mail.osinet.com has no CNAME records.
Question and response
Question
dig mail.osinet.com. NS
Answer
The response has no answer records.
Authority
osinet.com. 141 SOA dns1.pacificinternet.com. noc.pacificinternet.com. 2026012802 7200 1800 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0