[GRLUG] SMTP reverse DNS validation

[Michael Mol]

On Thu, Apr 23, 2015 at 12:14 PM L. V. Lammert <lvl at omnitec.net> wrote:

> On Thu, 23 Apr 2015, Mark Farver wrote:
>
> > Not sure what you are saying...did you get more than one result to a PTR
> > lookup?  Can you paste dig output displaying the condition?
> >
> MX
> crownpack.com.          2841    IN      MX      10 cpbsvf01.crownpack.com.
>
> ;; ADDITIONAL SECTION:
> cpbsvf01.crownpack.com. 2841    IN      A       67.221.227.25
>
> ;; ANSWER SECTION:
> 25.227.221.67.in-addr.arpa. 3600 IN     PTR     cpbsvf01.crownpack.
> 25.227.221.67.in-addr.arpa. 3600 IN     PTR     67-221-227-25.xiolink.com.
>
>
We ran into a similar problem here at VirtualInterconnect, but on the
reverse side. You may have noticed I've been the one sending the Friday
After Five emails lately, even when I wasn't the one going. That's because
we'd switched our outbound MX to go through AT&T business fiber...and even
though we'd given them correct instructions for setting up PTR records for
the IP in question, they *added* the PTR record, rather than replace or
edit the existing PTR record. So emails sent to the grlug list had a
fifty-fifty chance of coming back with a good PTR record or a bad one.

The solution, in our case? have them delegate the zone to our nameservers.
It's all good, now.

(Incidentally, if you have Comcast Business Cable, you *can* have them
delegate DNS to you. Their tier 1 people cannot get it through their head
that that's distinct from having them update a PTR record, though; I had to
have a tier 1 guy leave a dictated note to a tier 2 guy so I'd get a
callback from someone who knew what they were talking about...The Comcast
Business people aren't what they used to be. They're still the cheapest
source of upstream bandwidth at about $5/Mb beyond the base price, though.)
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