mx1.denic.de has no MX records.
Question and response
Question
dig mx1.denic.de. MX
Answer
The response has no answer records.
Authority
denic.de. 1800 SOA ns1.denic.de. dns-operations.denic.de. 1771644086 10800 1800 3600000 1800
Additional
. 0 OPT ; payload 1452, xrcode 0, version 0, flags 0