When you use googles 'less secure apps' option, gmail will deliberately block you every so often forcing you to logon to their webmail to reset the 'use less secure apps' option. This is something Thunderbird has no control over. It is gmail being a pain. Gmail OAuth method - one logon fits all access - was designed to cope with people using google to logon to various webpages via a browser or phone, by using a token instead of normal password. If you have a good normal password eg: length 12 digits of mixed letters - upper and lower case, numbers and other keyboard options like ! , then you are not using a less secure option. It's just gmail scarmongering. However, because they choose to block you every so often, it is just convenient to set the Authentication Method to 'OAuth'. I would try altering the Authentication Method for incoming and smtp in the Account Settings and then restarting Thunderbird.