spf.sk-nic.sk has no MX records.
Question and response
Question
dig spf.sk-nic.sk. MX
Answer
The response has no answer records.
Authority
sk-nic.sk. 86400 SOA a.tld.sk. hostmaster.sk-nic.sk. 2025011485 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0