Nowhere, This would be done in DNS (Create an MX record), then config your
server to use the default gateway provided by your ISP (or your internal
If you have an SMTP relay (like IIS) that is in the DMZ, then you would
modify default SMTP -> access - relay and add the internal Exchanger server
that is allowed to relay to the DMZ SMTP box.
Hope it helps.
exchange 2000 I need to change my out going mail