I’ve always felt that discounts in Easy Digital Downloads should have an email requirement/limitation, such as the one seen in WooCommerce. This means that admins can create discounts that can be used only when a customer’s email is authorized. In order for a discount to be applied to the customer’s cart, the customer’s email address is run through a verification process that checks to see if it is in the list of required emails for the discount. If not, then the discount is not applied.
The EDD Discount Emails plugin brings this feature to Easy Digital Downloads. You can download it for free from the WordPress plugin repository.
To add an email requirement to a discount, simply enter one or more emails to the requirement field. If you are using more than one email, separate each with a comma.
Lastly, note that to use a discount with an email requirement, the customer must first enter his or her email into the email checkout field. Otherwise, the plugin will not be able to check the customer’s email against the list of required emails for the discount.