Here are a few links to some interesting articles on possible problems with
C/R systems:
http://db.tidbits.com/getbits.acgi?tbart=07181
http://www.politechbot.com/p-04746.html
The biggest problem seem to be dealing with mailing lists. An interesting
quote from one article on existing solutions and rules:
"A relatively easy to solve problem with challenge systems is that most of
them are written by dimwits who don't understand the way that e-mail
really works. In 1983 the 4.3BSD Berkeley Unix "vacation" program
correctly dealt with mail from lists and other mechanical sources, yet 20
years later I still see out-of-office replies from Lotus Notes and MS
Exchange to list mail every day."
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