mail18a.sapsf.com has no NS records.
NS records for this zone are defined at sapsf.com.
NS records for this zone are defined at sapsf.com.
Question and response
Question
dig mail18a.sapsf.com. NS
Answer
The response has no answer records.
Authority
sapsf.com. 300 SOA ns1.sap.net. dns.sap-ag.de. 2019077556 3511 1800 1814400 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0