using cname for redirection?

[Bill Larson]

On Dec 29, 2007, at 1:11 PM, <aklist_bind at enigmedia.com>  
<aklist_bind at enigmedia.com> wrote:

> Hi All: Is there any valid way in DNS to point requests for
> "something.domain1.com" to "somethingelse.domain2.com"?
>
> Can a CNAME be used for that?

Isn't this exactly the point of a CNAME?  Just because the target  
doesn't belong in the same zone doesn't matter.

> In this particular instance, I have a domain where the mail is  
> being hosted
> at godaddy.com (email.secureserver.net), and when godaddy  
> maintained the NS,
> they were aliasing "webmail.yourdomain.com" to  
> "email.secureserver.net".
>
> If I take over the DNS, normally I'd need to create an A record for
> "webmail" and point it at the IP for "email.secureserver.net"...but  
> what if
> there is more than one IP for that address?

This is an issue for the email server configuration rather than just  
DNS.  The email server has to recognize the name(s) for the domains  
that it is serving mail for.  When they create a CNAME record for  
"webmail.yourdomain.com" that resolves to "email.secureserver.net",  
unless they have also configured their mail server to accept mail  
addressed to "webmail.yourdomain.com" (and very likely  
"yourdomain.com") this mail will be bounced when it is sent there.

This email configuration isn't necessarily controlled by DNS.   
Imagine if it were, then I were simply identify that my mail, when  
addressed as USER at example.com, and example.com were to point to  
207.158.46.202, the IP address for enigmedia.com, then should I  
expect that this mail would be accepted by your server?   
Emphatically, NO!  It would bounce because this server isn't  
configured to accept mail addressed to "example.com".

You need to coordinate the effort of "taking over the DNS" with the  
organizations involved.  Obviously, this is you or whomever you are  
using for DNS services, but this will also include your registrar to  
insure that the parent registration can be changed, your current DNS  
hosting service to insure that the old DNS information is removed,  
and your email hosting service to insure that they will still  
function.  At the same time, you will need to insure that you have a  
properly operating DNS service that fulfills the recommendations of  
RFC2182/BCP16, "Selection and Operation of Secondary DNS Servers".

Bill Larson