mail.appstore.com has no NS records.
NS records for this zone are defined at appstore.com.
NS records for this zone are defined at appstore.com.
Question and response
Question
dig mail.appstore.com. NS
Answer
The response has no answer records.
Authority
appstore.com. 300 SOA ns-ext-prod.jackfruit.apple.com. dnscontact.apple.com. 2025051400 7200 5400 3628800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0