BTF protocol: how to "correlate" incoming delivery receipts with messages in "Transmission completed successfully. Waiting for an acknowledgement" state

Hello,

I have a scenario in which I need to execute some code (orchestration) when delivery receipt comes to the sending BizTalk – so when some message is delivered/acknowledged (BTF assembler is used on send pipeline).

My current problem is … I have activated ochestration with delivery receipt and I can read the value of this element "/Envelope/Header/properties/identity" (xmlns 'http://schemas.biztalk.org/btf-2-0/envelope'), that value is in format uuid:5af85196-d327-449e-81ca-0bbba10ae6a9 and I don't know what this guid means. I tryied to find out match with some context properties of the message but nothing, there is no match with MessageID, InstanceID, MessagePartID …. nothing.

Do somebody knows how exactly BTF internally works ?

 Many thanks for help.

 Jiri