Apex domains cannot have CNAME records.
Question and response
Question
dig o2imt.de. NS
Answer
o2imt.de. 5 NS ns2.syzygy.de.
o2imt.de. 5 NS ns8.colt.net.
Authority
The response has no authority records.
Additional
ns2.syzygy.de. 5 A 46.28.184.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0