mx-a.wcss.pl has no CNAME records.
Question and response
Question
dig mx-a.wcss.pl. NS
Answer
The response has no answer records.
Authority
wcss.pl. 4924 SOA wask.wask.wroc.pl. admin.wask.wroc.pl. 2026021601 28800 7200 604800 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0