Please tell us which version of Thunderbird you're using, and attach a screenshot of your SMTP server panel: To get it, open Account Settings, click on your account name near the top left, then scroll down on the right until you see the Edit SMTP Server ... button. Click that and make a screenshot of the panel that appears. If that's not easy for you, just tell us exactly what words and numbers you see in the blanks in that panel. For instance, I see Google Mail, smtp.gmail.com, 465, SSL/TLS, OAuth2, and my correct email address. You don't need to post your email address; just check it to make sure it's correct in that small panel, and tell us it's correct.