mail.ops-netman.net has no CNAME records.
Question and response
Question
dig mail.ops-netman.net. NS
Answer
The response has no answer records.
Authority
ops-netman.net. 10800 SOA ops-netman.net. hostmaster.ops-netman.net. 2016032312 21600 3600 2592000 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0