Subjects ->
Computer Networks ->
Lectures ->
Lecture #05
INT20CN Computer Networks
Practical Exercises #5
- This question is only relevant to on-campus students who regularly
use the Unix systems. When you receive mail on the departmental
Unix systems, it is stored in your system mailbox. This is a text
file in "mailbox format". Examine your system mailbox and explain
what "mailbox format" looks like. In particular, how do you tell
where one message ends and the next begins? On some systems you can
discover where your mailbox is by typing
echo
$MAIL
at the shell prompt.
- Note:
- If you don't normally read and/or send your mail on
the Unix systems, don't worry too much about this exercise. On the
other hand, maybe you could look at the format of the files which your
particular mail agent uses to store messages -- for example, Netscape
Mail uses a file called "Inbox" on some systems.
- The "mail spooling" system on a Unix host can be examined using the
mailq
command. Try it. Same proviso as previous question.
- Investigate mail forwarding on the Unix systems. This is
done by creating a file called
.forward
in your
home directory, containing the address you want your mail forwarded
to. You also have to ensure that the file is readable and writable
only by yourself: use the following Unix command to do this:
chmod 600 .forward
. For example, you
could set a .forward
pointing to your
"university-supplied" email address (eg
yourID@students.latrobe.edu.au
), or if you use
an external ISP you could redirect your mail to that email address.
That way, mail sent to you on the Unix systems will be delivered to
you at your preferred address.
- Depending on which user agent you use for reading mail, you can
configure what happens when different MIME message types are
received. For example,
audio/basic
messages
probably cause a sound file player to be opened, whereas
image/gif
normally opens an image viewer.
Discover where this behaviour is specified (possibly in a
"Preferences" menu item) and customise it. Can you control the MIME
types of enclosures, or attachments, which you send from your mail
agent?
- (optional) One of the nicest things about using Unix for reading
your email is the range of tools available for processing incoming
mail. The best of these is
procmail
. Look up
procmail
and procmailrc
in
the Unix man
pages and see what it can do for
you. Have a look at the file
~pscott/.procmailrc
on the Unix systems (your
lecturer's personal procmail configuration) to see how he uses it.
Note same proviso as question 1.
- The SMTP protocol can be employed in useful ways by the average
network guru. For example, you can check on the validity of an
email address by telnetting to the SMTP port (25) and invoking the
VRFY
command. Similarly, you can expand an
email alias using the EXPN
command. Telnet to
port 25 on ironbark and VRFY
the username
pscott
. Then see if you can
EXPN
the alias scott
- OK, time for some experimental computer science. In the lecture,
you saw a "by hand" SMTP session -- telnetting to port 25 and
typing the SMTP commands to the remote server. Try it yourself, and
send a message to someone -- perhaps even to yourself, or another
email address which you have. Be aware that every
electronic mail transaction is logged on all systems, so you would
be well advised to stick to local hosts, and addresses of people
you know -- like your own...
This set of practical exercises accompanies
Tutorial #5.
[Previous Practical]
[Index]
[Next Practical]
Copyright © 2001 by
Phil Scott,
La Trobe University.