Did you edit the stored password? * In Settings > Privacy & Security * Scroll down to Passwords section * click on 'Saved Passwords' * Click on 'Show Passwords' If prompted for password: If you have previously set up to use 'Primary Password' then enter the Primary Password - do not be confused this is not a mail account password. If you have not set up 'Primary Password' then you ay see a 'Windows Security' window asking for password. When you start computer and enter user account password to see desktop - that is the password you need to enter. Mail account will have two lines, one for incomin and one for outgoing smtp. * Right click on each line and select 'Edit Password' * Completely clear all content and then carefully type the correct password. * When finished, click on 'Close' Now Exit Thunderbird , wait a few moments for background processes to complete and restart Thunderbird. It should then use the updated password.