ASPMX4.GOOGLEMAIL.com has no NS records.
NS records for this zone are defined at GOOGLEMAIL.com.
NS records for this zone are defined at GOOGLEMAIL.com.
Question and response
Question
dig ASPMX4.GOOGLEMAIL.com. NS
Answer
The response has no answer records.
Authority
GOOGLEMAIL.com. 60 SOA ns1.google.com. dns-admin.google.com. 873285235 900 900 1800 60
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0