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http://www.exim.org/bugzilla/show_bug.cgi?id=488
------- Comment #7 from marc@??? 2007-03-22 18:16 -------
graeme@??? wrote:
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> http://www.exim.org/bugzilla/show_bug.cgi?id=488
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> ------- Comment #6 from graeme@??? 2007-03-22 17:57 -------
> On Thu, 2007-03-22 at 13:19 +0000, marc@??? wrote:
>
>> OK - this might be a way to simulate the problem. Set your /etc/resolv.conf in
>> the Exim server to some local caching name server that you control. Pick a test
>> domain and look up the name server BS records. hen on the name server machine
>> run this:
>>
>> iptables -v -I INPUT -s ns1.domain.com -j DROP
>> iptables -v -I INPUT -s ns2.domain.com -j DROP
>>
>> I hope this code is right. The idea being that you block your resolving name
>> server from accessing the name servers of the domain that you are emailing.
>> That's what happened to me. Due to the routing problem my nameservers couldn't
>> rote to the name servers of the destination and because it was cut off mail
>> bounced instantly as unroutable.
>>
>
> And quite right too. If the lookups for the domain timeout completely,
> how do your resolvers (and by extension Exim, or any other application
> relying on DNS) know that it's a network problem?
>
> If you can't lookup the records for a domain *regardless of the reason*,
> the domain becomes unrouteable. Hence the error condition.
>
> DNS is, after all, the application-layer glue that holds stuff like SMTP
> together. Without it, we're back in the dark ages!
>
> I still don't think this is a bug.
>
> Graeme
>
I'm not sure that I would say that it's not a bug. There might not be an
easy way to resolve it. It might be something we have to live with if we
can't distinguish between a valid domain with DNS problems and an
invalid domain.
But - I thought I'd bring it to your attention in case it could be fixed.
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