A zone file is a small set of instructions for resolving specified Internet domain names to the appropriate number form of an Internet Protocol address (an IP address). These instructions are ordinarily quite simple and reside in a file on the server that administers a site. Zone files can be used with HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), or SMTP (Simple Mail Transfer Protocol) addresses.
Ideally, a Web zone file should allow resolution of domains either with or without the three letters www. For example, both of these Internet addresses yield the same result:
This indicates that the server administrator has written the zone file properly for this Web domain.