Just restarted my PC and can no longer connect to Outlook365 via Thunderbird... When I start in Troubleshooting mode, it pops up a window which says Enter your password for xxx@xxxxxxxx.me.uk on outlook.office365.com: which I do (using my normal password that I also use for the https://outlook.office.com/mail/ web portal) The status bar tells me xxx@xxxxxxxx.me.uk Connected to outlook.office365.com... I then click on "Get Messages" as it has not downloaded any new messages the status bar tells me Host contacted, Sending login information and a window pops up saying Sending of password for user xxx@xxxxxxxx.me.uk did not succeed. Mail server outlook.office365.com responded: Logon failure: unknown user name or bad password. I click on OK and the window changes to Login to server outlook.office365.com with username xxx@xxxxxxxx.me.uk failed. If I click "Retry" I get the same result If I click "Enter New Password" I get the Enter your password for xxx@xxxxxxxx.me.uk on outlook.office365.com: window again. I enter my password (which still works on the web portal) I get the same error message as above... The troubleshooting page tells me my account is account1 (pop3) outlook.office365.com:995 SSL/TLS Normal password smtp.office365.com:587 STARTTLS Normal password true and I have made no changes to either Thunderbird or my E-Mail account recently... I restarted the PC yesterday evening and everything was working fine then...