Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi! Sorry to hear you’re having trouble with this situation. Has he received a postmaster delivery notification saying that the email was not delivered? It may have gone to his Junk Email folder. That message could help us understand what is happening.
Also, are you having trouble receiving emails from anyone else, or only from this sender? And is he sending from an Outlook address or from a different email domain?