Sending, receiving, and organizing email in Outlook.com
Due to a lot of spam abuse, Microsoft has placed certain restrictions and imposed a daily limit on emails, especially if the email was recently created.
Sending limits in Outlook.com
https://support.microsoft.com/outlook/sending-limits-in-outlook-com
Please post the complete bounce-back message, including the code (e.g., 4810 550 5.5.7, for the next steps.
I look forward to hearing from you to get the results of the troubleshooting.