Lets get this very clear. If you are asked for a primary password you have one, and you set it. If you do not know it there are instructions [https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password#w_resetting-your-primary-password-if-you-have-forgotten-it here ]as to how to clear it, and all saved passwords. However you will most likely not have a primary password, few do. In that case use the password manager to view and edit your passwords. https://support.mozilla.org/en-US/kb/password-manager-remember-delete-change-tb Note this well, refusal to connect which result in a prompts to enter a new password is rarely that. Thunderbird has not forgotten a password. It is more likely you antivirus is simply messing up the connection attempt so Thunderbird asks you to give it a working authentication password. As you have provided basically no context. I hope this goes some way towards answering your question, because I am guessing and extrapolating based on past experience, not current information from you.