I see where people have questioned if someone else has there email address, the answer by the Microsoft persons have always been no way. Such as this reply.
Brian Tillman [MVP-Outlook]replied on
A:No one can have the same address as you. It's just not possible. However, "me @hotmail.com" and "me @outlook.com" are completely separate addresses. It could be that someone signed up for an address that is the same as yours in front of the @, but a different domain after the @, but forgot their address and subscribed to something with the wrong domain and it just happens to match your address.
Well Mr. Tillman and others the following is what has happened to me, and the info I receive through a chat yesterday with someone named Kumar J.
I was trying to add my wife's outlook.com email address to Outlook 2016. It, no matter how many times I tried would not accept the password. I could use that password to sign in to Microsoft, and Her account on outlook.com.
Wondering if maybe it would help if I added Her outlook.com as an alias on Her Microsoft account I attempted it. Her Microsoft account kept telling the this address already existed. Now I knew that already because I was signed in to Her outlook.com email.
I set Her outlook.com account up sometime ago and did NOT receive any indication that email address was in use.
During the chat I discovered that another outlook.com account existed with the same email address, the alternate email on that account was an icloud email address, with two phone numbers associated to it ending in 07, and 46. The icloud account nor the phone numbers belong to us. As you can imagine it raised a very large red flag with me. After much back and forth, with me asking Kumar several times to escalate the issue to someone who could provide answers as to how this could happen, the chat suddenly closed. So, I still want answers to my questions, and to know for sure that my wife's account has not been hacked.