mx01.hh02.uptime.de has no CNAME records.
Question and response
Question
dig mx01.hh02.uptime.de. NS
Answer
The response has no answer records.
Authority
hh02.uptime.de. 138 SOA ns.uptime.de. hostmaster.uptime.de. 2025062500 10800 3600 1814400 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0