mail.teclem.com has no CNAME records.
Question and response
Question
dig mail.teclem.com. NS
Answer
The response has no answer records.
Authority
teclem.com. 5589 SOA ns1.he.net. hostmaster.he.net. 2023092900 10800 1800 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0