smtp.rank.com.co has no MX records.
Question and response
Question
dig smtp.rank.com.co. MX
Answer
The response has no answer records.
Authority
rank.com.co. 3600 SOA ns8.wixdns.net. support.wix.com. 2015102813 10800 3600 1209600 3600
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0