CNAMES to different domain

[Steven Mooij]

Barry Margolin wrote:

> In article <B52CB3B0.BA8A%thomas at neweve.com>,
> Thomas Deliduka  <thomas at neweve.com> wrote:
> >Wait, so what you're saying is that I could have the CNAME defined for www
> >like:
> >
> >www.dialmattress.com. IN CNAME mattress.com.
> >
> >But not for the straight domain.
>
> I believe that's precisely what I said.
>
> >I guess that defeats the point of having a CNAME point to a separate domain.
> >I wanted one place to change the IP if it ever changed rather than 100
> >different files.
>
> Or you could give up on using the domain name without the "www" prefix as
> the hostname.

A different reason than Thomas to make a CNAME pointing from mydomain to
anotherdomain is that mail-to addresses will be changed based upon a CNAME RR. My
ISP filters out the SMTP protocol in their firewall, but does provide me with a
fixed IP-adress and a DNS-name (anotherdomain). I registered my own domain
(mydomain) and run my own nameserver for this domain. Now I would like it to be
possible to use email addresses like myname at mydomain. (My ISP did create a
MX-record for anotherdomain, but won't relay email to mydomain (and I can't change
my ISP).)
It is now possible to create a RR like:
mail.mydomain    IN    CNAME    anotherdomain.
which allows me to receive mail send to myname at mail.mydomain as if it were sent to
myname at anotherdomain. For receiving email send to myname at mydomain I think I would
need a CNAME pointing from mydomain to anotherdomain.

Is this really impossible? Or is there any other way to achieve this?

Steven.