mx01.hop.sfr.net has no CNAME records.
Question and response
Question
dig mx01.hop.sfr.net. NS
Answer
The response has no answer records.
Authority
hop.sfr.net. 7537 SOA nspriprov.dns.sfr.net. support.dns.sfr.net. 2024101600 10800 3600 1814400 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0