What aspect does NOT fall under the responsibility of the Message Engine?

The responsibility of the Message Engine primarily revolves around facilitating communication and processing messages within the system. This includes connecting to external parties to send and receive messages, processing incoming messages to ensure they are handled appropriately, and storing outgoing messages to maintain a record of communications that have been initiated.

Defining message structures, however, involves the creation of protocols or formats for how messages should be constructed and interpreted. This task typically falls under the domain of system design or a messaging framework rather than the operational responsibilities of the Message Engine itself. The Message Engine operates based on the predefined structures rather than creating them, which keeps its focus on the functions of sending, receiving, and managing messages rather than establishing the foundational formats for those messages. This distinction clarifies why defining message structures does not belong to the core responsibilities of the Message Engine.