INT21CN Computer Networks

Practical Exercises #4

  1. As you may be aware, the Department of Information Technology has an official policy of only sending student emails to their "official" address. Many students find it tedious to check this email account regularly because they normally use some other email system. What they don't realise is that they can use the email server as an additional POP server for their normal email software.

    If your email client software can be configured to handle multiple POP servers, try adding your account. This way, you'll automatically fetch all of your official email into your favourite mail handler.
    Note to Serious Hackers: if you're running Linux on your home computer, you can do something similar with the excellent fetchmail utility. How to get it working is, however, outside the scope of this prac!

  2. 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.
    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.

  3. The "mail spooling" system on a Unix host can be examined using the mailq command. Try it. Same proviso as previous question.

  4. (HIGHLY Recommended) Set up email forwarding on the Unix systems. This is done by creating a one-line text file called .forward in your home directory, containing the email address you want your mail forwarded to. You also have to ensure that the .forward file is readable and writable only by yourself: use the following Unix command to do this: chmod 600 .forward. For example, you could create a .forward pointing to your "university-supplied" email address (eg, 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.

  5. 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?

  6. 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

  7. 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 pretty much every electronic mail transaction is logged on our systems, so you would be well advised to stick to local hosts, and addresses of people you know -- like your own...
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Copyright 2004 by Phil Scott, La Trobe University.
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