mail.levelsys.com has no CNAME records.
Question and response
Question
dig mail.levelsys.com. NS
Answer
The response has no answer records.
Authority
levelsys.com. 3543 SOA ns0.levelsys.com. dns.levelsys.com. 2026020600 21600 3600 691200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0