mx1.leon.pl has no CNAME records.
Question and response
Question
dig mx1.leon.pl. NS
Answer
The response has no answer records.
Authority
leon.pl. 2303 SOA ns1.leon.pl. admin.leon.pl. 2026020902 3600 1200 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0