 |
  
Computer News No. 106, Nov-Dec 2003 |
|
Computer News No. 106, Nov-Dec 2003 |
The number of spam (unsolicited junk emails) has grown tremendously all over the world in 2003. The Computer Centre has introduced an enhanced spam handling scheme for the central mail servers HKUCC and HKUSUA in June 2003. Upon input from users, the Information Infrastructure Advisory Group, the Information Services Advisory Group and the Senate Computer Committee, a further enhanced anti-spam control scheme, as described below, is being implemented by the Computer Centre. The new scheme is designed to solve the dilemma that some users would prefer a more aggressive approach for filtering out more spam while others would have the concern of missing emails that could come from black-listed spam-sites.
The new scheme will allow the users to choose one of the three spam filtering
options as depicted in Figure 1 and explained below. As shown in the figure,
only the Aggressive Filter would reject emails coming from black-listed
email servers, and all messages that are not rejected will be assigned
a spam-rating score by a spam-rating software called SpamAssassin. Users
are allowed to set a threshold so that any emails carrying a spam-rating
score above the threshold are treated as probable spam and saved in the
spam folder.
(a) No Filtering - By this option, all emails including spam are delivered into the user's incoming mailbox on the mail server. (b) Basic Filtering (the default option) - Emails rated with a spam-rating score equal to or higher than the spam-rating threshold chosen by the user are considered probable spam. By this option, the email server filters out the probable spam and save them into the spam folder "spam-of-YYYYMM", where YYYY and MM are the year and month of the date when a spam message is saved. (c) Aggressive Filtering - In addition to (b), the spam-site black-lists are first checked and all emails that are sent from the black-listed sites are rejected. |
Figure 1: Three spam filtering option in the new scheme
|
Note:
Users should not choose the Agressive Filtering option if they would have concerns on the possbility that emails would be rejected due to anti-spam filtering.
Users can examine the messages saved in the spam folder spam-of-YYYYMM of the current month using webmail (or other email programs based on the IMAP protocol) from time to time to see if any email saved there could be useful. All spam folders created before the last month will be deleted by the system.
The current spam handling scheme consists of four options as depicted in Figure 2. The default option is "Basic Filtering". (The details of the current spamhandling scheme are described in the article in Computer News issue no. 103.) By comparing Figures 1 and 2, it can be noted that the new scheme is easier to understand. When the new scheme is rolled out (in mid-January 2004), the four options of the current scheme will be mapped to the three options of the new scheme as shown in Table 1 below:
|
Figure 2: Four spam filtering option in the current scheme
|
Table 1: Mapping between the spam filtering options of the curent and new anti-spam control scheme
Current spam filtering scheme (Figure 2) |
New spam filtering scheme (Figure 1) |
Option (1) - no filtering |
Option (a) - no filtering |
Option (2) - basic filtering (default setting) |
Option (b) - basic filtering (default setting) |
Option (3) - aggressive filtering with spam retention |
Option (b) - basic filtering (default setting) |
Option (4) - aggressive filtering and deletion |
Option (c) - aggressive filtering |
You can set or change the spam filter option by means of one of the following procedures:
(A) login HKU Portal (https://hkuportal.hku.hk)
=> click the tab MyFavourites
=> click the link Set Spam Filter in the Email Utilities
section
=> choose one of the options
(B) visit http://webmail.hku.hk
=> click the link Set Spam Filter at the top of the page
=> login the mail server
=> choose one of the options
Advanced feature of the new scheme:- Users can change the spam-rating
threshold so as to change the way how probable spam are decided. The default
value of the spam-rating threshold is 5. Users can change the threshold
to a value betwene 1 and 9. Choosing a higher threshold would reduce the
chance of treating normal messages as probable spam but at the same time
increase the chance of treating spam as normal messages.
For more information about spam filtering on the central email servers,
the user can consult the FAQ
page or contact ithelp@hku.hk or the
undersigned.
