mx1.mailprovider.com has no CNAME records.
Question and response
Question
dig mx1.mailprovider.com. NS
Answer
The response has no answer records.
Authority
mailprovider.com. 138 SOA everton.ns.cloudflare.com. dns.cloudflare.com. 2396867980 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0