DNS on Windows Server 2003, 3rd Edition

CNAMEs in the Resource Record Data

For any other record besides a CNAME record, you must have the canonical domain name in the resource record data. Applications and name servers won’t operate correctly otherwise. As we mentioned back in Chapter 5, for example, many mailers recognize only the canonical name of the local host on the right side of an MX record. If a mailer doesn’t recognize the local host, it won’t strip out the right MX records when paring down the MX list and may deliver mail to itself or to less-preferred mail exchangers, causing mail to loop.