Are you talking about the Master/Primary Password? That is the only password which is controlled by Thunderbird. If you mean 'outlook.office365.com' is not accepting the password. Do you normally enter the password everytime you want to access the server or did you set up Thunderbird to remember the password ? Did you recently logon to the outlook.com webmail account and change the password? If yes, did you then access the stored password in Thunderbird and edit it to match the new modified password? Are you using 'Authentication Method: Oauth2' for both incoming server settings and outgoing server settings ? OR 'Authentication Method : Normal Password' ?