That's from a year ago -- May 5, 2025. It sort of relates in that Microsoft are authentication sticklers now but doesn't really help somebody troubleshoot the root cause.
Microsoft saying DKIM failure when SPF and DMARC are both passing (and the messare seems to pass DKIM auth checks elsewhere) fits a pattern that others are seeing, where some other, unspecified problem with a message's headers, body, encoding, or something else, is causing some sort of modification to the message that results in a DKIM signature failure, at Microsoft, only. It's rarely clear what the source is, and it can be painful to troubleshoot. On Fri, May 8, 2026 at 3:29 PM Graeme Slogrove via mailop <[email protected]> wrote: > > I noticed this announcement the other day, which may explain the issues > members are having delivering to Outlook/Hotmail/live since the 5th May. > > I know that DKIM/DMARC is right for those members, so purely putting this > here for awareness. > > https://dmarcian.com/microsoft-enforces-spf-dkim-dmarc/ > > --- > "Microsoft Enforces SPF, DKIM, DMARC for High-Volume Senders" > > Beginning May 5, Microsoft will reject emails that don't meet their new bulk > sender requirements. Instead of going to the junk folder, messages that don't > comply won't be delivered at all. > > The rejected messages will be designated as "550; 5.7.15 Access denied, > sending domain does meet the required authentication level." > --- > > Graeme > > -----Original Message----- > From: mailop <[email protected]> On Behalf Of John R Levine via mailop > Sent: Saturday, May 9, 2026 7:42 AM > To: Randolf Richardson, Postmaster <[email protected]>; > [email protected] > Subject: Re: [mailop] Microsoft bogus authentication failures > > > I've noticed that Microsoft's systems fail intermittently to validate > > DNS lookups for DMARC, SPF, DKIM, and PTR records. Some users have > > become accustomed to trying again later to get their eMails through > > (which is not ideal). > > > > Although it doesn't happen very often, Microsoft's systems have been > > doing this since last year (and possibly earlier than that), and it > > doesn't seem to target any particular providers (e.g., a few of my > > clients with GMail accounts have asked me what the errors mean when > > they've received bounce-backs just like the one that you included). > > > > Feel free to send some test messages to > > [email protected] from that address if you want to > > confirm that your DKIM is working -- they'll be rejected if it isn't. > > Oh, I know the DKIM is OK, I can send messages to myself and everywhere else > and even usually Microsoft. I guess if they ask I'll have to remind them > that sometimes free services are worth what you pay for them. > > R's, > John > > >> We've been sending this person mail for years at an outlook.com.au > >> address and nearly all of them have worked, including several today. > >> > >> 550,5.7.515,Access denied, sending domain ARXIV.ORG 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 [SY8P300MB0731.AUSP300.PROD.OUTLOOK.COM > >> 2026-05-08T18:21:38.150Z 08DEAD0640C37A36] > >> [MW4PR04CA0059.namprd04.prod.outlook.com 2026-05-08T18:21:38.232Z > >> 08DEACE91EBF534A] [MW1PEPF0001615B.namprd21.prod.outlook.com > >> 2026-05-08T18:21:38.253Z 08DEACF5EA686851] > _______________________________________________ > mailop mailing list > [email protected] > https://list.mailop.org/listinfo/mailop > _______________________________________________ > mailop mailing list > [email protected] > https://list.mailop.org/listinfo/mailop -- Al Iverson // 312-725-0130 // Chicago http://www.spamresource.com // Deliverability http://www.aliverson.com // All about me https://xnnd.com/calendar // Book my calendar _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
