[T-A]

https://github.com/HotCakeX/MicrosoftDomains

...and microsoftonline.com is not among them (unlike microsoftonline.net and other variants). But it seems to have been registered in 2002, and the record looks legit:

https://whois.domaintools.com/microsoftonline.com

[balakk]

It's definitely a Microsoft owned domain and actively used - for example in Azure Active Directory (Entra).

[e40]

I did not expect 645 entries!! That is insane.

[KomoD]

microsoftonline.com is in that list.

[T-A]

You're right. I wonder how I managed to miss it. For a moment I thought I must have looked at

https://github.com/HotCakeX/MicrosoftDomains/blob/main/Micro...

but that one doesn't contain any microsoftonline.

[HDBaseT]

1drv.ms always catches me out.

[cuteboy19]

but microsoftgenuinerewardsrc.com is! shameful!