I am running Exchange 5.5 sp3 on NT 4.0 sp 4. The server has been added to the mail-abuse.org RSS list. I have closed the open relay but it will still accept any e-mail with the valid domain – whether or not it exists in the address list. I have followed the instructions in the MS article “Is your exchange server relay-secure” and set reroute incoming SMTP mail and set the routing restrictions to Hosts and clients with these IP address – which is left blank. The server still accepts e-mail addressed to users who are not in the address list ie. invalidemail@mydomain.com.
