mail.oscgre.com has no CNAME records.
Question and response
Question
dig mail.oscgre.com. NS
Answer
The response has no answer records.
Authority
oscgre.com. 600 SOA ns43.domaincontrol.com. dns.jomax.net. 2025060400 28800 7200 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0