smtp.GOOGLE.COM has no CNAME records.
Question and response
Question
dig smtp.GOOGLE.COM. NS
Answer
The response has no answer records.
Authority
GOOGLE.COM. 60 SOA ns1.GOOGLE.COM. dns-admin.GOOGLE.COM. 873978624 900 900 1800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0