mail.idff.edu.do has no CNAME records.
Question and response
Question
dig mail.idff.edu.do. NS
Answer
The response has no answer records.
Authority
idff.edu.do. 1117 SOA ns1.contabo.net. hostmaster.contabo.de. 1772462736 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0