When you send a message to an email address hosted by one of the Microsoft owned email providers, you receive a bounce-back message or error in your Exim log that is similar to the following:
550 5.7.1 Unfortunately, messages from [xxx.xxx.xxx.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. [DB3EUR04FT062.eop-eur04.prod.protection.outlook.com]
This can happen for a number of different reasons, including, but not limited to:
- Bad SPF, DKIM, or other email-related DNS records for your domain
- The content of messages originating from your IP has characteristics that are similar to a spam message
- A website on your server has been compromised and is sending out spam messages
Below we will outline some of the steps that you can take to mitigate or resolve this issue.
NOTE: It is important to go through the entire list of potential solutions below and ensure that you have resolved any problems that you have found on your server first. Once you are sure that any potential configuration problems, or spam problems have been resolved, you may need to wait a short time for your server to be removed from the Microsoft blocklist. If your server continues to have problems sending to Microsoft owned email providers even after fixing all related problems, you can submit a support ticket to them to review the issue at the link provided in step 8.
- Use the Email Deliverability feature in cPanel to check the health of your domain's DNS records and fix any problems that you find there: What is the Email Deliverability feature within cPanel?
- Review very helpful information that Microsoft provides about what you can do in this situation: Microsoft PostMaster - Troubleshooting Mail Errors
- Check to see if your server's IP address is on a blacklist. One tool that you may consider for this task is the MXToolbox blacklist check tool.
- Review our documentation to help educate your self more about how to keep your messages out of the spam folder: cPanel Docs - How to keep your email out of the spam folder
- Sign up for tools provided by the various large providers to help monitor your mail server's reputation: How can I monitor my email server's IP reputation with large providers such as Gmail, Microsoft, and Yahoo?
- Make use of the Mail Status Probe tool to check for signs of outgoing spam from your server: Using cPanel's Mail Status Probe (MSP) script to diagnose spam-related issues
- Learn more about identifying the source of spam on your server: How to find the source of spam emails
- Learn more about preventing email abuse: How can I prevent email abuse?
- If you are sure that you have resolved all potential problems on your server but you are still unable to send to Microsoft owned email providers, you may submit a support request to them at the following link to review the issue: Microsoft Support Request Submission