_spf.cvt.stuba.sk has no MX records.
Question and response
Question
dig _spf.cvt.stuba.sk. MX
Answer
The response has no answer records.
Authority
cvt.stuba.sk. 86400 SOA ns.cvt.stuba.sk. postmaster.stuba.sk. 2025122900 3600 1800 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0