mail.ipexgroup.com has no CNAME records.
Question and response
Question
dig mail.ipexgroup.com. NS
Answer
The response has no answer records.
Authority
ipexgroup.com. 180 SOA ns10.digicertdns.com. dns.digicertdns.com. 2009010491 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0