Receiving error “A new record cannot be created. Node is a CNAME DNS record.” when adding an MX record to Windows Server 2003 DNS

Question

we're trying to add an MX record to a Windows Server 2003 DNS server and getting the following error:

"A new record cannot be created. Node is a CNAME DNS record."

The domain is xyz.com. We create a new MX record and leave the "Host or child domain:" field blank, then we're putting "cluster122.us.messagelabs.com" in the "Fully qualified domain name (FQDN) of mail server:" field and leaving the default Priority of 10.

Are we missing something?

Answer 1

If you are trying to set an MX record for a hostname such as corp.example.com (for mail to user@corp.example.com) and that name exists as a CNAME record instead of an A record, it would result in this error. If a host exists as a CNAME, it cannot also have other record types associated with it. You would need to re-create the hostname as an A record and then add the MX record to it.

Answer 2

RFC 2181 forbids the use of a CNAME value in a MX record:

10.3. MX and NS records
   The domain name used as the value of a NS resource record, or part of
   the value of a MX resource record must not be an alias.  Not only is
   the specification clear on this point, but using an alias in either
   of these positions neither works as well as might be hoped, nor well
   fulfills the ambition that may have led to this approach.  This
   domain name must have as its value one or more address records.
   Currently those will be A records, however in the future other record
   types giving addressing information may be acceptable.  It can also
   have other RRs, but never a CNAME RR.

Microsoft specifically has this to say on the subject.

Answer 3

Try adding a trailing dot to "cluster122.us.messagelabs.com"

That's something I constantly forget, and it doesn't work without it.