smtp03.mi.com.co has no MX records.
Question and response
Question
dig smtp03.mi.com.co. MX
Answer
The response has no answer records.
Authority
mi.com.co. 1800 SOA quincy.ns.cloudflare.com. dns.cloudflare.com. 2397393339 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0