mail.sfire.pl has no CNAME records.
Question and response
Question
dig mail.sfire.pl. NS
Answer
The response has no answer records.
Authority
sfire.pl. 1995 SOA ns1.seohost.pl. hostmaster.sfire.pl. 2025120800 2000 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0