_dmarc.convento.de has no CNAME records.
Question and response
Question
dig _dmarc.convento.de. NS
Answer
The response has no answer records.
Authority
convento.de. 244 SOA x.ns.joker.com. hostmaster.joker.com. 2026021763 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0