mail-c.linkedin.com has no NS records.
NS records for this zone are defined at linkedin.com.
NS records for this zone are defined at linkedin.com.
Question and response
Question
dig mail-c.linkedin.com. NS
Answer
The response has no answer records.
Authority
linkedin.com. 60 SOA ns1-42.azure-dns.com. hostmaster.linkedin.com. 1 3600 300 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0