mailserver6.internet-estatements.com has no CNAME records.
Question and response
Question
dig mailserver6.internet-estatements.com. NS
Answer
The response has no answer records.
Authority
internet-estatements.com. 60 SOA a1-66.akam.net. admin.dnstinations.com. 250 10800 3600 2419200 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0