Microsoft 365 outage slows email recovery due to built-in store-and-forward architecture
A global outage of Microsoft 365 services that began on 12 November 2026 has left email traffic congested, causing delayed delivery even after the service is restored.
A worldwide outage of Microsoft 365 that started on 12 November 2026 disrupted Teams, Copilot and, most notably, Outlook email for businesses, governments and schools. Microsoft said on 13 November that service availability was improving, but some users might still face intermittent access or delayed email delivery.
Email’s “store-and-forward” design, unlike the “closed-door” behavior of many cloud apps, means messages continue to be sent to affected accounts from other providers. Those external servers queue the messages and repeatedly retry delivery, creating a massive backlog that can persist for hours or days after the outage is resolved.
Analysts compare the situation to a highway accident that blocks lanes while traffic from distant on-ramps keeps entering, eventually causing a gridlock that must be cleared before normal flow resumes. When Microsoft restores Outlook servers, they must process the accumulated queues without overwhelming the system, which explains the prolonged recovery period.
The incident highlights the reliance of many organizations on a few large email providers, making a single service failure capable of stalling communication across entire sectors.