mx2.ri-server.de has no CNAME records.
Question and response
Question
dig mx2.ri-server.de. NS
Answer
The response has no answer records.
Authority
ri-server.de. 10729 SOA a.ns14.net. baader.rundblick.de. 2026012300 43200 14400 604800 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0