How to send authenticated email as same email for public folder with MS Exchange

Question

Is it possible to create an authenticated MSExchange user that can send email on behalf of any other user in the system (public folder emails as well) without configuring it on a user-alias basis?

If we have a public folder and all [e-mail] is routed to it, how do we get our server software to send email on it's behalf.

I figured that a super-user could be created that could spoof any valid email in the system.

We have a robot that was doing this, unauthenticated via an SMTP server but we want to connect to our exghost... exchange service and send them direct from our organization now.