ns4.nic.do has no MX records.
Question and response
Question
dig ns4.nic.do. MX
Answer
The response has no answer records.
Authority
nic.do. 60 SOA ns.nic.do. hostmaster.nic.do. 2025070301 3600 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0