On Wed, Jun 10, 2009 09:24:09 AM +0200, Gabriel Hahmann wrote:
> Good morning,
> 
> I'm looking for a tool that can handle confirmation emails with
> captcha and that works with postfix.
> ... 
> Using a tool like this I can stop all spam mail that arrives my inbox.

Gabriel,

tools like these are called "challenge-response (C-R)
systems". Regardless of how you implement them, with Postfix or any
other way, they are bad. It is much more likely that using a tool like
that you will stop ALL email coming to you, including what you wanted
to receive:

- how do you handle mailing lists? As far as I can remember, I've
  never sent email to you before, but if I receive a C-R message to
  make you read my answer, I'll just drop it and never answer your
  email again. So will do most subscribers of every mailing list
  anywhere. Why should they help people who make helping them
  difficult?

- what if you include your email address in a resume? What will your
  potential employer do when he/she will receive the confirmation
  email? discard it and call instead the next candidate who doesn't
  annoys him, or waste time playing confirmation games? In real world,
  the only non-spammers who answer to C-R email are people to whom you
  own money.

- add to all I said the reasons in this other message
  http://www.irbs.net/internet/postfix/0611/0854.html

  (by the way, the rest of that thread is just what you wanted:
  answers to how do C-R through postfix, and they mostly are "don't")

- also useful, in that same thread, are the resources listed here:

  http://www.irbs.net/internet/postfix/0611/0899.html

  especially http://fedoraproject.org/wiki/UOL, about a Brazilian ISP
  who got blacklisted just because of doing what you want to do

if you aren't convinced yet, there is also
http://www.cl.cam.ac.uk/~rnc1/cr/index.html

HTH,
        Marco Fioretti
        Digital rights writings at http://mfioretti.com
-- 
Your own civil rights and the quality of your life heavily depend on how
software is used *around* you:            http://digifreedom.net/node/84

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