This:
> $ host mailgate.compuserve.com
> mailgate.compuserve.com is a nickname for mx3.compuserve.com
> mx3.compuserve.com has address 149.174.206.135
> mx3.compuserve.com has address 149.174.177.136
> mx3.compuserve.com has address 149.174.217.133
> mx3.compuserve.com has address 149.174.217.137
> mx3.compuserve.com has address 149.174.217.136
> mx3.compuserve.com has address 149.174.217.135
> mx3.compuserve.com has address 149.174.177.134
> mx3.compuserve.com has address 149.174.177.133
> mx3.compuserve.com has address 149.174.206.137
> mx3.compuserve.com has address 149.174.206.136
...is NOT a variance from RFC1123 or any other specification. It is
completely appropriate for a mail domain to be a CNAME pointing at a
handful of A's. It's not ok to _advertise_ one of these, as for example
in an exported "From:" header, but there's no problem just from being
willing to accept mail sent to such a domain or to set up DNS in this
way.
Make the DontExpandCnames option true in your /etc/sendmail.cf, and when
customers start bitching that they can't send mail to CompuServe addresses,
tell them that it is CIS's fault, and give them the CIS customer service
number 
Please don't do that. CIS is committing some real sins against the RFCs
elsewhere, and since this isn't one of them it would muddy the waters if
we contrive to get them yelled at for it.
Paul A Vixie <paul@vix.com> said:
This:
[deleted]
...is NOT a variance from RFC1123 or any other specification.
That's true (as far as it goes), and I certainly don't see that bouncing
mail with a "mailbox is full" error is a violation of RFC1123 section
5.3.3.
But the following piece of evidence was not mentioned before:
compuserve.com. MX 10 mailgate.compuserve.com.
That MX, in conjunction with the CNAME (which was mentioned before):
mailgate.compuserve.com. CNAME mx3.compuserve.com.
adds up to a violation of RFC 1034 section 3.6.2:
"Domain names in RRs which point at another name should always
point at the primary name and not the alias."
(which esentially means "If a name appears on the left hand side of a
CNAME record then that name should not also appear on the right hand side
of any other record").
It is
completely appropriate for a mail domain to be a CNAME pointing at a
handful of A's. It's not ok to _advertise_ one of these, as for example
in an exported "From:" header,
I am not sure that my reading of RFC 1123 section 5.2.2 awould support
you there. But anyway, the "compuserve.com" domain *does* get advertised
in "From:" headers, so there is clearly a problem.
--apb (Alan Barrett)
from the quill of Alan Barrett <apb@iafrica.com> on scroll
<Pine.NEB.3.95.961117113159.131G-100000@apb.iafrica.com>
I certainly don't see that bouncing
mail with a "mailbox is full" error is a violation of RFC1123 section
5.3.3.
The fact that there was a bounce was not the complaint. The fact that the
bounce went back to the author of the article, not the sender was the
complaint.
b.