During check-out, the shopper is asked if they would like to be added to the store's email marketing list that they are checking out with.
You will see whether a shopper opted-in in two places:
- On the Locally order screen, beneath the shoppers information, you'll see "Provided Marketing Consent: Yes/No"
- Run an export from your Order History screen (using the "export" icon at the top right of the page), and see the column "Marketing Consent Status:"
Only add shopper emails to your email marketing lists if they've opted in.