mx.demo5.de has no MX records.
Question and response
Question
dig mx.demo5.de. MX
Answer
The response has no answer records.
Authority
demo5.de. 897 SOA ns.megagroup.ru. dnsmaster.megagroup.ru. 71 21600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0