Thanks Ken (and Laura), So I'm guessing the only thing that has changed is that the requirement announced last year has finally been implemented for us (or, perhaps as John suggests, either the 5000 threshold has been changed, or the period over which it applies).
Anyway, I configured a minimal DKIM and it has certainly helped with delivery, so it has got me over that hurdle. And while the reporting form may not have helped me, in its current broken state it won't be any use to me if there is something I actually do have to report in the future. Is there a reporting form for reporting form problems? 🙂 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 Ken O'Driscoll via mailop <[email protected]> Sent: 03 March 2026 5:08 PM To: [email protected] <[email protected]> Subject: Re: [mailop] Outlook rate limiting, just us? On 3 Mar 2026, at 16:52, Jethro Binks via mailop <[email protected]> wrote: 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. Lack of DKIM is likely the problem, they require all messages to be DKIM signed<https://techcommunity.microsoft.com/blog/microsoftdefenderforoffice365blog/strengthening-email-ecosystem-outlook%E2%80%99s-new-requirements-for-high%E2%80%90volume-senders/4399730> and have been rolling out enforcement since last year. Well, anyway, I thought I'd take one of the suggested routes in the forums and report athttps://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. This message is related to a different issue connected to a different SMTP response code. 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<http://www.strath.ac.uk/>", but apparently MS knows better and I'm wrong. Maybe they are strictly enforcing the must be a TLD bit and excluding a lot of working domains. But adding DKIM will make that bounce go away without having to contact them. Ken.
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