What is NOT part of a Mule 4 event?

In Mule 4, an event is a core concept that encapsulates all the information about the data being processed at a certain point in the application flow. A Mule event is composed of three main components: the message, the attributes, and the variables.

The message component contains the actual data being processed, while the attributes include metadata related to the message, such as its headers, which can give context about the message (like content type or status). Variables, on the other hand, are used within the flow to store temporary data that can affect the processing of the message.

Outbound properties, while they are important in the context of message routing and communication with external systems (they typically represent data you send out when making HTTP requests or similar operations), are not considered part of the Mule event itself. Instead, they are more like additional information that is managed alongside events but do not form part of the event structure.

Thus, the correct answer identifies outbound properties as the element that is not part of a Mule 4 event.