domains - All about Internet domains
In the Unix world there are things known as domains. Domains are basically specific machines that are knowledgable (mail-wise) of other machines in that domain. For example, the authority for the .com domain is the site called ucbvax. The domain that governs most of the ProLine network is called .cts, and is a second level domain or “park” (cts stands for Crash Time Sharing).
My site, crash, is the official registered authority for the .cts domain. So then, .cts.com really is crash, the authority that presides over that domain. Sites on any network that use what is known as Internet addressing, will know about the various registered domains — at the very least .com, (ucbvax) and .cts.com (crash) as well.
The idea is that any site that is connected to a domain can be addressed via that domain. And any Internet site that knows about domains can basically get the mail through by looking at domain authorities. Domains are akin to ZIP codes we add to our postal addresses. With them, the Post Office can usually get mail to us even if the address is missing a city and state, and sometimes even your house number and street! Domain usage is similar, though an address has to, at the least, contain a user name, and the user’s home system name.
Mailing to email@example.com means “send mail to bblue at site crash in domain .cts in domain .com.” If a given Internet site does not recognize .cts.com, it will recognize .com and send the message along. The .com authority will know about .cts.com and pass it along. The .cts.com authority will certainly know about crash (because it is crash!) and deliver the mail to bblue.
This also means that any site that crash knows about can be referenced simply in an Internet address. So firstname.lastname@example.org or email@example.com are legitimate because crash knows about pnet01 and pro-sol, and crash is the authority of the .cts.com domain. Get it?
A domain-owning site, like crash, knows about all the sites under its influence because of the mapping system we use. For more details on maps and mapping, see the map(NET) manual.