smtp.telecom.pt has no CNAME records.
Question and response
Question
dig smtp.telecom.pt. NS
Answer
The response has no answer records.
Authority
telecom.pt. 300 SOA dnsbho1aut02.local. dnsmaster.webside.pt. 2023062499 3600 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0