Microsoft has confirmed a fresh Exchange Online incident, tracked as EX1467029, causing delays for users sending and receiving email messages from external domains.
The company first acknowledged the disruption on September 4, 2026, flagging it as a service degradation issue affecting Exchange Online, one of the most widely used business email platforms in the world.
According to Microsoft’s service health updates, the outage began around 3:49 PM GMT+5:30 and has continued through multiple status revisions issued that afternoon, with updates posted at 4:06 PM, 4:33 PM, and 5:56 PM.
Affected users have reported intermittent “Server busy” errors when attempting to communicate with recipients outside their own organization, a symptom that typically signals backend processing delays rather than a complete mail-flow failure. Microsoft has classified the event as an incident, a designation the company reserves for issues with noticeable, widespread user impact rather than isolated glitches.
In its advisories, Microsoft said its engineering teams have identified that anti-spam protections may be compounding the problem for a subset of affected accounts, effectively slowing down legitimate mail even further as filtering systems interact with the underlying fault.
The company noted it is “continuing to analyse the behaviour and review service telemetry to better understand the underlying cause and determine the most effective mitigation path,” but has not yet provided a fixed timeline for full resolution.
Notably, this is not an isolated event. Exchange Online has suffered a string of disruptions in recent months, including a major multi-day outage tracked as EX1464935 that began August 31, 2026, and caused authentication failures, mailbox search problems, and delayed message delivery across the service before Microsoft declared it fully mitigated on September 3.
That earlier incident was traced to a fault in a core authentication component shared across multiple Microsoft 365 services, requiring engineers to test and gradually roll out remediation across affected infrastructure.
The recurrence of email delivery problems within days of the previous outage’s resolution raises fresh questions about the resilience of Microsoft’s cloud email backbone, which underpins communications for millions of enterprises worldwide.
Organizations relying on Exchange Online for time-sensitive external communication, such as customer support, vendor coordination, or security alerting, may want to monitor the Microsoft 365 admin center’s Service Health dashboard directly for real-time updates tied to issue ID EX1467029.
Security teams should also be aware that prolonged mail delays can create downstream risks, including missed threat notifications, delayed multi-factor authentication emails, and backlog-related phishing attempts that exploit user confusion during outages.
Until Microsoft confirms a root cause and rollout of a permanent fix, administrators are advised to check affected mailboxes for delivery backlogs and avoid resending messages unnecessarily, as duplicate sends can further strain the recovering mail queues. Cyber Security News will continue tracking this incident as Microsoft releases further updates.
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