MX (Mail Exchanger) RR

Provide the name of a mail server for a domain
    kame.net. 1D IN MX 10 orange.kame.net.
orange.kame.net handles e-mail to "whatever@kame.net"
10: preference
define priority among multiple servers
the IP address of the mail server must be provided separately
Why MX?
improve reliability of mail delivery
allow the sender to send mail to the nearest available server
flexibility between domain name for mail address and server host names
"jinmei@kame.net," not "jinmei@orange.kame.net"
we may have host "kame.net.", but we may want to run mail server on a different machine