How can you determine that a message was successfully delivered to the recipient?

To determine that a message has been successfully delivered to the recipient, acknowledgements are usually used.

In different systems, this is implemented in various ways:

• In network protocols (e.g., TCP), delivery acknowledgment is built into the protocol level.
• In messaging systems (RabbitMQ, Kafka), the recipient sends an acknowledgment (ACK) after successfully processing the message.
• In HTTP API, the response status (e.g., 200 OK) can serve as confirmation.

In Python, when working with such systems, you can use appropriate libraries that provide acknowledgment mechanisms. For example, in pika (RabbitMQ):

channel.basic_consume(queue='task_queue', on_message_callback=callback, auto_ack=False)

def callback(ch, method, properties, body):
    # message processing
    ch.basic_ack(delivery_tag=method.delivery_tag)

If acknowledgment is not received, the message may be re-sent or re-processed.

Thus, successful delivery is determined by receiving an explicit acknowledgment from the recipient or the system that guarantees delivery.