@John Huebner actually @beee has a bad idea, it’s a better one, definitely do-able, but some thing are design-wrong there – you would need to fetch all the data, even if you are trying to add just a single email address.
It is a quick solution, if you have a low rate emails/product (and you know it will ever be so – which you probably don’t and can’t know).
acf/save_post is a good start, but I think you should store it to product/post meta table – one row per 1 email – they can have same key…
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