mailrelay.layer23.nl has no MX records.
Question and response
Question
dig mailrelay.layer23.nl. MX
Answer
The response has no answer records.
Authority
layer23.nl. 3600 SOA ns2.ip-security.nl. maarten.layer23.nl. 1704628871 10800 3600 604800 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0