My wife has been sent an encrypted email to her talktalk.net email address. In order to read it she clicks a button in the message which takes her to a page hosted on outlook.office365.com which gives her a couple of options in order to read the message, the only one of which is valid is to 'Sign in with a one time passcode'. When she clicks the button that reads 'Sign in with a one time passcode', she is presented with a page saying 'We sent a one-time passcode to xxxx@talktalk.net' and asking for the one time passcode to be entered within the next 15 minutes. She tried multiple times yesterday to request the one time passcode and most never arrived, though two did around 5am (not very useful and well past the 15 minute expiry time). She has also tried multiple times today and so far none of the passcode emails have arrived.
I see others have had the exact same problem. Please investigate and unblock what ever is blocking these legitimate emails from microsoft.
