MX records make it possible to deliver e-mail addressed to hosts that do not themselves run mail software, to hosts that are not connected to the network (and therefore lack A records), or even to mail addresses that do not correspond to any physical machine at all.

The MX records of a host should list one or more "mail exchanger" (MX) hosts that are willing to receive mail on behalf of that host.

Your installation of NameSurfer may have been set up to display a selector box with predefined MX alternatives. In this case, you can define all the MX records of a domain name at once, simply by selecting an entry in the selector box. Each selector entry lists the mail exchangers as a comma-separated list, in order from most preferred to least preferred.

If none of the alternatives is acceptable, select [Define new] and press the OK submit button. You will then be prompted for the names of your desired mail exchanger hosts.

If there are no predefined MX alternatives, MX records are entered using a set of text entry fields. Each field should contain the name of one mail exchanger, in order from most preferred to least preferred. If there are more entry fields than mail exchanger hosts, the leftover fields should be left blank.

The first (most preferred) mail exchanger host should be the one where the final delivery of mail will take place (in other words, the server machine containing the users' mailboxes). The other MXs will be used only as backups in the case when the most preferred MX is not responding. Typically, these "fallback MXs" will simply store the mail temporarily and re-send it to the most preferred MX when it comes back to life.

Each mail exchanger is accompanied by a preference value. This preference value should be a positive integer and indicates the mail exchanger's priority. The most preferred mail exchanger should have the lowest preference value.

It is recommended that you define MX records for all your hosts. If you do this, you should also make sure that the mail server listed in your first MX record is correctly configured to accept mail addressed to other machines.

NameSurfer checks that the mail exchange really is an existing domain name, and issues a warning if the name does not exist.