All, We were seeing these temporary deferrals for MS-related consumer domains from time to time in the last couple of weeks, after maybe a couple of days it would clear up and messages would be delivered onwards.
However starting on 27th Feb we've got something different. Full hard rejections with: "550 5.7.515 Access denied, sending domain STRATH.AC.UK doesn't meet the required authentication level. The sender's domain in the 5322.From address doesn't meet the authentication requirements defined for the sender. To learn how to fix this see: https://go.microsoft.com/fwlink/p/?linkid=2319303 Spf= Pass , Dkim= Fail , DMARC= Pass" For the particular server of ours that's involved in this (we've been sending from its IP for maybe 15 years), we are not doing any DKIM signing for Reasons. I had thought (rightly or wrongly) that either of SPF pass or DKIM pass was fine, that's certainly been the situation up to now. Something's changed somewhere though lately. Well, anyway, I thought I'd take one of the suggested routes in the forums and report at https://olcsupport.office.com/. There's a big banner at the top: "We are aware of an issue that may result in certain IP addresses being temporarily rejected at higher rates. We are actively investigating the issue. Please continue to submit tickets if you are experiencing this problem.". Is that the temporary defer problem? Or the permanent reject one? Or some other problem? No idea, so I'll fill the form in anyway. Except, I can't submit it. I get the error: "Website URL must start with http:// or https:// and contain a valid domain and top level domain.". I'd like to think I'd know my website address is "http://www.strath.ac.uk";, but apparently MS knows better and I'm wrong. I'd be happy to read suggestions on: 1. How to make the form accept my website address 2. Which "issue" the form suggests they are aware of and investigating 3. Whether I can no longer avoid DKIM signing messages and must stop relying on only SPF (And I see https://aka.ms/postmaster is still broken). Jethro. . . . . . . . . . . . . . . . . . . . . . . . . . Jethro R Binks, Network Manager, Information Services Directorate, University Of Strathclyde, Glasgow, UK The University of Strathclyde is a charitable body, registered in Scotland, number SC015263. ________________________________ From: mailop <[email protected]> on behalf of Lukas Adrian Kron via mailop <[email protected]> Sent: 03 March 2026 12:10 PM To: [email protected] <[email protected]> Subject: Re: [mailop] Outlook rate limiting, just us? Something did change indeed. We, as a small volume sender are seeing 451 4.7.650 S775 errors for the first time. No blockage. Maybe they switched over from sending the 451's to any IP in the /24 and actually sending it to the IP. But just a thought. Mit freundlichen Grüßen Lukas Adrian Kron Geschäftsführung Bitte denken Sie an die Umwelt, bevor Sie diese Nachricht drucken. [email protected]<mailto:[email protected]>, www.lugges.eu<http://www.lugges.eu>, +49 2302-9838905 lugges UG (haftungsbeschränkt), Heintzmannstraße 174 44801 Bochum AG Bochum HRB 19066, GF.: Lukas Adrian Kron Am 24.02.2026 um 14:47 schrieb Dominique Rousseau via mailop: Le Tue, Feb 24, 2026 at 12:45:09PM +0000, Gellner, Oliver via mailop [[email protected]<mailto:[email protected]>] a écrit: Microsoft's spam handling is broken, simple as that. No need to argue about that. We receive the same error messages for all servers since 2026-02-23 18:45 UTC. It's unlikely that Microsoft suddenly received spam from all IP addresses of all kind of unrelated organizations yesterday evening. Probably some algorithm went nuts there. Browse the list archives. Those errors when sending to "outlook" adresses run for a while now. Seems like they made new rules with dynamic throttle, which nobody understands for now. For the servers (low volume) I run which encountered the probleme I limited to one SMTP connection every 10s. ( which would probably bothersome for quit high volume sender, OK for us )
_______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
