mx2.sendclean.net has no CNAME records.
Question and response
Question
dig mx2.sendclean.net. NS
Answer
The response has no answer records.
Authority
sendclean.net. 988 SOA aryanna.ns.cloudflare.com. dns.cloudflare.com. 2396664284 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0