Which component is NOT part of a Mule 4 event?

In Mule 4, each event is composed of three primary components: the message, attributes, and payload. The message contains the data that is processed within your application. Attributes include metadata that provides additional context about the event, such as headers and communication protocol details. The payload is the actual data being transferred with the event, which can vary depending on the type of application or service you are integrating.

Inbound properties, on the other hand, are tied to the context in which a message is received and are not considered a formal part of the event structure in Mule 4. While they can provide useful information such as HTTP headers when processing requests, they are not a primary component of the event as defined in the Mule 4 architecture. Thus, this makes inboundProperties the correct answer as it does not belong to the essential components that constitute a Mule 4 event.