The e-mail passes through three steps before being received by
the right person. The following list outlines the three steps, referring to the
numbers on the figure. Afterward, I'll give a more detailed explanation of these
steps.
|
1. |
Barney sends the e-mail to the ISP2 e-mail
server.
|
|
2. |
The ISP2 e-mail server sends the e-mail to the fredsco.com
e-mail server.
|
|
3. |
The intended recipient checks his e-mail at the fredso.com
e-mail server, retrieving the e-mail.
|
In the first step, Barney has visited the fredsco.com website,
where he saw information telling him about some bowling balls for sale. Barney
wants to beat Fred the next time they bowl, using a brand new bowling ball built
by Fred's own company. So, Barney e-mails the sales department at Fred's Company
by sending an e-mail to the address of sales@fredsco.com.
Barney does not actually send the e-mail directly to a computer
at Fred's Company. Barney sends the e-mail to his e-mail server, which for an
individual Internet user like Barney, typically sits inside the ISP network to
which the user is connected. An e-mail server is a server that
receives, forwards, or holds e-mail, much like the service performed by the
postal service. That e-mail server forwards the e-mail to the e-mail server at
Fred's Company. By using these two steps, Barney can send the e-mail, even if
the e-mail server for Fred's Company is not currently connected to the Internet.
ISP2 keeps its e-mail server up and available all the time, just like you would
for a web server. The e-mail server at ISP2 simply waits until it can
successfully forward the e-mail to Fred's e-mail server.
Finally, when the e-mail sits in the fredsco.com e-mail server,
the end user (in this case, a friendly salesman at Fred's Company) can retrieve
the e-mail messages at his convenience (Step 3 in Figure 2-8). So, after a morning golf "sales call," the
salesman might come in and check his e-mail, finding Barney's e-mail.
The terms e-mail client and client have specific meanings in
networking. Generically, any application program that an end user uses to access
some network server is called a client. A web browser, for instance, is a client
program. An e-mail client is the client software used for e-mail. Microsoft
Outlook is one of the more popular e-mail client programs.
E-mail has become one of the most common networking
applications, with a large portion of the population, both young and old, able
to send messages to each other for no incremental cost. Even my parents, who
grew up in a world where many people did not even have telephones, use e-mail
today.
Just like web applications, e-mail works just fine inside a
single enterprise network. However, the Internet allows pervasive access to
e-mail for literally billions of people, so you can communicate with friends and
acquaintances all over the world.
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