mx1.icm.edu.pl has no CNAME records.
Question and response
Question
dig mx1.icm.edu.pl. NS
Answer
The response has no answer records.
Authority
icm.edu.pl. 2477 SOA ns.icm.edu.pl. hostmaster.icm.edu.pl. 2026012901 7200 900 604800 36000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0