mx1.telenet-ops.be has no CNAME records.
Question and response
Question
dig mx1.telenet-ops.be. NS
Answer
The response has no answer records.
Authority
telenet-ops.be. 1987 SOA ns.telenet-ops.be. systemgroup.telenet-ops.be. 2026030601 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0