Hi Joseph, I've had the same issue that started a year ago. Eventually they removed the subnet, but it was blocked again a week later. It seems to me they import a third party block list containing my subnet, which re-blocks it shortly after removal, and they won't whitelist. They wouldn't tell me the source (nor the reason). I've repeated the remove/block cycle a few times and then just gave up and renumbered my mail servers. They don't seem to care. At all. Your mileage may vary though. If you do get to a solution I'd appreciate hearing about it :) Good luck! -- Regards,    Terrence Koeman, PhD/MTh/BPsy      Darkness Reigns (Holding) B.V. Please quote relevant replies. Spelling errors courtesy of my 'smart'phone. ________________________________ From: Joseph Jenkins <joe@breathe-underwater.com> Sent: Saturday, 9 May 2020 04:36 To: NANOG Subject: anyone on from hotmail.com, msn.com, live.com smtp?

We are getting this messages when sending emails from our domain. We've submitted tickets, but haven't received a response yet. Anyone have any insights?

550 5.7.1 Unfortunately, messages from [1.1.1.1] 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. [ AM5EUR03FT014.eop-EUR03.prod.protection.outlook.com]

It's our own address and everything on the Microsoft site says we are clean with no issues.