mail.arpa.teredo.pl has no CNAME records.
Question and response
Question
dig mail.arpa.teredo.pl. NS
Answer
The response has no answer records.
Authority
arpa.teredo.pl. 3600 SOA webh.pro. tech.webh.pro. 2021033822 3600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0