Inbound Relay Error Behind Proxy Server

[ATCal]

I setup a multihomed box running MS Proxy 2 in fron of a properly functioning Exchange 5.5 server. The Proxy server is a PDC in its own Domain as it is providing access to two seperate domains that are not allowed to access eachother.In order to do this, two WSPCONFIG files needed to be created to allow port 25,110,etc to pass through to the Exchange server which went successfully (I think).
When I try to manually send using telnet (thanks Zel) I get a 550 unable to relay to ..address...
My external NIC has a different domain listing in DNS (required for ISP) then my internal which is used by the Mail server and noted in the MX Record.
Proxy is supposed to simply send the 25 traffic straight to the Mail server. Do I need to set some type of relay?

Any help would be appreciated.
PLEASE!!!!

 

[ATCal]

Never mind, solved my own problem. One of the technophobes started the IIS SMTP service. That combined with the fact that the Exchange box unlike the other Proxy server clients requires DNS server entries.