ns02.zixcorp.com has no CNAME records.
Question and response
Question
dig ns02.zixcorp.com. NS
Answer
The response has no answer records.
Authority
zixcorp.com. 300 SOA ns01.zixcorp.com. noc.zixcorp.com. 2026030201 3600 300 2419200 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0