Exchange 2010 Transport Rule to prevent internal emails from getting outside

Is it possible to do the following in Exchange 2010 SP3 roll up 10?

Create an Exchange server side rule that will scan an email header from a certain originating IP address and prevent it from leaving the exchange organization, i.e. going to an outside email domain?

Also, this exchange environment sits behind a netscaler, so when a message is processed the originating IP is changed to the IP of the net scaler. In a case where a NLB is not used, does the originating IP in the header line up with the IP address of the client PC that the email was sent from?