What is an Email?
Email, short for electronic mail, may be thought of as an electronic version of the
Post Office. If you type a message on your computer and send it to me, my email address is
in the To-address field, yours is in the From-address field.
This email packet is sent to me via the Internet, a world-wide network of computers,
wired together to send such packets from point A to point B.
A letter would be sent to the To country, then state, then city, street, and mail box. If my
email address were alex@hotmail.com, the packet would be sent to the domain (hotmail.com)
first, then the mailbox associated with the user (alex).
Okay, so What's an IP Address?
Each computer that is directly attached to the Internet is represented by a set of four numbers,
called an IP address. The domain name is translated into an IP address, like 12.72.106.43,
where each of these four numbers is be between zero and 255. That's a LOT of possibilities: over
four billion addresses! But lately we are running out of addresses, so many of the computers that
are directly connected to the Internet represent many others that are behind them. To stay within
these limitations, a computer (called a firewall) connects to the Internet and manages many
other computers that connect to the internet indirectly, through that firewall computer. These
internal computers are usually all part of the same company or institution, and are often referred
to as an Intranet. They each have unique IP addresses, but these addresses need only be unique
inside thier Intranet, so the same number may exist at a lot of companies; each company's firewall
knows about the 10.1.1.82 computer on it's Intranet, for example, but it knows nothing about
any of the 10.1.1.82 computers on any other Intranet. There is a special set of IP addresses set aside
by agreement for internal networks. An international group called the Internet Engineering Task Force
(see www.IETF.org for more information) manages such things.
How do I find a Sender's IP Address?
If you use an email program on your computer, Microsoft's Outlook for example, you can discover the
Originating IP address (the address in the From field) of an incoming email by right-clicking on the
email's subject line and select "Options" for a detailed description of how this particular email got
to your mailbox. These details are often referred to as the "headers" of an email. One of these details
is labeled as the Originating IP. There are several web sites that will translate an IP address into a
host name. Use any Internet search engine to find one that you like, and add it to your list of Favorites
for some later experiments.
Why would you care about all of this? People who send threatening letters don't put their real return
address on them. Similarly, an email with a computer virus attached will probably have a fake email
address in the From field. You can find more information on this technique by searching for IP
Spoofing on an Internet search engine.
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