Thunderbird isn't telling you the password is wrong. Thunderbird doesn't know whether the password is wrong. All it knows is that it cannot connect to the server using the password you've told it to use, so it tells you to check that the password is correct, <i>in case that could be the problem</i>, but the problem could be something else. It could be that Thunderbird is trying to connect to the wrong mail server or it could be the username that's wrong and that's why the password isn't accepted. Which is your email provider? If they publish the settings needed to configure the mail client (most of them do) and you post a screenshot of the server settings you're trying to use, we may check whether you're properly setting up the account in Thunderbird.