Mythic Beasts reported on November 9, 2026, that Microsoft-run mail systems, including Hotmail and Outlook.com, were rejecting messages from domains without DMARC records. The hosting provider said adding a record with a p=none policy restored delivery for some affected domains. Its account gives mail administrators a concrete symptom to investigate, while the cause and wider scope remain uncertain.
The provider said its logs contained more than 500 such rejections on the preceding Thursday and none before then. According to Mythic Beasts, the affected messages had valid SPF and DKIM authentication but lacked DMARC records. Those are the provider's observations, rather than results independently reproduced by MrKeyoor.
A workaround does not establish a new policy
The Register reported on November 9 that a moderator in Microsoft's support forum had described the problem as a service degradation and said engineering teams were investigating. The publication said it had asked Microsoft for further information and had not received a response. That is a reported support response, rather than a published explanation of the root cause.
The Register also reported intermittent delivery: a message rejected on one attempt could succeed when resent. That limits what an administrator can infer from a single successful retry. A delivery check needs enough context to distinguish a DNS change from a service that was already behaving inconsistently.
Compare the symptom before changing DNS
Mythic Beasts said it subsequently deployed p=none DMARC records across many customer domains. A DMARC policy tells recipients how a domain wants authentication failures handled. The provider's before-and-after account makes a missing record worth checking when the rejection matches, without establishing that every SPF-related bounce has the same cause.
Watch for Microsoft's explanation of the affected sender conditions and a recovery statement. The Register's report leaves the cause unresolved, and a workaround at one provider cannot establish that delivery has recovered elsewhere.