What happens to the attributes of a Mule event in a flow after an outbound...

Attributes are replaced with new attributes from the HTTP Request response.

Attributes include everything apart from Payload/body. For ex: Headers, query parameters, URI parameters.

So, when outbound HTTP request is made, new attributes need to passthe outbound HTTP request and old attributes are replaced.

I have created below diagram to make it easy for you to understand:

Diagram Description automatically generated