Apex domains cannot have CNAME records.
Question and response
Question
dig 208-28.116.10.217.in-addr.arpa. NS
Answer
208-28.116.10.217.in-addr.arpa. 5 NS unit.nmugroup.com.
208-28.116.10.217.in-addr.arpa. 5 NS origo.nmugroup.com.
208-28.116.10.217.in-addr.arpa. 5 NS ephemera.nmugroup.se.
Authority
The response has no authority records.
Additional
unit.nmugroup.com. 5 A 217.10.116.210
origo.nmugroup.com. 5 A 193.183.80.4
ephemera.nmugroup.se. 5 A 85.30.129.28
unit.nmugroup.com. 5 AAAA 2001:4db8:e004:0:0:0:0:2
origo.nmugroup.com. 5 AAAA 2001:67c:1b2c:0:0:0:0:4
ephemera.nmugroup.se. 5 AAAA 2a02:80:3ffe:0:0:0:0:28
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0