mta1.vocsmail.com has no NS records.
NS records for this zone are defined at vocsmail.com.
NS records for this zone are defined at vocsmail.com.
Question and response
Question
dig mta1.vocsmail.com. NS
Answer
The response has no answer records.
Authority
vocsmail.com. 1800 SOA dom.ns.cloudflare.com. dns.cloudflare.com. 2396876896 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0