In addition, the Microsoft Outlook 365 app also doesn't work. The problem started today, as until the 17th of November Thunderbird worked as usual. It might be connected to Microsoft's changing Live Hotmail to Outlook Mail recently, but that wouldn't explain why it doesn't seem to work with Microsoft Outlook either. I've also tried a few different Internet connections (in different locations), switching to IMAP, adding exceptions to the Firewall, cleaning the registry, re-running the setup (primarily to change from live.com addresses to outlook.com addresses) and updating Thunderbird. The error message I get is... Sending of password for user ------------@hotmail.com did not succeed. Mail server pop-mail.outlook.com responded: Authentication failure: unknown user name or bad password. [Error="AuthFailed:LogonDenied-FederatedStsUnreachable-<X-forwarded-for:82.208.53.234><ADFS-Business-582ms>failed logon error - STSFailure - '<S:Fault xmlns:S='http://www.w3.org/2003/05/soap-envelope'><S:Code><S:Value>S:Sender</S:Value><S:Subcode><S:Value>wst:InvalidRequest</S:Value></S:Subcode></S:Code><S:Reason><S:Text xml:lang='en-US'>Invalid Request</S:Text></S:Reason><S:Detail><psf:error xmlns:psf='http://schemas.microsoft.com/Passport/S]