Re: [exim] Sender callout verification on BATV signed addres…

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Auteur: David Saez Padros
Date:  
À: John Horne
CC: Exim users
Sujet: Re: [exim] Sender callout verification on BATV signed addresses
Hi

> I think you will find that the MX's for ols.es are indeed listed at
> backscatterer.org :
>
>       Testresult for 78.129.233.52:
>       This IP IS CURRENTLY LISTED in our Database.


just thinking a bit about this: this is the kind of useless rbl
that seems more a revenge of the author against the world than
something useful (*) If you see how ip's are listed in this rbl
you will notice that both bounces and callouts are exclusivelly
done by real servers. So if you use it to reject anything from
those ip's you will mostly reject legitimate mail, if you use this
rbl to reject callouts then mail comming from your server to
the servers listed in this rbl will be rejected (because it will
fail the callout). In the other hand we do callouts with a special
username (not <>) to avoid problems with servers rejecting bounces
so you can use this rbl to reject callouts but you will not catch
our callouts (and many others). The only use of this rbl as a
blacklist is if you are under a ddos attack (*)

If you read the arguments against callout it says that callouts are
a broken technique but that's not true (at most a deficient
implementation of sender callout could be broken) and the problem
he has is not about sender callouts is about people forging his
domain, which he can prevent by publishing spf records. Same for
backscatter, there is nothing in any RFC i have read that says that
bounces are only for local users, in fact what you can read in RFC's
about bounces is that you should accept them (another question is
that is obvious that is much better to reject at smtp time than
generate bounces)

(*) Please notice that as this rbl only lists real email servers
in fact it can be used as a whitelist, which is the most useful
use i can image of it

--
Best regards ...

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    David Saez Padros                http://www.ols.es
    On-Line Services 2000 S.L.       telf    +34 902 50 29 75
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