mail.linux.itsoul.com has no CNAME records.
Question and response
Question
dig mail.linux.itsoul.com. NS
Answer
The response has no answer records.
Authority
itsoul.com. 7044 SOA doma126122.mercury.orderbox-dns.com. domains.itsoul.com. 2026012703 7200 7200 172800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0