mail4.fiserv.com has no NS records.
NS records for this zone are defined at fiserv.com.
NS records for this zone are defined at fiserv.com.
Question and response
Question
dig mail4.fiserv.com. NS
Answer
The response has no answer records.
Authority
fiserv.com. 300 SOA dns2.p07.nsone.net. domainadmin.firstdata.com. 763100884 1200 180 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0