Why did you leave the password blank during set-up? If you'd entered that everything else would have been done automatically. I'd delete the account and set it up again filling in the password this time.

If you want to try and salvage it here are the details you need:—

Server Settings:—

 Server Name: imap.gmail.com
 Port: 993
 User Name: <your e-mail address>
 Connection security:  SSL/TLS
 Authentication method: OAuth2

  Outgoing Server (SMTP):—

 Server Name: smtp.gmail.com
 Port: 465
 Connection security: STARTTLS
 Authentication method:  OAuth2
 User Name: <your e-mail address>

Numerous posts on help forums indicate leaving the password blank will cause the browser to open and prompt for password. This happened once, but I can't get it to do it again. If I enter the password during initial setup, I get an error message stating authentication failed , so I leave it blank to keep things supposedly moving.

I changed the smtp server settings as above, even though default port is 587. But my connection problem is with imap - incoming mail.

Thank, Jeff

When I set mine up I just went to Add Account, entered username and password and the rest looked after itself. On first checking for new messages a box popped up for me to give Google permission to let Thunderbird access my account. The settings I gave you above are copied from my account and certainly work.

The only other thing I can suggest is going to Settings > Privacy & Security and clicking Show Cookies and then deleting any to do with Google. Hopefully that'll make it do the authentication again.

The snag with finding information on-line is that sound advice goes out-of-date so quickly. What works now may well not in even a few months time.

Make sure to allow cookies in Thunderbird. See https://support.mozilla.org/kb/automatic-conversion-google-mail-accounts-oauth20

Thank you to everyone for submitting helpful tips. I ended up leveraging my Protonmail account to resolve. PM has an ‘easy switch’ feature. Basically a very easy to use import feature for all gmail, then I used the PM Bridge to sync the gmail import into TB. Going forward, I set a forwarding rule in gmail to PM that syncs to TB. Seems like a lot, but setup was easy across the board, and far more effective than struggling with the gmail setup in TB. Protonmail is an excellent, safe and secure system. If you haven’t already done so, try a free account. TB is a great application that works in tandem with PM. The two go great together by providing an offline repository for your PM email. Thanks again everyone. Jeff