How is SNS guaranteed to receive messages from event sources?

Question

I know that AWS SNS receive message from publisher, and send message to Consumer(subscriber).

And SNS FAQ said SNS guarantee message delivered to subscribed endpoint.
(SNS to Subscriber)

Then, how are messages guaranteed to be received from publisher?
(Publisher to SNS)

Accepted Answer

There is no guarantee that the messages are received from the publisher. For this reason the Publish API is synchronous. The publisher calls the API and it should receive an Ack (200 OK) that the message was received. If it does not receive the Ack, it should retry. When SNS sends an Ack, it is a guarantee that the message was received.

How is SNS guaranteed to receive messages from event sources?

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