The App Store's abusive rules will not not even let you use a collected email opted in to promotions to notify of better pricing: "Developers cannot use inform

The App Store's abusive rules will not not even let you use a collected email opted in to promotions to notify of better pricing: "Developers cannot use information obtained within the app to target individual users outside of the app to use purchasing methods other than in-app purchase (such as sending an individual user an email about other purchasing methods after that individual signs up for an account within the app)." You have to flag that user's email in your database as permanently tainted and unable to learn certain truths even if they have long switched to another competitors' device.