Apex domains cannot have CNAME records.
Question and response
Question
dig mx.staeher.net. NS
Answer
mx.staeher.net. 5 NS b.dns.staeher.net.
mx.staeher.net. 5 NS a.dns.staeher.net.
Authority
The response has no authority records.
Additional
a.dns.staeher.net. 5 A 121.127.37.233
b.dns.staeher.net. 5 A 194.164.245.83
a.dns.staeher.net. 5 AAAA 2a13:d207:0:443:0:0:0:1
a.dns.staeher.net. 5 AAAA 2a13:d207:0:443:0:0:0:2
a.dns.staeher.net. 5 AAAA 2a13:d207:0:443:0:0:0:3
a.dns.staeher.net. 5 AAAA 2a13:d207:0:443:0:0:0:4
b.dns.staeher.net. 5 AAAA 2a13:d207:0:2d0:0:0:0:1
b.dns.staeher.net. 5 AAAA 2a13:d207:0:2d0:0:0:0:2
b.dns.staeher.net. 5 AAAA 2a13:d207:0:2d0:0:0:0:3
b.dns.staeher.net. 5 AAAA 2a13:d207:0:2d0:0:0:0:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0