mailb2b.tigo.com.co has no CNAME records.
Question and response
Question
dig mailb2b.tigo.com.co. NS
Answer
The response has no answer records.
Authority
tigo.com.co. 300 SOA lauta.une.net.co. root.une.net.co. 2026022701 2160 3600 86400 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0