mail.silicomp.be has no CNAME records.
Question and response
Question
dig mail.silicomp.be. NS
Answer
The response has no answer records.
Authority
be. 600 SOA a.nsset.be. be-hostmaster.dnsbelgium.be. 1028235667 3600 1800 2419200 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0