mx4.saas.lu has no CNAME records.
Question and response
Question
dig mx4.saas.lu. NS
Answer
The response has no answer records.
Authority
saas.lu. 5484 SOA ns1.eurodns.com. hostmaster.eurodns.com. 2026022300 43200 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0