When will a customer need to confirm marketing opt-in with my Shopify store?
When a customer completes a purchase through the checkout and confirms they wish to receive marketing emails by checking the box, consent to receive is confirmed by the purchaser, so an opt-in confirmation email WILL NOT be sent.
If you process a customer's order through the Shopify POS app and the customer consent box is checked, the customer will be sent an opt-in confirmation email.
If you use the Shopify subscription form on your website, the customer will be sent an opt-in confirmation email.
For all of the above, the customer will be subscribed to the list "Accepted Marketing" - this cannot be changed.