mx1.mcs.de has no CNAME records.
Question and response
Question
dig mx1.mcs.de. NS
Answer
The response has no answer records.
Authority
mcs.de. 219 SOA ns1.mcs.de. hostmaster.mcs.de. 2026012200 14400 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0