my.mailbux.com has no CNAME records.
Question and response
Question
dig my.mailbux.com. NS
Answer
The response has no answer records.
Authority
mailbux.com. 10800 SOA ns2.fullspeed.net. support.fullspeed.net. 2026020707 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0