Your UDF may find membership Chris but using a Distribution List for controlling access for security is not really supported.


The Role of Groups and Access Control Lists in Exchange 2000 Server Deployment
http://www.microsoft.com/technet/prodtechnol/exchange/2000/deploy/access.mspx

http://www.slipstick.com/contacts/dl.htm

http://support.microsoft.com/?kbid=242039