Hello,
The issue you're experiencing could be due to server limitations or restrictions. We recommend having your server administrator look into the matter to see if there are any specific limitations on the number of recipients allowed for outgoing emails.
Additionally, it's worth noting that Outlook itself may have certain limitations or restrictions in place to prevent mass mailing or potential spam behavior. If the server settings seem to be fine, you can also check the Outlook settings and ensure that there are no restrictions set for the number of recipients in a single email.
If the issue persists or you have any further questions, please feel free to reach out. We are here to assist you.
Best regards,
Amanda