mail.sd.netserwer24.pl has no CNAME records.
Question and response
Question
dig mail.sd.netserwer24.pl. NS
Answer
The response has no answer records.
Authority
sd.netserwer24.pl. 3600 SOA dns3.hitme.net.pl. hostmaster.sd.netserwer24.pl. 2024040900 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0