mailsg.sg.dc.integral.net has no CNAME records.
Question and response
Question
dig mailsg.sg.dc.integral.net. NS
Answer
The response has no answer records.
Authority
integral.net. 209 SOA ns-542.awsdns-03.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0