OK, so you DO NOT send NDRs, yet with your IIS platform you *cannot* turn off NDRs. Lets get this straight, you have turned off NDRs on a platform that you *cannot* turn off NDRs. Cool.
I don't mean that in a mean way, but man, chill out a bit...
You can also have the receiving server dirt-nap DNS. No NDR's. Done.
Any more questions?