As of version 38 Thunderbird uses OAuth2 for authentication of Gmail accounts. This is the only way considered 'secure' by Google. http://techcrunch.com/2012/09/17/google-oauth-2-0-for-gmail-and-talk/ Basically you authenticate with your Gmail account once, and Google provides you with an authentication token. This is what Thunderbird saves as 'password'. It's not your actual Gmail password. The token will expire at some point, so you'll have to renew it in the future. If you want to go back to the previous behavior Google lets you jump through some more hoops. You need to either allow 'less secure apps' in your Google settings, or turn on 2-step authentication in connection with an application specific password. https://support.google.com/mail/answer/78754 In Thunderbird account settings change 'authentication type' to 'normal password' for your Gmail account. Up to you.