ns5.cloudflare.net has no MX records.
Question and response
Question
dig ns5.cloudflare.net. MX
Answer
The response has no answer records.
Authority
cloudflare.net. 1800 SOA ns1.cloudflare.net. dns.cloudflare.com. 2396714781 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0