mx23.litvpn.com has no NS records.
NS records for this zone are defined at litvpn.com.
NS records for this zone are defined at litvpn.com.
Question and response
Question
dig mx23.litvpn.com. NS
Answer
The response has no answer records.
Authority
litvpn.com. 1200 SOA ns1.dnsexit.com. admin.netdorm.com. 2000060701 86000 180000 1814400 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0