C/R or Challenge Response

A service that issues a challenge to make sure that a human is sending a mail.
When they challenge spam and viruses, they bother innocent people.
If they use SMTP rejects, then only real senders will get the challenges.
Generally an expensive method of spam control, and spammers can easily get around the challenge if they care to by redirecting the challenge to a porn site and promising free porn to the humans that visit the site and answer the challenge.

A challenge response system that does not use SMTP rejects is prone to sending e-mail to spamtraps which will cause other mail servers to refuse the challenges.
The only way that a challenge response system that does not use SMTP rejects to avoid hitting spam traps is if it makes sure that it never issues a challenge to a forged address in a spam or a virus. And of course if it knew how to do that, it would not need to issue a challenge (Actually this last statement is in error as it made the assumption that the purpose of using a challenge response system was limited to detecting spam. As indicated in the following, there are other reasons one may chose to use a challenge response system.

SpamCop.net itself has used challenges for spam filtering in the past; and currently uses challenges to determine how to handle admin replies to reporters.

• 1 Challenge/response spam filtering - SpamCop abandoned this method of filtering after a short test period in 2001.

• 2 Report reply handling - Forward only replies from sentient people -
  SpamCop challenges "administrators" by making them respond to an email to determine if they are people or robots.
  

  (Mike Easter newsgroup post extraction)

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CategorySpamCopGlossaryWikiC

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