Outlook.com Is Quietly Rejecting Email from Domains Without DMARC

Microsoft's Outlook.com has been quietly rejecting email from domains that don't publish a DMARC record since November 5, 2026, resulting in bounced emails with unclear error messages. Domains without DMARC records are being rejected, even if they have SPF and DKIM, while domains with more than 5,000 daily messages to Outlook.com must pass all three protocols to avoid being blocked. This issue affects businesses that send emails to personal addresses, causing missed invoices, appointment confirmations, and replies.