If you are receiving bounce-back messages when sending emails to Microsoft email addresses (@hotmail.com, @outlook.com, @live.com, Office 365), and the error indicates your sending IP address is blocked (often mentioning codes like S3150 or messages like "part of their network is on our block list" or "messages weren't sent"), it means Microsoft has temporarily stopped accepting mail from your server's IP address.
This usually happens because Microsoft's systems detected activity from your IP address (or the network it belongs to) that might indicate spam or configuration issues, leading to a poor sending reputation.
Microsoft provides a self-service tool to request removal from their block list. Follow these steps:
Microsoft typically processes delisting requests within a few hours to 48 hours. Ensuring the server configuration (PTR, SPF, DKIM) is correct and the IP reputation is clean increases the likelihood of success and helps prevent future blocks.
If you have submitted the delisting request via the portal and are still experiencing issues after 48 hours, please contact our support team with the details of the bounce message.