1. Check the settings in Microsoft Classroom and confirm that email notifications to students are enabled.
2. Verify the email address associated with each student account can be found in Classroom settings.
3. Contact your organization's IT team if you think the issue is related to other authentication systems.
4. Test sending notifications to a small group of users to see if they are able to receive emails.
5. Revert any changes that had been made to the Microsoft Classroom and try again.