mx.pt.lu has no CNAME records.
Question and response
Question
dig mx.pt.lu. NS
Answer
The response has no answer records.
Authority
pt.lu. 427 SOA ns1.pt.lu. hostmaster.ns1.pt.lu. 2026021800 10800 3600 2419200 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0