Topic Last Modified: 2007-02-01

An e-mail domain must be able to be resolved through Domain Name System (DNS). Two DNS records 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's possible to only 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 enables an SMTP administrator to specify an ordered list of servers to use for clients sending mail to that e-mail domain. The SMTP service always checks first for an MX record before falling back to an A record. Therefore setting up MX records on your virtual server can improve performance. In some cases the A record is also used for other purposes, such as HTTP, while the MX record is used only for SMTP servers. The MX record enables one server to handle http://example.com. HTTP clients use the A record. Also, the MX record enables another server to handle someone@example.com. SMTP clients use the MX record.

The SMTP service provides two options for specifying an FQDN. You can use the full computer name that is specified on the Computer Name tab of the 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 Computer Name tab of the System Properties is automatically used for the FQDN of the SMTP virtual server. If you change the name manually or by joining a domain, the new name is automatically used for the FQDN the next time that 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 Computer Name tab, change the FQDN in the Advanced Delivery dialog box, accessed through the Delivery tab. The SMTP service then uses the designated name instead of the one specified on the Computer Name tab.

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