Re: [mailop] [EXTERNAL] Anyone from Outlook? S3150 block list mirage

[Michael Denney via mailop]

Sigh. Microsoft - helpful as always. At least now we can just tell people upset that it’s an issue on your end with arbitrary “dynamic” throttling. Even on long-established mailing IPs with good reputations and a solid history. Thank you, Michael Denney MDDHosting LLC https://www.mddhosting.com/ On Feb 20, 2026, at 6:29 PM, Michael Wise <michael.w...@microsoft.com> wrote:    … slower.   Aloha, Michael. -- Michael J Wise Microsoft Corporation| Spam Analysis "Your Spam Specimen Has Been Processed." Open a ticket for Hotmail ?   From: Michael Denney <mich...@mddhosting.com> Sent: Friday, February 20, 2026 3:27 PM To: Michael Wise <michael.w...@microsoft.com> Cc: Matthew Pounsett <m...@conundrum.com>; mailop@mailop.org Subject: Re: [mailop] [EXTERNAL] Anyone from Outlook? S3150 block list mirage   You don't often get email from mich...@mddhosting.com. Learn why this is important We’ve also been seeing this. Clients that have dedicated mailing IPs that haven’t had issues and have been established for a long time. No new increased flows - normal transactional emails.   Even opened a ticket and got told everything was fine.   If it’s throttling - why not just say that?   So what do we tell customers? “Microsoft things you’re sending too much mail and there’s nothing you can do but send less mail.”?   Thank you, Michael Denney MDDHosting LLC https://www.mddhosting.com/ On Feb 20, 2026, at 6:11 PM, Michael Wise via mailop <mailop@mailop.org> wrote:    It’s IP specific, and is dynamically assigned.   Aloha, Michael. -- Michael J Wise Microsoft Corporation| Spam Analysis "Your Spam Specimen Has Been Processed." Open a ticket for Hotmail ?   From: Matthew Pounsett <m...@conundrum.com> Sent: Friday, February 20, 2026 2:50 PM To: Michael Wise <michael.w...@microsoft.com> Cc: mailop@mailop.org Subject: Re: [EXTERNAL] [mailop] Anyone from Outlook? S3150 block list mirage       On Fri, Feb 20, 2026 at 5:01 PM Michael Wise <michael.w...@microsoft.com> wrote: It’s throttling. Slow down your deliveries.   The rate limit must be incredibly low, if that's the case.   We sent less than 1500 messages to outlook.com mail servers all day on February 20th.     If it is a rate limit, then please share where the rate limit is documented, so that I can set the throttle appropriately.  I can't keep under a rate limit if I don't know what it is.   And if it's a rate limit, why are we getting 500 errors instead of 400?  That should be a temporary error.   _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop

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