Easy Digital Downloads MailChimp Addon:

This extension integrates your Easy Digital Downloads store with Mailchimp and provides access to Mailchimp’s extensive eCommerce automation features.

Through this extension you can automatically subscribe customers to specific lists and groups based the item(s) they have purchased. You can also allow customers to opt themselves into a list subscription during checkout, and you can choose to enable or disable double opt-in for email subscriptions.

With complete support for Mailchimp’s eCommerce tracking, this extension also provides you with access to the eCommerce reports and automation tools inside of your Mailchimp account.