Human-Computer Etiquette

338 Human– Computer etiquette

white lists based on channels. It does not reject ISP controlled lists,

but just lets users make their own choices as well. List maintenance,

a problem for centralized lists, occurs easily at the local level as every

sent message implies an open channel and every rejected message

closes a channel. Users naturally opening and closing channels in nor-

mal e-mail use eectively dene their local lists. Channel e-mail gives

e-mail users a choice they should have had in the rst place.

13.1.4.6 Feasibility Challenge e-mail systems already use a three-step

send–challenge–resend protocol. e challenge “Captcha” question is a

task supposedly easy for people but hard for computers, like to read a

blurry word. A sender