ns4.unyc.io has no MX records.
Question and response
Question
dig ns4.unyc.io. MX
Answer
The response has no answer records.
Authority
unyc.io. 1800 SOA ns1.planet-work.com. nsadmin.planet-work.com. 2602120008 14400 3600 604800 1800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0