dk.vpnunlimited.com has no MX records.
Question and response
Question
dig dk.vpnunlimited.com. MX
Answer
The response has no answer records.
Authority
vpnunlimited.com. 1800 SOA hope.ns.cloudflare.com. dns.cloudflare.com. 2396867386 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0