Since November 5, 2026, Outlook.com and Hotmail have started bouncing some mail sent from domains that do not publish a DMARC record — even when SPF and DKIM are configured and valid. The rejection shows up as 550 5.7.1 Message rejected: Message lacks SPF/DKIM/DMARC Auth Records (AS9031519).
What was observed
The behavior was first spotted in MailRoute's outbound logs on November 5 and reported by mail administrators on the mailop list on November 6. Independent tests reproduced the problem: dmarkoff.com sent messages from a subdomain with no DMARC to 16 Outlook.com and Hotmail test mailboxes, and all 16 were refused; with a DMARC record published — on the domain itself or on its parent domain — the same messages were accepted. EasyDMARC reproduced the rejection on November 8.
Who is affected
The key point is that passing SPF and DKIM is not enough: without a DMARC record, Outlook.com treats the message as unauthenticated. The rejection hits only some messages — the behavior is intermittent — and, according to the published tests, corporate Microsoft 365 mailboxes were not affected as recipients; the targets are consumer Outlook.com, Hotmail, Live and MSN mailboxes.
How to fix it
The fix is simple: publish a _dmarc TXT record in the sending domain's DNS, with the value v=DMARC1; p=none. The p=none policy is already enough to stop the rejection, without changing how other providers treat the mail. Remember that DMARC only passes when SPF or DKIM passes in alignment with the domain in the From address.
Context and caveat
The background is Microsoft's rule announced in May 2025, which required SPF, DKIM and DMARC only from bulk senders — domains sending more than 5,000 messages a day to Outlook.com, under penalty of error 550 5.7.515. The rejection observed in November goes further: it hits ordinary senders, at any volume. As of November 8, Microsoft had published no announcement, notice or support entry about the new rejection, and no spokesperson confirmed the change — so it should be treated as behavior observed and documented by independent operators, not as an officially announced policy. Since there was no statement, the behavior could be widened, narrowed or rolled back at any time.
Image credit: Microsoft Outlook icon, by Microsoft, via Wikimedia Commons (public domain).
Fontes:
- MailRoute — Outlook.com Is Quietly Rejecting Email From Domains Without DMARC
- EasyDMARC — Microsoft Rejecting Emails Without DMARC
- dmarkoff — Outlook AS9031519: Mail Rejected Without a DMARC Record
- mxio — Outlook 550 5.7.1 “Lacks SPF/DKIM/DMARC Auth Records”
- Windows Forum — Outlook.com and Hotmail Reject Emails With 550 Errors
Transparency: this article was produced with the help of artificial intelligence, based on public posts and the internet sources cited above. The facts were cross-checked across independent sources; the absence of an official announcement from Microsoft is explicitly noted in the text. Consult the original sources to confirm the information.
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