mailserver.tigo.bo has no CNAME records.
Question and response
Question
dig mailserver.tigo.bo. NS
Answer
The response has no answer records.
Authority
tigo.bo. 900 SOA dns1.wimaxtigo.bo. please_set_email.absolutely.nowhere.tigo.bo. 81 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0