mail1.o2spin.de has no CNAME records.
Question and response
Question
dig mail1.o2spin.de. NS
Answer
The response has no answer records.
Authority
o2spin.de. 7049 SOA ns2.syzygy.de. hostmaster.syzygy.de. 2021120312 10800 1800 1209600 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0