Since November 5, 2026, Microsoft's Outlook.com service has begun rejecting email from domains that lack a DMARC record, affecting not only bulk senders but also ordinary low-volume users. The rejection occurs silently, with some messages bouncing while others through, making the issue difficult to detect. Affected domains typically have working SPF and DKIM but are missing the DMARC record that ties authentication to the sender's From address.
The bounce message simply states that SPF/DKIM/DMARC Auth Records are missing, without specifying which failed. The fix requires adding a single TXT DNS record: _dmarc with value v=DMARC1; p=none. This record declares DMARC usage and requests reports but takes no action on failures.
It is crucial that DMARC passes only when SPF or DKIM passes for the domain in the From address; if neither aligns, the record alone will not prevent rejection. Domains without any DMARC record are exposed, and the inconsistency of bounces can quietly disrupt business communications such as invoices and appointment confirmations for customers at personal addresses.
Source: Hacker News · Summarized by HeadlinesBriefing