secondary.maxnameserver.net has no MX records.
Question and response
Question
dig secondary.maxnameserver.net. MX
Answer
The response has no answer records.
Authority
maxnameserver.net. 782 SOA dns.dns1.de. hostmaster.internetwire.de. 2019070301 900 7200 604800 900
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0