Hi Chris Thunderbird needs to use the same password that works to access your email account online. Did anything change recently with your online account? Specifically, either the password, or possibly 2 factor authentication? If you are able to, please log in (manually) to your online webmail, and check that the password works there. If you are successful, enter the same password for Thunderbird when prompted. If that online account password does not work, you may need to reset both - the online password first, and then set Thunderbird password to match. Best wishes, Agnes