Reverse lookup mx records and cnames

[Mark Andrews]

> Hello.
> I'm not sure what to do.
> 
> I have lots of servers which have a record such as
>  mail.customerdomain IN A 10.1.1.1
> The MX record for each domain is something like
>  customerdomain IN MX mail.customerdomain

	Why?  "customerdomain IN MX your.server" will work just as
	well and be more managable in the long term if you ever
	need to change its address.
 
> This works fine, but you can get a listing of all customers by doing a
> reverse lookup on 10.1.1.1, which is our mail server. This isn't good.
> 
> I've thought of two ways to fix this:
>  1. Use a CNAME for the MX record to point to our mail server.
>    This isn't allowed or recommended.
>  2. Hack the reverse zone to only return our mail server name.
>    This is a hack.

	Actually this is quite common.  There is no need to have a
	PTR record for every A record.  In fact it does not scale
	as you will find out once you get enough customers to exceed
	the DNS/TCP message size of 64k.

	Things that care about PTR/A relationships want there to be
	a A record to match the PTR record not the other way around.

> Can anyone offer me any advice?
> 
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org