Exchange 5.5 blocking Extensions

I have windows NT server 4.0 with exchange 5.5 and norton anti-virus protection installed. I have the norton scanning for extensions such as .bat, .exe and double extensions but there is no way of blocking them. So my question is this is there a wayin exchange server 5.5 to block extensions and if so where exactly do I go in the config to do this. Please email me with your answer to wroming@ci.killeen.tx.us and in your techrepublic answer just type see email and I will rate your answer as quickly as possible. Thank you and have a nice day.