I am trying to move Gmail accounts from an old Outlook to Thunderbird due to new OAuth2 rules but can't get the accounts set up in Thunderbird on Windows 10: I installed a fresh copy of 31.8 and Imported emails and address books from Outlook ok. I then installed (upgraded to) 91.10 and tried to set up my existing Gmail account: I type in my gmail username and password and choose POP3 then Done and the Google Credentials window pops up. I enter my email and password and it asks to give Thunderbird access so I choose Allow. The Account Setup screen then says Checking Password and Unable to log in at server. Probably wrong configuration, username or password... If I choose Done it just goes in the same loop. If I Configure Manually I can see all the info and pop/smtp servers are correct and using SSL/TLS and OAuth2 but when I try to Get Messages for the account it just pops up the Google Credentials window and after I put in the username/password again no email is downloaded. There is never anything stored in Saved Passwords either so presumably the OAuth2 token is not being saved? I have tried: Reinstalling Thunderbird (including deleting any leftover Thunderbird folders in Programs and User Data) New profile Ensured Cookies are all allowed Added https://accounts.google.com as specifically Allowed exception In my Google account it says Thunderbird IS allowed access (it adds another allow access entry every time I enter the Credentials) Disabled antivirus (Kaspersky) My Gmail username and password are 100% correct - I can log into webmail using them no problem. I have tried to set up 3 different Gmail accounts and all fail with same errors. Hope you can help as I am completely stuck now, thanks

   'Menu app icon' > 'Preferences' > 'Privacy & Security ' 

   Menu app icon > Help > More Troubleshooting Information
   Under 'Application Basics' - Profile Folder - click on 'Open Folder' 

   Exit Thunderbird now - this is important. 

   cert8.db - obselete file
   key3.db - obselete file
   pkcs11.txt (some people report this file missing)
   secmod.db - obselete file
   session.json
   xulstore.json 

   key4.db
   cert9.db
   logins.json