Which of the following is NOT a component of SOAP messages?

In the context of SOAP (Simple Object Access Protocol) messages, the key components include the Envelope, Header, and Body. The Envelope is a critical part that defines the start and end of the message, encapsulating all the elements within a SOAP message. The Header acts as metadata that can contain various information related to the message processing, such as security or transaction management details. The Body is where the actual message content resides, containing the payload of the request or response.

While the term "payload" is often used in web services and messaging contexts to refer to the actual data being transferred, it is not a specific component defined in the SOAP structure. Instead, in SOAP, the payload is generally considered to be the content within the Body element. Thus, identifying "payload" as not a specific component of SOAP messages clarifies its distinction from the formally recognized elements like Envelope, Header, and Body.