Glossary - Challenge/Response schemes (a.k.a., C/R systems)

C/R schemes are, in effect, outsourced automated whitelisting schemes that are incorrectly promoted as a solution to the spam problem.  C/R schemes are typically viewed as "spam amplifiers" among spam-fighters because new messages are automatically generated and then relayed to a possibly forged sender, which actually assist spammers in abusing their victims through a third party when the sender eMail address is a forgery (forgery is a common spammer tactic).

In short, the main problems with C/R schemes include (full details are available here):

• Delegation of the recipient's consent to unknown third parties...
• Off-loading costs...
• Spam amplifiers...
• Language barriers...
• Privacy concerns...
• Deadlocks between C/R challenges...

See also

• eMail fatigue
• Spam

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