rtfm.dimenoc.com has no CNAME records.
Question and response
Question
dig rtfm.dimenoc.com. NS
Answer
The response has no answer records.
Authority
dimenoc.com. 10782 SOA ns1.dimenoc.com. network.dimenoc.com. 2019062997 300 300 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0