Thanks Laura. Feel free to share the link with me as well, as I
suspect it will be an interesting read.
By the way, my clients who encountered these problems recently are
using common eMail programs like Mozilla Thunderbird, the built-in
mail apps for Android and iPhone, one older person who is using
Pegasus Mail, and/or MS-OutLook. As far as I know, these programs
don't cause standards violations (except for MS-OutLook with its
horrible TNEF/winmail.dat mess, but Microsoft's systems don't treat
that as erroneous as far as I know).
> There are multiple things going on with MS authentication. Yes, sometimes
> there is an obvious reason for the DKIM (or SPF) failure. But in other cases
> there´s nothing obvious going on - and why are they rejecting mail that they
> admit passes DMARC, anyway. Also, some senders are retrying the send and its
> delivered the next time.
>
> I´m tracking these failures with a few other folks trying to understand
> what´s going on. When I next get to my laptop I´ll drop you a link to the
> current problem summary write up (although I´ve not had time to update it in
> the last couple weeks).
>
> Laura
>
> Sent from my iPhone
>
> > On May 8, 2026, at 9:29PM, 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]
> > _______________________________________________
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> > [email protected]
> > https://list.mailop.org/listinfo/mailop
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--
Postmaster - [email protected]
Randolf Richardson, CNA - [email protected]
Inter-Corporate Computer & Network Services, Inc.
Vancouver, Beautiful British Columbia, Canada
https://www.inter-corporate.com/
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