How to programmatically add ip to list of servers, which are allowed to relay mails through the virtual smtp server

Hi!
I write a setup programm in c++ which must configure IIS 8. For SMTP you have got to change metabase data and I don't know how to do this in native code. So I use the script adsutil.vbs and call it via ShellExecute (). It is not elegant but it works for many settings.
In the "Relay Restrictions" Dialog I want to select "Only the list below" and add the loop back adapter 127.0.0.1 to the list. Adsutil enum /Smtpsvc/1 only gives me the attribute RelayForAuth relay options.
How can I achiev the above configuration by using adsutil, or can (or must) I use a different way?
Btw: There is the same problem with the connection dialog.
Thanks in advance
Frank