mx.qfilter.nl has no CNAME records.
Question and response
Question
dig mx.qfilter.nl. NS
Answer
The response has no answer records.
Authority
qfilter.nl. 1343 SOA ns1.qweb.net. hostmaster.qweb.nl. 2026011900 3600 3600 604800 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0