mail1.bgl.lu has no CNAME records.
Question and response
Question
dig mail1.bgl.lu. NS
Answer
The response has no answer records.
Authority
bgl.lu. 600 SOA ns1.bnpparibas.com. i_names.bnpparibas.com. 345 14400 3600 2419200 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0