Acknowledgement messages

Hi Everybody,

I'd like to get a suggestion on how to implement this scenario:

FILE ADAPTER -> XI -> R/3 (ASYNC ABAP PROXY)

My issue is: I need to have an application ack on XI, driven programatically by my ABAP code inside the R/3 inbound proxy.

1- I read that somewhere in the outgoing message from XI I should set an "ack required" (header?) attribute... but how do I do that?

2- Can I work with "fault message" somehow?

3- ... other ideas?

Thanx guys. Any help is greatly appreciated!

Alex