What property of a Mule message is immutable?

• A. Inbound properties
• B. Outbound properties
• C. Payload
• D. Attributes

Answer: (A)

Inbound properties hold details about how the message arrived, such as the transport endpoint, HTTP method, path, and headers as they originally came in. These values are fixed for the life of the message so components can rely on the original context regardless of how the payload or other metadata change later in the flow. The payload is typically transformed, so it is not immutable. Outbound properties are set to influence how the message is sent out and can be changed as processing continues. Attributes can also evolve as the message moves through transports and processors. So the immutable part of a Mule message is the inbound properties.