mail.mncable.net has no CNAME records.
Question and response
Question
dig mail.mncable.net. NS
Answer
The response has no answer records.
Authority
mncable.net. 222 SOA auth1.america.net. dns.america.net. 2026021002 3600 600 864000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0