+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / MADNAME / / / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
MADNAME A <domain-name> which specifies a host which has a mail agent for the domain which should be able to deliver mail for the domain.
MD records cause additional section processing which looks up an A type record corresponding to MADNAME.
MD is obsolete. See the definition of MX and [RFC-974] for details of the new scheme. The recommended policy for dealing with MD RRs found in a master file is to reject them, or to convert them to MX RRs with a preference of 0.