Apex domains cannot have CNAME records.
Question and response
Question
dig blueserver.eu. NS
Answer
blueserver.eu. 5 NS ns1.bmsdns.de.
blueserver.eu. 5 NS ns3.bmsdns.eu.
blueserver.eu. 5 NS ns2.bmsdns.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0