sk has no MX records.
Question and response
Question
dig sk. MX
Answer
The response has no answer records.
Authority
sk. 86400 SOA m.tld.sk. hostmaster.sk-nic.sk. 2018461250 60 300 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0