For most digital products, you have buyers download after purchasing.
That's a mistake because you've potentially lost the buyer after one sale.
The better option is to have the buyer directed to a sign in form to receive your product via email. I use aweber but all autoresponder email services provide you with customizable opt-in forms.
When the buyer is directed to the sign in form upon purchasing the product, I then have an autofollow message sent to them with the product link inside.
Now I have a list of buyers for that product.
I've used lists for years, but only for lead, not actual buyers.
Hoping this helps you as I'm sure it will help me quite a bit next time I pitch a product.