We’d be happy to explain why this behavior is occurring and a potential recommendation.
When an order is placed in the POS, the WooCommerce status of Processing is used for the order indicating an order was received. Same behavior as the front-end online store. Based upon your WooCommerce > Settings > Email you have setup a Customer email notification for the Processing order status. As a result, this will send an email to the customer.
Once the order status is marked as Completed, if you have under WooCommerce > Settings > Email a Customer email notification for the Completed order status, this will also send out an email.
Our recommendation would be to review the email settings and modify the WooCommerce Email Customer Setting for Processing status, if you would like to no longer send this email or the Completed email notifications to customers.
I hope that helps explain the behavior of the emails sending the POS.
