Do we also need to send “Close Message” confirmation for Back to Back shipments destined to CP or CN Rail or YYZ Warehouses (i.e.: Menzies / ACI etc.) ? Or they will be able to identify it in their system?

Do we also need to send “Close Message” confirmation for Back to Back shipments destined to CP or CN Rail or YYZ Warehouses (i.e.: Menzies / ACI etc.) ? Or they will be able to identify it in their system?

Yes. The close message also establishes the link of the house bill with the previous (in this case the primary ccn).