mx.dotplex.com has no CNAME records.
Question and response
Question
dig mx.dotplex.com. NS
Answer
The response has no answer records.
Authority
dotplex.com. 3559 SOA ns.dotplex.net. support.dotplex.com. 2026022302 86400 10800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0