Microsoft Fixes Outlook and Exchange Online Email Access Disruptions
Microsoft moved to resolve two separate email access problems affecting Outlook and Exchange Online users. In Exchange Online, a newly introduced virtual account change intermittently blocked some users from accessing cloud mailboxes through Outlook mobile apps and the new Outlook for Mac, prompting Microsoft to classify the issue as a service outage under EX1256020. After infrastructure restarts failed to restore access, the company identified the change as the root cause and began disabling it across affected environments.
Microsoft also fixed a classic Outlook bug that caused Gmail and Yahoo accounts to stop synchronizing, triggering errors 0x800CCC0F and 0x80070057 after users stopped receiving sign-in prompts. The company said the service-side fix was deployed, but some users could continue seeing sync failures until their OAuth token expires, such as after a password change. Microsoft published a temporary workaround to force a new sign-in prompt and noted it is still investigating other Outlook-related problems, including Exchange Web Services group creation failures and a Teams Meeting Add-in issue that can make classic Outlook unusable.
Timeline
Apr 28, 2026
Microsoft resolves Outlook.com outage and tells iPhone users to reauthenticate
Microsoft said it resolved a widespread Outlook.com service degradation on April 28, 2026, after users worldwide experienced intermittent sign-in failures, account sign-outs, and 'too many requests' errors. After service health returned to normal, the company instructed iPhone users to manually re-enter credentials in the iOS Mail app to restore access to Outlook and Hotmail accounts.
Apr 1, 2026
Microsoft reopens Exchange Online mailbox incident after continued impact
Microsoft said the Exchange Online mailbox access issue previously tracked as EX1256020 was marked resolved on April 1, 2026, but was later reopened under incident EX1268771 after affected tenants continued reporting intermittent access problems. The company said it was restarting the Notification Broker service on affected infrastructure while continuing root-cause analysis and work to prevent recurrence.
Mar 23, 2026
Microsoft identifies Exchange Online root cause and rolls back change
Microsoft determined that a newly introduced virtual account change in Exchange Online was causing the mailbox access issues and began disabling the change across affected environments after infrastructure restarts did not resolve the problem.
Mar 20, 2026
Microsoft deploys fix for Outlook Gmail/Yahoo sync bug
Microsoft said it deployed a service-side fix on Friday for the classic Outlook bug affecting Gmail and Yahoo synchronization, though some users could continue seeing issues until their OAuth token expired. The company also shared a temporary workaround to force a new sign-in prompt.
Mar 19, 2026
Exchange Online change starts blocking some mailbox access
Beginning on Thursday, some Exchange Online users were intermittently blocked from accessing cloud mailboxes through Outlook mobile apps and the new Outlook for Mac. Microsoft later tracked the incident as EX1256020 and classified it as a service outage.
Feb 26, 2026
Outlook sync failures begin for Gmail and Yahoo accounts
Microsoft said a classic Outlook issue started causing Gmail and Yahoo accounts to stop synchronizing on February 26, 2026, with affected users seeing errors such as 0x800CCC0F and 0x80070057 and no longer receiving sign-in prompts.
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