I purchased a cloud server recently and come to find out when emailing Microsoft Addresses I would get a bounce back that I was in a block list. Here are the domains in question:

hotmail.com
live.com
msn.com
outlook.com

Click to view error message

This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:   xxxxxxx@msn.com     host msn-com.olc.protection.outlook.com [104.47.18.161]     SMTP error from remote mail server after pipelined MAIL FROM:<xxxx@fabozzi.net> SIZE=6584:     550 5.7.1 Unfortunately, messages from [xx.xx.xx.xxx] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [AM7EUR06FT052.eop-eur06.prod.protection.outlook.com] Reporting-MTA: dns; xxxxxxxx.domain.com Action: failed Final-Recipient: rfc822;xxxxxx@msn.com Status: 5.0.0 Remote-MTA: dns; msn-com.olc.protection.outlook.com Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [xx.xx.xx.xxx] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [AM7EUR06FT052.eop-eur06.prod.protection.outlook.com]

First I went here to check if I was on a blacklist server and I was not:

https://mxtoolbox.com/blacklists.aspx

After some searching I found the following website to request your IP be removed:

https://support.microsoft.com/en-us/supportrequestform/8ad563e3-288e-2a61-8122-3ba03d6b8d75

My request has been submitted and I will see if that resolved the issue.

Reference: https://www.noomle.com/unfortunately-messages-werent-sent-please-contact-your-internet-service-provider/