For routing mail, adds routing information to the local Mail
    Exchanger (MX) database.

    Each entry contains a list of hosts that can accept mail for
    the specified destination. The list is in order of routing
    preference.

    The local MX information is stored in the routes database.

    The MX entry is one of the record types in the BIND database. In
    addition, a BIND server might provide an MX record.

    SMTP is designed to determine where the sending system should try
    to relay mail. It is also designed to identify where the sending
    system actually tries to relay mail. To find a destination
    address, the MX routing lookup process follows this sequence:

    1. Local MX database

    2. Remote MX database

    3. BIND database

    4. Local hosts database

    Related command: SHOW MX_RECORD

    Formats

      SET MX_RECORD  destination

                     /GATEWAY=host

                     /PREFERENCE=n

      SET NOMX_RECORD  destination

                       [ /GATEWAY=host ]