Microsoft’s Ongoing Efforts to Resolve Exchange Online Mailbox Access Challenges

Microsoft Investigating Exchange Online Mailbox Access Issues

Microsoft is actively investigating and addressing Exchange Online mailbox access issues that have been impacting Outlook mobile and macOS users intermittently for several weeks now.

The problem, initially identified as service issue EX1256020 on March 11, was attributed to a newly introduced virtual account. Although Microsoft declared it resolved on April 1, the incident resurfaced under a different identifier (EX1268771) in the admin message center.

According to Microsoft, affected tenants have reported ongoing impact scenarios related to the issue. The company is taking steps to restart the Notification Broker service within the Exchange Online service infrastructure to mitigate the impact while continuing to investigate the root cause.

Users accessing their Exchange Online mailboxes through Outlook mobile apps or the new Outlook for Mac desktop client may experience intermittent disruptions. Microsoft assures that updates will be provided as the investigation progresses.

In a recent update issued on Thursday evening, the Exchange Online team confirmed that they are still investigating the root cause and implementing additional measures to prevent a recurrence of the issue.

Although Microsoft has not disclosed the specific regions or number of users affected by the three-week-long problem, it has classified it as an incident, indicating significant user impact.

Earlier this month, Microsoft resolved an Exchange Online outage that prevented users from accessing mailboxes and calendars via various Outlook platforms. Additionally, a separate issue affecting Office.com and Microsoft 365 Copilot web sign-in services was also promptly addressed.

Previous Exchange Online service outages, such as those involving IMAP4 and the classic Outlook desktop client, have been successfully resolved by Microsoft in the past.

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