Managing personal Outlook.com account settings, security, and privacy
The daily message limit helps us free the world from spammers
Yes. That is a legit message from the Microsoft Mail server. It is saying that you have exceeded your Daily Sending Limit (not receiving).
Did you get this right after sending an email to a large number of people? Or after sending a lot of emails in quick succession?
The posted limits are pretty high, but can be much lower for a Personal outlook.com account, or if Mother Microsoft thinks you might be sending out Spam.
https://support.microsoft.com/en-us/outlook/sending-limits-in-outlook-com
Limits may vary based on usage history and will be lower for non-subscribers [Non MS 365 accounts]