Im running Thunderbird and can no longer log into my Outlook.com email. I have the OAuth2 server protocol enabled and its been working fine for ages, but over the last week or so has increasingly failed to login. It finds the server but hangs on login, finally after a minute or so returning "Authentication failure while connecting to server outlook.office365.com". I have not made any changes to the settings. Logging into Outlook via my web browser works fine. And here's the weird thing- enabling my VPN to change my IP to another nearby OR disconnecting from my wifi and instead hot-spotting from my 4G mobile phone, which also changes the IP- the login works fine again. Seems Microsoft have for some reason blocked my Thunderbird login at my home IP from their server end- a Real pain in the ass. I cannot find any info what to do online- how to reconfigure Thunderbird or contact Microsoft. Help!