mx2.heinlein-support.de has no CNAME records.
Question and response
Question
dig mx2.heinlein-support.de. NS
Answer
The response has no answer records.
Authority
heinlein-support.de. 300 SOA ns.jpberlin.de. root.jpberlin.de. 2026021001 40000 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0