Hi Shaun,

Thank you for a helpful response.  I am CC'ing the list with this so I can
get your response posted there.



-----Original Message-----
From: Shaun Sturby
Sent: Wednesday, November 21, 2012 9:01 AM
To: imailad...@bcwebhost.net
Subject: RE: [Declude.JunkMail] MX, DNS and other weird stuff

Hello Ben,

(I get Declude mailing list messages but can't reply for some reason)

I used the DNSStuff ISP Cached DNS records tester for mail.bcwebhost.net and
all the records came back with the IP EXCEPT for Comcast (NJ)
which came back with "mail.bcwebhost.net. 0 IN A".  Note that
is a very short TTL

If you connect to that IP address you will see that the URL changes to

Yet a DNS Cache Check using http://dns.comcast.net/ shows the correct .200

They did change DNS recently as this announcement shows.
Comcast recursive resolver IPs (,, and
will no longer be supported after October 12, 2012. If you manually
any of these IPs on your device, please allow DHCP to update your DNS
IP addresses or update manually with and

It looks like they intercept all A records to allow them to re-direct people
to their management portal. I have seen this done before with ISP's like
when you need to register the MAC address of your router with your account
typically this uses a RFC 1918 private IP space and not live IP addresses.

This is not the solution to your problem but is additional information to
you when you deal with ComCast.

Shaun Sturby
Technical Services Manager
Optrics Engineering | www.Optrics.com
  6810 - 104 Street, Edmonton, AB, T6H 2L6
  TF: 877-463-7638    Fax: 780-432-5630
  1740 S 300 West #10, Clearfield, UT, 84015
  TF: 877-386-3763    Fax: 801-705-3150

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From: Imail Admin [mailto:imailad...@bcwebhost.net]
Sent: Tuesday, November 20, 2012 5:05 PM
To: Declude.JunkMail@declude.com
Subject: [Declude.JunkMail] MX, DNS and other weird stuff


This is a question about DNS records and MX records and how I'm getting some
weird behavior.  It's not strictly speaking Declude issue, but I have a lot
respect for the people that used to hang out here and I'm hoping there's
someone around who can give me some insights.

Original problem:
We use Comcast for our upstream provider.  A few years ago, when we switched
to them from our telecom provider, they told us that their DNS servers would
sometimes intercept DNS calls even though we have our own DNS server.  This
was supposedly because we only rent a small IP subnet from them.  At the
they had us send copies of our zone records to them so that their DNS
would have the same information as our DNS server.  This worked fine until
this fall, when we installed a new mail server on a new IP address.  Our DNS
server, of course, was updated to reflect this change.  However, mail
sometimes shows up at the old mail server anyway, in a more or less random

It apprears to me that most of the time when people send mail to us, their
mail servers correctly getting the IP address resolved by our DNS server.
However, about 25% of the time, it appears that the DNS request from those
sending mail servers receives an outdated response from some unidentified
Comcast DNS server, resulting in the wrong IP address and the mail ends up
going to our old mail server.

Suppose, for example, that you send a message to imailad...@bcwebhost.net
address I'm using here, which is a misnomer since our new mail server is
running SmarterMail).  The MX records for bcwebhost.net points to
mail.bcwebhost.net and the A record mail.bcwebhost.net points to our new
server IP (ending in .200).  So your email should arrive at our new mail
server.  However, sometimes it will arrive at the old mail server named
mail2.bcwebhost.net (IP ending in .193).  The old DNS records had the
bcwebhost.net MX record pointing to mail2.bcwebhost.net, for which the A
record pointed to .193 (the old server).

I've been going in circles for about a month with Comcast on this and they
don't recall that they're the ones who told me three years ago that they
sometimes intercept DNS calls.  I was wondering if anyone has any ideas or
suggestions on how to track down the errant DNS calls?

Second problem:
In our new DNS records, I have it set up something like this:

two MX records:
bcwebhost.net MX mail.bcwebhost.net
mail.bcwebhost.net MX mail.bcwebhost.net

one A record:
mail.bcwebhost.net A (IP.200)

Is there any reason I can't have the same name for both an MX and an A
(in this case, mail.bcwebhost.net)? The Comcast people claimed this was
and that the MX record should point to an IP address directly instead of a
host name (which I'm sure is wrong).

They tried to claim that this is the cause of my original problem but even
they're right about this, then it still doesn't explain the original



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