SBS 2003 Premium - Open Relay

It appears I have an open relay and am sending out spam. "Allow messages to be relayed to these domains" is not checked. I have a SMTP connector and a POP connector. What am I missing
I noticed a lot of router collisions, and checked IP NAT Transactions. I have several hundred NAT connections from the private address of the server (on ports ranging from 1000 to 60,000) to the routable address that is mapped to the server (also on ports ranging from 1000 to 60,000). From my routable address the connections go out to various public IP addresses on port 25. Nslookup indicates I am relaying to hotmail servers

Please advise

Thanks