How does a MQTT broker works?

The broker is the central service of the MQTT protocol. The broker's job is to filter messages and redirect messages that arrive from publishers and are sent to subscribers. Since the publishers and subscribers do not know each other, the broker holds the information of the two agents so that, through the message topics, it knows where to send the message. All credentials or authentication methods are verified by the broker. As an example, the publisher can only send a message with the defined topic if he has the necessary authorization to do so.

In short, the broker is almost like a signal policeman, who redirects messages to the intended destination.