Hi, Jethro, So… a client came to me yesterday with the same error message and the same SPF / DKIM / DMARC. Their mail is all OK and they are signing with DKIM (and it’s passing as well I can see looking at the raw messages). Their SPF is also passing and aligned. This particular client uses 2 ESPs and the same email is delivering fine from one ESP but is getting that message on mail from the other ESP.
While I would recommend you sign with DKIM as it is overall good practice, this might be yet another another chapter in the ever evolving handbook titled “Microsoft and Email: A tragedy in X+1 parts" The fact that the form is broken isn’t surprising and I don’t have a lot of suggestions there. But based on my client’s experience, I’m not sure that even filling out the form is going to be helpful here. laura > 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. > > 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 <http://www.strath.ac.uk/>", but apparently MS > knows better and I'm wrong. > > I'd be happy to read suggestions on: > > How to make the form accept my website address > Which "issue" the form suggests they are aware of and investigating > 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] <mailto:[email protected]>> > on behalf of Lukas Adrian Kron via mailop <[email protected] > <mailto:[email protected]>> > Sent: 03 March 2026 12:10 PM > To: [email protected] <mailto:[email protected]> <[email protected] > <mailto:[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] <mailto:[email protected]> > https://list.mailop.org/listinfo/mailop -- The Delivery Expert Laura Atkins Word to the Wise [email protected] Delivery hints and commentary: http://www.wordtothewise.com/blog
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