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First, the student should check to make sure it's not being caught in the "Other" mailbox by following the steps on this guide.
If that does not resolve the issue, then the faculty member's email address may be blocked in the student's email settings. Check using the Outlook WebApp by using the instructions found here here Managing Blocked/Safe Senders in the Microsoft 365 Outlook Webapp or or in Outlook by using the instructions found here here Managing Blocked/Safe Senders in Outlook.
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