ns3.register.be has no MX records.
Question and response
Question
dig ns3.register.be. MX
Answer
The response has no answer records.
Authority
register.be. 60 SOA ns1.register.be. info.register.be. 1733225934 300 3600 86400 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0