Re: Criminals, The Network, and You [Was: Something Else]

[Stephen Satchell <list () satchell net>]

My mail servers return 5xx on NXDOMAIN.  If my little shop can spend not 
too much money for three-9s reliability in the DNS servers, other shops 
can as well.  When I first deployed the system, the overwhelming 
majority of the rejects were from otherwise known spam locations 
(looking at Spamhaus, Spamcop, and a couple of other well-known DNSBLs). 
 The number of false positives were so small that whitelisting was easy 
and simple to maintain.

If a shop is not multihomed, they can contract with one or more DNS 
hosts to provide high-availability DNS, particularly for their 
in-addr.arpa zones.

It's not hard.  Nor expensive.

Paul Ferguson wrote:
> Re-sending due to Merit's minor outage.
>
> - ferg
>
>
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> - -- Robert Blayzor <rblayzor () inoc net> wrote:
>
> > The fact that they're rejecting on a 5xx error based on no DNS PTR is a=
>
> bit harsh.  While I'm all for requiring all hosts to have valid PTR
> records, there are times when transient or problem servers can cause a
> DNS lookup failure or miss, etc.  If anything they should be returning a=
>
> 4xx to have the remote host"try again later".
>
> Oh, wait till you realize that some of the HTTP returns are bogus
> altogether -- and actually still serve malware.
>
> It's pretty rampant right now. :-/
>
> - - ferg
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> --
> "Fergie", a.k.a. Paul Ferguson
>  Engineering Architecture for the Internet
>  fergdawg(at)netzero.net
>  ferg's tech blog: http://fergdawg.blogspot.com/