How limit smtp authenticated user to use his own email address for mail from address???

Let's start to use authenticated SMTP clients, servers are configured correctly, are exchange 2007, but we find an unwanted behavior.

If a user is authenticated, the SMTP server does not validate that the smtp address of origin, is that corresponding to the user can put any other mail is dispatched

How limit smtp authenticated user to use his own email address for mail from address???

Thanks

Marcelo