[exim-dev] [Bug 488] Failed name server leads to unroutable …

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Author: bug488
To: exim-dev
Subject: [exim-dev] [Bug 488] Failed name server leads to unroutable address error
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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.


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