ns01.tue.nl has no MX records.
Question and response
Question
dig ns01.tue.nl. MX
Answer
The response has no answer records.
Authority
tue.nl. 900 SOA ipam.tue.nl. hostmaster.tue.nl. 34671 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0