If you receive an Error message when you try to send to an Outlook, Hotmail or Live email address that looks like the below...
<<< 550 5.7.1 Unfortunately, messages from [###.###.###.###] 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 https://sendersupport.olc.protection.outlook.com/pm/troubleshooting#errors.
[Name=Protocol Filter Agent][AGT=PFA][MxId=11BCECEA1E99658F]
[BN3PEPF0000B371.namprd21.prod.outlook.com 2026-02-28T15:20:25.658Z 08DE76750FA39C6E]
Or to put simply, 'Part of your sending network is on a block list, causing your sending IP to be blocked. Delist from the link provided.
...Then you will need to submit a delisting request via https://sender.office.com to resolve this issue.
Use the following info:
* Your email address
* The IP from the error (e.g. 203.89.231.55)
Follow the instructions presented to you and submit a delisting ticket.
