Canonical CNAMEs?

[Doug Barton]

Per Goetterup wrote:
> 
> peter at icke-reklam.ipsec.nu.invalid wrote:
> 
> > Per Goetterup <per at netgroup.dk> wrote:
> 
> >> The question is therefore this: Is the version 2 setup legal or not, i.e. is
> >> it possible to have an MX referring to a mail host which is defined as a CNAME
> >> which points to an A record from another zone? - It works just fine (bind
> >> 8.2.3) but is it allowed?
> > No. An MX target must not be a CNAME.  Why not use "mail.master.com." as
> > RHS of the MX in the first place ?
> 
> That's what we used to do, 

	You cannot use a cname on the RHS of an MX record, no matter how stupid
your customers are. 

> but we have a customer that insists on having his
> own domains *everywhere* to the extent that even the MX records must point to
> a server using only their own domains. But then we break the reverse on the
> mailservers IP which of course must resolve to some central name, i.e.
> mail.master.com or similar.

	You have two choices. Either explain to your customer that the fact that
the forward and the reverse for the mail host don't match will prevent some
mail from being delivered to their site, or you can add the customer's mx
hostname to the PTR record for the machine. In my experience the vast
majority of sites that check forwards and reverses on an mx host before
delivery are satisfied if the forward name is included in the PTR record,
it does not have to be the only name. 

	Either way, you're opening yourself up to problems, however you're the
only one who can decide which is the lesser of two evils. 

Good luck,

Doug
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