mail.linuxpl.com has no CNAME records.
Question and response
Question
dig mail.linuxpl.com. NS
Answer
The response has no answer records.
Authority
linuxpl.com. 9 SOA dns10.linuxpl.com. root.linuxpl.com. 2024121700 300 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0