Gmail has decided to completely change what they accept as password, basically gmail is deliberately blocking your access, so you will need to do the following. Thunderbird has made alterations so now both POP and IMAP accounts can use OAuth2 for gmail. * Select 'Menu app icon' > 'Preferences' > 'Privacy & Security ' Under 'Web Content' * Select 'Accept cookies from sites' It may also be a good idea to make exception: * Click on 'Exceptions..' button * Enter: https://accounts.google.com * Set to 'Allow' * click on 'Save Changes' Whilst in Privacy & Security - remove stored passwords Under 'Passwords' section * Click on 'Saved Passwords' * Click on 'Show Passwords' You will have a mailbox:// line and a smtp:// line for the gmail account. * Select each line and click on 'Remove' '''Now make changes to Account Settings:''' * Right click on gmail pop/imap account name in Folder Pane and select 'Settings' This opens the Account Settings in new tab The pop/imap account name should be selected Look bottom right for Outgoing Server (SMTP) * Click on 'Edit Server _SMTP' button * Set Authentication Method : '''OAuth2''' * Click on OK Now set the incoming authentication: * select 'Server Settings' for gmail account * server name: pop.gmail.com * Port: 995 * Connection Security: SSL/TLS * Set Authentication Method : '''OAuth2 ''' Exit Thunderbird and wait a few moments for background processes to complete Start Thunderbird Gmail will prompt you to enter gmail email address and normal password you use to access webmail account. Follow instructions. It will ask this to allow Thunderbird to access server. An Oauth token will get stored in Thunderbird - same place as passwords and from then onwards Thunderbird will use it to access server.