postal.cyso.net has no MX records.
Question and response
Question
dig postal.cyso.net. MX
Answer
The response has no answer records.
Authority
postal.cyso.net. 300 SOA ns1.cyso.nl. dnsadmin.cysonet.com. 1771459200 16384 2048 1048576 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0