Microsoft Still Working to Fix Exchange Online Mailbox Access Issues

Microsoft Still Working to Fix Exchange Online Mailbox Access Issues

Microsoft continues to grapple with Exchange Online mailbox access problems that have intermittently affected Outlook mobile and macOS users for several weeks. The issue first emerged in the service health communications as EX1256020, with Microsoft attributing the disruption to a newly introduced virtual account. Although the company said the incident was resolved on April 1, the matter was subsequently re-listed in the admin Message Center under a different identifier, EX1268771.

In the latest update, the Exchange Online team notes that affected tenants are still experiencing impact tied to the originally communicated scenario. To address this, Microsoft says it is working to restart the Notification Broker service on portions of the Exchange Online service infrastructure that are impacted, all while continuing to analyze the underlying root cause. The notification is clear: the problem may be intermittent for some users trying to access their mailboxes through the Outlook mobile apps or the new Outlook for Mac desktop client. The company emphasizes that the incident classification signals a critical service issue with noticeable user impact, and that the situation section may be updated as investigations progress.

As of now, Microsoft has not disclosed how widespread the disruption is—whether by region or by the number of affected users—yet reaffirmed that this remains an ongoing incident. The guidance from the Exchange Online team centers on remediation efforts and preventive measures to ensure the problem does not recur, even while the root cause continues to be studied.

This renewed focus comes after a period in which Microsoft had previously mitigated an Exchange Online outage that blocked access to mailboxes and calendars via Outlook on the web, the desktop client, Exchange ActiveSync, and other Exchange Online connection protocols. On the same day, the company resolved another issue that caused sign‑in problems for Office.com or the Microsoft 365 Copilot web experiences affecting the Copilot desktop app, Copilot in Teams, and Copilot in Office apps. Historical service interruptions in Exchange Online have included outages that blocked access via IMAP4 in January and a separate outage that blocked access through the classic Outlook desktop client in November, underscoring a pattern of periodic service quality challenges across Exchange Online’s ecosystem.

Microsoft’s current posture is to continue investigation into the root cause while implementing additional safeguards to prevent similar disruptions in the future. The company has not issued a timetable for full restoration of seamless access for all affected users, but the ongoing work emphasizes a focus on service reliability and resilience as administrators monitor their environments for any lingering or emergent signs of impact.