Microsoft is currently grappling with a persistent set of Microsoft Exchange Online mailbox access issues that have left a segment of its user base unable to reliably access their email via mobile devices and macOS. Despite an earlier attempt to resolve the problem, the service disruption has resurfaced, forcing engineers back into a cycle of mitigation and root-cause analysis.
The instability primarily affects users of the Outlook mobile apps and the “novel” Outlook for Mac desktop client. While the company has not disclosed the exact number of affected tenants or the specific geographic regions impacted, it has categorized the problem as an “incident.” In Microsoft’s internal nomenclature, an incident designation is typically reserved for critical service issues that result in noticeable and significant user impact.
The current situation is particularly frustrating for IT administrators because the issue is a ghost from the recent past. Microsoft first acknowledged the problem under tracking ID EX1256020, attributing the failure to a newly introduced virtual account. The company officially flagged that specific issue as resolved on April 1, only for the same symptoms to reappear weeks later.
The recurring nature of the failure has led Microsoft to re-list the problem in the admin message center under a new tag, EX1268771. This shift suggests that the initial fix was either incomplete or that the underlying trigger was more complex than a single virtual account configuration.
The technical struggle: Restarting the Notification Broker
From a technical perspective, the current remediation effort centers on the Notification Broker service. For those of us who have spent time in the weeds of software engineering, the Notification Broker is essentially the traffic controller for “push” events; it tells the client application that new data is available on the server so the app can fetch it.
When this service falters, the connection between the Exchange Online infrastructure and the end-user’s device becomes brittle. This explains why the impact is described as “intermittent”—users may find their mail loads one moment and fails the next, or find that notifications simply stop arriving until the app is manually refreshed.
“We’ve received reports from affected tenants that the impact scenario originally communicated through SHD EX1256020 is still ongoing. We’re working to restart the Notification Broker service on affected portions of Exchange Online service infrastructure to remediate impact while we continue our analysis into the underlying root cause,” Microsoft says.
Restarting a service is a standard “stop-gap” measure. It clears the immediate blockage and restores access, but it does not fix the bug that caused the service to hang in the first place. In a Thursday evening update, the Exchange Online team admitted they are still investigating the root cause and are seeking additional measures to prevent the cycle from repeating.
A broader pattern of Exchange instability
This latest bout of connectivity issues does not exist in a vacuum. For enterprise users, it feels like a recurring theme in the stability of the Exchange Online ecosystem over the last several months. The current struggle with the Notification Broker is the latest in a string of disruptions that have affected various connection protocols and client versions.
Earlier this month, Microsoft had to mitigate a separate, wide-reaching outage that blocked access to mailboxes and calendars across Outlook on the web, the standard Outlook desktop client, and Exchange ActiveSync. On that same day, the company was simultaneously patching a sign-in failure affecting Microsoft 365 Copilot across Teams and Office apps, suggesting a period of heightened volatility across the M365 suite.
To understand the scale of these interruptions, a look at the recent timeline of Exchange Online disruptions reveals a pattern of fragmented failures:
| Approximate Date | Affected Service/Protocol | Impact Summary |
|---|---|---|
| November | Classic Outlook Desktop | Blocked access to Exchange Online mailboxes. |
| January | IMAP4 Protocol | Intermittent blocking of email via IMAP4. |
| April 1 | Outlook Mobile/Mac | Initial virtual account issue (EX1256020) flagged as resolved. |
| Recent (Current) | Outlook Mobile/New Mac Client | Intermittent access issues (EX1268771) via Notification Broker. |
What this means for IT administrators
For those managing corporate tenants, the “intermittent” nature of these bugs is often harder to manage than a total blackout. Total outages trigger immediate, clear tickets; intermittent failures lead to a trickle of “it’s acting weird” reports that are difficult to diagnose at the endpoint level.
Because What we have is a server-side infrastructure issue, there is little that end-users or local IT staff can do to permanently fix the connection. The resolution rests entirely with Microsoft’s ability to stabilize the Notification Broker service across its global infrastructure. Administrators are encouraged to monitor the Microsoft 365 Admin Center for the most current status updates regarding EX1268771.
The company’s current focus is on preventing recurrence. However, until a definitive root cause is identified and patched, users on macOS and mobile devices should expect occasional synchronization lapses.
Microsoft has not yet provided a definitive timeline for a permanent fix, but the team is expected to provide further updates as their analysis of the service infrastructure progresses. We will continue to monitor the admin center for confirmation of a final resolution.
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