On Tue, 11 Aug 2009, Exim wrote:
> From: Exim <exim@???>
> To: exim-users@???
> Date: Tue, 11 Aug 2009 18:30:39 -0500
> Subject: [exim] Are you human?
>
> 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 have heard of this idea some time ago, but for the life of me
> can't remember what it was or how to implement it
>
> (and no I don't want to do this, but sometimes you have to do what
> the client demands, rather than what is really best for them).
Once such client that implements this is the Tagged Message Delivery
Agent (TMDA):
http://tmda.net/
The documentation indicates that it works with exim. I've never
tried it so can't say for sure.
As others have pointed out, these challenge-response schemes are
considered a *BAD* idea by some. Google searches using keywords:
"challenge response email problem" will throw up articles reflecting
this view:
http://www.politechbot.com/p-04746.html
http://www.tardigrade.net/challengeresponse.html
There are probably other such articles lurking on the Internet.
I've found such systems to be bloody annoying when I've met them.
Especially when I've been privately replying to a request for help
on a mailing list. So I've I've been quite content to not reply and
be classified as non-human. Perhaps I'm just intolerant...
--
Dennis Davis, BUCS, University of Bath, Bath, BA2 7AY, UK
D.H.Davis@??? Phone: +44 1225 386101
