Si vuestro servidor os envía una respuesta de parte de los servidores de Microsoft tal como:
Hi. This is the qmail-send program at tuservidor.servidor.es.
I’m afraid I wasn’t able to deliver your message to the following addresses.
This is a permanent error; I’ve given up. Sorry it didn’t work out.
<usuariodehotmail@hotmail.com>:
Connected to 65.55.37.72 but sender was rejected.
Remote host said: 550 SC-001 (COL004-MC1F40) Unfortunately, messages from
150.76.24.136 (la ip de tu server) weren’t sent. Please contact your Internet service provider
since part of their network is on our block list. You can also refer your
provider to http://mail.live.com/mail/
Tenéis que revisar el porqué ha sucedido esto y solucionar el problema,
Una vez resuelto podéis solicitar el Delist de vuestro ip o dominio aquí:
o bién aquí:
https://support.microsoft.com/en-us/getsupport?oaspworkflow=start_1.0.0.0&wfname=capsub&productkey=edfsmsbl3&locale=en-us&ccsid=635612678637576127&wa=wsignin1.0
Espero que os haya sido de gran ayuda
https://support.microsoft.com/en-us/getsupportaspworkflow=start_1.0.0.0&wfname=capsub&productkey=edfsmsbl3&locale=en-us&wa=wsignin1.0&ccsid=635653882713130041