smtp.nwnexus.com has no CNAME records.
Question and response
Question
dig smtp.nwnexus.com. NS
Answer
The response has no answer records.
Authority
nwnexus.com. 8204 SOA ns-1.nuoz.net. postmaster.nwnexus.com. 2026022000 7200 3600 864000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0