Which document and exchange protocol are you using? Use outbound WS of B2B to send messages to B2B from back-end. This WS returns a positive response (isTransmitted element in response XML is set to true) if the message is delivered to the target server successfully.
You may refer section "21.2 Using the Outbound Web Service" at -
Edited by: Anuj Dwivedi on Dec 3, 2012 2:14 PM