Do you use Mailpoet for Email Marketing? The Mailpoet integration allows you to automatically add or remove new users to your email lists. You can integrate your account with Studiocart by installing the plugin on your WordPress site.
How To Integrate Mailpoet With Studiocart
Get started by Installing and Activating the Mailpoet Plugin on your WordPress site.

From here you can set up a Mailpoet integration by going to a Studiocart product and selecting “Mailpoet” from the services menu in the Integrations tab. You’ll see a Mailpoet List dropdown with a list of all the email lists you previously created in Mailpoet. Choose the list you would like to link to this product.
Note: If your Mailpoet Lists are not showing up in the dropdown, click the Renew Mailing Lists button to fetch your latest mailing list info.

In the example below the following will occur from the settings chosen. When a product is purchased with any payment plan a contact is added to the Newsletter Mailing list in Mailpoet.

You have the option to enable Required Consent. If turned on, only customers who have given consent will be added to the list. Note, you will also need to turn on the Opt-in Checkbox in the Form Fields tab for this feature to work.
Once you have finished filling out all the settings needed for your product, complete the order form by selecting Publish or Update.