Electronic Mail Addresses

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

In addition, some email addresses from other countries (or from the United States) end in a country code. Here are some examples:

US United States
CA CAnada
UK United Kingdom
DE Germany (DEutschland)
IL IsraeL
ES Spain (ESpaña)

Finally, there are seven new domain names that have been approved in November 2000. These are not yet widely used, but they will be in the near future. They are:

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.

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.

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.

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This page was prepared by Dr. David M. Marcovitz.

Last Updated: January 22, 2002