smtp.forwardemail.net has no CNAME records.
Question and response
Question
dig smtp.forwardemail.net. NS
Answer
The response has no answer records.
Authority
forwardemail.net. 1800 SOA greg.ns.cloudflare.com. dns.cloudflare.com. 2397597680 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0