mail.solidotel.lu has no CNAME records.
Question and response
Question
dig mail.solidotel.lu. NS
Answer
The response has no answer records.
Authority
solidotel.lu. 2403 SOA nspub1.dns.lu. domreg.dns.lu. 1771459200 14400 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0