It's a cliche about how to debug outbound Idoc triggered by one output type. There're dozens of good articles that already talked about
this, Including:
Just recap this, have a try the efficiency approach first before going through all various approaches.
1.Get the process code from WE20 by message Type;
2.Get the Function module by Process code;
3.Set the breakpoint at FM get from the above step and run the program
RSNAST0D.