Michael Heydon wrote:
> Exim wrote:
>
>> I just had a client ask for something I haven't done. He wants emails from
>> unknown users to be sent back with a "are you human" request they must
>> respond to correctly. If they do, then they will be automatically added to
>> a list of valid senders.
>>
>>
>
> I believe it is called challenge response filtering and it is the most
> horrible antispam tactic I have seen. If you really absolutely can not
> get out of doing it, please make sure that you do it as a last resort,
> check SPF, run SA, use DNSBLs.
>
>
Not only that, but two people, each using CR, will never get to talk to
each other; rather they will fire away their "are you human" messages at
each other. It only works if a tiny minority of people use it.
And, if you do use it, you will likely never hear from a large number of
people. I won't respond to them; many of those messages get caught in
real spam filters.
So all in all, it's a really bad idea.
Google for challenge-response. You will get a good variety of ideas.
--
o__
,>/'_ o__
(_)\(_) ,>/'_ o__
A day may come (_)\(_) ,>/'_ o__
when the courage of men fails, (_)\(_) ,>/'_
when we forsake our friends and break all (_)\(_)
bonds of fellowship, but it is not this day.
It is not this day!
This day we ride!
