ns7.coolcom.com has no CNAME records.
Question and response
Question
dig ns7.coolcom.com. NS
Answer
The response has no answer records.
Authority
coolcom.com. 256 SOA ns7.coolcom.com. serverhenk.coolcom.com. 2026022001 3600 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0