Some will get this joke, others not so much… “ …, Not Hotmail. “ I had some responsibilities on the Consumer Side a few years ago, and that’s how I remember the details. For more guidance, I’d suggest asking your peers in the sender community.
Aloha, Michael. -- Michael J Wise Microsoft Corporation| Spam Analysis "Your Spam Specimen Has Been Processed." Open a ticket for Hotmail<http://go.microsoft.com/fwlink/?LinkID=614866> ? From: Matthew Pounsett <[email protected]> Sent: Friday, February 20, 2026 3:23 PM To: Michael Wise <[email protected]> Cc: Michael Brown <[email protected]>; [email protected] Subject: Re: [mailop] [EXTERNAL] Anyone from Outlook? S3150 block list mirage On Fri, Feb 20, 2026 at 6:02 PM Michael Wise via mailop <[email protected]<mailto:[email protected]>> wrote: S3150 is what you get when you don't slow down after seeing 4xx. 😊 If that were the case I would have SO many questions. I'll get to those in a minute, but first: that doesn't track with what I'm seeing. I have exactly two (2) 4xx SMTP errors from outlook.com<http://outlook.com/> mail servers in the last 5 days. But let's assume you're right... here are my top two questions: 1. How would I be expected to know that, based on available information (the SMTP error message and the documentation it points to) 2. What mail server software implements a variable outgoing rate limit based on the recent rate of 4xx messages from a receiving mail server? Surely if this is how things are intended to work, someone has thought through how senders are expected to deal with the limit.
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