In Preferences > Saved Passwords, delete all entries for the affected account. In Account Settings, make sure incoming server authentication method is also set to OAuth2. Restart Thunderbird.

That worked, thanks a lot!

Good to know. You're welcome.

Hi Stans, I tried your solution but didn't work. Could you take a print of the individual email Server Settings and the Outgoing Server (SMTP) so I can see what I am doing wrong. I also tried to cancel one of my emails to try and reset it up as a new email but couldn't achieve that either. Thanks

Hi Stans, I tried your solution but didn't work. Could you take a print of the individual email Server Settings and the Outgoing Server (SMTP) so I can see what I am doing wrong. I also tried to cancel one of my emails to try and reset it up as a new email but couldn't achieve that either. Thanks

Incoming server name: imap.gmail.com port 993 Outgoing server name: smtp.gmail.com port 465 Connection Security: SSL/TLS Authentication Method: OAuth2 Username: full Gmail email address

If your account/server type is POP instead of IMAP, the incoming server name becomes pop.gmail.com and port 995

See https://support.google.com/mail/answer/7104828?hl=en

These are the settings that have been working for my several Gmail accounts. If you're using the latest Thunderbird (91), the switch to OAuth2 is automatic, but you still have to sign in to your Google account via a window that pops up when you check for and send mail.

If you've removed your account to add it afresh, fill in your name and email address in the account setup wizard. Leave the password field blank. Thunderbird will use automatic account configuration parameters (you'll just choose between POP and IMAP) and the sign in window will open automatically. If this is not happening on your end then something else is wrong and you need to start your own thread.