Just to add... I am logged into Gmail online using the same password

Gmail uses OAuth so if you enter a normal password then it's going to fail because it's expecting an oauth token. Please check a few settings: '''Firewall:''' Access Firewall which may be controlled by the OS or by an Anti-Virus program you installed. Thunderbird must be set up as an allowed program. '''VPN''' Please check computer and Anti-Virus product to see if a VPN has been enabled. Server does not like VPN, it will block access. So switch off VPN or create a split tunnelling and set up Thunderbird to use it. ''''Localhost'''' If you use a program that uses 'localhost' - some people manage websites so might use something like Apache Xampp - Switch it off until Oauth has been set up. In Thunderbird * Settings > Privacy & Security * WEb Content * Select : 'Accept cookies from sites' * Accept third party cookies 'Always' * Click on 'Exceptions' button * Set up: https://accounts.google.com as 'Allow' * Click on 'Save Changes' Scroll down to Passwords * Click on 'Saved Passwords' * Remove any line that mentions username = gmail email address you are trying to reset. * Click on 'Close' Check you are using correct gmail settings: Account Settings select 'Server SEttings' for the account '''IMAP''' * Server name: imap.gmail.com * Port: 993 * Connection Security: SSL/TLS * Authentication Method: Oauth2 * Username : full gmail email address '''SMTP:''' * Description: enter the same email address as shown in username (this helps you check you are using correct smtp when you have several gmail accounts) * Server name: smtp.gmail.com * Port: 465 * Connection Security: SSL/TLS * Authentication Method: Oauth2 * Username : full gmail email address EXit Thunderbird Wait a few moments for background files to update. Start Thunderbird At gmail prompt enter normal Password, then click on the 'Accept' to allow Thunderbird access to server.