Somewhat related, I had recently tried sending an email to legal@microsoft.com and my emails were rejected. I tried a couple of times using two domains and I could only assume they were blocked because I had "microsoft" in the username (so "microsoft@[mydomain].is" and "microsoft@[mydomain].xyz". I guess it's understandable as sending an email with "microsoft" in the username could be construed as a phishing attempt against Microsoft employees.