So you are referring to sender channel. It's more clear now.
Now can you confirm the URL on to which you sender system is sending those messages?
Your sender might be hitting the integration engine directly which is the reason you don't find any messages in channel.
If you want your sender to hit the soap channel your URL should be.
http://<host name> : <port name> /XISOAPAdapter/MessageServlet?channel=<party name> : <service name> : <channel name>