spf2.outlook.com has no NS records.
NS records for this zone are defined at outlook.com.
NS records for this zone are defined at outlook.com.
Question and response
Question
dig spf2.outlook.com. NS
Answer
The response has no answer records.
Authority
outlook.com. 60 SOA ns1-05.azure-dns.com. msnhst.microsoft.com. 2017971531 300 120 2419200 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0