smtp.rentingcolombia.com has no MX records.
Question and response
Question
dig smtp.rentingcolombia.com. MX
Answer
The response has no answer records.
Authority
rentingcolombia.com. 3600 SOA dominios2.bancolombia.com.co. dominios.bancolombia.com.co. 764117322 1200 180 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0