mx03.unet.nl has no MX records.
Question and response
Question
dig mx03.unet.nl. MX
Answer
The response has no answer records.
Authority
unet.nl. 300 SOA ns1.u-servers.net. postmaster.unet.nl. 2026011206 28800 7200 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0