Hello @St.JohnAA ,
Have you checked to make sure that he's not bouncing? This would display in the email's bounce report, or on his contact engagement. Additionally, has he checked his spam/junk folder in his email? Can you confirm that what's entered for his email address is the correct one?
Beyond these, the only other suggestion I'd have is to add him as a wholly new contact with a different email address. If you feel like this one particular contact needs further review, and absolutely cannot use a different email address, then I'd advise speaking with the Delivery team directly.
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