Electronic mail addresses can look very confusing if you don't
know how to read them. To the uninitiated, they are a jumble of
numbers, letters, and symbols with no apparent meaning. With a
little guidance (from this handout), they should be fairly easy
to decipher.
The Two Parts
Most electronic mail addresses have two parts, separated by an
at-sign, which looks like this:
To the left of the @ is the person's user name or mailbox. To
the right of the @ is the computer where the person's account
is.
User Names
User names come in many different styles. Many user names are
based in some way on the person's name. For example, my last name
is Marcovitz, but I think that is too long, so I have a user name
that is an abbreviation of that (marco). For many computer systems,
there is a policy that dictates what a person's user name will
be. For example, at Loyola, all student accounts are the person's
first initial, followed by the last name. For example, John Doe,
might have the user name jdoe. However, if jdoe is already taken
by someone (such as Jane Doe), then a number is appended to the
name: jdoe1.
Many email providers allow you to choose your own user name. You
may choose something based on your last name, or you may choose
something entirely made up. That is why you might see a user name
like catlover or terpfan.
Other email providers make up incomprehensible user names for
you. CompuServe used assign numbers to all of their users, so
many CompuServe addresses had names such as 90113467 (not very
easy to remember).
Other email providers use a combination of sensible things and
numbers. When I was in graduate school, I had an email address
that was
The "dmm" is my initials. The "g" stands for
graduate student. And I have no idea what the "1176"
stands for.
Machine Names
The trick to reading machine names is reading them from right
to left in order to go from the most general to the most specific.
Each part of the machine name is separated by a period (pronounced
dot). So my Loyola address:
would be pronounced "marco at Loyola dot E D U." The
machine name in this case has two parts: loyola and edu.
Domain Names (The Far Right)
At the far right side of the machine name is the domain name.
This tells you what kind of an institution has provided the email
account. The following are the most common domain names:
| EDU | EDUcational Institution |
| COM | Private COMpany |
| NET | NETwork Provider |
| GOV | GOVernmental Agency |
| ORG | Nonprofit ORGanization |
| MIL | MILitary Agency |
| US | United States |
| CA | CAnada |
| UK | United Kingdom |
| DE | Germany (DEutschland) |
| IL | IsraeL |
| ES | Spain (ESpaña) |
| AERO | Air Transport Insdustry |
| BIZ | Businesses |
| COOP | Non-profit Cooperatives |
| INFO | Information Services |
| MUSEUM | Museums |
| NAME | Personal Web Sites |
| PRO | Professionsal Services (doctors, lawyers, etc.) |
With this information, you
can look at the far right side of an email address and know what
kind of institution provided the email account. That doesn't necessarily
tell you too much about the person who has the account, but sometimes
it is a clue. Additionally, some of the addresses are open to
anyone while others are really restricted to those who fit the
category. For example, anyone can purchase a .ORG domain, regardless
of whether or not they are a non-profit organization, but only
government agencies can get a .GOV domain.
The trickiest situation is when an address ends in COM. In this
case, the email address could be for a person working for a private
company, or it could be for a person who got an email account
by subscribing to an online service. For example most addresses
ending with AOL.COM are for people who subscribe to America Online
(AOL), not people who work for AOL. On the other hand, most addresses
ending with HP.COM are for people who work for Hewlett Packard.
Subdomains (Moving to the Left)
The next part of an email address is the subdomain. This is more
specific than the domain, and it usually tells you the specific
company or organization that provided the email address. For example,
has EDU as the domain, so we know it is an educational institution.
Next is UIUC, which stands for University of Illinois at Urbana
Champaign. So, we know that the address is an educational institution,
and the specific institution is the University of Illinois at
Urbana Champaign. In the following address,
we can see by COM that this is a private company, and HP tells
us that the company is Hewlett Packard. Sometimes you will recognize
the company or organization and sometimes you won't.
Sometimes that is all. Many email address simply have a domain
and a subdomain. This could be because the company is small and
only has one computer, or it could be because the company has
a smart server that can send the email to the correct computer
without any additional information.
What If There Is More (Moving Further to the Left)
If there are more than two parts to the machine name (the part
after the @), then the next part will be more specific. This might
be an organization or group within the company. It might be a
specific facility within the company. It might be something you
can't figure out. But in almost all cases, it is more specific.
For example,
EDU tells us that this is an educational institution. UIUC tells
us that this is at the University of Illinois at Urbana Champaign.
CSO tells us that this is the Computing Services Organization
(the organization at UIUC that provides most student email accounts).
If we move all the way to the left, the last part might be the
actual machine name. In the above example, UXA is the name of
the computer that housed the account.
Some addresses will have fewer parts (but always at least two
for domain and subdomain), and others will have more. One account
that I used to have had the following address:
This address uses country domains (as do many K-12 schools). US
tells us that it is in the United States. FL tells us that it
is in Florida. K12 tells us that it is a K-12 school. Osceola
tells us that it is in Osceola County. PHS tells us that it is
at Poinciana High School. Every step from left to right gets a
little more specific and gives a little more information.
Capitalization
For email addresses, capitalization does not usually matter. Capitalization
never matters for anything after the @. Many systems will automatically
convert whatever you type after the @ to upper case anyway. I
do not believe that capitalization ever matters for the user name
(before the @), but it is best to type that part exactly as it
is given to you just in case the system cares.
Conclusion
You can not usually tell everything about an email address by
looking at it. Some email addresses are confusing and use initials
that you won't recognize. However, by breaking it down into parts,
it should not look to you like a jumble of random symbols, numbers,
and letters.
This page was prepared by Dr. David M. Marcovitz.
Last Updated: January 22, 2002