I'm trying to think of a way to limit one use of a coupon or discount per person. IF john@emailaddress.com used coupon "ABC" then coupon "ABC" is not valid for him. Or any other similar solution.

There is no built in feature for that. It's something you would need to have custom coded.
You might try the developers page here - https://www.ecommercetemplates.com/developers.asp

Just an FYI - Customers often have multiple email addresses, and you can create as many as you want for free with many services. So it's not going to be bulletproof.