Setting Fully Qualified Domain Names (IIS 6.0)

An e-mail domain must be able to be resolved through Domain Name System (DNS). There are two DNS records that are used to resolve an e-mail domain. In most cases, a mail exchanger (MX) record is set up to associate an e-mail domain with the fully qualified domain name (FQDN) of one or more Simple Mail Transfer Protocol (SMTP) virtual servers that serve that domain. Each SMTP server referenced in the MX record must have an address (A) record. The A record maps a given FQDN to its IP address.

It is possible to just have an A record set up for an e-mail domain. In this scenario, the A record maps the domain to the IP address or addresses of the SMTP virtual server or servers that serve that domain. Adding an MX record, however, is recommended over using an A record by itself, because an MX record allows an SMTP administrator to specify an ordered list of servers to use for clients sending mail to that e-mail domain. Microsoft SMTP Service always checks first for an MX record before falling back to an A record, so setting up MX records on your virtual server can improve performance. And, in some cases, the A record is used for other purposes, such as HTTP, although the MX record is generally used only for SMTP. The MX record allows one server to handle (HTTP clients use the A record) and another server to handle (SMTP clients use the MX record).

On the SMTP service, there are two options for specifying an FQDN. You can use the name specified on the Network Identification tab of System Properties in Control Panel, or you can specify a unique FQDN for the SMTP virtual server you are configuring.

At startup, the name designated on the Network Identification tab of System Properties is automatically used for the FQDN. If you change the name (either manually or by joining a domain), the new name is automatically used for the FQDN the next time the computer is restarted. No action is required to update the FQDN for the virtual server.

To override the automatic use of the computer and domain names on the Network Identification tab, change the FQDN in the Advanced Delivery dialog box, accessed through the Delivery tab. The SMTP service can then use the designated name instead of the one specified on the Network Identification tab.


You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /User:Administrative_AccountName "mmc systemroot\system32\inetsrv\iis.msc".


To change the FQDN


In IIS Manager, right-click the SMTP virtual server, and then click Properties.


Click the Delivery tab, and click Advanced.


In the Fully-qualified domain name box, type the FQDN.

Related Information

For information on setting the message hop count, see Setting the Message Hop Count.

For information on designating a server for all outgoing messages, see Configuring Smart Hosts.

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