mail66.mxf.infra.improvmx.com has no AAAA records.
Question and response
Question
dig mail66.mxf.infra.improvmx.com. AAAA
Answer
The response has no answer records.
Authority
improvmx.com. 1800 SOA logan.ns.cloudflare.com. dns.cloudflare.com. 2397754427 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0