fallback.werkonline.nu has no MX records.
Question and response
Question
dig fallback.werkonline.nu. MX
Answer
The response has no answer records.
Authority
werkonline.nu. 3600 SOA ns3.kpn.net. zonemaster.kpn.com. 2023030702 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0