It’s throttling. Slow down your deliveries. Aloha, Michael. — “Your Spam Specimen Has Been Processed,” ________________________________ From: mailop <[email protected]> on behalf of Matthew Pounsett via mailop <[email protected]> Sent: Friday, February 20, 2026 12:34:30 PM To: [email protected] <[email protected]> Subject: [EXTERNAL] [mailop] Anyone from Outlook? S3150 block list mirage
I'm suddenly getting 550 errors for mail addressed to @outlook.com<http://outlook.com/> users claiming my mail server's IP address is on a block list and referencing S3150, which I assume is an error code. The error message also has a link to http://mail.live.com/mail/troubleshooting.aspx#errors for more information. S3150 isn't mentioned on that page. Through a bunch of searching I have found a thing claiming to be the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com/. But, when I go through the steps there I'm told my IP is not blocked. Does anyone know more about this than I do? Anyone from Outlook here that could reach out and help me figure out what's going on?
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