Re: [dnsext] SPF, a cautionary tale

[Mark Andrews <[e-mail]>]

In message <CAL0qLwa-fWyB2NtVdMu02-iz8ZWnYo3+PJ4qFtxYeWe=[e-mail]>
, "Murray S. Kucherawy" writes:
> 
> On Sun, May 5, 2013 at 4:06 AM, Mark Andrews <[e-mail]> wrote:
> 
> >         I looked a 25579 unique domains that have sent me email
> >         over the last 20 odd years.
> 
> That's a far more constrained sample size than the RFC6686 surveys used,
> and I have some vague thoughts about likely bias of mail going to isc.org.

That list of domains includes personal as well as business
correspondence, spam sources, mail from various mailing lists.

And RFC6686 is biased as it use the Alexa top X which is known to
use more load balancers which are often not RFC 103[45] compliant
name servers.  They don't do negative answers properly.  Fixing one
set of nameservers in the Alexa top X can drastically change the
numbers as many domains Alexa top X are served by identical sets
of name servers.

The vast majority of name servers (from sites sending email or not)
respond to both TXT and SPF queries.  Of those that don't most are
broken for both TXT and SPF (and AAAA and NS and SOA).

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
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