smtp.tel-b2b.com has no CNAME records.
Question and response
Question
dig smtp.tel-b2b.com. NS
Answer
The response has no answer records.
Authority
tel-b2b.com. 158 SOA x.ns.joker.com. hostmaster.joker.com. 2023120491 14400 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0