A01 chaf6542 06 se fm indd

(b)

Open

inbox

ISP

(a)

Open

inbox

Email filter

Software used to identify 

spam according to its 

characteristics such as 

keywords.

Blacklist

A compilation of known 

sources of spam that are 

used to block email.

M11_CHAF6542_06_SE_C11.indd   584

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Chapter 11  Analysis and design

are often used in conjunction with filters to block emails. Brightmail (now Symantec 

Enterprise, 

www.symantec.com/products-solutions/families/?fid=email-security

) uses a 

global network of email addresses set up to trap and identify spam. Brightmail is increas-

ingly used by ISPs such as BT OpenWorld to block spam, but it is not a cheap service, 

costing $5 to $15 per year. This price could easily be justified by the time staff save over 

the year. This technique is also represented by Figure 11.30(b).