Chapter 15 Anti-Spam; Anti-Spam External Database - ZyXEL Communications Internet Security Appliance ZyWALL5UTM 4.0 User Manual

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This chapter covers how to use the ZyWALL's anti-spam feature to deal with junk e-mail

15.1 Anti-Spam Overview

The ZyWALL's anti-spam feature identifies unsolicited commercial or junk e-mail (spam).

You can set the ZyWALL to mark or discard spam. The ZyWALL can use an anti-spam

external database to help identify spam. Use the whitelist to identify legitimate e-mail. Use the

blacklist to identify spam e-mail.

If an e-mail does not match any of the whitelist or blacklist entries, the ZyWALL calculates a

digest (fingerprint ID) of the e-mail and sends it to the anti-spam external database. The anti-

spam external database checks the digest against (more than a million) known spam patterns.

The anti-spam external database uses the following spam detection engines in checking each

• SpamBulk: This engine identifies e-mail that has been sent in bulk or is similar to e-mail

that is sent in bulk.

• SpamRepute: This engine checks to see if most people want the e-mail.

• SpamContent: This engine checks to see if the message would generally be considered

• SpamTricks: This engine checks to see if the e-mail is formatted to be economical for

spammers or to circumvent anti-spam rules.

The anti-spam external database then uses a proprietary Bayesian

combine the results into one score of how likely the e-mail is to be spam and sends it to the

ZyWALL. The possible range for the spam score is 0~100. The closer the score is to 100, the

more likely the e-mail is to be spam. You must subscribe to and activate the anti-spam external

database service in order to use it (see

Bayesian analysis interprets probabilities as degrees of belief rather than as proportions,

frequencies and such. Bayesian analysis frequently uses Bayes' theorem, hence the name.

Chapter 15 Anti-Spam

ZyWALL 5/35/70 Series User's Guide

Section 15.1.7 on page 266

statistical formula to

for details).