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A Custom Message Responder allows you to define and send responses with a payload leveraging a custom message format, like mainframe message formats, binary formats, or any other kind of proprietary custom message format. These custom message formats are added to Virtualize via custom message formats via the Parasoft Extension Framework; for details on how to define these extensions, see 2025-01-29_11-21-02_About Parasofts Extension Framework Virt.
You can model your response payload as an XML document; the responder then automatically converts the XML to the native format before sending the message. If the responder receives a native format message, the responder can convert the message to XML so that you can attach tools such as the XML Data Bank to the incoming request.
When you add responders, you will see an option to add a responder named [Your Format] Message Responder. For instance, if your team extended Virtualize to support the FIX message format, you would see the following: 
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