We have a SBS server 2003 R2 with Exchange Server 2003 installed. We've shutdown all exchange services except for the SMTP. There is one SMTP virtual server defined. A new NIC was added to the server recently. We have an email program written in .NET. We noticed that we cannot connect to the SMTP server using the new IP address of the box.The error is: Unable to read data from the transport connection: net_io_connectionclosed.If running on the box itself, we cannot connect using 127.0.0.1 nor localhost. The error is the same. In other words, the only way to connect is to use the IP of the box when the Exchange server was installed. The SMTP virtual server is bound to "All Unassigned" IP addresses on the box. Connection and Relay permissions are configured to accept from both subnets. "netstat -an" shows that the SMTP server is listening on all IPs "0.0.0.0:25". Using telnet, we were able to connect to port 25 the box using both IPs and 127.0.0.1. However, only the connect to the working IP responds with the Microsoft ESMTP echo. It seems that the physical connection to the SMTP server can be made regardless of which IP is used, but the SMTP session can only be established on one IP. Does anybody know what the problem might be?We are not experts in Exchange admin so any help will be greatly appreciated!!