Hei,

QoS AtMostOnce is meant such that each device subscribed will get the message AtMostOnce. Ultimately, since multiple devices are subscribed, multiple devices will receive the message.

If you want to achieve similar functionality than SQS, you would need to use AtLastOnce QoS, and handle the delivery logic on your own. E.g., let each connected device have their own downstream MQTT topic, and then using a lambda function iteratively try to publish the packet on the next available topic/thing until it passes (i.e. until it receives a PUBACK). In that case, the clients would have to use CleanSession = True when they reconnect.

However I'm not sure if it's the most ideal use of AWS IoT core.