mail.plutoweb.io has no CNAME records.
Question and response
Question
dig mail.plutoweb.io. NS
Answer
The response has no answer records.
Authority
plutoweb.io. 3600 SOA ns1.world4you.at. hostmaster.world4you.com. 2025032663 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0