I was having the same issue as many with the email unavailable message on my blueyonder email. As mine in a secondary account, the main account was able to reset my password and that worked.... Coincidentally not long after this I got a few mailer daemon emails for sending to incorrect email addresses.... And then looking in my trash there was a further 30-40 spam emails that has been sent from my account that were nothing to do with me? They were all essentially the same fake recruitment email all claiming to be from different people but sent from my blueyonder email address!!!
I do hope this problem with our emails isn't due to a big data breach and you just aren't telling us, this all seems a very big coincidence as I'm pretty sure you can see.
I've changed my password and question but I'm very concerned that this has happened.
Can you advise and let me know what else I should do?