ns.zayo.com has no MX records.
Question and response
Question
dig ns.zayo.com. MX
Answer
The response has no answer records.
Authority
zayo.com. 1800 SOA amber.ns.cloudflare.com. dns.cloudflare.com. 2397019320 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0