mout.contabo.com has no MX records.
Question and response
Question
dig mout.contabo.com. MX
Answer
The response has no answer records.
Authority
contabo.com. 1800 SOA ben.ns.cloudflare.com. dns.cloudflare.com. 2396786938 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0