A Microsoft file hosting and synchronization service.
Hi,
A bit of a twist here - the Email is probably legit. But there have been a few reports that Microsoft is mistakenly sending emails about Storage being full.
As long as any of the Microsoft accounts you possess do not have storage full, you can simply discard the email.
I hope this information helps. If you have any more questions, don't hesitate to reach out.
Otherwise, please take a moment to rate the answer. Wishing you good luck!