mail.premiumwebservice.com has no CNAME records.
Question and response
Question
dig mail.premiumwebservice.com. NS
Answer
The response has no answer records.
Authority
premiumwebservice.com. 3600 SOA nxg1800.premiumwebservers.com. hostmaster.premiumwebservers.com. 33 900 600 86400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0