mail-in.dynadot.com has no CNAME records.
Question and response
Question
dig mail-in.dynadot.com. NS
Answer
The response has no answer records.
Authority
dynadot.com. 499 SOA magdalena.ns.cloudflare.com. dns.cloudflare.com. 2398086919 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0