dns3.iplanisp.com has no MX records.
Question and response
Question
dig dns3.iplanisp.com. MX
Answer
The response has no answer records.
Authority
iplanisp.com. 900 SOA dns1.iplanisp.com.ar. hostmaster.iplan.com.ar. 2018122808 3600 600 1400000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0