mail6.ash3.ciberserver.com has no CNAME records.
Question and response
Question
dig mail6.ash3.ciberserver.com. NS
Answer
The response has no answer records.
Authority
ash3.ciberserver.com. 1013 SOA ns1.ciberserver.com. status.ciberconceito.com. 2018052002 3600 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0