mxsspf.sendpulse.com has no NS records.
NS records for this zone are defined at sendpulse.com.
NS records for this zone are defined at sendpulse.com.
Question and response
Question
dig mxsspf.sendpulse.com. NS
Answer
The response has no answer records.
Authority
sendpulse.com. 900 SOA ns-181.awsdns-22.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0