Managing personal Outlook.com account settings, security, and privacy
Hi Melissa,
I believe to prevent spam, Microsoft has some limits. Do you have a 365 subscription? That has somewhat more relaxing limits.
You may email half of your contacts today, and half tomorrow as a workaround.
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!