dns4.servidoresdns.net has no MX records.
Question and response
Question
dig dns4.servidoresdns.net. MX
Answer
The response has no answer records.
Authority
servidoresdns.net. 3600 SOA atlante.servidoresdns.net. hostmaster.arsys.es. 2005152354 86400 7200 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0