[NTLUG:Discuss] Postfix Spam Blocking

[Steve Baker]

Kevin Brannen wrote:

> I'm curious what people think about challenge/response (C/R) for spam 
> control.  I can see it being fairly successful, but I can also see it 
> cutting down or eliminating real email from people you don't hear from 
> often enough to have whitelisted.  What are the thoughts of people on 
> this subject?

There are plenty of ways to change the whole way email works that would
eliminate spam completely - however, those changes have to happen over
the entire Internet with the agreement of absolutely everyone.  That's
not a realistic possibility.  If every version of sendmail kept a record
of every mail it sent - then when the challenge came through, compared
the mail it was accused of sending to the list it actually sent - then
it could issue the response automatically - but every version of sendmail
doesn't have that - so to start with, everyone has to respond to the
challenges themselves.  Even then, the format of a challenge email has
to be widely agreed or else they'll get filtered out - or worse still,
challenged in turn resulting in a mail bomb.

If such a system ever became sufficiently widespread  to become somewhat
automated would rapidly be co-opted by spammers.

Spammers who hijack other peoples machines to send spam might well
program them to respond to challenges correctly - so I think spam would
still make it through fairly frequently.

Some of the most interesting emails I get come from complete strangers.
Inserting a challenge/response system in the loop would at best delay
those emails by days - and at worst end up being filtered by people
who are upset by having to respond to challenges by hand.

---------------------------- Steve Baker -------------------------
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