This is a direct restatement of Q16 ' s underlying mechanism: the Event Notification Service is Marketing Cloud ' s real-time, webhook-based method for pushing granular send-status events — including Sent and NotSent outcomes — to an external, subscribed endpoint as they occur, rather than requiring the analytics team to poll or wait for a batch process. Given the explicit legal-obligation framing, where the team needs assured, immediate visibility into whether a transactional message actually reached the recipient, a push-based, real-time notification mechanism is the only option among those listed that genuinely delivers status ' in real time ' rather than on a delay. Platform Events API (A) is a Salesforce Sales/Service Cloud pub/sub messaging framework for custom Salesforce-side event architectures — it is not the native Marketing Cloud mechanism for transactional send-status notifications. ' Data Retrieves on the Send Object ' (B) is not a defined, real, real-time Marketing Cloud feature or standard terminology. Data View Export ' with every send ' (D) describes a batch or scheduled extraction pattern that, even if run frequently, introduces polling latency and operational overhead incompatible with genuine real-time delivery, unlike a push-based webhook subscription. Reference: Event Notification Service, Transactional Messaging.