smtp.tabdigital.eu has no CNAME records.
Question and response
Question
dig smtp.tabdigital.eu. NS
Answer
The response has no answer records.
Authority
tabdigital.eu. 598 SOA chris.ns.cloudflare.com. dns.cloudflare.com. 2397716163 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0