return.smtp2go.net has no CNAME records.
Question and response
Question
dig return.smtp2go.net. NS
Answer
The response has no answer records.
Authority
smtp2go.net. 236 SOA ada.ns.cloudflare.com. dns.cloudflare.com. 2397296279 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0