mail.jchost18.pl has no CNAME records.
Question and response
Question
dig mail.jchost18.pl. NS
Answer
The response has no answer records.
Authority
jchost18.pl. 2134 SOA ns1.jchost18.pl. hostmaster.jchost18.pl. 2026020503 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0