Easy Digital Downloads GetResponse Addon GPL Overview:

This extension integrates your Easy Digital Downloads store with GetResponse by letting you automatically subscribe customers to specific lists based on what they purchased, and allowing customers to opt themselves into a list during checkout. You can also subscribe customers to specific groups within a GetResponse list.

You can enable a “global” newsletter list, which all customers can have the option of signing up for during checkout. You can also select one or more lists that customers will be automatically subscribed to when purchasing specific products.