My 92 year old father has a (free) hotmail account. The only email device he has is Windows PC. When I look at the login activity I see his IMAP sync but also see a successful sync from IP 13.101.84.203 and 13.101.86.13 multiple times a day.
A whois lookup shows that those two IPs are owned by Microsoft. I suspect that this a valid MS sync of some kind but have looked at several other peoples hotmail logins and don’t see any activity like this.
Even after changing the password (using my pc), setting up 2FA and choosing log out all logged in devices (which MS has a big disclaimer for that says it wont log out some devices like Xbox and can take 24 hours) the 13.101 IPs are still syncing.
I contacted MS and they totally danced around the question, but would not address what was going on.
Anybody have any idea about what is actually happening?