Are you using a POP or an IMAP mail account ? When initially creating the account, you would enter name, full gmail email address, same password you use to logon to webmail account and select the checkbox option to remember password. Click on 'Continue'. Thunderbird then configures the account settings. By default Thunderbird usually creates the account as IMAP and sets the Authentication Method as Oauth2. Then you are diverted to a gmail logon to prove you really are you and an Oauth token is created and saved in same place as passwords. From then onwards the token is used to access server and not the password. Did you do anything different? Did you change to use POP ? Did you change the Authentication method? Is the gmail account Outgoing Server (SMTP) set up as follows: * Description: Google Mail (Description can be anything you like to help identify the account) * Server name: smtp.gmail.com * Port: 465 * Username: full gmail email address * Authentication Method: OAuth2 * Connection Security: SSL/TLS Is the gmail account set up to use that 'Google Mail' outgoing server smtp ? see images below.