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POP stands for Post Office Protocol. It is the protocol (a
common language that is used by computers to exchange
information between different hardware components, different
computers over a network etc'. A computer protocol is pretty
much the same as a regular human language) used to check any
non-web-based Email account. A web-based Email account is an
Email box that can only be used through a certain website.
During your stay in this website, you are exposed to ads
which the company who provides you with this mailbox profits
from. Web-based Email services are always free because
instead of paying, you pay the company who handles your
mailbox by watching these ads (unless this mailbox features
some extremely special services or features that cost more
money).
Hence, a non-web-based Email account is an account that is
accessed using an Email client or a regular telnet client,
if you know the necessary protocols (after you finish
reading this tutorial and the Sendmail tutorial, you would
know how Email works and how to compose and receive Email
without the need of any program besides a telnet client).
Non-web-based Email accounts use two protocols - SMTP
(Simple Mail Transfer Protocol) to send Email and POP (Post
Office Protocol) to receive Email. You can study the SMTP
protocol in the Sendmail tutorial, and as for POP - you'll
get to learn it right now. In case you're wondering, POP3 is
just a newer version of POP.
Why would I want to learn the POP protocol?
Oh, there are a lot of reasons why you would want to do
that. I'll give you a couple of examples out of my head:
a. Have you ever been mail-bombed? If not, can you imagine
how it is to have to receive and then delete hundreds or
even thousands of messages? Well, no more! After you'll read
this tutorial you would be able to delete Email right off
the mail server without having to receive it and then delete
it from your Email client (some Email clients won't let you
group several mails and delete all of them in one shot so
you have to delete them one by one, which would make your
job even more difficult).
b. You would have the ability to read your Email from
anywhere in the world. Sure, many people would say "but we
can always go to www.readmail.com, enter our Email address
and our password and we'll be presented with a nice
interface which will let us read our Email and delete
messages from anywhere around the world. Why would we want
to learn the POP3 protocol instead?" Well, there's a serious
security problem with using websites such as
www.readmail.com. For example: some browsers support an
option called "form completion". The browser records the
data you type into forms and then, when you return to a form
and start filling it out, it will fill all the rest for you.
c. Now, what happens if you use www.readmail.com on some
computer, and then someone else comes over and fills in your
Email address? That's right! The browser will complete the
rest of the form, thus reveal your password! This was just
an example of what insecurities readmail.com might pose.
The POP3 protocol isn't so complicated. In fact, it's quite
easy, so hell, why not learn it just for fun, huh? :-)
Alright, let's go!
The first thing you will need is a regular telnet
application. No need for anything fancy. Unix has a native
telnet client (simply type telnet hostname/IP to telnet to
that hostname or IP into port 23 or telnet hostname/IP port
to choose a port other than 23). Windows 95 and above also
come with a telnet application (it's in
c:\windows\telnet.exe, but you can also press start, run and
type telnet to run it, telnet hostname/IP to telnet to that
hostname or IP and into port 23 or specify a port other than
23 with telnet hostname/IP port).
Next, you need to find your POP3 mail server. Usually it
would be something like mail.your-isp.net. For example: my
ISP is netvision.net.il, so my POP3 server is located at
mail.netvision.net.il. If you already have an Email client
that is configured correctly for your POP3 box, go to your
preferences dialog boxes and you should be able to find your
incoming mail server address there.
Okay, looks like we're pretty much ready for this. Next
thing, we telnet to our POP3 server and into port 110 (the
default port for POP3). This is what I get when I telnet
into my POP3 page:
+OK POP3 [194.90.1.6] v7.60 server ready
Okay, looks good so far. Now we need to identify ourselves.
We need to supply our username and password. Your username
would usually be in your Email address. For example: my
Email address is barakirs@netvision.net.il, therefore my
username is barakirs. So we type:
user barakirs (or whatever username you have)
And the server replies with:
+OK User name accepted, password please
Next thing, we need a password, right? So we do:
pass your-password
And the server replies with:
+OK Mailbox open, x messages (when x is the number of
messages you have in your inbox)
Or with:
-ERR Bad login
If we supply the wrong password. Now, we want to see what
we have, so we first type list to see the list of Emails we
currently have (unless, of course, we have 0 new messages).
For each Email, we would get a separate line which will
contain a message number (a number that identifies each
message) and a number that would indicate the size of each
message.
Next thing, we want to read our messages. To do this, we
type retr #. Retr stands for retrieve. # should be replaces
by the message's number. We would then get a full message
header (see Sendmail tutorial) and the body of the message.
After we read the message, we would probably want to delete
it. In order to do that, we type dele #. Dele stands for
delete. # should be replaced by the message's number.
Once you're finished, type quit to close your session.
Final notes
Yup, that's all! Oh, just one more thing - when you log
into your POP3 mailbox, it gets locked up so noone can
access it while you're inside. A "lock file" is created when
you log in and is deleted when you log out, and whenever
someone tries to log in the server allows him access only if
the lock file does not exist (which means that there's
nobody currently logged in).
See? It's easy. I hate to tell you "I told you so"
but... :-)
Credits
Written by Raven
Date: 2/1/2000 |