If you have a e-mail list that you made from the sale of your product then to e-mail them want be a problem. But if you payed for a list you and  you send them offer they don't know you that is spam.

Because they don't know you thay don't want anything you have to offer!

Even if you made a list from the sale of your product and you send them e-mail and they tell you not to send them any e-mail and you send it anyway that is spam too!