How can you tell when an e-mail address isn’t correctly constructed or formatted? What about a website address or URL? Part of recognizing bad addresses and knowing how to address an e-mail correctly is understanding and knowing what the top level domains are, and how domain names are structured.
A web URL (Uniform Resource Locator) and an e-mail address have part of their addresses in common, and that part is the ‘domain name’.
This would be the inetdaemon.com part of http://www.inetdaemon.com or username@inetdaemon.com. Domain names are registered and are organized under a group of top level domains. So what are the ‘top level domains’? This is the .com part in inetdaemon.com. It is also the .edu part in stanford.edu. It is the .biz part of somecompany.biz. Those are some of the ‘standard’ top level domains. These are selected by a comittee within IANA (Internet Assigned Numbers Authority) who manages the top level domains and creates new ones based on demand. IANA also manages the IP addresses for the entire world.