mail.server.odontolaboral.com.do has no CNAME records.
Question and response
Question
dig mail.server.odontolaboral.com.do. NS
Answer
The response has no answer records.
Authority
server.odontolaboral.com.do. 4871 SOA ns181224129103.a2dns.com. root.server.odontolaboral.com.do. 2026020100 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0