smtp01.mi.com.co has no NS records.
NS records for this zone are defined at mi.com.co.
NS records for this zone are defined at mi.com.co.
Question and response
Question
dig smtp01.mi.com.co. NS
Answer
The response has no answer records.
Authority
mi.com.co. 1800 SOA quincy.ns.cloudflare.com. dns.cloudflare.com. 2398129011 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0