mail.concentra.edu.do has no CNAME records.
Question and response
Question
dig mail.concentra.edu.do. NS
Answer
The response has no answer records.
Authority
concentra.edu.do. 600 SOA ns35.domaincontrol.com. dns.jomax.net. 2022072100 28800 7200 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0