Hi Midhhun!
In order to use proxy within your ICo you should additionaly maintain Sender/Receiver ID in transaction SXMB_ADM (or just run transaction SXMSIF):
and also set your previously created destination to RUNTIME parameter IS_URL in SXMB_ADM-Integration Engine Configuration with subparameter according to above setting:
With these settings your outbound proxy call will be sent to adapter engine, otherwise it will be sent to default destination (IS_URL without subparameter, which points to Integration Engine by default).
Regards, Evgeniy.