ns.hitachi.net.do has no MX records.
Question and response
Question
dig ns.hitachi.net.do. MX
Answer
The response has no answer records.
Authority
hitachi.net.do. 900 SOA ns.hitachi.net.do. root.hitachi.net.do. 2020062401 3600 1200 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0