mail.retn.net has no CNAME records.
Question and response
Question
dig mail.retn.net. NS
Answer
The response has no answer records.
Authority
retn.net. 10800 SOA nsa.retn.net. noc.retn.net. 2026030601 7200 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0