In designing a real-time analytics system for a global e-commerce platform, you are tasked with selecting a messaging service that guarantees no message is lost during transmission, even in the event of system failures. The system must handle high throughput and scale dynamically with the number of transactions, which can spike during sales events. Considering these requirements, which feature of Google Cloud Pub/Sub ensures that every message is delivered to subscribers at least once, providing the reliability needed for such a critical system? Choose the best option.