When sending digital receipts for online orders, even to subscribers who have previously unsubscribed from marketing communications, the appropriate send classification to use is the Transactional Send Classification. This classification is used for emails that are essential to a transaction or service requested by the customer, such as order confirmations, shipping notifications, and digital receipts.

Transactional emails are exempt from typical subscription preferences because they are considered necessary for the fulfillment of the service or transaction that the customer has engaged in. By using a Transactional Send Classification, Cloud Kicks ensures that all customers receive their digital receipts, maintaining compliance with best practices and customer service standards.

References: Salesforce Marketing Cloud documentation on send classifications delineates the distinctions between commercial and transactional sends, highlighting the use of transactional classifications for essential service-related communications regardless of subscription status.