Gmail have altered how you can access server when using third party email clients like Thunderbird. They do not accept normal passwords any more, but they do accept 'OAuth2'. Thunderbird has made alterations so now both POP and IMAP accounts can use OAuth2 for gmail. You need to do the following: * 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' Some people have needed to remove the old stored passwords, so I suggest you do this whilst you are in the 'Privacy & Security'. * Scroll to 'Passwords' section * Click on 'Saved Passwords' * Click on 'Show Passwords' * Make a note of the password * Select the mailbox:// and smtp:// lines and click on 'Remove'. * Click on Close 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 * Set Authentication Method : OAuth2 Exit Thunderbird and wait a few moments for background processes to complete Before you restart Thunderbird - double check that the password is correct. You can only do that by trying to logon to the gmail webmail account using a browser. 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.