Exchange Online Mailbox Outage Drags Into Fourth Week Despite Microsoft's Fix Claims

Microsoft prematurely closed a three-week-old Exchange Online incident (EX1256020) on April 1, only to reopen it under a new tracking ID (EX1268771) after affected tenants reported the problem persisting. The failure mode — intermittent mailbox access for Outlook mobile and new Outlook for Mac users — traces back to a virtual account change introduced March 11. Microsoft is restarting the Notification Broker service on affected infrastructure as a stopgap while root cause analysis continues.

No regional scope or user count has been disclosed, though Microsoft’s classification as an ‘incident’ rather than an advisory signals meaningful user impact. The company has not committed to a resolution timeline.

This is the latest in a string of Exchange Online reliability failures: a separate outage blocked web and desktop mailbox access earlier in April, an IMAP4 disruption hit in January, and a classic Outlook connectivity incident occurred in November. The pattern suggests systemic fragility in Exchange Online’s service infrastructure rather than isolated events.