mail500c7.megamailservers.com has no CNAME records.
Question and response
Question
dig mail500c7.megamailservers.com. NS
Answer
The response has no answer records.
Authority
megamailservers.com. 2371 SOA ns1.meganameservers.com. root.megamailservers.com. 509 86500 3600 3600000 345600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0