Microsoft newly rejecting mail lacking DMARC?
As of Friday night, November 6, 2026 (US time), multiple email admins on the Mailop mailing list (and elsewhere) are reporting seeing messages rejected when sending mail to Microsoft Outlook Consumer (Hotmail/Outlook.com, not Microsoft 365), meaning domains like outlook.com and hotmail.com, if the sending domain has no DMARC record present in DNS.
My understanding is that the mail is being rejected even if messages are passing SPF and DKIM authentication checks. The NDR/SMTP rejection is: 550 5.7.1 Message rejected: Message lacks SPF/DKIM/DMARC Auth Records
Microsoft announced back in 2005 that DMARC (along with SPF and DKIM) are all required for bulk senders, bulk meaning those sending more than 5,000 messages per day to Microsoft domains. It sounds as though something may have changed in the past day or two; with folks who don't necessarily meet the definition of "bulk" now seeing issues.
I'm not sure if this is an intended policy update in the world of Microsoft; time will tell. In the mean time, if you don't have a DMARC record in DNS for your domain, even with a p=none policy, now's the time to add one.
I'm not sure if this is an intended policy update in the world of Microsoft; time will tell. In the mean time, if you don't have a DMARC record in DNS for your domain, even with a p=none policy, now's the time to add one.