I have been trawling through all the past entries on this topic to no avail, basically I am running a single Exchange 2000 server SP2 which has it's SMTP virtual server to only allow relaying to the "list below" in the list I only have the three subnets that this server serves. I have been through the IIS settings on this server to ensure that this is the case for all entries in there also. I also have a server sitting in front of the exchange server scanning SMTP running Network Associates Webshield, this also has it's "Anti spam Relay" configured to only traffic from the three subnets, it also has IIS and SMTP disabled. However despite all this we are an open mail relay, I have even just stopped the virtual server and tried the external Relay tester again and it still came back as an open relay which tends to make me think that Exchange is configured correctly and this is something else. Does anybody have any ideas? I am getting desperate.