mx.demo5.de has no NS records.
NS records for this zone are defined at demo5.de.
NS records for this zone are defined at demo5.de.
Question and response
Question
dig mx.demo5.de. NS
Answer
The response has no answer records.
Authority
demo5.de. 900 SOA ns.megagroup.ru. dnsmaster.megagroup.ru. 71 21600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0