return-alt.smtp2go.net has no CNAME records.
Question and response
Question
dig return-alt.smtp2go.net. NS
Answer
The response has no answer records.
Authority
smtp2go.net. 1800 SOA ada.ns.cloudflare.com. dns.cloudflare.com. 2397681932 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0