new SendReply
{
    Request = submitPO,
    Content = SendContent.Create(new InArgument<int>( (e) => po.Get(e).Id)), // creates a SendMessageContent
    CorrelationInitializers =
    {
        new QueryCorrelationInitializer
        {
            // initializes a correlation based on the PurchaseOrder Id sent in the reply message and stores it in the handle
            CorrelationHandle = poidHandle,
            MessageQuerySet = new MessageQuerySet
            {
                // int is the name of the parameter being sent in the outgoing response
                { "PoId", new XPathMessageQuery("sm:body()/ser:int", Constants.XPathMessageContext) }
            }
        }
    }                        
},