Access Firewall Make sure the Thunderbird program is set up as an allowed program. In Thunderbird Please check you have the following set up: * In Settings > Privacy & Security * Web Content: * Select 'Accept cookies from sites' * Accept third party cookies: 'Always * Click on 'Exceptions' button * Add exceptions for these: outlook.com, hotmail.com or office365.com * Set it to 'Allow' each of above * click on 'Save Changes' '''re : I have turned off IPV6''' I presume you have set: network.dns.disableIPv6 to true Error message "User Authenticated but not Connected" - If a valid user name is presented but an invalid password, the server accepts the login, but subsequent commands fail displaying that error message. So please check to see what you have saved for that account in this location: * Settings > Privacy & Security * click on 'Saved Passwords' * Clickon 'Show Passwords' Do you see any saved passwords incoming or outgoing for that outlook account ? The Mail account Server settings and SMTP should be using Authentication Method: Oauth. So you should see an 'oauth://account...' line But do you see any other - if yes, then remove them. They may be 'mailbox://account... or Imap://account... or smtp://account