I am ready to buy it for 30 $<| sep |> You can almost smell the sweat pouring furiously from Shohashi ' s forehead when Derek begins to quiz him . My goodness , what an asshole . And they all call him supreme commander , I mean . WTF ! Ego much ? <| sep |> If you aren ' t sure , from something outside your network , telnet in to port 25 . See what answers . Exchange can be spotted quite easily if it is answering and that means the traffic doesn ' t see the proxy . If the proxy answers , then you need to do filtering there . I don ' t like SMTP proxies personally . They cause confusing . Either have the traffic go directly to Exchange or use another SMTP server in front of Exchange to filter the email before it is passed to Exchange .