+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | PREFERENCE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / EXCHANGE / / / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
PREFERENCE A 16 bit integer which specifies the preference given to this RR among others at the same owner. Lower values are preferred. EXCHANGE A <domain-name> which specifies a host willing to act as a mail exchange for the owner name.
MX records cause type A additional section processing for the host specified by EXCHANGE. The use of MX RRs is explained in detail in [RFC-974].