12/15   Months ago, some guy suggest to set up a FreeBSD / Linux box at front
        of Exchange Server to serve as a sort of MTA which greatly enhance
        the security of the email infrastructure.  I would like to know more
        on how to do that.  Any pointers?  Thanks.
        \_ the idea is by having inbound connections from the internet connect
           to the bsd/linux box you protect your exchange server from any
           security vulnerabilities associated w/ IIS (specifically the MTA
           piece of IIS). setting it up can be as simple as setting up the
           box w/ most defaults and being sure to set your MX for your domain
           on the inside to your exchange server... now you should at least
           disable relaying from the internet as well.
        \_ It's just a mail proxy that runs SA or whatever and then reforwards
           the surviving mail to exchange.