ns3.esmero.nl has no MX records.
Question and response
Question
dig ns3.esmero.nl. MX
Answer
The response has no answer records.
Authority
esmero.nl. 3600 SOA ns1.sectigoweb.com. admin.sectigo.com. 1658490578 86400 7200 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0