_spf.powermail.be has no MX records.
Question and response
Question
dig _spf.powermail.be. MX
Answer
The response has no answer records.
Authority
powermail.be. 3600 SOA ns3.european-server.com. hostmaster.powermail.be. 1768482087 10800 3600 604800 40000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0