...Learning E-Mail (4 of 5) -- Deciphering addresses

     So now you're ready to send e-mail to other people on the Net. Of
course, you need somebody's address to send them mail.  How do you get it?
     Alas, the simplest answer is not what you'd call the most elegant:
you call them up on the phone or write them a letter on paper and ask
them.  Residents of the electronic frontier are only beginning to develop
the equivalent of phone books, and the ones that exist today are far from
complete (still, later on, we'll show you how to use some of these
directories).
     Eventually, you'll start corresponding with people, which means
you'll want to know how to address mail to them.  It's vital to know how
to do this, because the smallest mistake -- using a comma when you should
have used a period, for instance, can bounce the message back to you,
undelivered.  In this sense, Net addresses are like phone numbers: one
wrong digit and you get the wrong person.  Fortunately, most net
addresses now adhere to a relatively easy-to-understand system.
     Earlier, you sent yourself a mail message using just your user-
name.  This was sort of like making a local phone call -- you didn't have
to dial a 1 or an area code.  This also works for mail to anybody else
who has an account on the same system as you.
     Sending mail outside of your system, though, will require the use of
the Net equivalent of area codes, called "domains." A basic Net address
will look something like this:

              tomg@world.std.com

     Tomg is somebody's user ID, and he is at (hence the @ sign) a site
or "domain" known as std.com.  Large organizations often have more than
one computer linked to the Internet; in this case, the name of the
particular machine is world (you will quickly notice that, like boat
owners, Internet computer owners always name their machines).
     Domains tell you the name of the organization that runs a given
e-mail site and what kind of site it is or, if it's not in the U.S., what
country it's located in.  Large organizations may have more than one
computer or gateway tied to the Internet, so you'll often see a two-part
domain name; and sometimes even three- or four-part domain names.
     In general, American addresses end in an organizational suffix, such
as ".edu," which means the site is at a college or university. Other
American suffixes include:

          .com for businesses
          .org for non-profit organizations
          .gov and .mil for government and military agencies
          .net for companies or organizations that run large networks.

     Sites in the rest of the world tend to use a two-letter code that
represents their country.  Most make sense, such as .ca for Canadian
sites, but there are a couple of seemingly odd ones.  Swiss sites end in
.ch, while South African ones end in .za.  Some smaller U.S. sites are
beginning to follow this international convention (such as
unixland.natick.ma.us).
    You'll notice that the above addresses are all in lower-case. Unlike
almost everything else having anything at all to do with Unix, Most Net
mailing systems don't care about case, so you can capitalize names if you
want, but you generally don't have to. Alas, there are a few exceptions
-- some public-access sites do allow for capital letters in user names.
When in doubt, ask the person you want to write to, or let her send you a
message first (recall how a person's e-mail address is usually found on
the top of her message).
   The domain name, the part of the address after the @ sign, never has
to be capitalized.
     It's all a fairly simple system that works very well, except, again,
it's vital to get the address exactly right -- just as you have to dial a
phone number exactly right.  Send a message to tomg@unm.edu (which is the
University of New Mexico) when you meant to send it to tomg@umn.edu (the
University of Minnesota), and your letter will either bounce back to you
undelivered, or go to the wrong person.
     If your message is bounced back to you as undeliverable, you'll get
an ominous looking-message from MAILER-DAEMON (actually a rather benign
Unix program that exists to handle mail), with an evil-looking header
followed by the text of your message. Sometimes, you can tell what went
wrong by looking at the first few lines of the bounced message.  Besides
an incorrect address, it's possible your host system does not have the
other site in the "map" it maintains of other host systems. Or you could
be trying to send mail to another network, such as  bitnet  or
CompuServe, that has special addressing requirements.
    Sometimes, figuring all this out can prove highly frustrating. But
remember the prime Net commandment: Ask.  Send a message to your system
administrator.  He or she might be able to help decipher the problem.
    There is one kind of address that may give your host system
particular problems.  There are two main ways that Unix systems exchange
mail.  One is known as  UUCP  and started out with a different addressing
system than the rest of the Net.  Most UUCP systems have since switched
over to the standard Net addressing system, but a few traditional sites
still cling to their original type, which tends to have lots of
exclamation points in it, like this:

               uunet!somesite!othersite!mybuddy

     The problem for many host sites is that exclamation points (also
known as "bangs") now mean something special in the more common systems
or "shells" used to operate many Unix computers. This means that
addressing mail to such a site (or even responding to a message you
received from one) could confuse the poor computer to no end and your
message never gets sent out. If that happens, try putting "forward"
backslashes in front of each exclamation point, so that you get an
address that looks like this:

               uunet\!somesite\!othersite\!mybuddy

Note that this means you may not be able to respond to such a message by
typing a lower-case "r"  -- you may get an error message and you'll have
to create a brand-new message.