Hey guys I have the exact same problem happening to me, starting maybe 4 days ago. It's driving me nuts. The reported IP address is 13.101.154.231 and its the same every time.
I've already changed by password 3 times and the messages keep coming back. I don't even use my microsoft live email address for anything so it's really hard to think it's been hijacked.
Maybe this is some kind of bug. Started happening after I ran an MS 365 Office update (the only recent change to my system I can think of) for my Mac.'
Edit: The 2 step authentication requires an authenticator app which is something I want to avoid. It's another app to install on my already bloated-with-unwanted-but-necessary-apps smartphone. Sheesh.