Since I turned on the two-factor login in googlemail, I cannot login from Thunderbird anymore. (Before it was all fine.)
What do I have to change in Thunderbird?
You have to get a 'Application-specific' password from Google. You can do this on the Security section of your Accounts page. Click on Settings in the 2-step verification section.
Here's the link to the Google help page on application-specific passwords.
Through no fault of Brad Google changed the process. I tried to follow the instructions Brad shared, from the website Aplication-speccific password: https://support.google.com/accounts/answer/185833?hl=en&ctx=ch_b/0/SmsAuthConfig
One moment: Before you go enabling things that you might not understand go here https://security.google.com/settings/security/activity
if everything check out, meaning you trust all the locations and apps accessing you account then proceed to the next step
You will have to go here and enable, Access for less secure apps. https://www.google.com/settings/security
Please heed any warning that good gives you!