mail.crossover.edu.do has no CNAME records.
Question and response
Question
dig mail.crossover.edu.do. NS
Answer
The response has no answer records.
Authority
crossover.edu.do. 3532 SOA ns1.contabo.net. hostmaster.contabo.de. 1772475116 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0