mail.eldip.pl has no CNAME records.
Question and response
Question
dig mail.eldip.pl. NS
Answer
The response has no answer records.
Authority
eldip.pl. 2320 SOA isp2.obslugasieci.pl. pczerw.sieci.net.pl. 2025122701 7200 540 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0