DNS on Windows Server 2003, 3rd Edition

Name

MX (mail exchanger) — (From RFC 1035, page 17)

Textual representation

owner ttl class 
MX preference exchange-dname

Example

ora.com.  IN  MX  0  ora.ora.com.
          IN  MX  10 ruby.ora.com.
          IN  MX  10 opal.ora.com.

Binary representation

MX type code: 15
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                  PREFERENCE                   |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                   EXCHANGE                    /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

PREFERENCE

Is a 16-bit integer that specifies the preference given to this RR among others at the same owner. Lower values are preferred.

EXCHANGE

Is a domain-name that specifies a host willing to act as a mail exchange for the owner name.