smtp01-ph2-sp2.mta.salesforce.com has no NS records.
NS records for this zone are defined at mta.salesforce.com.
NS records for this zone are defined at mta.salesforce.com.
Question and response
Question
dig smtp01-ph2-sp2.mta.salesforce.com. NS
Answer
The response has no answer records.
Authority
mta.salesforce.com. 600 SOA dns01.salesforce.com. hostmaster.salesforce.com. 2014069095 600 900 2592000 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0