us.zixport.com has no CNAME records.
Question and response
Question
dig us.zixport.com. NS
Answer
The response has no answer records.
Authority
zixport.com. 600 SOA ns.zixcorp.com. noc.zixcorp.com. 2025081801 3600 300 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0