mail.jchost04.pl has no CNAME records.
Question and response
Question
dig mail.jchost04.pl. NS
Answer
The response has no answer records.
Authority
jchost04.pl. 87 SOA ns1.jchost04.pl. hostmaster.jchost04.pl. 2025122303 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0