connection Security: SSL/TLS Authentication method: OAuth2 User Name: <my email address>

Next, confirm that cookies are allowed (see <Settings | Privacy & Security | Privacy | Web Content> and enable "Remember websites" and Accept cookies from sites". While you're there, click the "Show Cookies" button and remove any Google and Gmail cookies you find there.

Next, right below that you'll find the Passwords section. Click the "Show Passwords..." button. Remove all saved passwords for that Gmail account. There may be several listed.

Now restart Thunderbird (this may not be necessary, but it can't hurt.) When Thunderbird next tries to retrieve messages, Gmail should present you with a window asking for your credentials, and hopefully, it will like them this time.

Thanks for the reply. Turns out all that had to happen was enabling cookies so the OAuth token could download and set. Absolutely simple fix -- if only all the error messages could have said that!

Thanks again!