gmail-smtp-in.l.google.COM has no NS records.
NS records for this zone are defined at l.google.COM.
NS records for this zone are defined at l.google.COM.
Question and response
Question
dig gmail-smtp-in.l.google.COM. NS
Answer
The response has no answer records.
Authority
l.google.COM. 60 SOA ns1.google.COM. dns-admin.google.COM. 879012124 900 900 1800 60
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0