Overview

You are trying to send an email from a Kerio Connect domain to an external Microsoft domain like hotmail.com, live.com, outlook.com, or msn.com and receive a Non-Delivery Receipt (NDR) with the error:

Unfortunately, messages from [vvv.xxx.yyy.zzz] weren't sent. Please contact your
Internet service provider since part of their network is on our block list (S3150).
You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.

This article provides the steps to resolve this issue.

Solution

Below are the steps that need to be followed to send the emails successfully to external Microsoft domains:

• Make sure that your Kerio Connect server has the appropriate DMARC and DKIM records. Refer to configuring DNS for DKIM in Kerio Connect article for more information.
• Verify that your Kerio Connect server has all the needed records for sending emails successfully. All the records can be found in the article essential DNS records for mail delivery.
• Verify that the SSL certificate of the Kerio Connect server is valid.
• Since the NDR indicates that the server's IP is in Microsoft's block list, Microsoft should be contacted directly to get it out of their block list.
• If the issue persists further, as indicated in the NDR, the ISP should also be contacted, so they can mitigate this issue on the long term, and assist you with provisioning another IP address that is not on Microsoft's blocklist

Confirmation

Once all of the above are verified and resolved, you will be able to successfully send emails to external domains and no NDR will be received.

If the NDR is still being received, then, open a Support Request with us and in order to verify and make sure that all measures are taken for Kerio Connect.

Please note that the scope of support here will be limited to only actions that can be taken for Kerio Connect