Block External Emails From UAT

Here is the situation. 
We have a uat domain and have couple of websites hosted on it.We have one uat IIS smtp gateway forwarding emails to connector on our HUB .Our exchange 2010 is in a separate domain. I want to restrict emails being sent from the uat domain extrenally(gmail,hotmail etc.)
do i need to create a separate receive connector for that and drop extrenal emails? Bit confused