i2.ms01.atmailsvr.net has no CNAME records.
Question and response
Question
dig i2.ms01.atmailsvr.net. NS
Answer
The response has no answer records.
Authority
atmailsvr.net. 3600 SOA dns1.p06.nsone.net. hostmaster.nsone.net. 1577016060 3600 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0