This article was previously published under Q293800
It may be necessary to configure a Windows 2000 server to relay or act as a smart host for security reasons, such as in a perimeter network scenario (also known as DMZ, demilitarized zone, and screened subnet) when you do not want to have a server that participates in domain security available on the Internet or you do not need the full functionality that an Exchange server provides to do email for CDO and list serve-type applications.
Step 1: Verify the Installation of the SMTP Service
In Control Panel, open Add/Remove Programs, click Add/Remove Windows Components. Click the Internet Information Services (IIS) component, click Details, and then verify that the SMTP Service check box is selected. If it is not selected, click to select it, click OK, and then follow the installation directions that are displayed.
Step 2: Configure the SMTP Service to Relay for Internal Domains
Depending on the scenario, it may be necessary to configure the SMTP service to relay inbound messages for your internal domains.
Click Start, point to Programs, click Administrative Tools, and then click Internet Services Manager.
Expand the tree under the server name, and then expand the Default SMTP Virtual Server. By default, you should have a Local (Default) domain with the fully qualified domain name of the server.
Configure the domain for inbound:
Right-click the Domains icon, click New, and then click Domain.
Click Remote, click Next, and then type the domain name in the Name box. Click Finish.
Configure the domain for relay
In the properties for the domain that you just created, click to select the Allow the Incoming Mail to be Relayed to this Domain check box.
If this is being set up for a internal domain, you should specify the server that receives email for the domain name by the IP address in the Route domain dialog box.
Click the forward all email to smart host option, and then type the IP address of the server that is responsible for email for that domain in square brackets. For example:
Note: Typing the IP address of the server in brackets is necessary so that the server recognizes this is an IP address and not to attempt a DNS lookup.
Step 3: Specify the Hosts That You Want to Openly Relay to All Domains
Note: Anyone can send to the domains that you specified in Step 2.
This step is for hosts, which are most likely your internal servers that would need to send to all domains on the Internet. It is not recommended to not have any restrictions because anyone can use your server as an open relay. It is recommended to only allow the minimum, necessary hosts to openly relay to all domains. To do so:
Open the properties of the Default SMTP Virtual Server.
On the Access tab, click Relay.
Click Only the list below, click Add, and then add the hosts that need to use this SMTP host to send email. On the dialog box that appears, you have the following options:
Single computer: Specify one particular host that you want to relay off of this server. If you click the DNS Lookup button, you can lookup an IP address of a specific host.
Group of computers: Specify a base IP address for the computers that you want to relay. You have to specify the octets in the IP address for hosts that you will allow to relay. For example: If the IP address is 18.104.22.168, and you want any hosts with the first two octets 192.68 to relay, specify 255.255.0.0 for the subnet mask.
Domain: Select all of the computers in a domain by domain name that will openly relay. This option adds processing overhead, and might reduce the SMTP service performance because it includes reverse DNS lookups on all IP addresses that try to relay to verify their domain name.
Configure the other servers to use your relay server as a smart host
Depending on the other applications or mailers that will use your relay server, you may have a option where you can specify a smart host or SMTP relay. With Exchange 2000, you would create an SMTP connector and specify the Windows 2000 Relay server in the Forward all mail through this connector to the following smart host box.