This article describes how to configure a remote domain for an Internet Information Services (IIS) Simple Mail Transfer Protocol (SMTP) mail relay server.

IIS in Windows Server 2003 includes a full-featured SMTP virtual server that you can use to route mail on your internal network. The SMTP virtual server can also accept mail from the Internet. Although the SMTP Service does not include an easily accessible mechanism in which to retrieve mail, it can play a vital role in accepting mail from the Internet and relaying it to your SMTP/POP3 server. You can configure the SMTP virtual server to accept mail for the domain to which the computer belongs, and for other domains.

A stand-alone server that is running the SMTP Service provides a good measure of security because it acts as a layer of separation between the corporate mail server and inbound connections from the Internet. A stand-alone Windows Server 2003-based computer isolates the server from the Active Directory security boundaries of the internal network. You can configure the stand-alone SMTP virtual server to use the corporate mail server as a smart host. You can then configure the stand-alone SMTP virtual server to relay mail that is directed only to the remote domain. If you do this, all other mail is not relayed and is rejected.

How to Configure a Stand-Alone IIS SMTP Server to Relay to a Remote Domain

1. Start Internet Information Services Manager or open the Internet Information Services (IIS) snap-in.
2. Expand Server_name, where Server_name is the name of the server, and then expand Default SMTP Virtual Server.
3. Right-click Domains, point to New, and then click Domain.
4. Click Remote, and then click Next.
5. Type the name of the new remote domain in the Name box.
   
   You can specify a single domain, or you can use an asterisk (*) as a wildcard character (the asterisk must be at the beginning of the name and be separated from the rest of the name by a period) to specify more than one domain. For example, if you want the remote domain to accept mail for other-domain.com and all its subdomains, use the name *.other-domain.com.
6. Click Finish.
7. In the right pane, right-click the new remote domain that you just created, and then click Properties.
8. Click the General tab.
9. Under Select the appropriate settings for your remote domain, click to select the Allow incoming mail to be relayed to this domain check box to allow the SMTP server to act as a mail relay.
10. Under Route domain, click Forward all mail to smart host, and then type the IP address or the fully qualified domain name (FQDN) of the internal network's corporate mail server. If you use an IP address, make sure that you use brackets "[]" to enclose the IP address. For example, [nnn.nnn.nnn.nnn].
11. Click OK.
12. Stop and start the SMTP virtual server. To do so, right-click Default SMTP Virtual Server, and then click Stop. After the virtual server stops, right-click Default SMTP Virtual Server again, and then click Start.

Troubleshooting

After you configure the remote domain, all mail that is addressed to the remote domain name is relayed to the smart host that you configured. Mail that is not deliverable is stored in the Inetpub\Mailroot\Badmail folder.

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