mail.ct.co.cr has no CNAME records.
Question and response
Question
dig mail.ct.co.cr. NS
Answer
The response has no answer records.
Authority
ct.co.cr. 2214 SOA ns.ct.co.cr. root.ns.ct.co.cr. 2025063001 7200 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0