mx2.improvmx.com has no CNAME records.
Question and response
Question
dig mx2.improvmx.com. NS
Answer
The response has no answer records.
Authority
improvmx.com. 1549 SOA logan.ns.cloudflare.com. dns.cloudflare.com. 2396577174 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0