ns-u.dns.yourhosting.nu has no MX records.
Question and response
Question
dig ns-u.dns.yourhosting.nu. MX
Answer
The response has no answer records.
Authority
dns.yourhosting.nu. 3600 SOA ns1.cldin.eu. hostmaster.dns.yourhosting.nu. 1771952266 3600 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0