mx21.litvpn.com has no CNAME records.
Question and response
Question
dig mx21.litvpn.com. NS
Answer
The response has no answer records.
Authority
litvpn.com. 766 SOA ns1.dnsexit.com. admin.netdorm.com. 2000060701 86000 180000 1814400 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0