What is the primary function of MQTT?

The primary function of MQTT (Message Queuing Telemetry Transport) is to reliably transport messages for real-time applications. This lightweight messaging protocol is specifically designed for efficient communication in situations where bandwidth is limited or communication is unreliable, such as with Internet of Things (IoT) devices.

MQTT operates on a publish-subscribe model, allowing devices to send and receive messages without needing direct connections to each other. This is particularly advantageous for real-time applications since it enables quick and efficient data exchange. The protocol's emphasis on reliability and low overhead makes it ideal for scenarios where timely delivery of information is critical, such as monitoring systems, sensor networks, and messaging between devices in various environments.

Other options indicated different functionalities that do not align with MQTT's purpose. For instance, sending emails typically involves protocols like SMTP, connecting to FTP servers is related to file transfer activities, and enabling video streaming relies on protocols designed for high-bandwidth data transmission, such as RTSP or HLS. Thus, MQTT's specific design and focus on message transportation for real-time scenarios distinguishes it as the correct choice.