Since November 5, 2026, Microsoft's consumer mail service has been turning away some of the email from domains that don't publish a DMARC record. If your company emails customers, vendors or applicants with outlook.com, hotmail.com, live.com or msn.com addresses, some of that mail may be bouncing right now. Nobody announced it. The fix is one DNS record.
The wording suggests something is badly broken. Usually it isn't. The domains we have seen bounced mostly had working SPF, and many had DKIM too. What they were missing was the DMARC record that ties the two to the From address.
Microsoft does have published sender rules. Since May 2025, domains that send more than 5,000 messages a day to Outlook.com have had to pass SPF, DKIM and DMARC, or get 550 5.7.515 Access denied. That rule is aimed at marketers and bulk senders, and most small businesses rightly assumed it didn't apply to them.
