Thanks for reaching out to the Community! Accepting email marketing through Shopify should indeed add the customer to your Shopify - All Customers list. I recommend doing a search for the customer and checking their subscription status and engagement. There is a possibility they are getting your emails, but maybe don't know they need to check their promotions tab in gmail, or maybe they previously unsubscribed. If you would like us to dig into this further for you please send us the email address in question to social_support(at)constantcontact(dot)com or call our Support team at 866-289-2101 for on the spot troubleshooting.