mail4.provector.pl has no CNAME records.
Question and response
Question
dig mail4.provector.pl. NS
Answer
The response has no answer records.
Authority
provector.pl. 3483 SOA dns1.provector.pl. hostmaster.provector.pl. 2022123010 3600 1201 2592000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0