postalmta.rapidcompute.com has no CNAME records.
Question and response
Question
dig postalmta.rapidcompute.com. NS
Answer
The response has no answer records.
Authority
rapidcompute.com. 1800 SOA christian.ns.cloudflare.com. dns.cloudflare.com. 2396296772 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0