o2.ptr3873.sg2.adversus.dk has no CNAME records.
Question and response
Question
dig o2.ptr3873.sg2.adversus.dk. NS
Answer
The response has no answer records.
Authority
adversus.dk. 1084 SOA ns1.dlx.dk. ks.dlx.dk. 2026020302 14400 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0