I've a new install on an a work XP machine. The same install version on a home XP machine does not have the same problem with the same gmail accounts. On the work machine with a clean install of 31.3.0 thunderbird, I cannot use gmail smtp services. Other smtp services to yahoo and my own domain work properly. The error log; Timestamp: 1/7/2015 8:01:35 AM Error: An error occurred during a connection to smtp.googlemail.com:465. The server rejected the handshake because the client downgraded to a lower TLS version than the server supports. (Error code: ssl_error_inappropriate_fallback_alert) Following the guide for a firefox issue I followed the recommendation to modify the "security.tls.version.min" https://support.mozilla.org/en-US/questions/1038836 For values 0 and 1, the same error log appears. For values 2 and 3 no error log is written to the error console yet sending mail still fails with; Sending of message failed. The message could not be sent using SMTP server smtp.googlemail.com for an unknown reason. Please verify that your SMTP server settings are correct and try again, or contact your network administrator Any thoughts?