If you set up a Master Password and it is this 'master password' that you have forgotten then you will need to reset everything. This will mean the 'Master Password' is removed and also any saved passwords for any accounts. Info at this link: https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-master-password#w_removing-your-master-password-if-the-master-password-has-been-forgotten If you are talking about a mail account password which you have forgotten: Do you normally enter the pasword each time or did you instruct Thunderbird to remember it and use to automatically logon to server to get emails ? Maybe, it is still in the saved passwords area but for some unknown reason the server wants you to manually enter the password. Is it here: In versions 68* or earlier Menu app icon > Options > Options > Security > 'Passwords' tab click on 'Saved Passwords' click on 'Show Passwords' In versiona 78* or later Many app icon > Options > Privacy & Security Passwords section click on 'Saved Passwords' click on 'Show Passwords' You may get a prompt to enter your computer 'User Account' password to gain access. If there is nothing in the saved passwords in Thunderbird, then the password can only be created/modified/reset via the webmail account. So attempt to logon to webmail account via a browser and use the 'Forgotten password' link. Follow server instructions to regain access to webmail and reset the password. Then you can use that new password in Thunderbird.