Virtual DNS questiona and reverse lookup table conflicts

[Bruno Wolff III]

On Sat, Dec 06, 2008 at 15:31:14 -0800,
  "Daniel B. Thurman" <dant at cdkkt.com> wrote:
> Mikkel L. Ellertson wrote:
> Yes, as you said: "Reverse are easy if the domains have different IP  
> addresses,
> but a problem if they do not" and therein lies my problem.  The IP addresses
> are the same in the reverse lookup tables but the return domain name is not
> the same as they are based on the domain name itself.
>
> So, as I said earlier, if I do a reverse IP query, which
> will be returned?  host1.domain1.com or host1.domain2.com?

You can actually return both, but most likely the brain damaged mail
servers you are trying to appease will only look at one.

If you really anted to try being clever (probably too clever), you could
modify bind (or whatever) to return the ptr record pointing to the mostly
recently asked about A record. But again this isn't going to work perfectly
for a number of valid reasons and is a lot of effort to go to to appease
broken mail servers.

> So, I am trying to figure out how this is done.
>
> Do you know how the web-hosting sites do it?

They work with mail servers that aren't brain damaged enough to expect the
ptr records to match since there are lots of valid reasons to do this.