E-mail at HKU

Since E-mail is the most popular use of the Internet and a large percentage of our network traffic is e-mail,  it deserves to be the topic of discussion in this column on how the e-mail system at HKU works.  This article describes the different kinds and formats of email programs available and the advantages and disadvantages so that users can decide which e-mail program to use.

What is the client/server model?

Client/server describes the relationship between two computer programs in which one program, the client, makes a service request to another program, the server, which fulfills the request.  On the server, a mail program (usually called a mail daemon) is activated and waits for client requests. Typically, multiple e-mail clients share the services of a common mail server program.  For example, to check your e-mail on the server, the e-mail is sent to the client in your PC, which displays the e-mail messages for you. The e-mail messages can stay on the server while the client displays the messages or they can be pulled down from the server and stored in your client.

What is the difference between client-side and server-side e-mail?

Usually we refer to e-mail which is stored at the PC as client-side (e.g. Eudora) and e-mail that is stored on the server as server-side (e.g. Webmail).

For HKU staff who have their own PC's in their offices, they tend to use client-side e-mail programs.  The mail is pulled down from the server to be stored on the PC.  You can configure your email client to "leave mail on host" or not.  If you choose to leave a copy of your mail on the host, you must remember to clean up your inbox on the host every now and then to prevent exceeding your mail quota.

For students who do not have their own PC's,  it is easier to use server-side e-mail which does not store the mail in your PC but simply displays the mail at your PC. Server-side mail can be accessed by direct connection to the e-mail host (using the Telnet and Unix pine programs), or displaying the mail at the client (using the PC-pine program), or the most convenient way is by using the browser to access the 'Webmail'.

The advantage of client-side e-mail is that you can have it on your PC and print it to your printer conveniently.  However, the disadvantage is that you cannot access your mailboxes when you travel overseas because the mail is on your PC.

The advantage of server-side e-mail is that you can access your mailbox from anywhere in the world (e.g. by using a browser to access webmail).  The disadvantage of webmail is that it may be slow.  Also, with the Unix-pine program, the process of connecting to the remote server from overseas may be cumbersome.

What are SMTP, POP3 and IMAP protocols?

SMTP (Simple Mail Transfer Protocol) is a protocol used in sending and receiving e-mail.  It is usually used with two other protocols, POP3 or IMAP, which let you save messages in a server mailbox or download them from the server to be stored on the PC. In other words, users typically use a program that uses SMTP for sending e-mail and either POP3 or IMAP for receiving messages that have been delivered to their e-mail server. The SMTP server at HKU is called mail.hku.hk.

POP3 (Post Office Protocol 3) is the most recent version of a standard protocol for receiving e-mail. With POP3, when you read your mail, all of it is immediately downloaded to your computer and no longer maintain on the server. One of  the most popular POP3 e-mail client is Eudora. (You can configure Eudora to "leave mail on host" in which case you must remember to clean up your mailbox on the host.)

IMAP (Internet Message Access Protocol) is the other standard protocol for receiving e-mail. You can view just the heading and the sender of the letter and then decide whether to open the mail. With the IMAP, you can also create and manipulate folders or mailboxes or delete messages on the server. IMAP requires continuous access to the server during the time that you are working with your mail. One of the most popular IMAP e-mail client is PC-pine or Webmail.

You can configure your e-mail client in either the POP3 or IMAP receiving mode. E-mail clients such as Netscape Mail or Outlook Express can be set either in POP3 or IMAP mode.  However, the Eudora is only in POP3 mode.

Configuring your e-mail client?

Configuring your e-mail client means setting up your e-mail program telling it what receiving format you wish to use and where your outgoing and incoming servers are, and what your account name is.  Your outgoing server is the 'mail.hku.hk' if you are using the HKU network.  Your incoming server is your e-mail server (hkucc.hku.hk or hkusua.hku.hk), whichever account you use for email.

The table below lists the popular email programs used in HKU and what receiving modes (designated by 'x') you can set them at.
 

E-mail Program	Connect to server directly	IMAP (server-side)	POP  (client-side)
Unix-pine	x
PC-pine		x
Eudora			x
Netscape		x	x
Outlook Express		x	x
Webmail		x

Which e-mail program should I use?

Considering the above advantages and disadvantages, you have to make a choice as to which e-mail program to use and then stick to it.  The reason for not switching between various e-mail programs is that different e-mail programs store the mail in different mailboxes, whether they are on your PC or in your host computer.  In other words, what mail you see in one program is not viewable by another program.

About mail quotas and file size limits

Please read the article on disk quotas for mail and user files  in a previous issue.  If you exceed your mail quota on your e-mail host, you will receive a warning message from the mail system. So, if you receive a system message saying your mail quota is exceeded, you know it is referring to the INBOX in the server, not in your PC and you must proceed to clean up the INBOX in your server.

For sending out email, there is a file size limitation as well.   For sending mail, the limit is 10 MB.  If you mail is more than 10MB, it will not be sent and you will receive a system message saying that you have exceeded the file size limit.  You can (1) chop up your file into smaller chunks or (2) use file transfer (FTP) or (3) displaying your file in your website so that your recipient can just access your site and download it using a web browser.

For receiving email, the file size limit depends on the free disk space available in your INBOX.  If your inbox is totally free, the file size limit is 8 MB.  If your INBOX contents exceed 8 MB, then you will not be able to receive any new mail.
 

Mabel Chau
Tel: 2859 8934
Email: chaumabc@hku.hk