Outlook.com Is Quietly Rejecting Email from Domains Without DMARC

Since November 5, 2026, Microsoft's Outlook.com, Hotmail, Live, and MSN services have quietly begun rejecting emails from domains that lack a DMARC record, even from low-volume senders who previously weren't affected by Microsoft's bulk-sender rules. The rejection is inconsistent—some messages bounce while others pass through—making it easy to miss, though the fix is simple: adding a single DNS TXT record with "v=DMARC1; p=none." Microsoft has made no public announcement about this change despite its widespread impact on ordinary business communications.