mx1.offres-b2b.com has no CNAME records.
Question and response
Question
dig mx1.offres-b2b.com. NS
Answer
The response has no answer records.
Authority
offres-b2b.com. 33 SOA x.ns.joker.com. hostmaster.joker.com. 2025111452 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0