mail.ised.edu.do has no CNAME records.
Question and response
Question
dig mail.ised.edu.do. NS
Answer
The response has no answer records.
Authority
ised.edu.do. 1613 SOA edna.ns.cloudflare.com. dns.cloudflare.com. 2393215060 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0