Using Spam
Assassin Tags to Filter Your Mail
for Rice University
What is Spam
Assassin?
Spam Assassin is a
program that runs on Rice's e-mail servers. It
examines each incoming message and computes a "SPAM score" based on a
wide range of different criteria. If the score is high enough, it adds
a special flag to the headers of the message that you can use to
identify it as probable unsolicited commercial e-mail.
How does Spam
Assassin work?
|
I wash my hands of those who imagine
chattering to be knowledge...
|
When Rice's e-mail servers receive a message, Spam Assassin compares
the message to its database of different SPAM criteria. Spam Assassin
produces a numerical score based on those criteria. If the score is
higher than a threshold value, Spam
Assassin adds headers like these to the message:
X-Spam-Status:
Yes, hits=15.6 tagged_above=4.0 required=6.9 tests=BAYES_80,
CLICK_BELOW,
DATE_IN_FUTURE_03_06, DCC_CHECK, HTML_50_60, HTML_IMAGE_ONLY_04,
HTML_IMAGE_RATIO_02,
HTML_LINK_CLICK_HERE, HTTP_ESCAPED_HOST,
HTTP_EXCESSIVE_ESCAPES,
HTTP_USERNAME_USED, MIME_HTML_ONLY, MISSING_MIMEOLE,
NORMAL_HTTP_TO_IP,
UNSUB_PAGE, USERPASS
X-Spam-Level:
****************
X-Spam-Flag:
YES
If the SPAM score
is equal to 5.0 or higher, Spam Assassin adds ***SPAM***
to the beginning of the Subject line, like so:
Subject:
***SPAM*** I Must Be Crazy To Offer Such Low Prices on Tamales
Subject:
***SPAM*** Take a
Sugar Pill To Enlarge Your Tamale
Subject:
***SPAM*** AMAZING
Tamale Diet Gets Results! Viva los tamales!
Subject:
***SPAM*** Stuff
envelopes and make enough to buy a
tamale
Subject:
***SPAM*** M00rtgag3 your house to buy more tamales!
How accurate is
Spam Assassin?
Accuracy is
difficult to judge, since one person's SPAM may be a solicited message
for somebody else. Looking at some of the logs the Spam Assassin
generates, it appears to catch about 80% of SPAM. The rules that Spam
Assassin uses to identify SPAM are updated
and weighted differently with each revision of the software, so it will
keep up with changes in the nature of incoming SPAM.
Rarely, Spam
Assassin will tag a legitimate e-mail that has many
SPAM-like characteristics. This case is called a false positive. In
those cases, you may need to adjust your filtering rules to
automatically pass messages from the affected sender.
How can I filter
with Spam Assassin?
Filtering your
e-mail with Spam Assassin is easy. Just set-up your
mail software to filter on the ***SPAM***
Subject line. For details, see these pages
for the following e-mail readers:
If you use a
departmental server (ECE, BIOC, CS and others), you
can also use the filtering utilities available from your UNIX command
line, like procmail.
Consult your system admin for complete details, but you can find a very
simple procmail
tutorial here.
If you use our
RUF/Owlnet central mail system with webmail (TWIG or
IMP), or if you use Outlook with IMAP filtering and our central mail
system, then you must use a web-based filter to take advantage of the
Spam Assassin filter. Go to www.mail.rice.edu
to set-up a filter on the web.